DIESEL GENERATOR 

Connected Devices

1.      Cooling Tower Pump : Raw water tank Checking

2.      Cooling Tower Fan

3.      Air Compressor : 0 to 10 Kg/cm².

4.      Lub oil Priming pump :

5.      Fuel transfer pump

RELAYS USED FOR D.G. PANEL

1.      Restricted Earth Fault : Instantaneous Earth Fault – Type : CAG, Range : 1.5 to 4 Amps

2.      Negative phase sequence Relay: Negative sequence relay, Type: CTNM, Range:

3.      Earth fault relay: E/F relay(Inverse type) Type: CDG – Range: 0.5 to 2 Amps.

4.      Over Current Relay: (Inverse) Type: CDG- 3 NOS, Range: 2.5 to 10 Amps.

DG INCOMER PANEL (EPCC)

1.      Instantaneous Earth fault Relay: Type CAG, Range: 0.5 to 2 Amps,

setting: 1A (320 x 1=320)A

2.      Trip Circuit Supervision Relay: Type – VAX MK11, 110 – 125 Volts

3.      Definite Time Relay: Type VTT – 110V, setting: 0.5 sec delay on pick up

4.      Over current Relay(Inverse)Type CDG, Range :2.5 to 10 A,

setting: 3.75A (320 x 3.75 = 1200)A

5.      Earth fault relay(Inverse) Type CDG, Range: 0.5 to 2 A, Setting: 0.75A(320 x 0.75=240)A

6.      Over current relay(Inverse) Type DCG, Range: 2.5 to 10Amps

7.      Tripping relay: Type VAG

8.      Instantaneous over voltage relay: VAGM-ALSTOM. Normal voltage: 110 VAC, setting:132V, range 121 to 154V

9.      Instantaneous under voltage relay: VAGM:ALSTOM. Normal Voltage:110VAC,

 Range 44 to 88 V, setting: 88 volts

DG INCOMER PANEL (Control Panel)

1. Instantaneous Earth fault Relay: Type CAG, Range: 1 to 4 Amps, Setting: 1(269.4 x 1)

              3. Over current Relay(Inverse)Type CDG, Range :2.5 to 10Amps, Setting: 3.75 A, Full load

                   current: 1347 Amps. ( 269.4 x 3.75 = 1010 Amps)

              4.  Earth fault relay(Inverse) Type CDG, Range: 0.5 to 2 Amps, Setting: 0.5 (269.4 x 0.5 =                        134.7 Amps.

 DG panel meters: Ammeter, Voltmeter, PF meter, Energy meter, Frequency meter, DG- KVAR meter, KW meter, Excitation voltmeter & ammeter, enunciator 1 to 5, Double voltmeter, synchroscope meter, Double frequency meter.

DG GCU: Generator controller unit.

1. Digital governing, voltage regulation, synchronizing, load sharing, paralleling with main bus(Grid).  

2. Protection of Alternator against over current protection.

3. Analogue and digital AC output metering.

4. Battery monitoring system to check for weak condition.

5. Digital alarm and status massage display.

6. Generator set – Engine monitoring system

7. Smart stealing control feature

8. Network capability.

9. Ip-54 protection.

10. PC Compatibility.

* Battery supply – 24.5 VDC 200 Ah.

Ø  Min. time of operation without cooling water availability during start up

Ø  Max time require to start the diesel from preheated (cold) condition to bring up to rated speed and load up to its capacity without exceeding voltage and frequency limit

Ø  Ip-23: Ingress protection.

Where 2 stands for-12 mm gap,   eg: figure

 3 stands for direct spray of water up to 60⁰ C from vertical.

Ø  S – Motor stop condition tested

Ø  M – Motor running condition tested.

PROTECTION FOR DG SET

SN	Alternator side	Setting		SN	Panel side	Setting
1	High Lub oil temperature	1050C		1	Over Voltage	480 V
2	High cooling water temperature	70-950c		2	Over Current	1010A
3	Low lub oil pressure	2-7 kg/cm2		3	Restricted Earth fault	269.4A
4	Engine over speed	1650 rpm		4	Under Voltage	88%:345.8A
5	Generator Bearing temperature	720C		5	Frequency adjustment	+ 5%
6	Engine Bearing temperature	700C		6	Raw water inlet temp.	33.30C
7	Generator winding temperature	93- 960C		7	Raw water temp. raise	43.30C
8	Air pressure	7– 10.5 kg/cm2		8	Designed Amb.temp.	450C
9.		3 minutes.
10		15 Sec.

Back-up protection for alternator: The I.D.M.T.L relay is used for back up over current and earth fault protection of alternators.

Protection against unbalanced load: Alternators area protected against unbalanced load by negative sequence relay along with a filter unit.;

Negative sequence filter: The negative sequence filter being a sensor element segregates the negative sequence component and allows the same to pass through the relay coil.

Reverse power protection for parallel operation of alternator: During parallel operation if the input to the prime mover of an alternator is stopped or reduced then its E.M.F. will obviously become less than the bus bar voltage and then it will act as a synchronous motor drawing power from the bus bar instead of delivering power to the bus bar. So to avoid this abnormal situation reverse power protection is absolutely necessary for alternators running in parallel.

Protection from stator winding fault: As the stator winding fault may lead to burning of stator coils automatic protection is absolutely necessary to clear such fault in the quickest possible time in order to minimize the extend of damage to the expensive machinery.

For protection of alternators against stator winding faults differential protection (also known as Merz-price system) is commonly used due to its greater sensitivity and reliability.

Protection against abnormal vibration of alternator: Vibration detector is used for this purpose. When an abnormal vibration the radial deflection exceeds a preselected value it operates to trip the breaker of the machine.

HOW DG GETS ON

1.      In field exciter residual magnetism is available. When normal supply fails, command gets DG and 24VDC  Starter gets on, it rotates DG wheel & starter gets off. Due to this in the armature of exciter, EMF is produced.

2.      Produced is 3 ph AC which converts in DC due to rotating diode assembly on the shaft and feed to rotating field.

3.      Main Rotating Field: This rotating field cuts stationary conductor of stator then EMF in is borne in stator coil.

4.      Stator Of Generator: Here exactly armature is given. But for brushless generator, it is constructed over stator, This is why no need of brush. Due to brushless, efficiency will be more.

When generator starts, it is on no-load, its field voltage is 32V & field current is 1.2 A & line voltage is 425V. When generator is loaded, its voltage should be decrease. But it do not take place because of Automatic Voltage regulator. When load increases, voltage getting to AVR, then exciter field winding voltage increases. There is no difference in voltage during loading, un loading. Speed is maintained by governor which increases diesel flow when speed decreases. 

AVR(Automatic Voltage Regulator) : The electronic controller is the heart of system which maintains stable output DC voltage of the charger in spite of supply voltage fluctuations and load variations.

Starting procedure of DG set in detail

The main stator is provided power for excitation of the exciter field via the SX 440 or SX 421 AVR which is the controlling device governing the level of excitation provided to the exciter field. The AVR responds to voltage sensing signal derived from the main stator winding by controlling the low power of the exciter field control of the high power requirement of the main field is achieved through the rectifier our put of the exciter.

The  SX 421 AVR in addition to the SX440 features has three phase rms sensing and also provides for over voltage protection when used in conjunction with an external circuit breaker.

Permanent magnet Generator PMG excited AVR controlled generator.

 The permanent magnet generator provides power for excitation of the exciter field via the AVR (MX341 or MX321) which is the controlling device governing the level of excitation provided to the exciter field. The AVR responds to a voltage sensing signal derived via an isolating transformer in the case of MX321 AVR from the main stator winding. By controlling a low power of the exciter field. Main field is achieved through the rectified out put of the exciter armature.

The PMG system provides a constant source of excitation power irrespective of main stator loading and provides high motor starting capability as well as immunity to wave form distortion on the main stator out put created by non linear load 2.9 thyristor controlled DC motor.

The MX341 AVR senses average voltage on two phases ensuring close regulation in addition it defects engine speed and provides an adjustable voltage fall off with speed below a pre-selected speed (Hz) setting preventing over-excitation at low engine speed and softening the effect of load switching to relieve the burden on the engine. It also provides over-excitation delay, to de-excite the generator in the event of excessive exciter field voltage.

The MX321 provides the protection and engine relief features of the MX341 and additionally incorporates 3 phase rms sensing and over voltage protection.

The detailed function of all the AVR circuits is covered in the load testing section.

The SX440 and MX321 AVRs incorporate circuits which, when used in conjunction with accessories can provide for parallel operation either with drop or a static control AVR/PF control and in the case of the MX321 AVR, short circuit current limiting.

Function and adjustment of the accessories which can be fitted inside the generator terminal box are covered in the accessories section of the box.