1. 0 Introduction
An electrical generator is a machine which converters Mechanical energy (or power) into electrical energy. The energy conversion is based on the principle of the production of dynamically induced e.m.f whenever a conductor cuts magnetic flux dynamically induced e.m.f is produced in it according to Faraday’s laws of electromagnetic induction. This e.m.f causes a current to flow if the conductor circuit is closed. The basic essential parts of an electrical are: (1) a magnetic field and (2) A conductor or conductor which can so move as to cut the flux.
Main part’s of generator:
(1) Magnetic Frame or yoke.
(2) Pole coils or Field coil.
(3) Armature windings or conductors.
(4) Pole – cores and pole shoes.
(5) Brushes and Bearings.
(6) Armature core.
1.2 Principle of Generator:
This system is brush less without pilot exciter system. Without pilot exciter system is a small AC generator. To make the excitation of a generator completely independent of any external power source a small pilot exciter often included in the system. In this figure static part is stator and exciter field, and rotating part is exciter armature, rectifier and main field.
Some residual magnetism contained in the main field. When the prime mover begins to rotate the main field that time main stator induced minimum ac voltage. This ac voltage is through Automatic voltage Regulator (AVR) by auxiliary winding then the AVR filtering the harmonics and also rectifying the minimum induced ac voltage. The rectifying dc voltage goes to the exciter field then again induced ac voltage in the exciter armature. The induced ac voltage rectifying by bridge rectifier and finally the rectifying strong dc voltage go to the main field then produced desired voltage from the stator winding.
1.3 Major Parts of Alternator
AC Generator Means alternator, an alternator is an electromechanical device that converts mechanical energy to alternating current electrical energy. Most alternators use a rotating magnetic field but linear alternators are occasionally used. In principle, any AC electrical generator can be called an alternator, but usually the word refers to small rotating machines driven by automotive and other internal combustion engines.
Major parts Alternator:
The rotating part of an alternator, generator, dynamo or motor is called rotor. The rotor is the non-stationary part of a rotary electric motor or alternator, which rotates because the wires and magnetic field of the motor are arranged so that a torque is developed about the rotor’s axis. In some designs, the rotor can act to serve as the motor's armature, across which the input voltage is supplied. The stationary part of an electric motor is the stator. A common problem is called cogging torque.
Fig1.1: Generator plant.
Fig 1.2: Layout of Generator.
Fig1.3: Generator cylinder head, fuel line, manifold water line.
Fig1.4: Front side of one generator.
Fig1.6: Basic AC generating System
Fig 1.7: Alternator.
The stator of these devices may be either a permanent magnet or an electromagnet. Where the stator is an electromagnet, the coil which energizes it is known as the field coil or field winding. An AC alternator is able to produce power across multiple high-current power generation coils connected in parallel, eliminating the need for the Commutator. Placing the field coils on the rotor allows for an inexpensive slip ring mechanism to transfer high-voltage, low current power to the rotating field coil. It consists of a steel frame enclosing a hollow cylindrical core (made up of laminations of silicon steel). The laminations are to reduce hysteresis and eddy current losses.
The power-producing component of an alternator, generator, dynamo or motor is Armature. In a generator, alternator, or dynamo the armature windings generate the electrical current. The armature can be on either the rotor or the stator. In electrical engineering, an armature generally refers to one of the two principal electrical components of an electromechanical machine – a motor or generator, but may also mean the pole piece of a permanent magnet or electromagnet, or the moving iron part of a solenoid or relay. The other component is the field winding or field magnet. The role of the "field" component is simply to create a magnetic field (magnetic flux) for the armature to interact with, so this component can comprise either permanent magnets, or electromagnets formed by a conducting coil. The armature, in contrast, must carry current so it is always a conductor or a conductive coil, oriented normal to both the field and to the direction of motion, torque (rotating machine), or force (linear machine). The armature's role is two-fold: (a) to carry current crossing the field, thus creating shaft torque (in a rotating machine) or force (in a linear machine), and (b) to generate an electromotive force ("EMF"). In the armature, an electromotive force ("EMF") is created by the relative motion of the armature and the field. When the machine is acting as a motor, this EMF opposes the armature current, and the armature converts electrical power to mechanical torque (and power, unless the machine is stalled) and transfers it to the load via the shaft. When the machine is acting as a generator, the armature EMF drives the armature current, and shaft mechanical power is converted to electrical power and transferred to the load. (In an induction generator, these distinctions are blurred, since the generated power is drawn from the stator, which would normally be considered the field.)A growler is used to check the armature for shorts, opens and grounds.
Fig 1.10: Armature
The parts of an alternator or related equipment can be expressed in either mechanical terms or electrical terms. Although distinctly separate, these two sets of terminology are frequently used interchangeably or in combinations that include one mechanical term and one electrical term. This may cause confusion when working with compound machines such as brushless alternators, or in conversation among people who are accustomed to work with differently configured machinery.
The magnetic field component of an alternator, generator, dynamo or motor is field. The magnetic field of the dynamo or alternator can be provided by either electromagnets or permanent magnets mounted on either the rotor or the stator. (For a more technical discussion, refer to the Field coil article.) Because power transferred into the field circuit is much less than in the armature circuit, AC generators nearly always have the field winding on the rotor and the stator as the armature winding. Only a small amount of field current must be transferred to the moving rotor, using slip rings.
Fig1.11: Consequent field bipolar generator
Direct current machines necessarily have the Commutator on the rotating shaft, so the armature winding is on the rotor of the machine. A field coil is the magnetic field component of an alternator, generator, dynamo, motor, or rotary converter. The phrase is also often used in the plural form, as field coils. The field coils can be mounted on either the rotor or the stator, depending on whichever method is the most cost-effective for the device design.
Bipolar and Multi-polar Field,
Bipolar generators were universal prior to 1890 but in the years following it was replaced by the multi polar field magnets. Bipolar generators were then only made in very small sizes.
The stepping stone between these two major types was the consequent-pole bipolar generator, with two field coils arranged in a ring around the stator. This change was needed because higher voltages allow current to flow greater distances over small wires. To increase output voltage, a DC generator must be spun faster, but beyond a certain speed this is impractical for very large power transmission generators. By increasing the number of pole faces surrounding the Gramme ring, the ring can be made to cut across more magnetic lines of force in one revolution than a basic two-pole generator. Consequently a four-pole generator could output twice the voltage of a two-pole generator, a six-pole generator could output three times the voltage of a two-pole, and so forth. This allows output voltage to increase without also increasing the rotational rate. In a multi polar generator, the armature and field magnets are surrounded by a circular frame or ring yoke to which the field magnets are attached. This has the advantages of strength, simplicity, symmetrical appearance, and minimum magnetic leakage, since the pole pieces have the least possible surface and the path of the magnetic flux is shorter than in a two-pole design
Three basic types of excitation systems exist to provide DC supply to the field
In the early 1900s the 75 KVA direct-driven power station AC alternator, with a separate belt-driven exciter generator was invented.
http://en.wikipedia.org/wiki/File:Murray_Alternator_with_Belt-Driven_Exciter.jpgAn electric generator or electric motor that uses field coils rather than permanent magnets will require a current flow to be present in the field coils for the device to be able to work. If the field coils are not powered, the rotor in a generator can spin without producing any usable electrical energy, while the rotor of a motor may not spin at all. Very large power station generators often utilize a separate smaller generator to excite the field coils of the larger.
In the event of a severe widespread power outage where islanding of power stations has occurred, the stations may need to perform a black start to excite the fields of their largest generators, in order to restore customer power service.
To obtain and maintain a specific AC output voltage, a variable DC source is required to overcome the variation of excitation requirement.
Various load conditions:
• Three basic types of excitation systems exist to Main generator + exciter generator = two rotating machines. The magnetic circuit of the exciter and main field maintain sufficient residual magnetism to ensure voltage build up. The stator AC output voltage is rectified through the AVR to provide excitation to the field.
The exciter armature is energized by the DC source applied to the field. The exciter armature AC output is rectified through rotating diodes to provide DC excitation to the main field. The main field by rotating, creates the magnetic flux and the output AC voltage. The stator AC output voltage is in direct relation with the DC voltage provided to the exciter field.
Early radio receivers, called crystal radios, used a "cat's whisker" of fine wire pressing on a crystal of galena (lead sulfide) to serve as a point-contact rectifier or "crystal detector". In gas heating systems flame rectification can be used to detect a flame. Two metal electrodes in the outer layer of the flame provide a current path and rectification of an applied alternating voltage, but only while the flame is present for three-phase AC, six diodes are used. Typically there are three pairs of diodes, each pair, though, is not the same kind of double diode that would be used for a full wave single-phase rectifier. Instead the pairs are in series (anode to cathode). Typically, commercially available double diodes have four terminals so the user can configure them as single-phase split supply use, for half a bridge, or for three-phase use.
Fig1.12: Connection system of Rectifier
Fig1.13: Three-Phase Bridge Rectifier.
For three-phase AC, six diodes are used in typically automobile
Thehttp://en.wikipedia.org/wiki/File:Getting_behind_the_tridge_rectifier.jpgdisassembled automobile alternator, showing the six diodes that comprise a full-wave three-phase bridge rectifier. Most devices that generate alternating current (such devices are called alternators) generate three-phase AC. For example, an automobile alternator has six diodes inside it to function as a full-wave rectifier for battery charging applications.
Fig1.14: Rectifying System
Principle of AVR
Fig1.15: Automatic Voltage Regulator.
Coil-rotation AC voltage regulator,
Fig1.16: Basic design principle and circuit diagram for the rotating-coil AC voltage regulator.
This is an older type of regulator used in the 1920s that uses the principle of a fixed-position field coil and a second field coil that can be rotated on an axis in parallel with the fixed coil. When the movable coil is positioned perpendicular to the fixed coil, the magnetic forces acting on the movable coil balance each other out and voltage output is unchanged. Rotating the coil in one direction or the other away from the center position will increase or decrease voltage in the secondary movable coil.
This type of regulator can be automated via a servo control mechanism to advance the movable coil position in order to provide voltage increase or decrease. A braking mechanism or high ratio gearing is used to hold the rotating coil in place against the powerful magnetic forces acting on the moving coil.
The overall construction is extremely similar to the design of standard AC dynamo windings, with the primary difference being that the rotor does not spin in this device, and instead is held against spinning so the fields of the rotor and stator can act on each other to increase or decrease the line voltage.
1.11 Starter motor
The modern starter motor is either a permanent-magnet or a series- or series-parallel wound direct current electric motor with a solenoid switch (similar to a relay) mounted on it. When current from the starting battery is applied to the solenoid, usually through a key-operated switch, it pushes out the drive pinion on the starter driveshaft and meshes the pinion with the ring gear on the flywheel of the engine
The solenoid also closes high-current contacts for the starter motor, which begins to turn. Once the engine starts, the key-operated switch is opened; a spring in the solenoid assembly pulls the pinion gear away from the ring gear, and the starter motor stops. The starter's pinion is clutched to its driveshaft through an overrunning clutch which permits the pinion to transmit drive in only one direction. In this manner, drive is transmitted through the pinion to the flywheel ring gear, but if the pinion remains engaged (as for example because the operator fails to release the key as soon as the engine starts), the pinion will spin independently of its driveshaft. This prevents the engine driving the starter, for such back drive would cause the starter to spin so fast as to fly apart. However, this sprig clutch arrangement would preclude the use of the starter as a generator if employed in hybrid scheme mentioned above; unless modifications are made. This overrunning-clutch pinion arrangement was phased into use beginning in the early 1960s; before that time, a Bendix drive was used. The Bendix system places the starter drive pinion on a helically-cut driveshaft. When the starter motor begins turning, the inertia of the drive pinion assembly causes it to ride forward on the helix and thus engage with the ring gear. When the engine starts, back drive from the ring gear causes the drive pinion to exceed the rotating speed of the starter, at which point the drive pinion is forced back down the helical shaft and thus out of mesh with the ring gear.
Fig1.18: Connection of DC battery
Fig1.19: Diesel Generator Engine
|GENERATOR OPERATION||CHAPTER 02|
(1) Generator terminal strip
(2) Main armature (Stator)
(3) Main field (Rotor)
(4) Rotor shaft
(5) Permanent magnet pilot exciter
An engine supplies the power in order to turn rotor shaft (4). The armature of exciter (6) and main field (3) attach to the rotor shaft. As the rotor shaft turns, the exciter generates AC current. The rectifier components convert the AC exciter current to DC current. This DC current is supplied to the main field. A magnetic field is created around the poles of the main field. As the main field turns with the rotor shaft, the magnetic field also rotates. The magnetic field induces an AC voltage into stationary main armature (2). The main armature is a coil with many turns of wire. The current that flows through the main armature flows to the load. Two rectifiers supply DC current to main field (3). The load voltage is controlled by varying the current that goes to the. Exciter’s armature. There are two methods for excitation that are used on Generators:
- Permanent magnet pilot excited (PMPE)
- Self-excited (SE)
2.2Permanent Magnet Pilot Excited (PMPE) Generator
Fig2.2: PMPE Generator Wiring Diagram
(CR1 – CR6) Diodes
(L1) Exciter field (stator)
(L2) Exciter armature (rotor)
(L3) Main field (rotor)
(L4) Main armature (stator)
Media Search – SENR5359 – SR4B Generator Page 2 of 13
Permanent magnet pilot excited generators receive power for the voltage regulator from a pilot exciter. Self-excited generators receive power for the voltage regulator from the main armature. The pilot exciter consists of permanent magnet (PM) and Pilot Exciter Armature (L5). The pilot exciter operates independently from the generator output voltage. Constant excitation during a large load application is possible. Constant excitation is possible because the irregularities that occur in the generator output voltage are not fed back into the exciter. The irregularities that occur in the generator output voltage are caused by load conditions. The independent operation also allows the generator to sustain excessive currents for short periods of time. When the engine starts turning the Rotating Field Assembly (RFA), the permanent magnet (PM) induces an AC voltage in the pilot exciter armature (L5). The pilot exciter armature has three coils of wire. The pilot exciter armature generates three phase alternating current (AC). The resulting AC flows through wires "11", "12", and "13" to the voltage regulator. Within the voltage regulator, the three-phase alternating current is rectified to direct current (DC). A controlled amount of DC is fed to exciter field (L1) through terminals "F1" and "F2". Direct current now flows to exciter field (L1) which creates a magnetic field. Exciter armature (L2) rotates in this magnetic field. The exciter field and the exciter armature generate three-phase alternating current. The AC is then rectified by a three phase full-wave bridge rectifier circuit. This rectifier circuit is made of the following diodes: CR1, CR2, CR3, CR4, CR5 and CR6. The DC output from the bridge rectifier is carried to main field (L3) by conductors which are routed through a passage in the generator shaft. Current through the main field creates the magnetic field of the generator. As the main field rotates, the main field induces a three-phase AC voltage in main armature (L4). This voltage is sent to the following terminals: T0, T1, T2 and T3. These terminals are connections for the load.
To keep the output voltage constant with changing loads, it is necessary to control the exciter current. This control is the function of the voltage regulator. The voltage regulator senses the generator output voltage at the following wires: "20", "22" and "24". The regulator sends current to the exciter through wires "F1" and "F2". The amount of current is dependent on the sensed voltage. The current is drawn from the pilot exciter and the armature (wires "11", "12", and"13"). Regardless of the generators type (PMPE generator or self-excited generator), changing the exciter current has the same effect on the generator's operation. See the topic Self-Excited Generators for a description of generator operation when the exciter current changes.
Note: For more information on voltage regulation, see the appropriate voltage regulator service manual.
PMPE generators provide the magnetism for start-up of the generator. A Permanent Magnet (PM) supplies the initial magnetism that is required at start-up. Flashing the field is not required for start-up of the generator.
2.3 Self-Excited (SE) Generators
(CR1 – CR6) Diodes
(L1) Exciter field (stator)
(L2) Exciter armature (rotor)
(L3) Main field (rotor)
(L4) Main armature (stator)
(RFA) Rotating field assembly
(TR1) Optional Voltage droop transformer
(T0, T1, T2, T3, T7, T8, T9) Generator terminals and/or Generator leads Self-excited generators receive the power for excitation from the generator armature (the generator output). When the engine starts turning the Rotating Field Assembly (RFA), the residual magnetism in exciter field (L1) causes a small amount of AC voltage to be generated in exciter armature (L2). Induced voltage causes current to flow. This current is present in the exciter armature. The AC is then rectified by a three-phase full-wave bridge rectifier circuit. This rectifier circuit is made of the following diodes: CR1, CR2, CR3, CR4, CR5 and CR6. Direct current then flows through main field (L3). The flow of DC through the main field creates a magnetic field. This magnetic field adds to the existing residual magnetism of the main field. As the main field rotates, an AC voltage is induced into main armature (L4) which appears as a three-phase AC voltage at the following output terminals: T0, T1, T2 and T3. The voltage regulator taps the AC output through wires: "20", "22" and "24". During start-up, this tapped output is sensed by the voltage regulator. The voltage regulator senses the output as a low voltage output condition. Therefore, the voltage regulator output to the exciter field is increased so that the generator output will continue to increase up to the rated voltage. The amount of current which flows through the exciter directly affects the generator output voltage.
Fig 2.3: SE Generator Wiring Diagram
The voltage regulator maintains a constant generator output voltage with changing loads. The voltage regulator controls the DC voltage and the DC current. The DC voltage and the DC current is supplied to the exciter which produces the generator output voltage. The voltage regulator senses the generator's output voltage at wires: "20", "22" and "24". The voltage regulator then supplies a controlled DC voltage and DC current to the exciter through wires "F1" and "F2".
Note: For more information on voltage regulation, see Service Manual, "Voltage Regulator”. When the voltage regulator senses a decrease in output voltage, the voltage regulator will increase the DC voltage and the DC current. This DC voltage and DC current is sent through the exciter through wires "F1" and "F2". The exciter field's magnetic field increases. As the magnetic field in the exciter field is increased, the AC voltage that is induced in the exciter armature is increased. This increased AC voltage from exciter armature (L2) causes more AC current to flow. The AC current is then rectified by a three-phase full-wave bridge rectifier circuit. This rectifier circuit is made of the following diodes: CR1, CR2, CR3, CR4, CR5 and CR6. The increased DC output from the bridge rectifier is carried to main field coils (L3) by conductors. These conductors are routed through a passage in the generator shaft. Increased current through main field coils increases the magnetic field of the generator. The increased magnetic field induces a larger AC voltage into main armature (L4). The three-phase AC voltage increases until the voltage regulator no longer senses a decreased output voltage.
When the voltage regulator senses an increase in output voltage, the voltage regulator will decrease the DC voltage to the exciter. This will result in a decrease in generator output voltage.
Residual magnetism is necessary for start-up of the self-excited generator. The main field coils are wound on magnetic steel which retains a small amount of magnetism after shutdown. After time and certain conditions, the residual magnetism may decrease. The residual magnetism will then be insufficient to start the generating process. If this occurs, refer to Testing and Adjusting Section, "Exciter Field – Flash".
Fig2.4: Rectifier Circuit
2.4 Rectifier Circuits
2.4 Rectifier circuit
(CR1 – CR6) Diodes
(L2) Exciter armature (rotor)
(L3) Main field (rotor)
The following diodes form a bridge rectifier circuit: CR1, CR2, CR3, CR4, CR5 and CR6. The bridge rectifier circuit
receives three-phase alternating current from exciter armature (L2). The bridge rectifier circuit rectifies the alternating current into direct current. The DC power is then routed to main field (L3).
Diodes "CR1" through "CR6" are contained in rotating rectifier blocks. Three different rotating rectifier blocks are currently used on SR4B generators. The type of the generator and the size of the generator determine the rotating rectifier block that is used. There are three types of rotating rectifier blocks:
Two-diode rectifier block – The two-diode rectifier block contains two diodes. Three identical blocks are required.
Three-diode rectifier block – The three-diode rectifier block contains three diodes. Two different blocks are required. One block is positive and the other block is negative.
Six-diode rectifier block – The six-diode rectifier block contains six diodes. One block is required.
Rectifying the current creates heat. The rotating rectifier blocks are fastened to heat sinks. These heat sinks spread the heat. These heat sinks also allow the rotating rectifier blocks to operate at a cooler temperature.
2.5 Two-Diode Rectifier Block
(1) "L2" (wire passage)
(2) Heat sink assembly
(3) Three two-diode rectifier blocks
(4) "L3" (wire passage)
Fig2.5: Two-diode rectifier block
Fig2.6: The locations of the three two-diode rectifier blocks
Fig2.7: The wiring of the three two-diode rectifier blocks
Three identical two-diode rectifier blocks (3) are interconnected in order to form a bridge rectifier circuit. Each of the two diode rectifier blocks contains one of the following sets of two diodes:
- "CR1" and "CR4"
- "CR2" and "CR5"
Two-diode rectifier blocks must be wired correctly. Refer to Illustration 7. Each "AC" terminal connects to an exciter armature wire (1). The "+" terminals connect together. The "+" terminals also connect to one "L3" wire (4) of the main field. The "-" terminals connect together. The "-" terminals also connect to the other "L3" wire (4) of the main field. The two-diode rectifier blocks (3) are mounted to the heat sink assembly (2). The heat sink assembly is on the end of the generator shaft. Heat sink assembly (2) also contains a Varistor (6) and a resistor (5). The Varistor and the resistor are used to protect the generator circuit. Refer to Generator Operation, "Generator Circuit Protection".
2.6 Three-Diode Rectifier Block
(1) Positive rectifier block
(2) Negative rectifier block
Fig2.8: Three-diode rectifier blocks
Fig 2.9: The location of the two three-diode rectifier blocks
Fig2.10: The wiring of the three-diode rectifier blocks
(1) Positive rectifier block
(2) Negative rectifier block
(3) "L3" (two-wire passage)
(4) Heat sink assembly
(6) "L2" (three-wire passage)
In order to form a bridge rectifier circuit, two similar three-diode rectifier blocks are connected. Each of the three-diode rectifier blocks contain three diodes. Positive rectifier block (1) contains diodes "CR1", "CR2", and "CR3". Negative rectifier block (2) contains diodes "CR4", "CR5", and "CR6". Three-diode rectifier blocks must be wired correctly. Refer to Illustration 10. Each "AC" terminal connects to an "L2" wire from the exciter armature (6). The "+" terminals connect together. The "+" terminals also connect to one "L3" wire (3) of the main field. The "-" terminals connect together. The "-" terminals also connect to the other "L3" wire (3) of the main field.
The positive rectifier block (1) and the negative rectifier block (2) are mounted to heat sink assembly (4). The heat sink assembly is on the end of the generator shaft. Heat sink assembly (4) also contains a Varistor (7) and resistor (5). The Varistor and the resistor are used to protect the generator circuit. Refer to Generator Operation, "Generator Circuit Protection".
2.7 Six-Diode Rectifier Block
(2) Six-Diode Rectifier Block
(4) Main Field
The six-diode rectifier block contains the six diodes of the bridge rectifier circuit. Each "AC" terminal connects to an exciter armature wire. The "+" terminal and the "-" terminal connect to main field (4).
On inboard bearing type generators, the six-diode rectifier block is on the end of the generator shaft. On outboard bearing type generators, six-diode rectifier block (2) is mounted on disc (3). Disc (3) is between exciter (1) and main field (4) . The six -diode rectifier block also contains Varistor (CR7) which is used to protect the generator circuit. Refer to Generator Operation, "Generator Circuit Protection".
Fig2.11: Six-Diode Rectifier Block
Fig2.12: Six-Diode Rectifier Block Location (Inboard Bearing)
2.8 Generator Circuit Protection
(CR1 – CR6) Diodes
(L1) Exciter field (stator)
(L2) Exciter armature (rotor)
(L3) Main field (rotor)
(L4) Main armature (stator)
(L5) Pilot exciter armature
(PM) Permanent magnet
(RFA) Rotating field assembly
(TR1) Optional voltage droop transformer
(T0, T1, T2, T3, T7, T8, T9) Generator terminals and/or Generator leads
Fig2.13: Six-Diode Rectifier Block Location (Outboard Bearing)
Fig2.14: PMPE Generator Wiring Diagram
Fig2.15: Varistor (CR7)
Varistor (CR7) protects the following diodes by suppressing any abnormal transient peak voltages: CR1, CR2, CR3, CR4, CR5 and CR6. On generators that use the two-diode rectifier blocks or the three-diode rectifier blocks, Varistor (CR7) is a separate component and mounts on the heat sink assembly. On generators that use the six-diode rectifier block, Varistor (CR7) is contained within the six-diode rectifier block.
Note: Some generators are provided with another Varistor (CR8) for additional protection.
Resistor (R5) is a separate component and mounts on the heat sink assembly. This resistor is only used on some of the larger generators. Resistor (R5) provides a low resistance circuit from the insulated windings to the shaft and cores of revolving field assembly (RFA). Resistor (R5) is a 27000 ohm resistor. Air friction on the windings can cause an electrostatic charge. If this resistor is not installed, these charges can cause voltages to become high enough to destroy the winding insulation. Resistor (R5) allows charges to dissipate as the charges are generated. This resistor also prevents any buildup of voltage. Because of the resistance value and the power rating of resistor (R5), a ground failure at any point on revolving field assembly (RFA) will not prevent the generator from operating normally. A ground failure will not damage resistor (R5) . The voltage regulator and related components also protect the generator. All voltage regulators have fuses, which will stop the current flow to the exciter. When no voltage is applied to the exciter, the generator output voltage is reduced to a very low level. These fuses open very rapidly. This protects against secondary damage that is caused by another component failure. If any fuse is replaced, use only a fuse of the same type and amperage rating. A larger amperage rating or a fuse which does not open rapidly will not prevent damage to other components.
3.1 Engine: A diesel engine (Also known as a compression ignition Engine ) is an internal combustion engine that uses the heat of compression to initiate ignition to burn the Fuel ,Which is injected in to the combustion chamber, of this in contract to spark ignition engines . such as a petrol engine (Gasoline engine ) of gas engine (using gaseous fuel as appeased to gas line).which uses spark plug to ignite an air fuel mixture. the engine was developed by Rudolf Diesel in 1893 .
Fig3.1: Top View of Engine
Fig3.2: Right side view of Engine
3.2Classification of Engine
Primary condition engine two types
- Internal Combustion Engine.
- External Combustion Engine.
Internal engine are two types
- Petrol Engine
- Diesel Engine
- Gas Engine
- Two Stock Engines.
- Four Stock Engine
- Two Stock Engines.
- Four Stock Engine
- Cylinder Head
- Cylinder Block
- Piston ring
- Connecting rod
- Crank Shaft
- Fly wheel
- Intake Valve
- Exhaust Valve
- Breather Cap
- Rocker rum
- Valve Spring
- Valve Guide
- Push rod
- Cam shaft
- Spark plug
3.4 Main part of engine.
- Engine body
- Lubricating Circulation system
- Water Circulation System
- Fuel System
3.5Criteria for the Evaluation
Oil consumption: The oil consumption must not exceed two times the initial oil consumption during the evaluation .The initial oil consumption is established during the first 1000 hours of operation with the oil that is bending evaluated.
Valve Recession: The valves and the valve seats wear over time. This causes the valves to recede into the cylinder head. This condition is called “valve recession”. Measure the valve recession at the engine commissioning. This measurement is the baseline. The baseline is a reference for subsequent measurements. Measure the valve recession according to the engine’s Operation and Maintenance Manual, “Maintenance interval Schedule”. The valve recession must not exceed the limits that are established for the engine by Dealer. Refer to the engine’s Operation and Maintenance Manual, “Valve system projection- Measure/Record” topic for the limits for the valve recession.
Parts requirements: If a new engine used for the field evaluation, all of the engine’s cylinders must be inspected with a bores cope. The cylinder that shows the worst deposits or wear the cylinder that shows average deposits or were must be use for the visual inspection. If a use engine is used to evaluate the oil, two new sets of this component must be installing before the field evaluated: Piston, Piston rings, Cylinder liners, and cylinder heads. This new component examined during the final inspection.
Final Inspection: At the end of the field evaluation, these components from two cylinder must be removed and inspection.
- Piston ring
- Cylinder liners
- Cylinder heads
- Sticking of the piston ring
- Scuffing of the piston rings and /or cylinder liners
- Excessive wear of the piston ring
- Polishing of the cylinder liner bore must be confined to the area that is affected by the uppermost piston of the top piston ring.
3.6 Prime mover (Diesel engine):
A diesel engine is an internal combustion engine which operates using the diesel cycle (named after Dr. Rudolph Diesel). Diesel engines have the highest rate of energy to fuel (kwH/lbs) compared to any internal or external combustion engine. The defining feature of the diesel engine is the use of compression ignition to burn the fuel, which is injected into the combustion chamber during the final stage of compression.
Fig3.4: Cross Section of a V-type four stroke Diesel Engine.
This is in contrast to a petrol (gasoline) engine, which uses the Otto cycle, in which a fuel/air mixture is ignited by a spark plug. Diesel engines are manufactured in two stroke and four stroke versions. They were originally used as a more efficient replacement for stationary steam engines. Since the 1910s they have been used in submarines and ships. Use in locomotives, large trucks and electric generating plants followed later. In the 1930s, they slowly began to be used in a few automobiles. Since the 1970s, the use of diesel engines in larger on-road and off-road vehicles in the USA increased. As of 2007[update], about 50 percent of all new car sales in Europe are diesel.
3.7 Major Parts of Prime mover:
Crankshaft, Turbocharger, Piston, Flywheel Camshaft, Governor and Starter motor.
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation. To convert the reciprocating motion into rotation, the crankshaft has "crank throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank, to which the "big ends" of the connecting rods from each cylinder attach.
Fig3.5: Diesel Engine Crankshaft and Bearings.
It typically connects to a flywheel, to reduce the pulsation characteristic of the four-stroke cycle, and sometimes a torsional or vibrational damper at the opposite end, to reduce the torsion vibrations often caused along the length of the crankshaft by the cylinders farthest from the output end acting on the torsional elasticity of the metal.
Fig3.6: Air fuel oil bearing-supported turbocharger
The objective of a turbocharger is the same as a supercharger; to improve upon the size-to-output efficiency of an engine by solving one of its cardinal limitations. A naturally aspirated automobile engine uses only the downward stroke of a piston to create an area of low pressure in order to draw air into the cylinder through the intake valves. Because the pressure in the atmosphere is no more than 1 bar (approximately 14.7 psi), there ultimately will be a limit to the pressure difference across the intake valves and thus the amount of airflow entering the combustion chamber. This ability to fill the cylinder with air is its volumetric efficiency. Because the turbocharger increases the pressure at the point where air is entering the cylinder, a greater mass of air (oxygen) will be forced in as the inlet manifold pressure increases. The additional oxygen makes it possible to add more fuel, increasing the power and torque output of the engine.
Because the pressure in the cylinder must not go too high to avoid detonation and physical damage, the intake pressure must be controlled by controlling the rotational speed of the turbocharger. The control function is performed by a waste gate, which routes some of the exhaust flow away from the exhaust turbine. This controls shaft speed and regulates air pressure in the intake manifold.
Application of a compressor to increase pressure at the point of cylinder air intake is often referred to as forced induction. Centrifugal superchargers compress air in the same fashion as a turbocharger. However, the energy to spin the supercharger is taken from the rotating output energy of the engine’s crankshaft as opposed to normally exhausted gas from the engine. Superchargers use output energy from an engine to achieve a net gain, which must be provided from some of the engine’s total output. Turbochargers, on the other hand, convert some of the piston engine's exhaust into useful work. This energy would otherwise be wasted out the exhaust. This means that a turbocharger is a more efficient use of the heat energy obtained from the fuel than a supercharger.
A piston is a component of reciprocating engines, pumps and gas compressors. It is located in a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder wall.
Fig3.7: Piston and Piston Rod.
A flywheel is a mechanical device with significant moment of inertia used as a storage device for rotational energy. Flywheels resist changes in their rotational speed, which helps steady the rotation of the shaft when malfluctuating torque is exerted on it by its power source such as a
Flywheel from stationary engine. Note the castellated rim which was used to rotate the engine to the correct starting position by means of a lever.
Video of a flywheel that keeps its rotation rate higher than in a rigid design, constructed based on drawings by Leonardo Vinci
piston-based (reciprocating) engine, or when the load placed on it is intermittent (such as a piston pump). Flywheels can be used to produce very high power pulses as needed for some experiments, where drawing the power from the public network would produce unacceptable spikes. A small motor can accelerate the flywheel between the pulses. Recently, flywheels have become the subject of extensive research as power storage devices for uses in vehicles; see flywheel energy storage.
valves open by pressing on the valve, or on some intermediate mechanism, as they rotate.
Fig3.9: Camshaft position.
Diesel engine speed is controlled solely by the amount of fuel injected into the engine by the injectors. Because a diesel engine is not self-speed-limiting, it requires not only a means of changing engine speed (throttle control) but also a means of maintaining the desired speed. The governor provides the engine with the feedback mechanism to change speed as needed and to maintain a speed once reached. A governor is essentially a speed-sensitive device, designed to maintain a constant engine speed regardless of load variation. Since all governors used on diesel engines control engine speed through the regulation of the quantity of fuel delivered to the cylinders, these governors may be classified as speed-regulating governors. As with the engines there are many types and variations of governors. In this module, only the common mechanical-hydraulic type governor will be reviewed. The major function of the governor is determined by the application of the engine. In an engine that is required to come up and run at only a single speed regardless of load, the governor is called a constant-speed type governor. If the engine is manually controlled, or controlled by an outside device with engine speed being controlled over a range, the governor is called a variable- speed type governor. If the engine governor is designed to keep the engine speed above a minimum and below a maximum, then the governor is a speed-limiting type. The last category of governor is the load limiting type. This type of governor limits fuel, to ensure that the engine is not loaded above a specified limit. Note that many governors act to perform several of these functions simultaneously.
Operation of a Governor:
Following is an explanation of the operation of a constant speed, hydraulically compensated governor using the Woodward brand governor as an example. The principles involved are common in any mechanical and hydraulic governor. The Woodward speed governor operates the diesel engine fuel racks to ensure a constant engine speed is maintained at any load. The governor is a mechanical-hydraulic type governor and receives its supply of oil from the engine lubricating system. This means that a loss of lube oil pressure will cut off the supply of oil to the governor and cause the governor to shut down the engine. This provides the engine with a built-in shutdown device to protect the engine in the event of loss of lubricating oil pressure.
| Cooling system
4.1Function of cooling system.
The cooling system of modern gas engines is precisely balanced. The performance of the cooling system affects may of the engines components. Optimum performance can only be obtained by proper installation and maintenance of the cooling system.
The engine’s cooling system is designed to meet specific guidelines. The proper coolant/antifreeze will provide the following function.
- Adequate heat Transfer.
- Compatibility with the cooling system’s components such as hoses, seals and piping
- Protection from other cavitations erosion
- Protection from freezing and boiling
- Protection from the buildup of corrosion, of sludge, and of scale
- Leaks from hoses, from seals, and from piping
- Cavitations erosion
- Damage from freezing or from boiling
- Plugging of passages for the coolant/antifreeze in components such as radiators, after coolers, Oil coolers and other heat exchangers.
Many engine failures are related to the above conditions cranking of the cylinder head and/or of the engine block, piston seizure, and leakage of the water pump, failure of the water pump and pitting of the cylinder liners.
This problem can be avoided through proper maintenance of the cooling system. Periodically evaluate the maintenance practices in order to make sure that the cooling system is properly maintained.
Fig4.1: Water circulation System for cooling tower to engine.
4.2Water: Water is used in the cooling system in order to transfer heat.
4.3Deionized water or distilled water is recommended for use in engine cooling systems.
If distilled water or demonized water is not available, use water with the properties that are listed in
|Minimum Acceptable water Requirements|
(2.4 grains per US gal )
(5.9 grains per US gal )
(10 grains per US gal )
(20 grains per US gal )
||OF 5.5 TO 9.0|
Fig4.2: Water treatment plant
4.4 Requirement for Ventilating of the cooling system.
To achieve optimum service life for the water cooled components in the gas engine, the cooling system must be able to purge air. Air can be introduced into the cooling system by different means.
- Air can be trapped in the cooling system when the system is filled or when the system is refilled.
- Air that is entrained in the mixture of coolant/antifreeze can be released by cavitations.
- Combustion gas can leak into the cooling system.
The preferred method for venting of the engines cooling system is the installation of vent lines.
Follow these guidelines.
- The vent line must be routed from the highest point of the cooling system on the engine to a point that is higher than any of the engine’s water cooled components.
- Each component that is in a position which can trap air must be vented. For example, the turbocharger and the exhaust bypass valve are usually located at the highest points of the cooling system. One line contact removes the air from both components. If only one of the components is vented, the other component can still tap air. Both of the components must be vented.
- For each cooling circuit, route the vent line into the bottom of the expansion tank.
- The vent line must have a continuous up word slope. To avoid blockage in the vent line, make sure that the vent line is routed in a manner that will avoid trapped fluid. Do not allow any dips in the routing of the vent line.
Fig4.3: Ventilation Fan
4.5 Fundamental device of cooling system.
- Cooling tower/Radiator.
- Heat exchanger.
- Ventilating fan.
- Pump house.
- Cooling tower/ Radiator: Cooling tower use for cooling water.
- Heat exchanger: Heat exchanger use for recoiling water.
- Ventilating fan: Ventilating fan sue for generator outside body temperature rise.
- Pump house: Pump house use for water circulation by pump heat exchanger to cooling tower.
Fig 4.4: Water cooling system by cooling tower.
Fig 4.5: Water cooling system by cooling tower
Fig 4.6: Ventilating fan
Fig4.7: Pump house
Fig4.8: Heat exchanger
Fig4.9: Heat exchanger
5.1 Introduction of Power factor improvement (PFI) Plant.
The low power factor is mainly due to the fact that most of the power loads are inductive and therefore take lagging currents. In order to improve the power factor, some device taking leading power factor should be connected in parallel with the load. One of such device can be a capacitor. The capacitor draws a leading current and partly or completely neutralizes the lagging reactive component of load current. This raises the power factor of the load.
Fig5.1: PFI plant 01
Fig5.2: PFI Plant 02
5.2 Method of power factor Improvement.
Normally, the power factor of the whole load on a large generating station is in the region of 0.8 to 0.9. However, sometimes it is lower in such cases it is generally desirable to take special steps to improve the power fector.
- Static capacitor.
- Synchronous condenser.
- Phase advancers.
5.3 Main parts of PFI plant.
- Static Capacitor
- Synchronous condenser.
- Phase advances.
- Circuit Breaker.
5.4 Static capacitor
The factor can be improved by connecting capacitor in parallel with the equipment operating at lagging power factor. The capacitor draws a leading current and partly or completely neutralizes the lagging reactive component of the load current. This raises the power factor of the load. For three phase loads, the capacitor can be connected in delta or star as shown in figure. Static capacitors are invariably used for the power factors.
Fig5.3 Static Capacitor
5.5 The Advantage of Static capacitor.
1. They have low cost
2. They require little maintenance
3. They can work under ordinary temperature condition
5.6 Disadvantage of static capacitor.
- They have short servicing life from 8 to 10 year
- They are easily damaged if the voltage exceeds the rated value.
5.7 Synchronous condenser.
A synchronous motor takes a leading current when overexcited and therefore, behaves as a capacitor .And over excited synchronous motor running on no load is called synchronous condenser .When the a machine is connected in parallel with the supply, it takes a leading current which partly neutralizes the lagging reactive component of the load. Thus the power factor improved.
5.8 Advantage of synchronous condenser.
- By varying the field excitation the magnitude of current draw by the motor can be change by any amount.
- The motor winding has high thermal stability to short circuit current.
- The fault can remove easily.
5.9 Disadvantage of synchronous condenser.
There are considerable losses in the motor .The maintenance cost is high Except in sizes above 500 KVA, the cost is greater than that of static capacitor in same rating.
5.10 Definition of Fuse
A fuse is a short piece of metal, inserted in the circuit which is melt when excessive current flow through it thus breaks the circuit. The fuse element generally made of materials having melting point & conductivity. It is inserted in series with the circuit to be protected under normal condition it carries normal current flow without overheating. But abnormal condition the increasing current flow the fuse, produce high temperature and then fuse element melt &disconnected the circuit breaker.
5.11 Properties of fuse element.
The function of a fuse is to carry the normal current without overheating but when the current exceeds its normal value, it replay heats up to melting point and disconnects the circuit protected by it. The fuse element should have the flowing desirable characteristics.
- High conductivity
- Low melting point
- least deterioration due to oxidation
- Low coast e. g. lead, copper.
5.12 Circuit breaker.
A circuit breaker is a piece of equipment, which can
- Make or break a circuit either manually or by remote control under normal condition.
- To break a circuit automatically under fault condition.
- Make a circuit either manually or remote control under fault condition.
Fig5.5: Air circuit breaker Fig5.6: 2-Pole miniature circuit breaker
5.13 The classification of circuit breaker.
- Oil circuit breaker
- Bulk oil circuit breaker
- Plain Breaker oil circuit Breakers (POCB)
- Arc control oil circuit breaker
- Plain explosion pot.
- Cross jet explosion pot.
- Semi compensated explosion pot
- Minimum oil circuit breaker.
- Low oil circuit breaker.
- Air Beak circuit breaker.
- Sculpture hexafluoride circuit breaker (SF6)
- Vacuum circuit breaker.
5.14 PFI plant capacitor estimate
Calculating the necessary capacitor capacity to correct the power coefficient
Necessary reactive power for required power factor is calculated as below
= P (tan-tan)
= Reactive power
Cos=present power coefficient
Cos=Power co-efficient which is required to reach
(tan-tan) multiplying factor is shown in table-1
Example: Active power =5ooKW
Cos= 0.7 system, lets calculate the necessary capacitor power to make. Cos= o.96
= =510 Kvar
= =146 Kvar
==514-146 =364 Kvar
5.15 Power factor Improvement plant.
The cosine of angle between voltage and current in and a circuit is known as power factor. This angle depends on the impedance consist of various parameters of the circuit. Causes of low power factor
Low power factor is undesirable for economic point of view.
Normally, the power factor of the whole load on the supply system in lower than 0.8.
The following are the causes of low power factor:
- Most of the ac motor is of induction type which have low lagging power factor. this motor work at a power factor which is extremely small on light load (0.2 to 0.3) and rises to 0.8 or 0.9
|Lube oil||Oil filter difference||Jacket water||Line Gas Press||Engine gas press|
- Arc lams, electric discharge lamp and industrial heating furnaces operate at low lagging power factor.
- The load on the power system is varying being high during morning and evening and low magnetization current .This results in the decreased power factor .inductive or capacitive load is responsible to low power factor. As for example induction motor, transformer, industrial heating furnace, is lamps ballast of tube etc.
5.16 The low power factor has very bad effect over the plant
- of generator: With low power factor the KW capacities lowered Hence increase of current as well as generator copper loss increase. So efficiency is decrease.
- Effect of prime mover: At low power factor alternator develops more reactive power or the watt less power but certain energy is required to develop it, which is applied by the prime mover. So that due to low power factor efficiency of prime mover decrease.
- Effect of Transmission line: At low power factor more current flow through the conductor for transmission line of same power. As the line is to carry more current its cross sectional area will be have to increase, which increase the capital cost of the line. Also increase current, increase the line losses. Hence efficiency of the line is lowered and the line drop also increased.
- Effect of switch gear and bus bar: The cross sectional area of the switch gear must enlarged for the same power to be delivered at low power factor.
| Working description of Industrial power plant
|| chapter 06
6.1 Daily Check List.
- Check and ensure the proper oil level.
- Check and ensure the makeup water level.
- Check all generator input water flow pressure and temperature.
- All generator gas pressure condition after every one hour.
- All generators all data condition checks after one hour.
- All generator sound condition and vibration condition check after every one hour.
- All generators all dc Battery terminal and electro light condition check after one hour.
6.2 Daily Data record in log sheet like as following table.
For Generator 01.
|Time||Temperature of cylinder no (01 to 16)||Average||Stack
6.3 Daily cylinder temperature condition record.
6.4 Maintenance schedule.
|Job description||Frequency||Fist maintenance||maintenance||maintenance|
|Spark plug change||6000||250|
|Lube oil change||2000||83|
|Lube oil fitter change||4000||167|
|Air filter change||8000||333|
|Lube oil sampling test||500||21|
6.5 Working schedule of generator section.
- Every cooling tower should have schedule maintenance after every one week.
- Every pump packing change after every one week.
- Every pump strainer clean after every one week.
- Every motor bearing condition check every one week.
- Pump house schedule maintenance after every 15 days
- Generator power connection check after schedule Maintenance.
- Generator all electrical component connection checks after every six month.
- All Motor power cable connection check after every one month.
- All controlling cable connection check after every one month.
- All generator lube oil level checks after every one hour.
|6.6 Monthly bill calculation.
One Month Gas Bill Calculations For 3 mw Industrial power plant
|Meter Reading||Correction Factor||Cubic Meter||Rate per
7.1 Substation The assembly of apparatus used to change some characteristic (e.g. voltage, Current, AC to DC Frequency ,PF ,etc)of electric supply is called a substation .An electrical substation is a subsidiary station of an electrical generation, transmission and distribution system where voltage is transformed from high to low or the reverse using transformers. Electric power may be flow the several substations between generating plant and consumer, and may be changed in decreasing the current, while a step-down transformer decreases the voltage while increasing the current for domestic and commercial distribution system.
Fig7.2: Generator control panel.
Fig7.3: Generator power panel.
Fig7.4: Bus coupling panel
Fig7.5: PFI panel
7.2 Importance of substation.
Substation is an important part of power plant system. The continuity of supply depends to a considerable extent upon the successful operation of substation .It is therefore essential to exercise utmost care while designing and building substation. The following part is important point which must be kept in view while laying out a substation.
- It should be located at a proper site as far as possible it should be at the center of load.
- It should be provide safe and reliable arrangement. For safety consideration must be given to the maintenance abnormal occurrence such as possibility of explosion or fire etc. For reliability. Consideration must be given for design and construction. The provision of suitable protection gear etc.
- It should be easily operated and maintenance.
- It should involve minimum capital cost.
7.3 Classification of substation
7.3.1 According to service requirement
- Transformer Substation
- Switching Substation
- Power factor correction substation.
- Frequency changer substation.
- Converting substation.
- Industrial substation.
- .2 According to constructional feature the substation are classified.
- Indoor substation
- Outdoor substation
Those substations which change the voltage level of electrical supply are called transformer these substation receive power at some voltage and deliver it at some other voltage. Obviously, transformer will be the main component in such substation. Most of the substation in the power system is of type this.
7.5 Power factor correction substations
Those substations which improve the power factor of the system are called power factor correction substation. Such substation is generally located at the receiving end of transmission the power factor improvement equipment.
7.6 Switching Substation
These substations do not change the voltage level i.e. incoming and outgoing lines have the same the voltage .However they simple perform the switching operations of power line.
7.7 Frequency changer substation
Those substations which change the frequency are known as change substation, such a frequency change may be industrial utilization.
7.8 Converting substation
Those substation which change a.c power into d.c power are called converting substation. The substation which supply power with suitable apparatus (e.g. Ignitron) to supply for such purpose. As traction, electroplating, electric welding.
7.9 Industrial substation.
Those substations which supply power to individual industrial concern are known as industrial substation.
7.10 Indoor substation.
For voltage up to 11kv the equipment of the substation is installed indoor because of economic consideration. However when the atmosphere is contain with impurities these substation can be erected for voltage unto 66kv.
For voltage beyond 66kv, equipment is invariably installed out door. It is because for such voltage the clearance between conductor and the space required for switch, circuit breaker and equipment becomes so great it is not economical to install the equipment indoor.
7.12 Substation Types.
Although, there are generally fours types of substations that are a combination of two or more types.
- Step-up Transmit ions Substation
- Step-down Transmissions Substation
- Distribution Substation
- Underground Substation
- Substation Equipment
- Substation Function.
7.14 Step-down Transmissions Substation:
Step-down transmission substation are located at switching points in an electric grid. To connect different parts of a grid and source for sub-station voltage lines or distribution lines. The step-down substation can change the transmission voltage to a sub-stations voltage usually 69KV.The sub-transmission voltage lines can the serve as a source to distributions. Sometimes, power is taped from the sub-transmission line for use in an industrial facility along the way. The power goes to a distribution.
7.15 Distribution Substation:
Distribution Substation is located near to the end-users. Distribution substation transformers change the transmission or sub-transmission voltage to lower levels for use by end-users. Typical distribution voltages vary from 34,500Y/19,920 volts to 4,160Y/2400volts are interpreted as a three-phase circuit with a grounded neutral sources. This would have their high-voltage conductors or wires and one grounded neutral conductor, a total of four wires. The voltage between the three phase conductors or wire would be 34,500 volts and the voltage between one phase conductor and the neutral ground would be 19,920 volts. From here the power plant is distributed to industrial, commercial, and residential customers.
Fig7.6: Bus bar distribution system.(Bridge)
7.16 Underground Distribution substation:
Underground substation is also located near to the end-users. Distribution substation fig transformer changes the sub-transmission voltage to lower levels for use by end users. Typical distribution voltage vary from 34,500Y/19,920volts to 4, 160Y/2400 volts.
An underground system may consist of these parts:
- High-Voltage Underground Cables
- Transformer Vault
7.17 Function of substation: Substations are designed to accomplish the following functions, although not all substations have all these functions:
- Change voltage from one level to another.
- Regulate voltage to compensate for system voltage changes.
- Switch transmission and distribution circuits into and out of the grid system.
- Measure electric power qualities flowing in the circuits.
- Connect communication signals to the circuits.
- Eliminate lightning and other electrical surges from the system.
- Connect electric generation plants to the system.
- Make interconnections between the electric systems of more than one utility.
- Control reactive kilovolt-amperes supplied to and the flow of reactive kilovolt-amperes in the circuits.
|Air circuit breaker||Distribution Bus||Potheads|
|Batteries||Duct Runs||Power-line carrier|
|Bus Support Insulators||Frequency Changers||Power Transformers|
|Capacitor bank||Grounding Resistors||Rectifiers|
|Circuit Switchers||Grounding Transformers||Relays|
|Concrete Foundation||High-Voltage Underground Cables||SF6 Circuit Breakers|
|Conduits||High-Voltages Fuses||Shunt Reactors|
|Control House||Lighting Arresters||Steel Superstructures|
|Control panels||Manholes||Supervisory Control|
|Control Wires||Metal-clad Switchgear||Suspension Insulators|
|Converter station||Meters||Synchronous condenser|
7.18 The major components of typical substation are:
|One year cost analysis of 20mw Industrial power plant|
8.1 Manpower Cost Analysis of one month
|Designation||Salary||No .of post|
|Plant In charge||100000||01|
|Total Cost for one month||371000||18|
Manpower one month Cost taka 371000/=
Manpower one year cost taka 4452000/=
8.2 Fuel Cost Analysis of one year only for 3mw Generator.
|One year Gas Bill Calculations For 20 mw Industrial power plant|
|Meter Reading||Correction Factor||
|One year total cost For 3 MW Plant||24798717|
|One year total Taka For 1 MW Plant||8266239|
|One year total Taka For 20 MW Plant||165324783|
8.3 One year spare Parts consumption of 20mw power plant.
One year schedule changing parts consumption for 1 mw generator plant.
|Parts description||Change Frequency||Change Quantity||Unite Price||Total Price|
|Spark plug||6000hr/250Day||32 Pcs||7786||249152.00|
|Air filter||8000hr/333Day||2 Pcs||30755||61510.00|
|Lube oil filter||2500hr/104Day||6 Pcs||3806||22836.00|
|Lube oil change + Make up||2500hr/104 Day||(1110+3650)=4060 Liter/23 Dram||64000/Dram||1472000.00|
|Grease||1000hr/41 Day||9 Can||796||7164.00|
One Year schedule spare parts for 1 MW power plant. 18, 24,920.00
One Year schedule spare parts for 20 MW power plants. 3, 64, 98,400.00
One Year Troubleshooting spare spats consumptions
|Description||Unite Price||Total Price|
|Water pressure switch|
|Oil cooler kit|
Fuel and Lubricant Specification
9.1 Engine oil performs several functions.
- Keeping the engine clean
- Preventing rust and corrosion
- Acting as coolant
- Reducing friction and wear
9.2 Lubricating Maintenance system.
The flowing cost is associated with maintenance of the engine lubrication system.
- Initial Fill
- Analysis of the engine oil
- Replacement of the engine oil and engine oil filter
- Disposal of the used engine oil
Maintaining the engines lubricating system is usually between 10 and 20 percent of total coast of the engine maintenance .This percentage can be affected by the type of fuel, the engines duty cycle, and the maintenance practices.
9.3 Problem of use incorrect oil
The flowing problems can result from the use incorrect engine oil.
- Buildup of varnish (glazing) in the cylinder liners.
- Damage to bearings.
- Deposits on the valves that can lead to guttering of the valves.
- Oil cooking in the turbocharger.
- Piston rings and valves that stick.
9.4 Fuel Specification (General information):
Gaseous fuel consists primarily of hydrocarbons (Combinations of hydrocarbon and carbon) and some insert gases. Pipe line natural gas has been used for many years. Other types of fuels such as wellhead gas, biogas, and manufactured and gas need to be reviewed for acceptability.
Each commercial fuel gas is a mixture of gases. Some of the gases are combustible and some of the gases are inset. The compositions of these gas mixtures have extreme variation.
Gas engine will operated successfully on a board range of gaseous fuels. Adjustment must be made to the fuel system when the engine is commissioned or when fuel is changed. Consult your dealer about the proper adjustments.
Permissible fuels must be analyzed in order to determine the following characteristics.
Composition, Contaminants, Heat value, & Methane number.
Before the engine arrangement is ordered, use the methane number to determine the following characteristics for the new engine; Compression ratio. Fuel system components, Ignition timing & Rated load.
Fig9.1: Gas Filter
Fig9.2: Header Line gas pressure meter.
Fig9.3: Gas regulating meter with pressure meter.
Practical Aspect of Protective System of Generator
Electrical protective devices for generating power systems consist of fuses, circuit breakers, relays and other types of devices typically designed to interrupt the current flow in an electrical power system when fault occur. Protective device coordination is the process of determining the "best fit" timing of current interruption when abnormal electrical conditions occur. The goal is to minimize an unexpected but necessary power outage to the smallest extent possible. Modern methods normally include detailed computer based analysis and reporting.
10.2 Generator Protection
Generator protection requires the consideration of many abnormal conditions that are not present with other system elements. The abnormal conditions that may occur with generators include
Stator (due to overload or loss of cooling)
1. Rotor (due to over excitation, loss of cooling , negative sequence stator currents)
2. Winding faults
3. Stator (phase and ground faults)
4. Rotor (ground faults and shorted turns)
5. Over speed and under speed
6. Over voltage
7. Loss of excitation
9. Unbalanced current operation
10. Out of step
11. Sub-synchronous oscillations
12. Non synchronized connection
We generally evaluate the protection settings based on relay application manuals provided by the relay manufacturers and use variety of analytical tools and calculations where needed for further investigations to assess the adequacy of protection and relay performance.
A relay is an electrical switch that opens and closes under the control of another electrical circuit. In the original form, the switch is operated by an electromagnet to open or close one or many sets of contacts. It was invented by Joseph Henry in 1835. Protective relays are to be designed to isolate the faulted portion of the system at the earliest with minimum system disruption. When the relays meant to protect specific equipments, such as speed controller, synchronizer, programmable logic circuit, cranking motor. electric ignition system etc. The relays must also be able to discriminate between faulted conditions, normal operating conditions and abnormal operating conditions. Relay coordination calculation module must consider the operating characteristics of the relays and must determine the optimum relay settings to achieve the objectives stated. The parameters of the under frequency and under voltage relays can be set and their performance can be evaluated using transient stability analysis.
Relays are amazingly simple devices. There are four parts in every relay:
(b) Armature that can be attracted by the electromagnet
(d) Set of electrical contacts
10.4 Voltage Monitoring Relay
A relay consists of two separate and completely independent circuits. The first is at the bottom and drives the electromagnet. In this circuit, a switch is controlling power to the electromagnet. When the switch is on, the electromagnet is on, and it attracts the armature (blue). The armature is acting as a switch in the second circuit. When the electromagnet is energized, the armature completes the second circuit and the light is on. When the electromagnet is not energized, the spring pulls the armature away and the circuit is not complete. In that case, the light is dark.
Whether the contact (if only one contact is provided) is normally open (NO) or normally closed (NC)
10.4 Voltage Monitoring Relay
(a) Detects Phase Failure, Voltage Unbalance, Phase Reversal, and Under voltage
(b) Provides Pre-Start and Running Protection on the Line Side of the Point of Connection These monitors are used in a wide range of applications for protecting generator electronics device and other appliance against the damaging effects of single phasing and overloads
Wiring Diagram of Voltage Monitor
Fig10.2: Wiring diagram of Voltage Monitor.
Line Voltage Monitor — provides pre-start and running protection against abnormal voltage conditions on line side of voltage monitor only.
10.5 Speed Sensing Relay
Via the output frequency of the generator, the BZ1 detects the speed of the generator set to be supervised. The relay is provided with three independently adjustable elements for ignition speed, under- and over speed. The rated frequency can be changed from 50 Hz (left stop) to 60 Hz (right stop) by means of potentiometer CAL. At output CAL-A2 a current of 0 – 20 mA in proportion to the speed is available for indication of speed. BZ1-G is most commonly used to detect the speed of engines used in generating sets. The pick-up, situated close to the flywheel, produces a high frequency pulse train directly proportional to the number of teeth passing it. The frequency is converted by the ST3 into a mA signal directly proportional to the rotational speed of the flywheel. The relay provides the user with the following adjustments, which allows the control of start up and normal running and protects against over and under speeds of the generator. Adjustment of crank speed 10 to 50% Adjustment of under speed 50 to 100% Adjustment of over speed 100 to 133 % A mA output signal proportional to input frequency.
Fig10.3: Speed Sensing Relay
10.6 Auxiliary voltage supply
The unit BZ1 needs a separate auxiliary voltage supply. The supply voltage will be connected to terminals A1 –A2 Different status of the speed monitoring relay:- 1.Normal Condition: During normal condition fZ is normally closed in the point of 11 & 14 and f< is normally closed in the point 24&21. and also f> is normally closed in the point 34&31.
Fig10.4: Connection Terminal
2.Operation without Fault & unit dead ignition speed not achieved condition . During operation without fault condition fz is normally closed in the point of 11 & 12 .and f< is normally closed in the point 21&22. and also f> is normally closed in the point 34&31. During unit dead or ignition speed not achieved condition fz is shown that 14 &11 is closed position but f< is changed in the point of 21 & 24 where as it is closed. f> is also change in the point 0f 31 &34 shown closed.
Fig10.5: Operation without fault and dead condition
3. Under speed & Over speed Condition:- During under speed condition fz is normally closed the point of 11 & 12 .and f< is normally closed in the point 24&21. and also f> is normally closed in the point 34&31. During over speed condition fz is shown same position but f< is changed in the point of 21 & 22. f> is also change in the point of 31 &32 shown closed.
Fig10.6: Operation under speed and over speed
- Overload Relay
Fig10.7: Overload relay
Overload relays of various sorts have long been utilized in connection with the operation of electrical equipment, particularly electrical equipment drawing relatively high levels of power. Single-phase and multi-phase (e.g., three-phase) power systems typically include an overload relay for interrupting power in the power conductors when a fault condition occurs, such as a ground fault, phase loss, over current, or under current condition. Overload relays are normally used in conjunction with an electromechanical contactor, that may be used to disconnect power from equipment, for example, from a three-phase motor, when an overload condition exists. Electric motors are one type of electrical load which can be started and stopped using a contactor. The contactor includes a contact associated with each phase conductor connected to the motor. A contact of an overload relay is typically connected in series with the coil of the contactor to cause the contactor to open when an overload condition is sensed. The overload relay senses an overload condition by monitoring the current in each of the three-phases received by the motor windings. For a three-phase motor, the contactor would include three contacts which are opened and closed in unison. The overload relay includes current sensing elements that are wired in series with the three phases passing through the contactor. In this way, the overload relay can monitor current flowing in the three phases through the contactor, and based on current magnitude and duration, may interrupt the current flow through the contactor armature circuit to open the contactor contacts when an overload occurs. The mechanical motion required to open and close the contacts is provided by a solenoid including a coil. The coil is controlled by a basic circuit which includes a normally closed stop button, a normally open start button, and an overload switch. When an overload condition is experienced, power is supplied to a solenoid in the electromechanical trip mechanism causing a plunger to retract, which subsequently, through a series of levers or other mechanical components, causes the normally closed contacts to open. Many overload relays have been designed such that, once tripped, the relay remains open to prevent current flow to the contactor until the relay is manually reset by a system operator. A common resetting device is a reset push button selectable by an operator to reset the relay thereby allowing current to flow to and to close the contactor coil which in turn provides current to the linked equipment. An overload relay is usually designed to operate over a wide range of values and the user must set the trip current based upon the specifications of the motor in use. The trip current defines the value at which the relay is triggered into breaking the circuit between the load and the power. The trip point of the overload relay is selected by moving a pointer from one position on a scale to another position on the scale. The pointer is connected to a variable resistor in the overload sensing circuit such that as the pointer is moved from one positions to another along the scale the resistance of the variable resistor changes. The two most critical elements in the overload sensing circuit are the current transformers through which a current proportional to that flowing in the protected circuit is induced and the variable resistor which changes circuit characteristics such that the relay will initiate a trip at the selected overload current. In addition to the mechanical components, a fully featured relay assembly also typically includes a printed circuit board (PCB) including control circuitry for tripping and automatically resetting the relay, current sensors and various types of terminals for linking to power lines, the contactor and perhaps indicating lights. A variety of types of overload relays are available, ranging from simple thermal overload relays to more complex, solid-state relays which may include some intelligence and/or reporting capabilities. A thermal overload relay is a bimetallic device which provides motor protection for running and stalled rotor overloads. A strip bimetal in the overload relay is electrically heated by heater elements which carry the motor currents. Bimetal overload relays include a snap action electrical switch which has a contact that is movable between an un-actuated and an actuated position to make or break electrical connection with a stationary contact. This movable contact is mechanically coupled to a main bimetal element that is responsive to changes in temperature to operate the electrical switch. Excess heat is generated in the heater elements by an overloaded motor. The bimetals deflect to thermally open the normally closed contact, thereby opening a coil circuit of a magnetic contactor which disconnects the overloaded motor from the line. Thereafter the relay may be reset by pressing and releasing a reset rod. With advances in electronic circuitry, the bi-metallic element has been replaced with more complex circuitry. Overload relays have been designed to utilize electronic circuitry responsive to signals derived from the secondary windings of current transformers whose primary windings carry the motor phase currents. Such circuitry may sample current flow to the motor on a periodic basis and provide sophisticated overload prediction based not only on a simple threshold but on more complex trend analyses. The output of this circuitry is typically a low-powered overload signal. The electronic circuitry processes these signals on a current-time integral basis to determine when a current overload condition is sufficiently persistent to require interruption of the motor circuit. In order for this overload signal to control the contactor coil current, a solid state switch may be required, adding to the complexity and cost of the overload relay. The electronic circuitry can be readily designed to recognize not only overload conditions, but also high fault current conditions calling for circuit interruption without delay and hazardous ground fault conditions. Big metal and eutectic overload relays include heater elements in each phase which open when an excessive current flowing through the heater elements causes the element to exceed a specific temperature. Solid-state relays, on the other hand, include electronic devices for monitoring phase current and for determining, based on the monitored current, whether a fault condition has occurred. Solid-state relays typically can be configured to provide protection for ground fault, undercurrent and phase loss conditions, in addition to over current conditions. Solid state overload relays are commonly available in relatively compact, affordable packages that can be easily installed and serviced. In addition to circuitry for detecting fault conditions, such relays also commonly include power supply circuitry for storing energy from the load circuit being controlled.
10.8 Miniature Circuit breaker
A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.
Fig10.8: A 2 pole miniature circuit breaker
All circuit breakers have common features in their operation, although details vary substantially depending on the voltage class, current rating and type of the circuit breaker. The circuit breaker must detect a fault condition; in low-voltage circuit breakers this is usually done within the breaker enclosure. Circuit breakers for large currents or high voltages are usually arranged with pilot devices to sense a fault current and to operate the trip opening mechanism. The trip solenoid that releases the latch is usually energized by a separate battery, although some high-voltage circuit breakers are self-contained with current transformers, protection relays, and an internal control power source. Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit; some mechanically-stored energy (using something such as springs or compressed air) contained within the breaker is used to separate the contacts, although some of the energy required may be obtained from the fault current itself. Small circuit breakers may be manually operated; larger units have solenoids to trip the mechanism, and electric motors to restore energy to the springs. The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting the circuit. Contacts are made of copper or copper alloys, silver alloys, and other materials. Service life of the contacts is limited by the erosion due to interrupting the arc. Miniature circuit breakers are usually discarded when the contacts are worn, but power circuit breakers and high-voltage circuit breakers have replaceable contacts. When a current is interrupted, an arc is generated – this arc must be contained, cooled, and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas, or oil as the medium in which the arc forms. Different techniques are used to extinguish the arc including:
Lengthening of the arc Intensive cooling (in jet chambers)
Division into partial arcs Zero point quenching
Connecting capacitors in parallel with contacts in DC circuits
Finally, once the fault condition has been cleared, the contacts must again be closed to restore power to the interrupted circuit.
Must incorporate various features to divide and extinguish the arc.
The maximum short-circuit current that a breaker can interrupt is determined by testing. Application of a breaker in a circuit with a prospective short-circuit current higher than the breaker's interrupting capacity rating may result in failure of the breaker to safely interrupt a fault. In a worst-case scenario the breaker may successfully interrupt the fault, only to explode when reset.
Miniature circuit breakers used to protect control circuits or small appliances may not have sufficient interrupting capacity to use at a panel board these circuit breakers are called "supplemental circuit protectors" to distinguish them from distribution-type circuit breakers.
10.9 Air Circuit breaker (ACB)
Front panel of a 1250 A air circuit breaker manufactured by ABB. This low voltage power circuit breaker can be withdrawn from its housing for servicing. Trip characteristics are configurable via DIP switches on the front panel.
Many different classifications of circuit breakers can be made, based on their features such as voltage class, construction type, interrupting type, and structural features.
Fig10.9: Air Circuit breaker
10.10 Low voltage circuit breakers:
Low voltage (less than 1000 VAC) types are common in domestic, commercial and industrial application, include:
Fig10.10: Photo of inside of a circuit breaker
MCB (Miniature Circuit Breaker)—rated current not more than 100 A. Trip characteristics normally not adjustable. Thermal or thermal-magnetic operation. Breakers illustrated above are in this category.
MCCB (Molded Case Circuit Breaker)—rated current up to 1000 A. Thermal or thermal-magnetic operation. Trip current may be adjustable in larger ratings. Low voltage power circuit breakers can be mounted in multi-tiers in LV switchboards or switchgear cabinets.
Electronic symbols for a fuse. IEC (upper) and American (lower two) versions. n electronics and electrical engineering a fuse (short for fusible link) is a type of over current protection device. Its essential component is a metal wire or strip that melts when too much current flows, which breaks the circuit in which it is connected, thus protecting the circuit's other components from damage due to excessive current.
A practical fuse was one of the essential features of Thomas Edison's electrical power distribution system.
Fuses (and other over current devices) are an essential part of a power distribution system to prevent fire or damage. When too much current flows through a wire, it may overheat and be damaged, or even start a fire. Wiring regulations give the maximum rating of a fuse for protection of a particular circuit. Local authorities will incorporate national wiring regulations as part of law. Fuses are selected to allow passage of normal currents, but to quickly interrupt a short circuit or overload condition.
10.12 Rated current IN
This is the maximum current that the fuse can continuously pass without interruption to the circuit, or harmful effects on its surroundings.
The speed at which a fuse operates depends on how many current flows through it and the material of which the fuse is made. In addition, temperature influences the resistance of the fuse. Manufacturers of fuses plot a time-current characteristic curve, which shows the time required melting the fuse and the time required to clear the circuit for any given level of overload current.
Fuses are often characterized as "fast-blow", "slow-blow" or "time-delay", according to the time they take to respond to an over current condition. The selection of the characteristic depends on what equipment is being protected. Semiconductor devices may need a fast or ultra fast fuse for protection since semiconductors may have little capacity to withstand even a momentary overload. Fuses applied on motor circuits may have a time-delay characteristic, since the surge of current required at motor start soon decreases and is harmless to wiring and the motor.
10.14 The L2t value:
This is a measure of the energy required to blow the fuse element and is an important characteristic of the fuse. It is an indication of the "let-through" energy passed by the fuse which downstream circuit elements must withstand before the fuse opens the circuit.
10.15 Voltage drop:
The values of the voltage drop across a fuse are usually given by the manufacturer. A fuse may become hot due to the energy dissipation in the fuse element at rated current conditions. The voltage drop should be taken into account particularly when using a fuse in low-voltage applications.
10.16 Breaking capacity:
The breaking capacity is the maximum current that can safely be interrupted by the fuse. Generally this should be higher than the prospective short circuit current. Miniature fuses may have an interrupting rating only 10 times their rated current. Some fuses are designated High Rupture Capacity (HRC) and are usually filled with sand or a similar material. Fuses for small low-voltage wiring systems are commonly rated to interrupt 10,000 amperes. Fuses for larger power systems must have higher interrupting ratings, with some low-voltage current-limiting HRC fuses rated for 300,000 amperes. Fuses for high-voltage equipment, up to 115,000 volts, are rated by the total apparent power (megavolt-amperes, MVA) of the fault level on the circuit.
10.17 Rated voltage:
The voltage rating of a fuse should always be greater than or equal to the circuit voltage. For example, glass tube fuses rated 32 volts should never be used in line-operated (mains-operated) equipment even if the fuse physically can fit the fuse holder. Fuses carrying a 250 V rating may be safely used in a 125 V circuit, but the reverse is not true as the fuse may not be capable of safely interrupting the arc in a circuit of a higher voltage. Low-voltage fuses can generally be used at any voltage up to their rating.
Medium-voltage fuses rated for a few thousand volts are never used on low voltage circuits, due to their expense and because they cannot properly clear the circuit when operating at very low voltages.
All power system of today operates with grounded neutrals. Neutral grounding offers several advantages. The neutral point of generator, transformer, circuit rotating, machines etc. is connected to earth directly or through a reactance .In some cases the neutral point is earthed though an adjustable reactor of a reactance matched with line to earth capacitance of a line. The neutral earthing is one of the most important features of system design to a switchgear and protection engineer, neutral grounding is important.
Fig11.1: Earthing Pit
The word of ‘earth’ or ‘ground’ means many difference things to many electrical engineers. In an electrical installation these word can be used to mean either the protective conductor in a mains cord, the common bonding network of the building, the earth mass electrode of the lighting protection system, the conductor of the mains supply that is connected to an earth mass electrode at the distribution transformer.
The earth fault protection is based on the method of neutral earthing. The system voltage during earth fault depends on neutral earthing, neutral earthing has associated, neutral earthing is provided basically for the purpose of protection against arcing ground, unbalanced voltage with respect to earth, protection, from ear ting and improvement of the system. The word a earthing and grounding have the same meaning. The earthing is used in U.K. and grounding in U.S..A . Ground means earth .Equipment earthing is different from neutral point earthing. Equipment earthing is connecting to earth the non-current carrying metallic parts in the neibour hood of electrical circuit.
The non-current carrying parts include the following:
- Motor body, switchgear metal enclosure, transformer tank, conduits o wiring etc.
- Support structures, tower, pole etc.
- Sheets of cables.
- Body of portable equipment such as iron, oven etc, thus the purpose of neutral Earthing,
- Equipment Earthing is distinctly.
11.3 Earth conductor
This is the part of earthing system, which joins or bonds together all the metal parts of an installation. The earth conductor shall have a short tine capacity adequate for the fault current which can floe in the grounding conductors for the operating time of the system.
The flowing table gives the minimum size of copper circuit conductor.
Minimum cross sectional area of the copper earth conductors in relation to the area of the associated phase conductor.
Table size of earth conductor
|Cross-Sectional area of the phase conductor(mm2)||Minimum cross-sectional area of the corresponding earth conductor (mm2)|
|Less than 16||Same as cross-sectional area of the phase conductor but not less than 14 SWG.|
|16 or greater but less than 35||16|
|35 or greater||Half of the cross-sectional area of phase conductor.|
11.4 Earthing lead
Earthing lead is the link, which provides connection between the earth conductors and the earth electrode.
11.5 Earthing Electrode
The earthing electrode shall has far pa practicable into permanently moist soil p-referable below associated ground water table . This resistance of earth electrodes shall be not more than one ohm.
Some important things for the earth electrodes.
-copper rod shall have a minimum diameter of 12.7
-GI pipes shall have a minimum diameter of 50mm.
-Copper plate shall not be less then 600mm, 600 in size, with 6mm thickness.
11.6 Definition Of Important Terms
1. Earthing or grounding: connecting to earth or ground.
2. Neutral earthling: connecting to earth, the neutral point i.e. the star point of generator, transformer, rotating machine, neutral point of a grounding transformer.
3. Reactance earthling: connecting to the neutral point to earth through a reactance.
4. Resistance earthling: connecting to the neutral point to earth through a resistance.
5. No effecting earthling: when an intentional resistance or reactance is connected between neutral point and earth.
6. Solid earth or effective earthling: connecting the neutral point to earth without intentional resistance or reactance co-efficient earthling.
7. Resonant earthling: earthling through a reactance of such as value that power frequency current in the neutral to ground connection is almost equal opposite to power frequency capacitance current between unallied line and earth.
4. Co-efficient of earthling: coefficient of earthling is defined as the, ratio of highest r. m .s voltage of healthy line to earth to the line to line r. m. s voltage.
9. Petersen coil suppression coil, ground fault neutralized: all the three terms have the same meaning the adjustable reactor connected between neutral to earth.
10. Underground system: the system whose neutral points are not earthed the system is also called insolated neutral system.
11. Earth fault factor: it is calculated at the selected the selected point of the system for a given system. It is a ratio earth fault factor=V1/V2.
11.7 Equipment Earthing Ensure safety.
The potential of the earthed body does not reach to dangerous high voltage above the earth since it is connected to the earth. The earth fault current flows through the earthing and may readily causes operation of fuse or an earth fault protection. The value of earth resistance dose not remain constants on the soil and this maximum during dry season.
The following valves of earth resistance will give satisfactory result.
- Large power ststion-0.5 ohm
- Major power station-1.0 ohm
- Small power ststion-2.0 ohm
- Earth electrode
- Earth lead
- Earth continuity conductor
According to Earth Electrode, the Earthing system can be classified as:
- Strip or wire earthing
- Rod earthing
- Pipe earthing
- Plate earthing
|Sl No||Details||Size||Quantity||Unit Run(feet)|
|1||NYY||120m||2runs,neutral to earthing pit|
|2||NYY||95m||2 run, alternator body to earthing pit|
|3||NYY||50m||4 runs,(control panel, starting motor ,engine body, other panel) to earthing pit|
|4||PVC/PVC||16m||1 run, Battery charger to earthing pit|
|5||Cable Socket||16m||4 pcs|
|6||Cable Socket||50m||10 pcs|
|7||Cable Socket||95m||4 pcs|
|9||GI Socket||inch||8 pcs|
|11||Stranded copper wire||95m||340|
|12||Copper Bar(bas bar)||inch||2 pcs|
|13||Copper Nut-bolt||inch||30 pcs|
11.9 Method of Earthing.
The useful method of earthing is to join the exposed metal to earth via continuity conductors connected to an electrode buried in the ground. There elements required for earthing system are Earth conductor, Earthing lead and Earth electrode.
|Conclusion and Future work||Chapter 12|
During preparing this thesis documents we had to travel various industrial complexes to see and compare the methods that they follow. Accordingly we had to visit the suppliers of the generator s to collect the manuals and compare the information with this manuals those we received from the various users. During visit of different industries we needed to take some photo but some of the industries did not allow us to take photograph, in this respect it was very hard for us. Later with the help of a senior we finally succeeded to have the photos
In earlier days, electrical energy was supplied by the localized generators. But with the advancement of time the generators were interconnected which results in the development of more and more complex power system and now the interconnected system is very efficient in reliable transmission and distribution of electrical power due to proper modeling and design of the power system with adequate facilities of protective devices. The protective relaying scheme senses the abnormal conditions in a part of the power system and gives an alarm or isolates that part from the healthy system. The relays are compact, self contained devices which respond to abnormal condition. The relays distinguish between normal and abnormal conditions. Whenever an abnormal condition develops, the relays close its contacts, there by the trip circuit of the circuit breaker is closed and the circuit breaker opens and the faulty part is disconnected from the system. In this thesis we improve the system loss to use PFI plant up to 0.65%.
12.2 Future Work
The electrical response of the voltage transformers has successfully been tested under 50 conditions. Nevertheless, when the input frequency or the electrical voltage is higher, as is the case of the lighting test, the behavior is influenced by the inertia of the masses of the system. These forces are for the high mechanical stresses generated by the actuator, which deforms easily the housing and produce deformations and accelerations with significant associated inertial forces. In order to overcome this problem different suggestion for future work are purposed.
 “Installation Manual” Caterpillar Engine, 2004, USA.
 “Complementary Information” Caterpillar Engine, 2001, USA.
 “Operation and maintenance manual” Caterpillar Engine, 2001, USA.
 “ Mechanical Systems”, Energypac Power Generation Ltd. Bangladesh. & http://en.wikipedia.org.
 “Electrical Manual”, Energypac Power Generation Ltd. Bangladesh. & http://en.wikipedia.org.
 Switchgear Protection and Power Systems, Sunil S. Rao, Twelfth Edition, 2007. Protection Systems Energypac power generation Ltd.” Energypac Power Generation Ltd.” Bangladesh.
 en.wikipedia.org/wiki/Electrical _ Substation.
 en.wikipedia.org/wiki/Transformer_ types.
 en.wikipedia.org/wiki/Current_ transformer