9905-973 WOODWARD

The START FUEL LIMIT potentiometer provides a means of limiting the fuel-rack 

position when starting diesel engines. Adjustment of the potentiometer sets the 

maximum actuator position desired. This limit position is automatically enabled 

prior to start-up, and is turned off when speed control takes over.

RESET, GAIN and ACTUATOR COMPENSATION potentiometers adjust the 

control amplifier to accommodate various types of prime-mover systems. The 

RESET adjustment affects prime mover reaction time when recovering after a 

sudden load change. The magnitude of the speed change resulting from a 

sudden change in load is controlled by adjusting the GAIN. ACTUATOR 

COMPENSATION compensates for the time the actuator and prime mover 

system takes to react to signals from the control.

The time taken by the prime mover to accelerate from idle to rated speed, and 

the recommended idle speed, are set with the RAMP TIME and LOW IDLE 

SPEED potentiometers respectively.

Terminals for External Devices

Terminal blocks for wiring the control to the system are at the lower front panel of 

the control. Additional terminals are included for connecting other external 

devices as shown in Figure 4-3.

Paralleling

There are two basic methods used for paralleling: droop, where speed decreases 

with load, and isochronous, where speed remains constant. The paralleling 

system as shown in Figure 4-4 consists of:

· Load Matching circuit (1)

· a Load Amplifier circuit (2)

An auxiliary contact on the generator tie-breaker connected from terminal 16 (or 

terminal 0 on high voltage controls) to terminal 14 is used to select isochronous 

load-sharing operation. A contact in series with the auxiliary contact may be used 

to select either the droop or isochronous mode of operation.

If either the auxiliary contact or the droop contact is open, the control is in droop. 

When they are both closed, the control is in isochronous load sharing.

With only one unit on line, the generator picks up the available load and remains 

at isochronous speed. If additional units are on line, the Load Matching circuit 

corrects the fuel output to proportion load.

An amplifier in the load-sensing circuit computes the load carried by each phase 

of the generator. The current load on each phase is multiplied by the cosine of 

the phase difference between the current and the voltage, and the three phases 

are added to determine the total load.

The output of the load amplifier is adjusted by the LOAD GAIN potentiometer 

shown in Figure 4-5. By setting the load-gain voltage on each unit to the same 

level at full load, proportional load sharing is achieved. Regardless of differences 

in generator-set capacities in the system, each generator set is loaded to the 

same percentage of its capacity. A final adjustment of the individual LOAD GAIN 

potentiometers will compensate for minor differences in the generator sets.