Sy nchronization Panel

When the Main AC Bus is energized and another generator supply is to be connected to the Main AC Bus, it is essential to match their voltage and frequencies before closing the Generator Circuit Breaker. This is accomplished by comparing the two frequencies by means of the Synchronization Box (shown in Figure 2-11).

When the front panel SYNC switch is in the OFF position, the Sync panel VOLT meter indicates the Main AC Bus voltage. The needle of the SYNCHROSCOPE and the SYNC LIGHTS compare the frequencies of the Main AC Bus and the on-coming generator. The needle of the SYNCHROSCOPE rotates and the SYNC LIGHTS illuminate brightly when the two frequencies are out of phase. When the frequencies and phases are identical, there is no potential across the scope and the lights. As a result, the SYNCHROSCOPE needle remains stationary in the vertical position and both SYNC LIGHTS extinguish.

Document number D257272-1200-MAN-002 Revision 01

Page 24

www.nov.com 24 HOUR SERVICE (281) 569-3050 2.3.4 Engine Governor

The electronic Engine Governor controls the engine speed and horsepower, and thereby regulate the generator frequency (refer to Figures 2-13 and 2-14). Located in the AC

Control Module, the Engine Governor is a feedback control circuit. See the Unique Devices section of this manual for a general description of the feedback control circuit.

The governor output is connected to a Throttle Control Actuator (this controls the engine fuel line valve). The Throttle Control Actuator opens the valve in direct proportion to the current applied by the governor through its coil. The coil signal can be monitored at the AC Control Module across Pin 533 (Throttle+) and Pin 545 (Throttle-).

Document number D257272-1200-MAN-002 Revision 01

Page 25

www.nov.com 24 HOUR SERVICE (281) 569-3050 ENGINE GOVERNOR (Continued)

Figure 2-10. Generator Unit Block Diagram

Document number D257272-1200-MAN-002 Revision 01

Page 26

www.nov.com 24 HOUR SERVICE (281) 569-3050

Figure 2-11. Generator Unit Circuit

Document number D257272-1200-MAN-002 Revision 01

Page 27

www.nov.com 24 HOUR SERVICE (281) 569-3050

Figure 2-11. Generator Unit Circuit (Continued)

Document number D257272-1200-MAN-002 Revision 01

Page 28

www.nov.com 24 HOUR SERVICE (281) 569-3050

Figure 2-11. Generator Unit Circuit (Continued)

Document number D257272-1200-MAN-002 Revision 01

Page 29

www.nov.com 24 HOUR SERVICE (281) 569-3050

Figure 2-11. Generator Unit Circuit (Concluded)

Document number D257272-1200-MAN-002 Revision 01

Page 30

www.nov.com 24 HOUR SERVICE (281) 569-3050

Figure 2-12. Hands-Off Circuit (HOC)

Document number D257272-1200-MAN-002 Revision 01

Page 31

www.nov.com 24 HOUR SERVICE (281) 569-3050

Figure 2-13. Engine Governor Block Diagram

RAMP CKT.

Ι REAL FEEDBACK SPEED FEEDBACK

Document number D257272-1200-MAN-002 Revision 01

Page 32

www.nov.com 24 HOUR SERVICE (281) 569-3050

Figure 2-14. AC Module Circuit

Document number D257272-1200-MAN-002 Revision 01

Page 33

www.nov.com 24 HOUR SERVICE (281) 569-3050

Figure 2-14. AC Module Circuit (Continued)

Document number D257272-1200-MAN-002 Revision 01

Page 34

www.nov.com 24 HOUR SERVICE (281) 569-3050

Figure 2-14. AC Module Circuit (Continued)

Document number D257272-1200-MAN-002 Revision 01

Page 35

www.nov.com 24 HOUR SERVICE (281) 569-3050

Figure 2-14. AC Module Circuit (Concluded)

Document number D257272-1200-MAN-002 Revision 01

Page 36

www.nov.com 24 HOUR SERVICE (281) 569-3050

The engine governor employs two feedback control loops. The Outer Speed Control Loop matches the actual generator frequency to the applied speed command. The Inner Current Control Loop matches the horsepower (KW) output of all engines on line.

Speed Control Loop

Op Amp Z8 issues a speed command which is proportional to the difference between the Speed Command and the Composite Speed Feedback. Speed Command is the Speed Reference signal as modified by the Engine Control switch ramp circuit and the

Master/Slave Logic signal. Composite Speed Feedback is the sum of the Speed Feedback and Throttle Limit signals.

Speed Reference

This signal is set by the operator on the front panel SPEED ADJUST knob. The SPEED ADJUST knob is linked to a potentiometer which outputs a Zero to +11 VDC signal (pin 551). This corresponds to ≈46 to 54 Hz generator frequency.

Engine Control Switch

When the ENGINE CONTROL switch is moved from IDLE to RUN, the ramp circuit generates an ascending ramp. This steadily increases the gain of Op Amp Z8. The ramp circuit generates a descending ramp when the switch is moved from RUN to IDLE.

Changeovers in engine speed are thus accomplished smoothly over a 10 Second time span.

Master/Slave Logic

A signal from the Master/Slave Logic circuit disables the Speed Reference signal when the Generator Unit is in the Slave mode.

Speed Feedback

This signal is a low-level DC analog of the engine speed. At TP 19 in the AC Control Module, the Speed Feedback signal is -2.5 VDC at 50 Hz and ≈+5.0 VDC at 35 to 40 Hz (the IDLE frequency). The Speed Feedback signal is derived either through a Tachometer Pulse Pickup circuit or a Voltage Demodulator circuit.

Document number D257272-1200-MAN-002 Revision 01

Page 37

www.nov.com 24 HOUR SERVICE (281) 569-3050 Pulse Pickup Circuit

A magnetic pickup device is mounted near the flywheel of the engine. The magnetic Pickup device emits a pulse each time a flywheel tooth passes by. These pulses are applied to the Pulse Pickup circuit in the AC Control Module as Tach+ (pin 526) and Tach- (pin 527). The pulse signal is processed to derive the Speed Feedback signal. The

magnetic pickup device generates it's own voltage and must produce ±2 VRMS. The Pulse Pickup also activates the HOC circuit (refer to Figure 2-12). This allows the HOC batteries to power the AC Control Module during the time that the generator voltage is building up.

Frequency Demodulator Circuit

Generator phase voltages out of AC Regulator transformer T10 are processed through a Demodulator circuit in the AC Control Module. The Demodulator output is inverted via Op Amp Z5 to obtain a negative Speed Feedback signal.

Speed Feedback Switch

The AC Control module is equipped with a circuit that permits the tachometer circuit to provide a speed feedback signal until the generator voltage is >200 VAC. When this occurs, the Speed Feedback Switch operates to connect the Frequency Demodulator Circuit output to the Frequency Regulator as the speed feedback signal.

Speed Control Loop

Op Amp Z9 issues a Throttle Current Command which is proportional to the error in signal levels between the Speed Command from Op Amp Z8 and the IREAL (KW) feedback. The output of Op Amp Z9 output is amplified through transistor Q4 and then applied to the Throttle Actuator Coil via Throttle+ (Pin 533) and Throttle- (Pin 545).

Master/Slave Logic

The Master/Slave circuit decides which current command Z9 should receive. If the

generator is a Master, the Generator Cubicle M/S switch selects the Z8 output. If, however, the generator is a Slave, the Generator Cubicle M/S switch selects the Master/Slave signal (pin 543). This signal is the Master generator Z8 output.

The Master/Slave Logic circuit detects whether the generator is the Master or Slave. The Master/Slave Logic circuit receives the M/S Logic signal from the Generator Circuit Breaker (pin 544) and Slave signals which are the M/S Logic signals of the other generators (pins 537 through 542). Table 2-7 is the Master/Slave Truth Table.

Document number D257272-1200-MAN-002 Revision 01

Page 38

www.nov.com 24 HOUR SERVICE (281) 569-3050

Figure 2-15 shows the Master/Slave circuit. The Master/Slave Logic switches from ≈10 VDC (this voltage is approximate since it is partially dropped through a resistor) to -16 VDC when the circuit breaker is closed to connect the generator to the Main AC Bus. The

Master/Slave Logic of each generator is connected to the Slave inputs of the following higher-numbered generators. As a result, the Master generator is always the one with the lowest number. Generator 1 is never a Slave unit since it doesn't receive any Slave inputs.

If Generator 1 is off, the lowest-numbered generator connected to the Main AC Bus becomes the master.

Note that Master/Slave lines of all generators are tied together.

Table 2-7. Master/Slave Truth Table M/S Logic Slave Result

≈10 VDC ≈10 VDC The ge nerator is disconnected from the Main AC Bus.

IREAL is a low-level DC analog of the real current produced by the generator (IREAL x E = KW). Generator phase voltages out of transformer T10 and line currents out of CT1, CT2, and CT3 are processed in the AC Control Module through a current demodulator to

develop ITOTAL, I REAL and IREACTIVE signals (refer to Figure 2-10).