1. Kozhikode Diesel Power Project

KOZHIKODE DIESEL POWER PROJECT

1.  KOZHIKODE DIESEL POWER PROJECT

INTRODUCTION

KDPP is the second diesel power generating station of Kerala state electricity board. The first project is BDPP at Ernakulam. There are 8 no of generators installed in this plant and each has a capacity of 16MW. Total capacity is 128MW. Diesel engine is the prime mover of the alternator generating voltage of each alternator is 11 KV. 2 alternators are synchronized and connected in parallel in common bus bar through independent VCB at MV room and is connected to generator transformer of capacity 38 MVA, 1lkV/1l0kV.Thus there are 4 no. of GT's provided for eight engines and on service and another GT is provided for a spare at generator transformer yard .

DIESEL GENERATOR HALL

The DG hall houses the entire prime mover alternator set. The prime mover used at KDPP is 18 V 46 C WARTS1LA diesel engines. It is a 4 stroke turbo charged and inter cooled engine with direct twin fuel injection. The engine uses two fuels - primary fuel being LSHS. Diesel is used for starting and stopping purposes.

·  Cylinder bore : 460 mm

·  Stroke : 580 mm

·  No. of valve : 2 inlet& 2 outlets

·  Cylinder configuration : 18 in v form

·  V-angle : 45

·  Compression ratio : 14:1

·  Direction of rotation : clockwise

·  Cylinder output : 1050 kW

·  Speed : 500 rpm

·  Piston speed : 9.7 m/s

·  Mean effective pressure : 26.1 bar

·  Firing pressure : 200 bar

·  Charge air pressure : 3.1 bar

The engine has 18 cylinders, arranged in two banks with 9 cylinders in each bank. The banks are aligned in V - shape at an angle of 45 degrees. The cylinders have a diameter of 46 cm. The firing order of the engine is given below:

A1-B8-A7-B6-A4-B3-A2-B9-A8

B5-A6-B1-A3-B7-A9-B4-A5-B2

The piston reciprocates in these cylinders with a stroke length of 580 cm. each cylinder has a set of valves – inlet valve and exhaust valve and a fuel injection system. A cam mounted on a cam shaft operates these valves. The cam shaft is coupled to the crank shaft with asset of gears. The profile of the cams is arranged suitably for the perfect timing of the operation of the valves. Cam shaft is composed of a number of cams connected together to form a single shaft. This arrangement provides an economic method for replacement of individual cams during faults. The fuel injection system can be broadly divided into two parts -pressurizing unit and atomizing unit. Pressurizing unit consists of a plunger which reciprocates in a cylinder called barrel. These together forms a fuel pump which pressurize the fuel to about 450 bars. Atomizing units are nozzles which provide a fine spray of fuels into the cylinder. Two nozzles–main nozzle and pilot nozzle are present in each cylinder. A cam provides the up and down motion of the plunger in the barrel.

The speed of the engine is maintained constant even when the load on the alternator varies. This is attained with the help of a governor. It adjusts the fuel input to the cylinder with load, which more fuel is supplied when the load is high and less fuel when the load is low. The quantity of fuel is controlled by providing a helical groove on the plunger. The relative angular position of the groove with spill pot determines the amount of fuel injected to the cylinder. This angular displacement is obtained by a rack and pinion arrangement.

A mechanical over speed trip device is fitted at one end of the cam shaft. A centrifugal force which comes to play at high speeds of the shaft activates the device and the fuel supply is cut off. This device is set for a speed of 565 rpm. A safety valve is provided at the top of the cylinder. It is set for a maximum pressure of 240 bars. To improve the efficiency of the engine a turbocharger is provided which is a turbine- compressor system. The turbine is driven by the exhaust gas which in turn drives the compressor. Hence the air is compressed to about 3 bars. The compressed air is cooled to maintain a particular temperature using HT water. The turbocharger works at 15000 rpm. For every 150 hrs the turbine is washed which is known as turbo wash.

STARTING

The starting sequences of the engine are given below

1.  Start

2.  Blow Through Process

3.  Starting air cranks the shaft[ 120rpm]

4.  Diesel ignition started[350rpm]

5.  Excitation started[5MW -10%.of rated load]

6.  LSHS ignition started[7MW]

7.  Back field excitation stared

Maximum over speed of the machine is limited such that engine will electrically trip at 555 rpm and if the relay is not operated mechanical tripping occurs at 565 rpm. The signal voltage corresponding to 555rpm is 8.46 volt.

Engine starting conditions

·  Lube oil inlet pressure > 0.5 bar

·  Fuel oil inlet pressure > 2 bar

·  Starting air pressure > 18 bar

·  HT water A bank outlet temperature > 50° C

·  HT water B bank outlet temperature > 50° C

·  Turning gear disengaged

·  Mechanical over speed put down inactive

·  Electric pneumatic stop valve closed

·  Earthing switch open

·  MCB not open in AVR circuit

·  Protection relay fault inactive

·  Breaker trip alarm inactive

·  Shutdown alarm inactive

·  Engine stopped

·  Power plant emergency stop inactive

·  CFE emergency stop inactive

Safety Check Conditions

·  HT/LT Water : 3 bar normal

: 2 bar alarm

: 1.5 bar trip

·  Lube Oil : 4 bar normal

: 3 bar alarm

: 2 bar trip

·  Electrical over speed : 555 rpm

·  Mechanical over speed : 565 rpm

Running condition of Engine

·  Charge air : 2.9 bar

·  Starting air : 20.5 bar

·  LT water : 3.4 bar

·  HT water : 2.9 bar

·  Fuel : 0.2 bar

·  Lube oil : 4.6 bar

·  Speed : 500 rpm

·  Ignition pressure : 170 bar

ALTERNATOR

Alternator (3-phase) is used to convert mechanical energy into electrical energy. The alternator is a synchronous machine which runs at synchronous speed generating 3-phase supply. Rating of alternator used in this plant is 18.8MVA, 11KV, 0.8pf, 988A.The winding used is lap winding. Rotating pole is a salient pole type. There are 12 poles. The machine runs at 500 rpm.

N= 120f/p

P= no of poles=12,

N= speed in rpm=500 So the voltage produced is of frequency 50Hz. The speed of alternator is low compared with turbo generator, so salient pole rotor is used. One of the 8 alternators is made by Siemens and others by BHEL.

The excitation system used in this plant is brushless excitation. In this system the ac exciter driven by the main synchronous machine has stationary field and rotating armature. The 3-phase power from the ac exciter is fed along the main shaft to the rotating silicon diode 3-phase rectifier mounted on the same shaft. The output from the alternator is also given along the main shaft to the main alternator field without any slip rings and brushes. So this system is called brushless excitation system.

Specification of exciter

·  Input : 76V, 9.1 A

·  Output : 146V, 405 A

·  RPM : 500

·  Frequency : 66.7

·  Capacity : 59.1 KW

·  Connection : Star

·  No. of stator poles : 16

·  No. of rotor pole : 96

·  Rotor DC terminal

Resistance : 0.5 ohm

GENERATING TRANSFORMER

Specifications

·  Type : outdoor

·  No. of winding per phase : 3

·  Cooling : ONAF

·  Rating : 38 MVA

·  Voltage : 11/110 KV

·  Current : 1996.85 A at LV

: 199.68 A at HV

·  Connection : Delta / Star

·  Tapping : On load

·  Normal tap position : 6

·  Make : BHEL

STATION TRANSFORMER

The 4 ST's installed in the plant provide the low voltage of 415 for the station purposes. Its capacity is 2000KVA with 11000/415v rating. There is one standby station transformer

MV SWITCH GEAR

The MV Switchgear is located in the MV room. In this plant there are 8 generators each producing a voltage of 11KV. There are 4 transformers and one transformer standby. The outputs of 2 generators are connected to a single bus. Thus there are four buses in total (Bus A, Bus B, Bus C, Bus D). For the outputs of the 2 generators to be connected to a bus it must be synchronized,ie the voltage , frequency & phase of each generator output should be same. The bus bar current is 2000 ampere. All these operations are done in MV Switchgear room. This room mainly consists of circuit breakers .There are different type of circuit breakers, e.g. Vacuum CB, SF6 CB. The main use of CB is to quench the arc that is formed when a conducting line is open circuited. Here we use vacuum CB. The circuit breaker current carrying capacity is 1250 ampere.

The output of generators is connected to MV room by cables. They are connected to bus through circuit breakers. Now the bus voltage is 11KV and it has to be stepped up to 110 KV. For this bus is connected to a step up transformer through a circuit breaker. Each generator is grounded through 635 ohm resistor. This resistance bank is known as Neutral Grounding Resistance [NGR]. For measuring the bus voltage and current there is a potential transformer. The bus is connected to the station transformer through a circuit breaker. The station transformer provides the working voltage for the machines and motors in the plant. There are so many relays such as 1.Trip Circuit Supervision Relay, 2.0ver Current Relay, 3.Over Fluxing Relay, 4.Earth Fault Relay, Stripping Relay, 6.Definite Time Relay. Lightning Arrester is also provided for protection.

LV SWITCH GEAR

LV switchgear is located in the LV room. Low voltage switch gear supplies power to all the motors and machines within the plant. LV switch gear is constituted by a number of buses called MCC (Motor Control Cubicle). Such 14 MCCs are present in the plant. Supply to the MCCs is taken from the station transformers. The MCC works at 440V. Outputs of the four transformers are connected to four different MCCs through Circuit breakers. These MCCs are also interconnected through Circuit breakers. This interconnection helps in providing supply to any of the MCCs if supply is present in at least one MCC. Separate MCCs are present for each engine. The supply to drive the auxiliary system of each engine is taken from the corresponding MCC. So a total of 8 MCCs are responsible for the supply to the engines. MCC9 is considered as the most important MCC as all the important operations in the plant gets supply from this MCC. Supply to MCC9 is ensured always. A black start generator is connected to MCC9 so that supply can be obtained from it even during a complete blackout of the entire power grid. The operations of the other MCC are given below:

·  MCC 10 -Lighting purpose

·  MCC11 -Fuel treatment house

·  MCC 12 -fire water pump house

·  MCC 13 -water treatment plant

·  MCC 14 –BPCL

BATTERY ROOM

In the battery room, there are 55 cells of 2 volts each, giving 110 volt. It has a capacity of 300 Ahrs. It is a float rectifier cum boost charger. The battery supplies the necessary dc voltage for display and lighting purposes at emergency

BLACK START DIESEL GENERATOR

It is provided to prevent the plant shut down during the grid failure. It is an AC generator Specification of generator are given below.

·  Rating : 500KVA

·  Voltage : 415

·  Current : 695.6

·  Speed : 1500 rpm

·  Rotor : Salient pole

·  Excitation : Self excited ac

Parallel Operation

Back synchronizing is done as given below.

·  Speed is increased to get the rated frequency

·  The synchroscope switch is closed and the governor of the incoming set is adjusted until the pointer of the synchroscope is rotating as slow as possible

·  Excitation is increased around the rated voltage

·  As the pointer of the synchroscope approaches the top vertical position when rotating in the clockwise direction, main switch is closed.

·  The governor is adjusted to take the rated load

ENGINE AUXTLLARY SYSTEMS

Engine auxiliary systems are necessary for the proper functioning of the Diesel Engine. Even though the auxiliary system is not a part of the engine, it ensures that all the necessary conditions required for the engine to operate are met. It is provided near by the diesel engine and for each engine a separate auxiliary system is present. The Engine Auxiliary System consists of the following parts:

·  Fuel system

·  Lubricating oil system

·  Compressed air system

·  Cooling water system

·  Charge air and exhaust gas system

FUEL SYSTEM: FUEL TREATMENT HOUSE

The fuel system is the most important auxiliary system of an engine, the fuel being the most necessary criterion for the engine to function. KDPP uses two types of fuels for the running of the Diesel Engine. The primary fuel is LSI-IS (Low Sulphur Heavy Stock), also named HFO (Heavy Fuel Oil).Diesel is the secondary fuel. It is also termed as LFO (Light Fuel Oil). Correspondingly, the fuel system is divided into two: HFO System and LFO System.

LSHS lies among the last products obtained in petroleum refineries. It is a tar like substance having very high viscosity and low pour point. A single engine requires about 3 tone fuels for working one hour. Hence the low cost and low sulphur content of LSHS makes it more prominent in use as a fuel than diesel. But diesel is used while starting and stopping an engine except during emergency where the engine is stopped with LSHS.