Chapter 3. Operation and Adjustment

Initial Pre-Start Settings

Show/hide table

WARNING-READ FULL PROCEDURE Read this entire procedure before starting the prime mover.

Show/hide table

CAUTION-DO NOT TURN POTS BEYOND THEIR STOPS The Rated Speed Potentiometer is the only multi-turn pot in this control. All other pots are single-turn. Take care not to turn these pots beyond their stops.

1. RATED SPEED

A. Set the RATED SPEED potentiometer to minimum (fully counterclockwise).

B. Set the external Speed Trim, if used, to mid-position.

2. RESET- Set at mid-position.

3. GAIN- Set at mid-position.

4. RAMP TIME- Set at maximum (fully clockwise- be careful not to overtorque the pot ).

5. LOW IDLE SPEED- Set at maximum (fully clockwise- be careful not to overtorque the pot ).

6. LOAD GAIN- Set at mid-position.

7. DROOP- Set at minimum (fully counterclockwise- be careful not to overtorque the pot ).

8. ACTUATOR COMPENSATION.

A. Set the ACTUATOR COMPENSATION potentiometer at 2 on the 0 to 10 potentiometer scale for diesel, gas turbine, or fuel-injected gasoline prime movers.

B. Set the ACTUATOR COMPENSATION potentiometer at 6 on the 0 to 10 potentiometer scale for carbureted-gas or gasoline prime movers, and steam turbines.

9. START FUEL LIMIT- Set at maximum (fully clockwise- be careful not to overtorque the pot ).

10. Be sure the actuator is connected to terminals 20 and 21.

Start-up Adjustments

1. Complete the installation checkout procedure in Chapter 2, and the initial prestart settings above.

Show/hide table

CAUTION-SPEED RANGE SWITCH Be sure the speed range switch is set on the right speed range for your application as described in Chapter 2.

2. Close the Close for Rated contact. Set the control for isochronous operation by closing the droop contact.

NOTE: This is for initial prime mover start-up only. For normal start-up, the Close For Rated contact (open for idle/close for rated) should be open if the prime mover is to start at idle.

3. Apply input power to the control.

4. Preset rated speed.

If a signal generator is not used, set the RATED SPEED potentiometer at minimum (fully counterclockwise).

When using a signal generator to set rated speed, set the signal generator for the frequency of the speed sensor at rated speed, and connect it to terminals 28 and 29. (The rated speed frequency in Hz equals the rated prime mover speed in rpm times the number of teeth on the speed-sensing gear divided by 60.) Put the Close For Rated contact in the rated (closed) position. Set the speed trim potentiometer, if used, to mid-position. Connect a dc analog voltmeter to terminals 20 (+) and 21 (-) to read actuator voltage.

If the actuator voltage is at minimum (minimum will be approximately 0 volts), slowly turn the RATED SPEED potentiometer clockwise (counterclockwise for reverse-acting controls) until the voltage just begins to move to maximum.

If the actuator voltage is at maximum, slowly turn the RATED SPEED potentiometer counterclockwise (clockwise for reverse-acting controls) until the voltage just begins to move to minimum.

Continue to very slowly adjust the RATED SPEED potentiometer in the appropriate direction, trying to stop the actuator voltage between the minimum and maximum voltages. Because it is not possible to stop the motion, cease adjusting when the voltage changes slowly. The RATED SPEED potentiometer is now set very close to desired speed. A slight adjustment when the engine is running will achieve the exact speed.

5. Check the speed sensor.

Minimum voltage required from the speed sensor to operate the electronic controls is 1.0 Vrms, measured at cranking speed or the lowest controlling speed. For this test, measure the voltage while cranking, with the speed sensor connected to the control. Before cranking, be sure to prevent the prime mover from starting. At 5% of the lower value of the control's speed range, the failed speed sensing circuit is cleared. For example 100 Hz is required on the 2000 to 6000 Hz speed range (2000 Hz. x 0.05 = 100 Hz).

Show/hide table

WARNING-START-UP Be prepared to make an emergency shutdown when starting the engine, turbine, or other type of prime mover, to protect against runaway or overspeed with possible personal injury, loss of life, or property damage.

6. Start the prime mover.

Adjust for Stable Operation

If prime-mover operation is stable, go to the "Speed Setting Adjustment" procedure.

If the prime mover is hunting at a rapid rate, slowly decrease the GAIN (turn the potentiometer counterclockwise) until performance is stable. Adjusting the GAIN may cause a momentary speed change which can be minimized by turning the GAIN potentiometer slowly.

If the prime mover is hunting at a slow rate, slowly increase the RESET (turn the potentiometer clockwise) until the prime mover stabilizes. If increasing the RESET potentiometer does not stabilize the prime mover, it also may be necessary to either:

* Slowly decrease the GAIN (turn the potentiometer counterclockwise) or

* Slowly decrease the GAIN and increase the ACTUATOR COMPENSATION.

Speed Setting Adjustment

With the prime mover operating stably, and the external speed trim potentiometer (if used) set at mid-position, adjust the RATED SPEED potentiometer to bring the prime mover to the desired operating speed.

Dynamic Adjustment

The object of the GAIN and RESET potentiometer adjustment is to obtain the optimum, or desired, stable prime-mover-speed response.

Connect a dc analog voltmeter to terminals 20 (+) and 21 (-) to monitor the actuator voltage.

NOTE: Adjusting the GAIN may cause momentary changes in speed which can be minimized by turning the GAIN potentiometer slowly.

Increasing the setting of the GAIN potentiometer provides faster transient response (decreases magnitude of the speed change from a sudden change in load). To achieve optimum response, slowly increase the GAIN (turn the potentiometer clockwise) until the voltage on the voltmeter becomes slightly unstable, then slowly turn the GAIN back counterclockwise as necessary to stabilize the meter reading. Step load the generator, or bump the actuator terminal shaft, to make sure that the prime mover returns to the proper speed with little overshoot or undershoot of the speed setting. To reduce overshoot, increase the RESET (turn the potentiometer clockwise).

When the RESET potentiometer in the lower part of its adjustment (0 to 3 on the potentiometer scale), increasing the RESET clockwise may require decreasing the GAIN (turning the GAIN potentiometer counterclockwise) to maintain stable operation.

If the prime mover is slow in returning to the proper speed, decrease the RESET by turning the potentiometer counterclockwise.

Figure 3-1 illustrates prime mover starts with the RAMP TIME potentiometer fully counterclockwise (no ramp- be careful not to overtorque the pot), step loadings at four different RESET potentiometer settings, and stable, steady-state running conditions. These are typical performance curves on a naturally aspirated (non-turbocharged) diesel engine.

NOTE: Optimum performance is not necessarily obtained with the GAIN potentiometer at the maximum stable clockwise position. In some cases, the gain must be reduced slightly to ensure stability under widely varying conditions.

Actuator Compensation Adjustment

If the ACTUATOR COMPENSATION is set as described under Initial Prestart Settings, no further adjustment is normally required. If a slow periodic instability remains, slightly increase the ACTUATOR COMPENSATION (turn the potentiometer clockwise), and repeat the GAIN and RESET adjustments. Continue to increase the ACTUATOR COMPENSATION and readjust the GAIN and RESET until stability is achieved.

If a fast instability or extremely active actuator is evident, slightly decrease the ACTUATOR COMPENSATION (turn the potentiometer counterclockwise). If necessary, the ACTUATOR COMPENSATION may be set fully counterclockwise ( be careful not to overtorque the pot). This may be required when engine torsionals cause excessive fuel-linkage movement.

Low Idle Speed Adjustment

1. The prime mover should be approximately at rated speed with the LOW IDLE SPEED potentiometer set at maximum (fully clockwise- be careful not to overtorque the pot). Open the external CLOSE FOR RATED contact.

2. Decrease the LOW IDLE SPEED (turn the potentiometer counterclockwise) until the recommended idle speed is reached.

NOTE: Make certain that the prime-mover speed is controlled by the LOW IDLE SPEED potentiometer in a range above the minimum-fuel position (mechanical stop) of the actuator or prime-mover fuel rack.

Ramp Time Adjustment

Adjust the RAMP TIME potentiometer to achieve satisfactory prime mover acceleration to rated speed with minimum overshoot. First, start at the fully clockwise (maximum ramp time- be careful not to overtorque the pot) position and work back in the counterclockwise direction until the unit ramps as rapidly as desired.

Figure 3-1. Diesel Engine Performance Curves

Start Fuel Limit Adjustment

NOTE: Start-fuel limit is not recommended for use with reverse-acting controls. With loss of speed signal, the reverse-acting control will position the actuator at the start-fuel level if the failed-speed-signal override is activated. Reverse-acting systems normally require the control to demand full fuel on loss of speed signal to allow the mechanical backup governor to control the system. The Start Fuel Limit can be deactivated by turning the potentiometer fully clockwise ( be careful not to overtorque the pot).

With the prime mover operating at rated speed and no load, record the voltage across actuator terminals 20 (+) and 21 (-). Shut down the prime mover and activate the Failed Speed Signal Override by closing the override contact. The voltage to the actuator should now be adjustable by the START FUEL LIMIT potentiometer. Set the actuator voltage approximately 10% higher than the voltage obtained at rated speed for forward-acting controls and 10% lower than rated speed voltage for reverse-acting controls. Remove the Failed Speed Signal Override contact if not required to start the prime mover.

Start the prime mover and observe the start time, overshoot of speed setting, and smoke emissions obtained. The START FUEL LIMIT may be adjusted as required to optimize the prime-mover starting characteristics. The fuel-limiting function is turned off automatically when the speed control takes over.

NOTE: For prime movers not requiring start-fuel limiting, the START FUEL LIMIT function can be deactivated by turning the potentiometer fully clockwise ( be careful not to overtorque the pot).

Speed Sensor Check

If the sensor is a magnetic pickup, measure the voltage across terminals 28 and 29 to be sure there is a minimum of 1.0 V at cranking speed, and a maximum of 30 Vrms at rated speed. If the voltage exceeds 30 V, increase the gap of the speed sensor, and be sure that there is still a minimum of 1.0 V at cranking speed.

Current Transformer (CT) Phasing Check

NOTE: This control contains internal current transformers. Due to their low impedance, shorting their inputs is not effective. The current input must be removed from the control and shorted externally.

Show/hide table

WARNING-HIGH VOLTAGE Never disconnect any wire attached to load sensor terminals 4 through 9 when the prime mover is running unless temporary 1 ohm, 5 W resistors are Installed as shown in Figure 3-2, and all load is removed. The current transformers can develop dangerously high voltages when open circuited while the prime mover is running.

1. Connect a dc voltmeter to control terminals 11 (-) and 13 (+) to measure the load signal.

2. Start the prime mover. With the generator operating in the isochronous mode and not paralleled, load the generator to as near to full load as possible. Measure the load-signal voltage.

3. Unload and shut down the prime mover. Disconnect the wire from terminal 5, and connect both wires from phase A CT to terminal 4.

4. Start the prime mover, apply full load (or the same load as obtained in step 2) and again measure the load signal at terminals 11 and 13. If the load signal voltage is not 1/3 lower than the reading obtained in step 2, the phasing is incorrect. Unload and shut down the prime mover. Reconnect phase A CT wire from terminal 4 to terminal 5, maintaining the original polarity.

If the phasing is incorrect, proceed to the Phase Correction Procedure.

If the phasing appears correct, skip the Phase Correction Procedure and go to the Load Gain Adjustment procedure.

NOTE: If after completing the LOAD GAIN and DROOP adjustments, the control loading is extremely sensitive to changes in the power factor when operating in parallel, complete the Phase Correction Procedure.

Phase Correction Procedure

NOTE: This procedure requires a minimum power factor of 0.9. If a 0.9 power factor cannot be obtained, tracing through the wiring is the only means of correcting the current-transformer phasing.

The highest positive voltage will be obtained when the CTs are correctly matched to the load-sensor terminals in both phase and polarity. The following procedure will assure the correct connection of the current transformers. It is required only if the phasing check indicates incorrect phasing, or loading stability is extremely sensitive to the power factor.

Trial connections of the first CT to all three load-sensor inputs, polarized both ways, are made (a total of six connections). The load-signal voltage is recorded for each connection and the first CT is then connected to the terminals that produce the highest positive voltage, and with the polarity that produces the highest positive voltage.

The second CT is tried on each of the remaining two CT input terminals, in each polarity, and the voltage recorded. The second CT is then connected to the terminals that produce (and with the polarity that produces) the highest positive voltage.

The last CT is then tried on the remaining input terminals, polarized both ways, and the voltage recorded. Connecting the last CT in the polarity that produces the highest voltage completes the procedure.

The Phase Correction Procedure requires that the prime mover be shut down many times to disconnect the current transformers. For convenience, a temporary method of connection the current transformers shown in Figure 3-2 is recommended. Connecting a 1 ohm, 5W burden resistor across each current transformer allows the current transformers to be disconnected from the terminal strip with the prime mover running, after removing all load.

Show/hide table

WARNING-HIGH VOLTAGE The current transformers can develop dangerously high voltages. Do not disconnect a current transformer while the prime mover is running unless temporary 1 ohm, 5 W resistors are Installed as shown in Figure 3-2, and all load is removed.

Figure 3-2. Temporary Wiring for Transformer Phase Correction

If the temporary burden resistors described and shown in Figure 3-2 are not used, the prime mover MUST be shut down in addition to removing the load in the following procedure.

Measure the load-signal voltage in this procedure by connecting a voltmeter across the Load Signal terminals 11 (-) and 13 (+).

1. Shut down the prime mover.

2. Label each CT wire with the phase and polarity that you think it should be. Even though this identification may prove to be incorrect, this step is necessary so that the individual wires may be identified during the description of the procedure.

3. Disconnect the phase B CT wires from terminals 6 and 7. Connect these two wires together using a small screw and nut, and tape the connection.

4. Disconnect the phase C CT wires from terminals 8 and 9. Connect and tap these two wires together as in step 3.

5. Connect the two wires from the phase A CT to the phase A input terminals 4 and 5.

6. Start the prime mover, apply full load, and measure the load signal voltage. Start a list and record this voltage.

7. Unload the system and reverse the phase A CT wires on terminals 4 and 5. *

8. Apply full load, measure the load signal, and record this voltage.

9. Unload the system, remove the phase A CT wires from terminals 4 and 5, and connect them to phase B input terminals 6 and 7. *

10. Apply full load, measure the load signal, and record this voltage.

11. Unload the system and reverse the phase A CT wires on terminals 6 and 7. *

12. Apply full load, measure the load signal, and record this voltage.

13. Unload the system, remove the phase A CT wires from terminals 6 and 7, and connect them to phase C input terminals 8 and 9. *

14. Apply full load, measure the load signal, and record this voltage.

15. Unload the system and reverse the phase A CT wires on terminals 8 and 9. *

16. Apply full load, measure the load signal, and record this voltage.

17. Unload the system and compare the six voltage readings. *

18. Remove the phase A CT wires from terminal 8 and 9 and connect the phase A wires to the pair of terminals that produced the highest positive load-signal voltage and in the polarity that produced the highest positive load-signal voltage.

19. Untape and disconnect the phase B CT wires. Connect the phase B CT wires to one pair of the two remaining pair of CT input terminals on the load sensor.

20. Apply full load and measure the load signal. Start a new list and record this voltage.

21. Unload the system, and reverse the phase B CT wires on the same terminals. *

22. Apply full load, measure the load signal, and record this voltage.

23. Unload the system, remove the phase B CT wires, and connect them to the other pair of terminals. *

24. Apply full load, measure the load signal, and record this voltage.

25. Unload the system and reverse the phase B CT wires on the same terminals. *

26. Apply full load and measure the load signal. Record this voltage, and compare the four voltages on the list.

27. Unload the system. Remove the phase B CT wires and connect them to the pair of CT input terminals that produced the highest positive load signal voltage and with the polarity that produced the highest positive load signal voltage. *

28. Untape and disconnect the phase C CT wires. Connect these two wires to the remaining pair of CT input terminals.

29. Apply full load, measure the load signal, and record this voltage.

30. Unload the system and reverse the phase C CT wires on the same terminals. *

31. Apply full load, measure the load signal, and record this voltage.

32. Unload and shut down the system. Compare the two voltages. *

33. Connect the phase C CT wires to the same pair of CT input terminals, but in the polarity that produced the highest positive load-signal voltage.

34. Re-label each wire with the phase designation of the terminal that it is now connected to.

35. Remove the burden resistors and terminal block.

* -Be sure to shut down the prime mover if the temporary burden resistors are not used.

Load Gain Adjustment

For this procedure, the generator must be running isochronously and not paralleled. Connect a dc voltmeter across terminals 11 (-) and 13 (+) to measure the load-signal voltage.

Start the prime mover and apply full load. Measure the load signal voltage and adjust the LOAD GAIN potentiometer for 6.0 V. * If full load is not obtainable, decrease the LOAD GAIN proportionally to the load. For example, at 50% load adjust the LOAD GAIN to 3 V.

When paralleled in the isochronous mode or on an isolated bus, generator speeds must be the same. If they are not equal, load sharing will not remain proportional as the load varies. Any difference in loads between the units can be correct by adjusting the Load Gain Potentiometer. Increasing the LOAD GAIN (turning the potentiometer clockwise) will cause that generator to carry less load. If stability problems occur when paralleled at a particular load-signal voltage, reduce the voltage by reducing the LOAD GAIN (turn the potentiometer counterclockwise), and reduce the load-signal voltage setting of all other generators in the system to the same voltage. When the load-signal voltages of all generators in a system are reduced, the load-sharing gain will be reduced, and this may result in some loss of load-sharing sensitivity.

* If 6 volts at full load (or a lower voltage proportional to a load less than 100%) cannot be obtained, and the phasing has been checked and is correct, the current transformers are probably the wrong size. The current-transformer output must be from 3 to 7 A (5 A nominal) at full load.

It may be necessary to reduce the load-signal voltage of each unit in the system to as low as 3 V in cases of extremely poor system dynamics. If your system requires a load-signal voltage as low as 3 V, consult Woodward for suggestions for possible remedies.

Droop Adjustment

Adjustment of the DROOP potentiometer is necessary when the generator set is to be operated in the droop mode. Droop in a load sensor is usually expressed as a percentage and calculated by the following formula.

The method of setting droop depends on whether the load of the generator set is an isolated load or an infinite bus.

Setting Droop for an Isolated Load

1. Open the droop contact connected to terminal 14.

2. Start the prime mover and adjust the RATED SPEED potentiometer for rated speed with no load.

3. Apply full load. *

4. Adjust the DROOP potentiometer to give the desired speed.

Example: Operating 60 Hz, 57 Hz at full load indicates 5% droop.

*-If only 50% loading is possible, 58.5 Hz would indicate 5% droop (see Figure 3-3).

Figure 3-3. Droop Adjustment

Setting Droop when Against Utility

Use the following procedure to set the Droop and Load Gain potentiometers with the utility as the only load.

1. Calculate the fully load speed (or frequency) of the generator when running at 100% load.

No load frequency = rated frequency x (1 + droop %)

Example:

Rated frequency = 60.0 HzDesired droop = 3% (0.03)No Load Frequency = 60 x (1 + 0.03) = 61.8

2. Run the generator at the speed calculated in step 1, with no load. Record the setting of your speed-setting device:

* Potentiometer-record setting with a pencil mark.

* MOP or Other-measure and record the value of the speed-setting voltage (at the control).

3. Reduce system speed to rated (frequency).

4. Preset both the Load Gain and Droop potentiometers fully clockwise ( be careful not to overtorque the pot).

Show/hide table

WARNING-OVERLOAD If when you close the breaker, the load on the unit increases rapidly, open the breaker and shut the unit down. Check the phasing of the CTs and PTs. Permitting the unit to continue to pick up load or continuing to operate the system without correcting this condition may cause damage to equipment, and injury or death to personnel.

5. Synchronize, close the generator breaker, and increase the load by increasing the speed setting to the setting recorded in step 2.

Show/hide table

CAUTION-OVERLOAD The adjustments in steps 6 and 7 are non-linear. Make changes in small increments to prevent overload.

6. Increase the load on the unit by turning the Droop potentiometer counterclockwise until the Load Gain Voltage reads 6.0 Vdc*.

7. Increase load by turning the Load Gain potentiometer counterclockwise until the load is at the desired 100% value.

NOTE: Most systems use a Load Gain Voltage of 6.0 Vdc at full load. To perform this procedure at less than full load, use a Load Gain Voltage value that is proportional to the percent load used. For example, if the Load Gain Voltage at full load is 6.0 Vdc, you would adjust for a Load Gain Voltage of 3.0 Vdc at 50% load.

Figure 3.4. 3% Droop at 60 Hz

Chapter 4. Description of Operation

Introduction

The speed and load sharing section of these 2301A models monitors and controls two functions.

* Speed-The speed control section keeps the prime mover at the correct speed.

* Load Sharing-During parallel operation of two or more generators, the load sharing section senses the load carried by its generator and causes the loads of all generators in the system to be shared proportionally.

Speed Control

The Speed Control system as shown in Figure 4-1 consists of:

* a device (1) to sense the speed of the prime mover

* a Frequency to Voltage Converter (2)

* a Speed Reference (3) to which the prime mover speed can be compared

* A Speed Summer/Amplifier (4) with an output proportional to the amount of fuel or steam required to maintain the desired speed at any given load

* An Actuator (5) to position the fuel or steam mechanism of the prime mover

Figure 4-1. Speed Control System

A speed-sensing device, such as a magnetic pickup, senses the speed of the prime mover, and converts it to an ac signal with a frequency proportional to prime-mover speed.

The frequency-to-voltage converter receives the ac signal from the speed sensor and changes it to a proportional dc voltage.

A speed-reference circuit generates a dc "reference" voltage to which the speed-signal voltage is compared. See Woodward manual 82510, Magnetic Pickups & Proximity Switches for Electronic Controls, for more information on magnetic pickups.

The speed-signal voltage is compared to the reference voltage at the summing point. If the speed-signal voltage is lower or higher than the reference voltage, a signal is sent by the control amplifier calling for an increase or decrease in speed.

The actuator responds to the signal from the control amplifier by repositioning the fuel or steam rack, changing the speed of the prime move until the speed-signal voltage and the reference voltage are equal.

A failed-speed-signal circuit monitors the speed-signal input. When no signal is detected, it calls for minimum fuel. The minimum-fuel signal is sufficient to cause the actuator to go to the minimum position if not restricted. However, due to linkage adjustment or other restrictions in the external system, minimum actuator position may not permit prime-mover shutdown.

For controls with actuator current of 20 to 160 mA, minimum fuel is defined as:

* Actuator current less than 10 mA for forward-acting controls.

* Actuator current greater than 180 mA reverse-acting controls.

For controls with actuator current of 40 to 320 mA, minimum fuel is defined as:

* Actuator current less than 20 mA for forward-acting controls.

* Actuator current greater than 360 mA reverse-acting controls.

A contact to override the failed-speed-signal circuit can be connected in series with terminal 18 and terminal 16 (or terminal 0 on high voltage controls). Temporarily closing the contact overrides the failed-speed-signal circuit, which may be required for start-up.

Because of the variety of installations, plus system and component tolerances, the control must be tuned to each system for optimum performance. The potentiometers for setting and adjusting these circuits are located in the upper right corner of the control as shown in Figure 4-2. They include:

* the RATED SPEED potentiometer

* the START FUEL LIMIT potentiometer

* RESET, GAIN and ACTUATOR COMPENSATION

* RAMP TIME and LOW IDLE SPEED potentiometers

Figure 4-2. Speed Control Adjustments

The RATED SPEED potentiometer is adjusted so that at rated speed, the converter-speed voltage and the reference-speed voltage are equal.

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 systems 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.

Figure 4-3. Terminal Connections

Figure 4-4. Paralleling System

Figure 4-5. Paralleling Adjustments

As mentioned in the general information section, droop mode allows operation of a generator on an infinite bus or in parallel with other engine generator units using hydromechanical governors. In droop, speed changes as the load on generator changes. An increase in load results in a decrease in speed. The amount of speed change or droop is expressed in percent, and is set by the DROOP potentiometer shown in Figure 4-5.

The 2301A Load Sharing and Speed Control is powered by a dc-dc isolated power supply, which allows operation over a wide voltage range without generating excessive heat. This isolation protects the system from interference caused by ground loops, particularly through the load-sharing lines, and allows load sharing with earlier models of Woodward load-sharing controls.