Power generation is the most important sector for any developing country. As a developing country Bangladesh is now very concern about power generation. The present government is trying to reduce the supply and demand gap in power sector. For this government choose to set up picking power plant. Katakhali 50 MW peaking Power Plant Rajshahi is one of these government establish situated in Katakhali, Rajshahi. It is a diesel engine power plant with the capacity of 50MW. We were lucky enough to visit this power plant for our internship purpose. During the visit, we achieveda lot of practical experience like power generation and its control system, transmission and protection system. We also observed fuel system, the cooling system etc. Now we would like to discuss about the Katakhali power plant and its power generation.

Katakhali 50 MW Power Plant-Katakhali peaking power plant

Katakhali peaking power plant

he supply and demand gap in power sector. For this government choose to set up picking power plant. Katakhali 50 MW Power Plant is one of these government establish situated in Katakhali, Rajshahi. It is a diesel engine power plant with the capacity of 50MW. We were lucky enough to visit this power plant for our internship purpose. During the visit, we achieveda lot of practical experience like power generation and its control system, transmission and protection system. We also observed fuel system, the cooling system etc. Now we would like to discuss about the Katakhali power plant and its power generation.

 

Fuel processing

In a power plant fuel processing is very important part. In Katakhali 50 MW peaking Power Plant Rajshahi furnace oil is used as fuel though it is a diesel engine power plant to reduce the production cost. Diesel is only used when the power plant is starting and when it is stopping. Before using furnace oil as fuel of the generator it should remember that the temperature of the furnace oil can’t be over 110C. Then at first the furnace oil comes to the storage tank where the temperature must be 40-450 C and then it goes to the buffer tank. In the buffer tank the temperature should maximum 850 C after this the oil then goes to Day tank through two pumps. There is a HFO separator where the temperature will be 900 C. In HFO separator purifies the oil and the pure oil goes to the day tank and the slush goes to the slush tank. Into the day tank temperature maintains at maximum 1000C. To run this separation process it has to give some extra water outside of the separator bowl to open and close the bowl. At the beginning of this process there are three particle as pure oil, water and hard particle. When the bowl starting is starting rotate at 26000rpm the hard particle goes far away than water and pure oil. So the water and the hard particle both go to the slush tank. The pure oil goes to day tank to booster unit where temperature controls at 110-1150C. This pure oil then goes to engine through change over unit. Now the pure oil is ready for use. Diesel is again filtered before injecting into the engine by the fuel injection pump. The fuel is supplied to the engine according to the load of the plant.

Diesel engine

Diesel engine power plant’s is in the range of 2 to 50 MW capacity. They are used as central station for small or medium power supplies.Katakhali 50 MW peaking Power Plant Rajshahi is also called diesel engine power plant.A diesel engine power station uses a diesel engine as prime mover for generation of electrical energy.  Diesel engines or compression ignition engines as they are called are generally classified as two stroke engine and four stroke engines. In diesel engine, air admitted into the cylinder is compressed, the compression ratio being 12 to 20. At the end of compression stroke, fuel is injected. It burns and the burning gases expand and do work on the position. The engine is directly coupled to the generator. The gases are then exhausted from the cylinder to atmosphere. The model of the engine used in katakhali is MAN 18V 32/40. This engine rotates at 750 RPM. The engine is at  Katakhali 50 MW peaking Power Plant Rajshahi is a 4 stroke diesel engine-
1. Suction
2.Compression
3.Expansion
4.Exhaust

Before starting a diesel engine it should remember to check something carefully. First is to check the fuel level (HFO, LFO, Buffer and Day tank). Then should check out the de-mineralized water where the PH of the water will be (6.8-9). There is some process to check and control the ph of the water. Should check the external cooling water, start-up boiler fuel, engine lube oil level and also should check all the pipes and valves are used in this process to leakage problem.

Suction: In this stroke the inlet valve is open and the exhaust valve is closed. The piston moves for top dead centre to bottom dead centre. As the piston moves for top to bottom dead centre the inlet valve open so that the air of the atmospheric pressure comes into the cylinder
Compression: The air which is comes at the suction stroke it now compressed and the pressure is high also the temperature but the piston moves from bottom to top dead centre. In this stroke both inlet and the exhaust valve are closed.

Expansion: In this step both valves are remain close initially but when the piston reach the bottom dead centre the exhaust valves start to open. At that time the fuel is injected into the cylinder by the spark plug. Then the fuel starts burning. Now the piston moves to top dead centre to bottom dead centre.

Exhaust: In this stroke the piston moves for bottom to top dead centre and the exhaust gases go out to the atmosphere through the exhaust valve. But when the piston reaches to the top dead centre the exhaust vale close and get ready for new start.

Air intake system:

Air filters are used to remove dust from the incoming air. Air filters may be dry type, which is made up of felt, wool or cloth. In oil bath type filters, the sir is swept over a bath of oil so that dust particles get coated.

Exhaust system:

In the exhaust system, silencer (muffler) is provided to reduce the noise.

 

Alternator of Katakhali 50 MW peaking Power Plant Rajshahi 

Katakhali 50 MW peaking Power Plant Rajshahi have AC generator. There are six generators in Katakhali power plant. In Katakhali 50MW power plant contain six generators and all are eight pole generator. Each generator can produce 8.7 MW of electricity. The generator is directly coupled with the engine and magnetic field is used as rotor. The engine is V shaped and has 18 cylinders. Produced voltage is 11KV and inside the generator it is Y connected. From this generator 6 wires is out and every two of them make a pair which is single phase. To increase the current carrying capacity,a phase is carried with two wires.The neutral wire is grounded through earth register panel. Generator can face three types of fault

  1. Over current fault.
  2. Over voltage fault.
  3. Differential voltage.

    Katakhali 50 MW peaking Power Plant Rajshahi-Coupled Alternator

    Katakhali Coupled Alternator

The three phase connection carry the same current to be balanced, if not there will produce  some leakage current these leakage current goes to the ground through neutral. From every generator there was a yellow wire which is goes to ground for safety. To make the neutral there should be maintained earth resistance 0.175Ω. From the six generators the three generator supply in one bus and the other three supply on the other bus. This 11KV, then goes into an 11/132 KV line.

Generated Voltage and supply 

Voltage

Katakhali 50 MW peaking Power Plant Rajshahi-132 KV line with national grid at Katakhali

Connection of the 132 KV line with national grid at Katakhali

The generating voltage of every power plant is initially lower but this lower voltage is step up by the transformer. In Katakhali 50 MW peaking Power Plant Rajshahi, the generated voltage is 11 KV and this goes to the step up transformer and raise to 132 KV.  At first the three phase connections of 11KV line fromthe bus bar go to the transformers and come out as a 132KV line. Form the three transformers there is three single phase 132KV come out. This 132KV line goes to the SF6 circuit breaker and then to isolator to PT to lighting arrester to the PGCB sub-station. This 132KV is being sent to the national grid.

Katakhali 50 MW peaking Power Plant Rajshahi-11/132 KV transformers at Katakhali

11/132 KV transformers at Katakhali

Auxiliary Systems

Though there are six engines in Katakhali 50 MW peaking Power Plant Rajshahi, but there are seven steam generators. Among the six of the steam generator is attached with six engines and the rest one is the auxiliary steam generator. When the machine starts initially the auxiliary steam generator has to start with Diesel and raise the temperature of the fuel which is used in the engines. After the engine starts the auxiliary steam generator is shutdown. Here two types of airs are used for three kinds of works. One of them is to start the engine which is known as compressed air to create pressure to move the pistons, which is around 25 bars. Another air is called instrument air or numeric air. This air is used for different types of numeric valves. There is an emergency diesel generator which is to be used only for emergency purpose. To run the full auxiliary systems of Katakhali power plant the needs of electricity is around 700KW which comes from the national grid.

Cooling System

To run a power plant cooling system is very important. Because in power plants controlling of two things is very important which are temperature and pressures. Temperature should be under control or low and pressure should be as high as possible. If reverse situation happened it’s a bigger problem. High temperature can damage the generators components as well as other equipment of the plant.The cooling system in Katakhali 50 MW peaking Power Plant Rajshahi, is well organized. There are two types of cooling system-

  1. Water cooling system

a)External cooling system
b)Internal cooling system

  1. Lube oil cooling system

Water cooling system 

For this there is a capacity full of water, to purify this water lots of chemical is used in it. This water is send to the de-mineralized tank through the pipe continuously. There are two kinds of water is used in Katakhali 50 MW peaking Power Plant Rajshahi for this system, HT water(high temperature water) and LT water (low temperature water). To cool the engine cylinder or jacket, HT water is used. Water is circulated inside the engine in water jackets which are passage around the cylinder, piston, combustion chamber etc. To keep the temperature at the reasonable level, hot water leaving the jacket is sent to heat exchanger. Raw water is made to flow through the heat exchanger, where it takes up the heat of jacket water. It is then cooled in the cooling tower and recirculates again.

Lube oil cooling system

The lubricating oil cooling system is pretty much famous cooling system now-a-days. In Katakhali 50 MW peaking Power Plant Rajshahi lube oil cooling system is used. The lube oil for cooling system was stored in the bottom of the crankcase which is known as sump. Unless a drain tank is set to beneath of the engine. The oil is taken by a pair of pump through a filter. This oil have to pass through a cooler just before to go to the engine. Then it distribute to different branch pipes. This lube oil goes to the bearing and some oil will pass to the crankshaft end bearing and to the connecting rod. There will be fine filters; one or more will be standby to work properly so that if one is operating. After using the lube oil all the necessary place or parts it will goes to the sump or drain tank and ready for further use. To proper maintenance a centrifuge is set to clean the lubricating oil in the system and oil can be provided form the storage tank. To circulate the oil the sea water is needed which pressure is lower than the oil. Now the oil which is used and heated now for the friction of the parts, this heated is cooled by the sea water before re-circulation. Mainly the lube oil is used to protect the parts, bearing damage because of friction.