Usage:
- SUPPLEMENT: 05/20/91
Service Magazine; April 22, 1991; Page 8; "Procedure To Set Voltage Droop On SR 4 Generators With VR3 Voltage Regulators Using Resistive Load Bank."
Illustrations 2 and 3 are showing the secondary polarity dots incorrectly. The correct illustrations follow.
Illustration 2. Circuit with the temporary harness installed between probe (6) and rheostat (3).
Illustration 3. Parts needed to assemble temporary harness.--------------- END SUPPLEMENT ---------------
On some SR 4 Generators, incorrect results in the droop setting can occur when only a resistive load bank is available for testing. Use the following procedure to set an approximate voltage droop when only a resistive load bank is available. This is NOT a substitute for making final adjustments with the actual load. Items such as the amount of governor droop and system power factor will affect the amount of voltage droop obtained. Final adjustment of circulating current between paralleled generators must always be made under actual operating conditions.
NOTE: This procedure can be adapted to earlier VR1 and VR2 voltage regulators with different connections to the regulator droop circuits.
Procedure To Set Droop With A Resistive Load Bank
 |
When servicing or repairing electric power generation equipment, do the following: a. Make sure the unit is off-line (disconnected from utility and/or other generators power service), and either locked out or tagged "DO NOT OPERATE." b. Make sure the generator engine is stopped. c. Make sure all batteries are disconnected. d. Make sure all capacitors are discharged. |
 |
Setup
Illustration 1. Standard droop current transformer circuit.
Illustration 2. Circuit with the temporary harness installed between probe (6) and rheostat (3).
1. Disconnect standard droop current transformer (4) at connections (1) and (2) on 7C8769 Rheostat Assembly (3).
2. Install jumper wire (7).
| NOTICE |
|---|
Make sure standard droop current transformer (4) has load resistor jumper wire (7) across secondary wires (5). If jumper wire (7) is not installed, the current transformer may be damaged.
|
3. Install 6V4960 AC Current Probe (6) on generator lead (T1). Place probe (6) around the same number of leads which pass through standard droop current transformer (4). Polarity arrow "P1
P2" on probe (3) must point toward the generator.
Illustration 3. Parts needed to assemble temporary harness.
NOTE: The 1-480698-01 Connector and 350547-01 Pins are manufactured by AMP and are available from most electrical supply stores.
4. Install the temporary harness. Connect red banana plug (8) to (S1) on probe (6). Connect black banana plug (9) to (S2) on probe (6). Connect amp connector assembly (10) to mating connector on rheostat (3).
Droop Calibration For Units With Isochronous Governors
1. Set the droop potentiometer to the minimum position (CCW).
2. Adjust the no load voltage.
3. Apply rated load at unity power factor with resistive load bank (1.0 pf). Make a note of the kW output.
4. Adjust droop potentiometer and kW until desired voltage droop is obtained at the kW noted in Step 3.
5. Shut the generator unit down and reconnect standard droop current transformer (4). See Illustration 1.
6. Generator unit will now provide approximately the desired voltage droop when run at 0.8 pf.
Droop Calibration For Units With Droop Governors
1. Set droop potentiometer to minimum position (CCW).
2. Adjust voltage regulator level and gain to obtain constant voltage from no load to full load, as given in the normal start-up procedures provided with the generator.
3. Apply rated load at unity power factor with resistive load bank (1.0 pf). Make a note of the kW output.
4. Adjust droop potentiometer and kW until the output voltage droops by an amount equal to desired droop percentage plus 15% of desired droop percentage plus 3% [example: desired droop % + (.15 × desired droop %) + 3%] at the kW noted in Step 3. For example, if 5% droop is desired, the droop would be set at 8.75%.
5. Shut the generator unit down and reconnect standard droop current transformer (4). See in Illustration 1.
6. Generator unit will now provide approximately the desired droop when run at 0.8 pf.