Diesel generating sets are used to generate electrical energy in emergency when the main supply is suddenly interrupted. In other words, we can say that these are used as standby source of electrical energy. These are available in different sizes varying from 5 to 500 Kilo-Volt-Ampere (KVA). As compared to another sources of electrical energy, these are cheap in initial cost, less commissioning time, easy to handle and very quick to start generation, as no warming time is required.
Requirement of large quantity of cooling water is the main problem in all other generating sources of electrical energy but these plants require very less quantity of water. Nowadays, radiator type fan cooled diesel generating sets are available in the market, which needs too less quantity of cooling water. Although we have used the spray pond for cooling purpose. In-spite of several advantages the diesel generating sets cannot be used as continuous source of electrical energy. Because the high-speed diesel is used as fuel in internal combustion engine (I. C. Engine), which is costlier than the fuel used by other generating sources and hence, there is increase in cost of generation. Although the working of a diesel generating set will be slightly differs depending upon the KVA rating and method of starting the diesel engine. However, the working of a diesel generating set in general is explained here.
Working: When the engine is started, the alternator starts moving. The magnetic field coils are mounted on rotor, which changes its position as the rotor moves, and three-phase winding is placed on the stator. So, three-phase supply will generate in the stator winding. Initially the supply will be generated due to residual magnetism of the pole shoes. For continuous and constant voltage generation, the pole shoe requires fixed quantity of external excitation for producing alternate north and south poles. So, the initially generated a.c. supply is converted into d.c. supply by metal rectifiers and feedback to armature through slip rings and carbon brush assembly.The change over switch should be operated before starting the engine. When full voltage builds up, the air circuit breaker is switched on. Different parts of a diesel generating set
Requirement of large quantity of cooling water is the main problem in all other generating sources of electrical energy but these plants require very less quantity of water. Nowadays, radiator type fan cooled diesel generating sets are available in the market, which needs too less quantity of cooling water. Although we have used the spray pond for cooling purpose. In-spite of several advantages the diesel generating sets cannot be used as continuous source of electrical energy. Because the high-speed diesel is used as fuel in internal combustion engine (I. C. Engine), which is costlier than the fuel used by other generating sources and hence, there is increase in cost of generation. Although the working of a diesel generating set will be slightly differs depending upon the KVA rating and method of starting the diesel engine. However, the working of a diesel generating set in general is explained here.
Working: When the engine is started, the alternator starts moving. The magnetic field coils are mounted on rotor, which changes its position as the rotor moves, and three-phase winding is placed on the stator. So, three-phase supply will generate in the stator winding. Initially the supply will be generated due to residual magnetism of the pole shoes. For continuous and constant voltage generation, the pole shoe requires fixed quantity of external excitation for producing alternate north and south poles. So, the initially generated a.c. supply is converted into d.c. supply by metal rectifiers and feedback to armature through slip rings and carbon brush assembly.The change over switch should be operated before starting the engine. When full voltage builds up, the air circuit breaker is switched on. Different parts of a diesel generating set
i. Engine
Engine is the most important part of a diesel generating set and which acts as a prime mover. The type of engine used is internal combustion engine (I.C. Enginer) and works on two stroke or four stroke cycle principle. High-speed diesel is used as fuel. The capacity of engine depends upon the K.V.A. rating of alternator and it should be capable of taking over loads for at least two hours, keeping the temperature with in safe limit. Generally high-speed diesel engines are preferred because the over all generation cost is reduced due to reduction in cost of engine and alternator, etc. Multi cylinder engines are also preferred to reduce the noise level and vibrations produced in the engine while working.
ii. Alternator
Alternator also known as “A.C. Generator” operates on the same principle of Faraday’s law of electro magnetic induction as d.c. generator. In these a. c. generators salient poles are keyed on rotor and field windings are mounted over it to produce permanent magnetic field with alternate north or south. The stator also consists of circular silicon stampings, having slots on its inner periphery for accommodating the stator winding may be single phase or three phase depending upon requirement. Slip rings are mounted on the rotor shaft to feed d.c voltage for excitation to produce magnetic field. This excitation may be supplied from small d.c. generator coupled to the same shaft or from metal rectifier. The alternator is used to generate a.c. voltage.
iii. Air Circuit Breaker and Bus Bar
The air circuit breaker is used to switch on or off the main supply generated by the alternator. The circuit breaker should be switched on when the alternator builds up full voltage. When it is switched on, the supply will energise the bus bar. A busbar is a bundle of conductors or thick copper strips, used to distribute the generated voltage with the help of change over switch. The change over switch is used to select the source of generation i.e. either generated or external source of supply.
iv. Engine Cooling System
This includes jacket water tank, used to make up the quantity of cooling water, jacket water pump for forced circulation of cooling water. Heat exchanger to exchange the heat of cooling water with circulating water, circulating water pump to spray the water in the spray pond and spray pond to cool down the temperature of circulating water.
v. Engine Fuel System
This system includes diesel tank to store the fuel and fuel transfer pump to transfer the fuel from fuel tank to engine. The strainer is used to restrict the flow of highly viscous liquid; fuel filter is used to filter the fuel and heater to main viscosity of fuel especially in winter season within limit.
vi. Engine intake and exhaust system
To ensure fresh and dust free air for the combustion of fuel, air filters are provided which may be cleaned by air pressure or replaced depending upon the conditions.To exhaust the burn out gases from the engine, exhaust pipe is used and muffler is used to reduce the noise level of exhaust gases. The exhaust pipe should be discharge to the atmosphere outside the room.
vii. Engine starting system
Depending upon the rated capacity of diesel generating sets, different types of starting systems are used. Small capacity D.G. sets (5KVA) are started manually with handle and above 5 KVA are started with 24 volts D.C motors, which are generally know as “Self-starter”. For this purpose higher A.H. capacity batteries are used to supply the d.c. voltage and are recharged with dynamo coupled with same shaft of alternator. Big capacity diesel generating sets also uses compressed air motor to start.
ii. Alternator
Alternator also known as “A.C. Generator” operates on the same principle of Faraday’s law of electro magnetic induction as d.c. generator. In these a. c. generators salient poles are keyed on rotor and field windings are mounted over it to produce permanent magnetic field with alternate north or south. The stator also consists of circular silicon stampings, having slots on its inner periphery for accommodating the stator winding may be single phase or three phase depending upon requirement. Slip rings are mounted on the rotor shaft to feed d.c voltage for excitation to produce magnetic field. This excitation may be supplied from small d.c. generator coupled to the same shaft or from metal rectifier. The alternator is used to generate a.c. voltage.
iii. Air Circuit Breaker and Bus Bar
The air circuit breaker is used to switch on or off the main supply generated by the alternator. The circuit breaker should be switched on when the alternator builds up full voltage. When it is switched on, the supply will energise the bus bar. A busbar is a bundle of conductors or thick copper strips, used to distribute the generated voltage with the help of change over switch. The change over switch is used to select the source of generation i.e. either generated or external source of supply.
iv. Engine Cooling System
This includes jacket water tank, used to make up the quantity of cooling water, jacket water pump for forced circulation of cooling water. Heat exchanger to exchange the heat of cooling water with circulating water, circulating water pump to spray the water in the spray pond and spray pond to cool down the temperature of circulating water.
v. Engine Fuel System
This system includes diesel tank to store the fuel and fuel transfer pump to transfer the fuel from fuel tank to engine. The strainer is used to restrict the flow of highly viscous liquid; fuel filter is used to filter the fuel and heater to main viscosity of fuel especially in winter season within limit.
vi. Engine intake and exhaust system
To ensure fresh and dust free air for the combustion of fuel, air filters are provided which may be cleaned by air pressure or replaced depending upon the conditions.To exhaust the burn out gases from the engine, exhaust pipe is used and muffler is used to reduce the noise level of exhaust gases. The exhaust pipe should be discharge to the atmosphere outside the room.
vii. Engine starting system
Depending upon the rated capacity of diesel generating sets, different types of starting systems are used. Small capacity D.G. sets (5KVA) are started manually with handle and above 5 KVA are started with 24 volts D.C motors, which are generally know as “Self-starter”. For this purpose higher A.H. capacity batteries are used to supply the d.c. voltage and are recharged with dynamo coupled with same shaft of alternator. Big capacity diesel generating sets also uses compressed air motor to start.
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