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1.0: Introduction

Energy can neither be created nor be destroyed. Generator use of prime mover and produce electrical power. We describe this chapter as working principal, practical procedure of a basic generator. Here, also discuses that main component, parts and construction of generator.

1.1: Generator Principle

In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge (usually carried by electrons) to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow (but does not create water). The source of mechanical energy may be a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, a wind turbine, a hand crank, compressed air or any other source of mechanical energy.

The reverse conversion of electrical energy into mechanical energy is done by an electric motor, and motors and generators have many similarities. In fact many motors can be mechanically driven to generate electricity, and very frequently make acceptable generators.

1.2: Historical developments

Before the connection between magnetism and electricity was discovered, electrostatic generators were invented that used electrostatic principles. These generated very high voltages and low currents. They operated by using moving electrically charged belts, plates and disks to carry charge to a high potential electrode. The charge was generated using either of two mechanisms:

Electrostatic induction

The turboelectric effect, where the contact between two insulators leaves them charged.

Because of their inefficiency and the difficulty of insulating machines producing very high voltages, electrostatic generators had low power ratings and were never used for generation of commercially significant quantities of electric power. The Wimshurst machine and Van de Graff generator are examples of these machines that have survived. [1]

1.3: Practical Generator

The simple loop generator has been considered in detail merely to bring out the basic principle underlying construction and working of an actual generator, which consists of the following essential parts:

  1. Magnetic Frame or Yoke
  2. Pole-Cores and Pole-Shoes
  3. Field Poles
  4. Field Coils
  5. Armature Core
  6. Armature Winding or Conductors
  7. Commutator
  8. Brushes and Bearing.

1.4: Main Parts of Generator:

Figure 1.1 Generator Main Parts [2]

1.5: The Component Parts of Generators

Figure 1.2 component parts of generators [3]

In the above figure, views A through E, shows the component parts of generators.

1.6: Yoke

Yoke is an outer frame. It serves two purposes

(i) It provides mechanical support for the poles and acts as a protecting cover for the whole machine and

(ii) It carries the magnetic flux produced by the poles.

In small generators where cheapness rather than weight is the main consideration, yokes are made of cast iron. But for large machines usually cast steel or rolled steel is employed. The modern process of forming the yoke consists of rolling a steel slab round a cylindrical mandrel and then welding it at the bottom. The feet and the terminal box etc are welded to the frame afterwards. Such yokes possess sufficient mechanical strength and have high permeability. [4]

1.7: Pole Cores and Pole Shoes

The field magnets consist of pole ores and pole shoes. The pole shoes have two purposes:-

(i) They spread out the flux in the air gap and also, being larger cross section, reduce the reluctance of the magnetic path

(ii) they support the exciting coils (field coils) [5]

1.8: Field Poles

The pole cores can be made from solid steel castings or from laminations. At the air gap, the pole usually fans out into what is known as a pole head or pole shoe. This is done to reduce the reluctance of the air gap. Normally the field coils are formed and placed on the pole cores and then the whole assembly is mounted to the yoke. [6]

1.9: Field Coils

The field coils are those windings, which are located on the poles and set up the magnetic fields in the machine. They also usually consist of copper wire are insulated from the poles. The field coils may be either shunt windings (in parallel with the armature winding) or series windings (in series with the armature winding) or a combination of both. [7]

1.10: Armature Core or Stack

The armature stack is made up thin magnetic steel laminations stamped from sheet steel with a blanking die. Slots are punched in the lamination with a slot die. Sometimes these two operations are done as one. The laminations are welded, riveted, bolted or bonded together.

It houses the armature conductors or coils and causes them to rotate and hence cut the magnetic flux of the field magnets. In addition to this its most important function is to provide a path of low reluctance to the flux through the armature from a N-pole to a S-pole. It is cylindrical or drum shaped and is built up of usually circular sheet steadies or laminations approximately 5mm thick. It is keyed to the shaft. [8]

1.11: Armature Windings

The armature windings are usually former-wound. These are first wound in the form of flat rectangular coils and are then pulled into their proper shape in a coil puller. Various conductors of the coil are insulated rom each other. The conductors are placed in the armature slots which are lined with tough insulating material. This slot insulation is folded over above the armature conductors placed in the slot and is secured in place by special hard wood or fiber wedges.

Figure 1.3 Two Pole Gramme Ring Winding [9]

1.12: Field Windings

The field windings provide the excitation necessary to set up the magnetic fields in the machine. There are various types of field windings that can be used in the generator or motor circuit. In addition to the following field winding types, permanent magnet fields are used on some smaller DC products. [10]

1.13: Shunt wound motor

Shunt wound motors, with the armature shunted across the field, offer relatively flat speed-torque characteristics. Combined with inherently controlled no-load speed, this provides good speed regulation over wide load ranges. While the starting torque is comparatively lower than the other DC winding types, shunt wound motors offer simplified control for reversing service.

Figure 1.4 Shunt Wound – DC Operation [11]

1.14: Compound wound motor

Compound wound (stabilized shunt) motors utilize a field winding in series with the armature in addition to the shunt field to obtain a compromise in performance between a series and shunt type motor. This type offers a combination of good starting torque and speed stability. Standard compounding is about 12%. Heavier compounding of up to 40 to 50% can be supplied for special high starting torque applications, such as hoists and cranes.


Figure 1.5 Compound Wound – DC Operation [12]

1.15: Series wound motor

Series wound motors have the armature connected in series with the field. While it offers very high starting torque and good torque output per ampere, the series motor has poor speed regulation. Speed of DC series motors is generally limited to 5000 rpm and below. Series motors should be avoided in applications where they are likely to lose there load because of their tendency to “run away” under no-load conditions. These are generally used on crane and hoist applications.

Figure 1.6 Series Wound – DC Operation [13]

1.16: Permanent magnet motor

Permanent magnet motors have no wound field and a conventional wound armature with Commutator and brushes. This motor has excellent starting torques, with speed regulation not as good as compound motors. However, the speed regulation can be improved with various designs, with corresponding lower rated torques for a given frame.

Because of permanent field, motor losses is less with better operating efficiencies. These motors can be dynamically braked and reversed at some low armature voltage (10%) but should not be plug reversed with full armature voltage. Reversing current can be no higher than the locked armature current.

Figure 1.7 Permanent Magnet – DC Operation [14]

1.17: Commutator

A Commutator is an electrical switch that periodically reverses the current in an electric motor or electrical generator. It converts the alternating current induced in the armature conductors into unidirectional current in the external load circuit.

Figure 1.8 Curve segments of Commutator

It typically consists of a set of copper contacts, fixed around the circumference of the rotating part of the machine (the rotor), and a set of spring-loaded carbon brushes fixed to the stationary part of the machine (the stator) that complete the electrical circuit from the rotor’s windings to the outside of the machine. Friction between the copper contacts and the brushes eventually causes wear to both surfaces. The carbon brushes, being made of a softer material, wear faster and are designed to be replaced easily without dismantling the machine. The copper contacts are usually inaccessible and, on small motors, are not designed to be repaired. On large motors the Commutator may be re-surfaced with abrasives. Each segment of the Commutator is insulated from the adjacent segments; a large motor may contain hundreds of segments. [15]

1.18: Brushes and Bearings

The brushes, whose function is to collect current from Commutator, are usually made of carbon or graphite and are in the shape of a rectangular block. These brushes are housed in brush-holders usually of the box type variety. [16]

Because of their reliability, ball-bearings are frequently employed, though for heavy duties, roller bearings are preferable. The ball and rollers are generally packed in hard oil for quieter operation and for reduced bearing wear, sleeve bearings are used which are lubricated by ring oilers fed from oil reservoir in the bearing bracket.

1.19: Alternator

Without a Commutator, a dynamo becomes an alternator, which is a synchronous singly fed generator. When used to feed an electric power grid, an alternator must always operate at a constant speed that is precisely synchronized to the electrical frequency of the power grid. A DC generator can operate at any speed within mechanical limits, but always outputs direct current.

Typical alternators use a rotating field winding excited with direct current, and a stationary (stator) winding that produces alternating current. Since the rotor field only requires a tiny fraction of the power generated by the machine, the brushes for the field contact can be relatively small. In the case of a brushless exciter, no brushes are used at all and the rotor shaft carries rectifiers to excite the main field winding. [17]

1.19.1: Construction of an Alternator

} A synchronous generator/alternator is a electrical machine which produces electrical power with a fixed frequency.

} The main construction of an alternator is same as a synchronous motor, where the stationary conductor carries the conductor and the rotation part contains the electromagnet which generates the flux to induce the voltage across the conductor.

} A DC current is applied to the rotor winding, which then produces a rotor magnetic field. The rotor is then turned by a prime mover (eg: Steam, water etc.) producing a rotating magnetic field. This rotating magnetic field induces a 3-phase set of voltages within the stator windings of the generator.

} DC source is used to excite the electromagnets to produce a constant magnetic flux.

} “Field windings” applies to the windings that produce the main magnetic field in a machine, and “armature windings” applies to the windings where the main voltage is induced. For synchronous machines, the field windings are on the rotor, so the terms “rotor windings” and “field windings” are used interchangeably.

} Generally a synchronous generator must have at least 2 components:

} a) Rotor Windings or Field Windings

} i. Salient Pole

} ii. Non Salient Pole

} b) Stator Windings or Armature Windings

Figure 1.9 Salient rotor for a synchronous machine

Figure 1.10 Non-salient rotor for a synchronous machine [18]

1.20: Excitation

An electric generator or electric motor that uses field coils rather than permanent magnets requires a current 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.

Smaller generators are sometimes self-excited, which means the field coils are powered by the current produced by the generator itself. The field coils are connected in series or parallel with the armature winding. When the generator first starts to turn, the small amount of remanent magnetism present in the iron core provides a magnetic field to get it started, generating a small current in the armature. This flows through the field coils, creating a larger magnetic field which generates a larger armature current. This “bootstrap” process continues until the magnetic field in the core levels off due to saturation and the generator reaches a steady state power output.

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. [19]

1.21: Alternator Excitation System

(i) A dc current must be supplied to the field circuit on the rotor. Since the rotor is rotating, a special arrangement is required to get the dc power to its field windings.

The common ways are:

> supply the dc power from an external dc source to the rotor by means of slip rings and brushes.

> Supply the dc power from a special dc power source mounted directly on the shaft of the synchronous generator.

(ii) Slip rings are metal rings completely encircling the shaft of a machine but insulated from it. One end of the dc rotor winding is tied to each of the 2 slip rings on the shaft of the synchronous machine, and a stationary brush rides on each slip ring. [20]

1.22: Other rotating electromagnetic generators

Other types of generators, such as the asynchronous or induction singly fed generator, the doubly fed generator, or the brushless wound-rotor doubly fed generator, do not incorporate permanent magnets or field windings (i.e., electromagnets) that establish a constant magnetic field, and as a result, are seeing success in variable speed constant frequency applications, such as wind turbines or other renewable energy technologies.

The full output performance of any generator can be optimized with electronic control but only the doubly fed generators or the brushless wound-rotor doubly fed generator incorporate electronic control with power ratings that are substantially less than the power output of the generator under control, a feature which, by itself, offers cost, reliability and efficiency benefits. [21]

The two main parts of a generator or motor can be described in either mechanical or electrical terms.

1.22.1: Mechanical

Rotor: The rotating part of an electrical machine

Stator: The stationary part of an electrical machine. [22]

1.22.2: Electrical

Armature: The power-producing component of an electrical machine. In a generator, alternator, or dynamo the armature windings generate the electric current. The armature can be on either the rotor or the stator.

Field: The magnetic field component of an electrical machine. 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.

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. Direct current machines (dynamos) require a Commutator on the rotating shaft to convert the alternating current produced by the armature to direct current, so the armature winding is on the rotor of the machine. [23]


2.0: Introduction

In this chapter we discuses about the function of diesels engine and 3-phase synchronous generator. Here, we discuses about not only the basic working procedure and description of each part of diesel engine and 3-phase synchronous generator but also the construction of diesel engine.

2.1: Basics of how engine work

Diesel engines can be constructed in many configurations, but for the most part the components and their environment are the same: high temperatures, heavy loads and stresses and expected long hours of service.

Figure 2.1 Pistons in Cylinder

The basic unit of the engine is the piston which moves up and down inside a cylinder. As air is compressed in the cylinder, fuel is injected on top of the piston. Under high pressure the fuel mixes with the hot air and self-ignites causing combustion.

The force of the combustion pushes the piston and connecting rod down turning the crankshaft and flywheel drive other components.

Figure 2.2 Four strokes of the piston

During engine operation the piston goes through four strokes: Intake, Compression, Power and Exhaust. During the four strokes, the piston moves down and up two complete cycles.

2.1.1: Intake

During the intake stroke the piston moves down in the cylinder pulling air past an open intake valve (s) into the combustion chamber.

2.1.2: Compression

During the compression stroke all valves are closed, and the piston moves up in the cylinder compressing the air. As the air molecules are compressed the air temperature increases dramatically to about 10000F (5370C). As the piston nears the top of its stroke, fuel is injected into the combustion chamber on top of the piston. The fuel mixes with the hot compressed air and causes.

2.1.3: Power

During the power stroke the valves are closed as the forces from combustion push the piston and connecting rod down, thereby turning the crankshaft. The heat energy has now been converted into mechanical power.

2.1.4: Exhaust

During the exhaust stroke the inertial force of the turning flywheel helps continue the rotation of the crankshaft to push the piston up again in the cylinder forcing the burned gases out the open exhaust valve (s). This completes the four strokes of the piston. These four strokes are repeated over and over as the engine operates.

Let’s look at the engine components individually and the role they have in generating and transferring engine power.

2.2: Cylinder Block

Figure 2.3 Cylinder Block

The cylinder block (or engine block) is the basic frame for the engine. It holds the crankshaft, pistons, connecting rods and other components in precise alignment. The block also contains the coolant and oil for the engine and provides a place for attaching external components like the water pump and oil filter. This cylinder blocks are cast from gray iron for strength to withstand stress, heat and vibration.

The lower half of the block, where the crankshaft is located, is known as the crankcase. An oil pan bolts to the bottom to hold the oil. Removing the oil pan allows access to the engine crankshaft bearings, which wear over the engine’s life and may be replaced during a lower and engine overhaul.

2.3: Cylinder Head

Figure 2.4 The cylinder head sits on top of the block

On smaller engines, with an in-line design, the cylinder head is a single casting that attaches to the top of the cylinder block. V – Engines and some of the larger in-line engines use two cylinder heads or multiple cylinder heads.

Figure 2.5 Top of the cylinder block

The cylinder head performs the following functions:

  • Forms the top sealing surface for the combustion chamber.
  • Dissipates heat as coolant travels through internal water passages.
  • Directs inlet and exhaust air in and out of the combustion chamber.
  • Supports the valves and injectors.

Cylinder heads are designed and manufactured to withstand extreme combustion heat and pressures. The machining process on cylinder heads is critical, especially in the following areas.

  • The finish on the cylinder head face must be smooth and flat for correct sealing. If not, the head gasket that seals the cylinder head and engine block can leak causing loss of compression and engine power.
  • Valve guide bores – If these bores are not exact, the valve (s) can leak excessive combustion gasses and possibly oil.
  • Valve seats or inserts, must fit precisely in the cylinder head for sealing the combustion chamber. If not precisely fit in the head, there will be improper contact between the insert and valve head possibly causing damage to the insert, valve and cylinder head.

2.4: Cylinder Bores & Liners

Figure 2.6 Cylinder bores & liner

Some engines use cylinder liners and some are liner less. Liner less engines have openings bored into the cylinder block for the piston. In either case, the function of the liners or cylinder bores is to:

  • From the walls of the combustion chamber and guide the piston movement.
  • Provide a good sealing surface for the piston rings to seat against.
  • Conduct heat away from the combustion chamber.

Figure 2.7 Top of the cylinder block

2.5: Connecting Rods

Figure 2.8.1 Connecting rod of the cylinder block

The connecting rod attaches the piston to the crankshaft. It changes the up and down motion of the piston into a rotary of the crankshaft.

Figure 2.8.2 Connecting rod of the cylinder block

The small end of the connecting rod attaches to the piston and the large end to the crankshaft. A press-fit bushing is used in the end of the piston pin bore so the connecting rod can turn freely around the piston pin. The crankshaft end of the connecting rod consists of two pieces – the connecting rod and the bolt-on rod cap. Bearings are used here to provide a good wear surface between the connecting rod and crankshaft.

Connecting rods are forged for high strength and toughness. They are hardened and machined to close tolerance to ensure straightness, correct weight and alignment, and to hold the bearings tightly in place during operation. On some earlier model large engines the connecting rods have internal oil passages that direct oil to the underside of the piston, for cooling.

During engine assembly a number is etched on the crankshaft rod end and rod cap. This shows that these two parts are a pair and were machined together. During engine overhaul these parts must always be used together as a pair.

2.6: Crankshaft

The piston and connecting rod drive the crankshaft, which in turn drives the flywheel and gears to power other components.

Figure 2.9 Crankshaft

The crankshaft is supported in the block by main bearings. These bearings and the connecting rod bearings are lubricated by oil that flows through drilled passages in the block and crankshaft. A thrust bearing prevents excessive end to end (back and forth) movement of the crankshaft.

Crankshaft must be extremely strong and balanced. The journal surfaces, the areas where the bearing ride, need to be heat treated for increased surface hardness and machined very smooth to provide long wear life and reusability. Journals on crankshafts are hardened above Rc 40 and polished to a 5 micro inch surface finish – the best in the industry.

2.7: Fuel Injectors

Along with the valves that control the air in and out of the combustion chamber the fuel system components control the amount and timing of the fuel injected into the cylinder; both functions are critical to efficient combustion.

Figure 2.10 Fuel Injector

2.8: Bearings

Figure 2.11 Bearing

Bearings are relatively inexpensive wear items designed to protect the expensive crankshaft, connecting rod and block. They do this by:

  • Providing a soft, smooth surface with a high load carrying capability. This protects crankshaft journal surfaces during engine start-ups and heavy loads.
  • Trapping or embedding small pieces of metal and debris in the soft bearing surface to prevent damage to the journal surfaces.
  • Maintaining correct oil flow and pressure between parts.

Bearings used between the connecting rod and crankshaft are called connecting rod bearings, or rod bearings. Bearings that help support the crankshaft in the engine block are called main bearings. To help carry the longitudinal thrust loads placed on the crankshaft there are thrust bearings, or thrust plates.

2.9: Precombustion (PC)

Figure 2.12 Precombustion

On precombustion engines fuel is pumped from the fuel injection pump housing where individual fuel pumps are located (one per cylinder) to fuel injectors. There is one fuel injector located in the precombustion chamber above each cylinder. The precision drilled holes in the end of the fuel injector direct fuel into the precombustion chamber where the fuel begins to ignite or “precombust”. The heat forces the remaining fuel and air mixture from the precombustion chamber and into the combustion chamber on top of the piston. As the name says, there is precombustion before the fuel moves into the cylinder for complete combustion.

2.10: Direct Injector (DI)

Figure 2.13 Direct Injector

The direct injection fuel (DI) system differs from the precombustion system in that there is no precombustion chamber and fuel is injected directly into the combustion chamber. The fuel injectors are located above the combustion chamber and inject atomized fuel directly on top of the piston. Again the name of the system describes it well, direct injection chamber.

2.11: Vibration Damper & Flywheel

Figure 2.14 Vibration dampers & flywheel

As the engine fires, the combustion forces twist the crankshaft causing a high frequency tensional vibration. The vibration damper limits tensional vibration to prevent damage to the crankshaft.

The vibration damper on the front of the crankshaft is basically a weight inside a metal housing. The space between the weight and the housing is filled with a thick fluid. As the weight moves through the fluid it dampens and absorbs the shock and tensional vibration of the crankshaft.

The flywheel is a large, heavy metal mass at the rear end of the crankshaft. It absorbs the power impulses and carries on the crankshaft momentum until the next cylinder fires. Basically it helps continue the rotary motion of the crankshaft during non-power portions of the combustion cycle.

The flywheel is also one of the means by which engine power is transferred from the engine to other components. Many drive train components are mounted directly to the flywheel. On machines with torque converters, the torque converter mounts directly to the flywheel. On direct drive machines, a clutch mounts directly to the flywheel. The starter motor mounts to the flywheel housing and starter gear teeth drive the teeth on the outer edge of the flywheel to start the engine.

2.12: Summary

Figure 2.15 Total review of the machine

Let’s quickly review how the above components work together to convert heat energy into mechanical torque or power output to drive other components. Internal combustion takes place in the combustion chamber. Critical to efficient combustion is the amount of air and the amount and timing of fuel injection. These functions are basically controlled by the valves and fuel injection system. Combustion forces push the piston and connecting rod down turning the crankshaft and resulting in mechanical power.

2.13: Torque & Torque Rise

In general terms engine torque is synonymous with engine power. Torque rise is different from torque.

Torque rise is the increase in torque in a heavy pulling application. Simple put, torque rise is the luggability of the engine. When an engine starts to lug and the rpms decrease, the torque or power increases so the machine can maintain its speed. For example, as an on-highway truck starts up a speed grade, the engine starts to lug and the engine torque increases or rise. Pilling the truck up the steep grade. What actually happens is that the fuel system delivers slightly more fuel to the engine, thereby creating an increase in power.

Torque rise is an important selling feature of this engine. They generally have a larger torque rise than competitive engines – giving the owner more power in lugging situations.

2.14: Fuel Consumption vs. Fuel Efficiency

Fuel consumption is the amount of fuel the engine consumes in one hour.

Fuel efficiency is the term used to relate fuel consumption to productivity. It tells how efficiently the engine converts heat from the fuel into usable horsepower.

Relating specifically to engines, fuel efficiency is expressed as gallons per horsepower hour. Fuel efficiency for machines in earthmoving applications is expressed as the amount of materials a machine can move per volume of fuel consumed – such as cubic yards per gallon or cubic meters per liter of fuel. [24]

2.15: Mechanical design

The three-phase synchronous generators comprise the main generator with salient pole rotor, stationary-pole exciter and excitation system. The rotating diode bridge to rectify the three-phase current of the exciter is mounted on the NDE shaft end. It is easily accessible through a service opening, in case the diodes need to be exchanged.

The exciter rotor and the diode bridge are mounted on a common bushing forming an integral unit. The digital voltage regulator used as standard is mounted on the generator terminal box at the N-end.

2.16: Stator

The stator is a single-piece welded construction resting on four foot plates. The laminated core consists of insulated circular electrical steel laminations. It is secured axially by bars welded to the back.

2.17: Rotor

The laminated rotor of the main generator is a directly wound salient pole rotor with the exciter rotor and the rotating rectifier bridge shrunk onto the same shaft. All rotors are dimensioned for operation at 60 Hz. The rotor core is clamped by clamping plates installed on the shaft.

2.18: Stator winding

The three-phase stator winding is embedded in the open slots of the core. It is designed as a chorded double layer integral coil winding. The conductor material is copper strips insulated with mica-glass-epoxy resin tapes. The coil connectors are brazed. The end windings are reliably supported by ties and spacers to withstand the mechanical stress occurring during switching operations. The complete stator winding is vacuum-pressure-impregnated with epoxy resin. The coils are locked in the slots by fiber glass-epoxy resin slot closers. For corona shielding, a low-resistance protective coat is applied on the bars in the slot portion and a high resistance coat at the slot ends. [25]

2.19: Rotor winding

The exciter coils are made of varnish-glass insulated copper strips wound directly on the integrally stamped poles. The voids are filled by the vacuum pressure impregnation. The tangential centrifugal forces are taken up by supports in the pole gaps. The coil connectors and the connections to the diode bridge are also supported.

The damper winding consists of round copper bars which are evenly distributed over the pole surfaces and welded to the steel clamping plates of the laminated core. [26]

2.20: Bearings

The brush-less synchronous generators are equipped with anti-friction bearings as standard. Sleeve bearings can be provided against extra charge upon request by the customer. When anti-friction bearings are fitted, a locating bearing is used at the D-end and a non-locating bearing at the N-end. The bearing heads are flanged to the end shields. If sleeve bearings are used to carry the rotor, they are designed as non- locating bearings and similarly flanged to the end shields. If properly maintained, the bearing life is practically unlimited. Both the D-end and N-end bearings can be insulated from the end shields. Depending on the frame size and speed, lubrication is either oil ring lubrication or flood lubrication (forced-oil lubrication). If two non-locating bearings are fitted, axial location must be ensured by the drive motor by way of a limited end-float coupling. [27]

2.21: Electrical design

2.21.1: Rated power

In the standard version (catalogue data), the synchronous generators are designed for a rated frequency of 50 Hz, rated voltage 5%, cost= 0.8 over-excited, internal air temperature 40°C, altitude < 1000 ms l. and a temperature rise in accordance with thermal class F. If air-to-water heat exchangers are used, a water inlet temperature of 27° C is required. With degree of protection IP 44 and air-to-water heat exchanger, the output power is independent of the ambient temperature. It is only dependent on the altitude, cooling water flow and the water inlet temperature. [28]

2.21.2: Differing output power assignment

The permissible output power for differing rated values of power factor, coolant temperature and altitude is a matter of consultation with VEM. In the case of other influencing factors which could require a differing output power assignment such as

  • Air filter
  • Operation at unbalanced load
  • Harmonic load
  • Temperature rise class B
  • Dynamic voltage change upon connection to line consultation with VEM is necessary. [29]

2.22: Stator winding connection

The stator winding is star-connected. The neutral is formed inside the machine and is brought out to a fourth terminal. If differential protection is provided, an open neutral

(6 terminals) is possible. [30]

2.23: Overload capability

The generators are designed to operate for 120 s at 1.5 x rated current. Considering the overload capability of combustion engines, the generators can be operated at 110% rated Current for one hour within six. The excitation system is amply dimensioned for dynamic processes, i.e. about 230% ceiling voltage is available. [31]

2.24: Short-circuit performance

2.24.1: Sudden short-circuit current

The sudden short-circuit current is far below the value IS < 15 x IN laid down in VDE 0530. [32]

2.24.2: Sustained short-circuit current

The generator auxiliary winding and the excitation winding are designed so that in case of a three-phase short circuit at the terminals a continuous short-circuit current of about 3 x IN is withstood for t < 5s. [33]

2.25: Unbalanced load

The generously dimensioned damper cage permits unbalanced loads. The generators dimensioned for continuous unbalanced load (negative-sequence current/rated current ratio) of I2/IN < 20 %. Optimum operation, however, is obtained with symmetrical loads. [34]

2.26: Dynamic voltage behavior

Sudden load changes result in voltage changes which are mainly determined by the transient generator parameters and the external system connection conditions such as:

(i) load connected

(ii) Cost during connection to system

(iii) Generator at no load or generator preloaded.

When connecting loads of approx. IN and cost < 0.4 transient voltage dips of 15-25% are to be expected. The transient response of the generator voltage is determined by the time constants of the main generator, the exciter and the regulation system. The amply dimensioned excitation system ensures short recovery times. The recovery time for transient voltage variations is about 600 ms, depending on the number of poles and the generator output. After about 300 ms, the voltage tolerance range is reached temporarily and, following correction, the specified static voltage tolerance range is then maintained. [35]

2.27: Classification of ships

The individual classification rules and regulations demand lower generator temperature rises for on-board use and thus require a corresponding derating


2.28: Series and routine tests performed on all generators

(i) Visual inspection (marking, completeness).

(ii) Loss tangent test on installed stator winding

(iii) Insulation resistances of windings, temperature sensors, space heaters, bearings

(iv) DC resistances of windings, temperature sensors, space heaters

(v) Adjustment of magnetic centre of generators with sleeve bearings

(vi) Measurement of rotor impedance

(vii) Phase-sequence test

(viii) Vibration severity measurement

(ix) Check of voltage balance

(x) No-load characteristic, generator mode

(xi) Short-circuit characteristic, generator mode

(xii) Shaft voltage measurement (where design permits)

(xiii) Shock pulse measurement, if SPM nipple is provided

(xiv) High-voltage test

(xv) Functional check of accessories

(xvi) Functional check of excitation system [36]

2.29: Additional tests / type tests

Type tests are performed on three-phase generator as a representative of the type, with the scope of testing depending on our technical capacities. The test is included in the generator price. Upon request, additional tests can be performed at extra charge to the customer:

(i) Over speed test with generator on balancing machine.

(ii) No-load characteristic.

(iii) Determination of iron and friction loss.

(iv) Noise measurement at no-load.

(v) Measurement of THF factor.

(vi) Moment of inertia in deceleration test.

(vii) Sudden short-circuit test.

(viii) Temperature rise test at rated data or equivalent load test.

(ix) Temperature rise time constants.

(x) Determination of nominal excitation current.

(xi) Determinations of synchronous machine characteristics (reactance, time constants).

(xii) Measurement of coolant flow rate.


3.0: Introduction

The loaded power plant face to overall fault and many alarm signal in operation period. This chapter I describe problem name, use instrument, work procedure, work precaution and remarks. This time I try to solve the all fault and run the generator. Maintenance is major part of power plant. Including all adjustments, the use of proper lubricants, fluids, filters, and the replacement of components due to normal wear and aging. Failure to adhere to proper maintenance intervals and procedures may result in diminished performance of the product and/or accelerated wear of components.

3.1: Problem: Engine load reduction

Instrument: The problem solve for use instrument

1. Engine operation key.

2. Multi measurement meter.

3. Electric tester.

4. Screw driver set etc.

Procedure: When running parallel with grid in AUTO control mode, the load reduction will reduce the engine’s actual power by 15 percents. However, the power is not allowed to go under the minimum power limit (Approximately 30% of the rated electrical output of the engine).

When running parallel with grid in MANUAL control mode or in island mode, the load reduction is only alarm for the operator. The alarm text is:

Engine load too high, reduce load 15% Shutdown danger.

Operator should take necessary action to reduce the power. If operator does not react, shutdown will occur according to the backup function of the measurement. When the alarm disappears, event will occur.

Engine load ok, shutdown avoided.

Precaution: The load reduction alarm is activated / deactivated in the following cases:

  • The engine load reduction is activated if the Exhaust Gas temperature average value for one cylinder is greater or equal to 520C for longer than 10 seconds. The load reduction alarm is deactivated if the Exhaust Gas temperature average values for all cylinders are below 520C for longer than 10 seconds. As a backup function shutdown will occur if he Exhaust Gas temperature average value for one cylinder is greater or equal to 550C for longer than 10 seconds.


  • The engine load reduction is activated if the HT-water outlet temperature is greater or equal to 105C for longer than 10 seconds. The load reduction alarm in deactivated if the HT-water outlet temperature is less than 100C for longer than 10 seconds. As a backup function shutdown will occur if HT water outlet temp exceeds 110C for 2 seconds.
  • The engine load reduction is activated if the HT-water inlet temperature is less or equal to 50C for longer than 10 seconds. The load reduction alarm is deactivated if the HT-water inlet temperature is greater than 50C for longer than 10 seconds. There is no backup shutdown defined for HT-water inlet temperature.

The actual load reduction is deactivated if the actual reason has been inactive for 2 minutes.

Picture: Air Filter Picture: Fuel Filter

Remarks: We are mind it that air filter, fuel filter also dusts free. Coolant or cooling water temperature, cylinder temperature and HT-water temperature allows stay normal position.

3.2: Problem: Starting motor was not working properly

Instrument: The problem solve for need to instruments.

  1. Sly range.
  2. Spanner set.
  3. L key set.

Procedure: We checked the starting motor & found not ok (starting motor air lock). We removed the air properly of starting motor. Start the Engine with above load & all parameter checked & found Fuel filter differential pressure high (1.75 bars). After we checked the Fuel tank & filter and changed the Fuel filter. And now start the Engine with above load & Engine working properly.

Precaution: The starting motor precautions cases:

· The compress air presser flow properly.

· Checked starting motor lube oil before the engine rune.

· We found that air lock is not locked.

Picture: Starting Motor

Remarks: We flow that compress air for