1. Generator:

1.5 Stator

 Bipolar and Multi-polar Field,

•  Compound

1.9 Rectifier

Fig1.14:  Rectifying System

Principle of AVR

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

GENERATOR OPERATION

CHAPTER 02

• Permanent magnet pilot excited (PMPE)
• Self-excited (SE)

• "CR1" and "CR4"
• "CR2" and "CR5"

ENGINE

CHAPTER 03

1. Internal Combustion Engine.
2. External Combustion Engine.

1. Petrol Engine
2. Diesel Engine
3. Gas Engine

1. Two Stock Engines.
2. Four Stock Engine

1. Two Stock Engines.
2. Four Stock Engine
3.  

1. Cylinder Head
2.  Cylinder Block
3.  Piston
4.  Piston ring
5. Connecting rod
6. Crank Shaft
7. Fly wheel
8. Gasket
9. Intake Valve
10. Exhaust Valve
11. Breather Cap
12. Rocker rum
13. Valve Spring
14. Valve Guide
15. Push rod
16. Cam shaft
17. Bearing
18. Spark plug

 

1. Engine body
2. Lubricating Circulation system
3. Water Circulation System
4. Fuel System

Fig3.3: Left side view of engine

 
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.

 None of the following condition are acceptable:

           
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.
3.8 Crankshaft
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.

3.9 Turbocharger: A turbocharger, or turbo, is a gas compressor used for forced-induction of an internal combustion engine. Like a supercharger, the purpose of a turbocharger is to increase the mass of air entering the engine to create more power. However, a turbocharger differs in that the compressor is powered by a turbine driven by the engine’s own exhaust gases.
.

A turbocharger, often called a turbo, is a small radial fan pump driven by the energy of the exhaust flow of an engine. A turbocharger consists of a turbine and a compressor on a shared shaft. The turbine inlet receives exhaust gases from the engine causing the turbine wheel to rotate. This rotation drives the compressor, compressing ambient air and delivering it to the air intake manifold of the engine at higher pressure, resulting in a greater mass of air entering each cylinder. In some instances, compressed air is routed through an intercooler before introduction to the intake manifold.
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.
3.10 Piston
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.

There are two ways that an internal combustion piston engine can transform combustion into motive power. These are the two-stroke cycle and the four-stroke cycle. A single cylinder two-stroke engine produces power every crankshaft revolution, while a single cylinder four-stroke engine produces power once every two revolutions. Older designs of small two-stroke engines produced more pollution than four stroke engines. However, modern two-stroke designs, like the Vespa ET2 Injection utilize fuel-injection and are as clean as four-strokes. Large diesel two-stroke engines, as used in ships and locomotives, have always used fuel injection and produce low emissions. One of the biggest internal combustion engines in the world, the Wärtsilä-Sulzer RTA96-C is a two-stroke; it is bigger than most two-story houses, has pistons nearly 1 meter in diameter and is one of the most efficient mobile engines in existence.
3.11 Flywheel
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
 

Fig3.8: Flywheel.
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.

The camshaft is an apparatus often used in piston engines to operate poppet valves. It consists of a cylindrical rod running the length of the cylinder bank with a number of oblong lobes or cams protruding from it, one for each valve. The cams force the
valves open by pressing on the valve, or on some intermediate mechanism, as they rotate.

Depending on the location of the camshaft, the cams operate the valves either directly or through a linkage of pushrods and rockers. Direct operation involves a simpler mechanism and leads to fewer failures, but requires the camshaft to be positioned at the top of the cylinders. In the past when engines were not as reliable as today this was seen as too much bother, but in modern gasoline engines the overhead cam system, where the camshaft is on top of the cylinder head, is quite common. Some engines use two camshafts each for the intake and exhaust valves; such an arrangement is known as a double or dual overhead cam (DOHC), thus, a V engine may have four camshafts.
 

A governor is a device used to measure and regulate the speed of a machine, such as an engine. A classic example is the centrifugal governor, also known as the Watt or fly-ball governor, which uses weights mounted on spring-loaded arms to determine how fast a shaft is spinning, and then uses proportional control to regulate the shaft speed.

Fig3.10:  Governor.
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.

 
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.

If a cooling system fails to perform any of the above function can occur.

 
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

 

 

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.

For maximum service life of the water cooled components, all of the air must be purged from the water jacket of each component. The presence of air can allow some of the coolant to convert into steam. This changes the properties of the coolant. Removal of the air reduces the possibility of the conversion. Removal of the air improves the service life of the coolant.
 
The preferred method for venting of the engines cooling system is the installation of vent lines.
Follow these guidelines.

In the some application, it may not be possible to install the recommended vents lines. In this case automatic vent lines must be installed .Install automatic valve that is 0.6 to 0.9m (2.00 to 3.00ft) above the highest point of the cooling system on the engine.
 
Fig4.3: Ventilation Fan
4.5 Fundamental device of cooling system.

  

       
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.

 
5.3 Main parts of PFI plant.

 
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.

 
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.
 

 
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.

Fig5.4: Fuse
 
           
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.
 

 
5.12 Circuit breaker.
 
A circuit breaker is a piece of equipment, which can

 
                        
Fig5.5: Air circuit breaker                        Fig5.6: 2-Pole miniature circuit breaker
5.13 The classification of circuit breaker.
 

            A. Self –blast oil circuit breakers.

            B. Forced-blast oil 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)
P=Active power
S=Apparent power
= 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
Solution:
=500
  =  =714Kva
 = =510 Kvar
  =  =520Kva
 = =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:
 

at full load.

 
5.16 The low power factor has very bad effect over the plant
 

 

 
6.1 Daily Check List.

 
6.2 Daily Data record in log sheet like as following table.
For Generator 01.
 

6.3 Daily cylinder temperature condition record.
 
6.4 Maintenance schedule.
 

 
 
6.5 Working schedule of generator section.
 

 
 
 

 
 

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.
 

 
 
 
 
 
 
 
 
 

 
Fig7.1: Substation.
 

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.
 

 
7.3 Classification of substation
 
 7.3.1 According to service requirement

 

 
7.4Transformer 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.
 
7.11Outdoor substation
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.

7.13 Step-up station: A step-up transmission on substation receives electric power from a nearby generating facility and uses a large power transformer to increase the voltage for transmit ion to distant locations. A transmit ion bus is used to distribute electric power to one or more transmit ion lines. There can also be tap on the incoming power feed from the generation plant provide electric power to operate equipment in the generation plant.
 
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:
 
Duct Runs

 
7.17 Function of substation: Substations are designed to accomplish the following functions, although not all substations have all these functions:

 
 

7.18 The major components of typical substation are:
 

 
 
 
 
Chapter 08
 
8.1 Manpower Cost Analysis of one month
 

 
Manpower one month Cost   taka 371000/=
Manpower one year cost taka 4452000/=
 
8.2 Fuel Cost Analysis of one year only for 3mw Generator.

 

Other Formula 20mw power plant one year gas bill calculation (Full Load)
8.3 One year spare Parts consumption of 20mw power plant.
 
One year schedule changing parts consumption for 1 mw generator plant.
 

 
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                                                                                            
 

 
 

9.1 Engine oil performs several functions.

Engines that use gaseous fuel require oils that are formulated with additives that are specific to these engines. There no Industry standards that define the performance specification of oils for this engines. Field evaluated must be used in order to determine oils that are acceptable. To aid in oil selection, guidelines are provided in this special publication.   
 
9.2 Lubricating Maintenance system.
The flowing cost is associated with maintenance of the engine lubrication system.

 
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.

To achieve the lowest maintenance costs for the lubrication system, maintain the engine oil to the minimum standards that are recommended in this special publication. 
 
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.
 

10.1 Introduction
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
 Overheating
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
8.      Motoring
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.
10.3 Relay
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:
(a) Electromagnet
(b) Armature that can be attracted by the electromagnet
(c) Spring
(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

E
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
Function
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 relays are electrical switches typically employed in industrial settings to protect electrical equipment from damage due to overheating in turn caused by excessive current flow. Overload relays are provided for protecting components connected to an electrical circuit in the event the current flowing through the circuit exceeds a predetermined level. An overload relay monitors the current flowing in the protected circuit and sends a signal to cause a contactor in the protected circuit to open when the current flowing in the protected circuit is higher than a pre selected level. Overload relays are more than simple circuit interrupters, they are sensors which, upon determining the existence of an overload or other undesirable circuit condition, break a circuit and in turn provide a control or an indicating function. Overload relays are specialized circuit breakers used with industrial motors to protect the motors from damages caused by overload or electrical faults. In a typical case, the electrical equipment is a three-phase motor which is connected to a power source through another relay commonly referred to as a contactor. The contactor is controlled by another switch which is typically remotely located.
 
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
Operation
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
http://en.wikipedia.org/wiki/File:LargeCircuitBreaker.jpg
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.
10.11 (Electrical)
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.
 

Fig10.11:  Fuse.
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.
10.13 Speed:
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.
 

11.1 Introduction of Neutral Earthing.
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
 
11.2 Earthing.
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:

 
 
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

 
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.
           

Elements of earthing:

 
According to Earth Electrode, the Earthing system can be classified as:
 

 11.8 Earthing Material List
 

 
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.
 
 

12.1 Discussion
 
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     
 
12.2Conclusion
 
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.
 
References:
           [1] “Installation Manual” Caterpillar Engine, 2004, USA.
           [2] “Complementary Information” Caterpillar Engine, 2001, USA.
           [3] “Operation and maintenance manual” Caterpillar Engine, 2001, USA.
 [4] “ Mechanical Systems”, Energypac Power Generation Ltd. Bangladesh. &   http://en.wikipedia.org.
[5] “Electrical Manual”, Energypac Power Generation Ltd. Bangladesh. &    http://en.wikipedia.org.
[6] Switchgear Protection and Power Systems, Sunil S. Rao, Twelfth Edition, 2007.    Protection Systems Energypac power generation Ltd.” Energypac Power Generation Ltd.” Bangladesh.
           [7] en.wikipedia.org/wiki/Electrical _ Substation.
           [8] en.wikipedia.org/wiki/Transformer
             [9] en.wikipedia.org/wiki/Transformer_ types.
           [10] en.wikipedia.org/wiki/Current_ transformer