SR 4 AND SRCR GENERATORS - OPERATION & MAINTENANCE Caterpillar

Initial Start-Up

Preparing a generator for parallel operation requires special attention. Before attempting to parallel units for the first time, all units must be checked to be sure the following three conditions are met:

1. Same phase rotation

2. Same alternating current frequency.

3. Same voltage adjustment

Phase Rotation

The phase rotation must be the same. A set of three light bulbs is used to determine whether the phase rotation of the incoming unit and the phase rotation of the line are the same.

1. Connect the light bulbs between the generator leads and the corresponding line phase, i.e., terminal 1 to line 1 across the open circuit breaker.

2. Start the units to be paralleled and bring them up to speed. As they approach the same speed the lights will start to blink.

a. If the lights blink in sequence one of the units is connected backward. To correct this remove generator leads 1 and 3 at the circuit breaker and exchange them. This reverses the direction of phase rotation. Line 2 should always be connected to line 2.

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Never attempt to work on electrically hot wiring. Stop the electric set before rewiring generator leads. Open circuit breakers before working on the equipment which they control.

b. If lights blink in unison the phase rotation of both engines is the same, and condition 1 has been met.

Frequency Adjustment

The speed of units to be paralleled must be the same. Speed refers to the alternating current frequency.

1. Allow each electric set to run under load long enough for the internal temperatures to stabilize (about one hour).

2. Adjust the governor control to give rated frequency at full load.

3. Remove the load and check the high idle speed; it should be approximately 3% above full load speed. If these speeds can not be obtained, contact your Caterpillar dealer.

4. For the most consistent results, repeat steps 2 and 3 until condition 2 has been met.

Voltage Adjustment

The voltage level and voltage droop adjustments determine the amount of circulating currents between generators. Carefully matched voltage regulator adjustments will reduce the circulating currents. Loads of .8 power factor (primarily motors) require a generator voltage droop of about 5%. Voltage droop is expressed as the percentage of voltage change from no load to full load. Use the same voltmeter to make adjustments on each unit to be paralleled.

1. Adjust voltage as described for Single Unit Operation, Initial Start-Up.

2. With the engine running at high idle, turn the voltage droop clockwise about 1/2 of full range.

If driven load is to be unity power factor, set the voltage droop control on all generators at 1/2 of full range and proceed to Step 7. If driven load is to be normal (0.8 power factor) proceed to Step 3.

3. Readjust the voltage level control until the voltage is about 5% above desired voltage.

4. Apply full load at .8 power factor.

NOTE: If a generator is to be paralleled with other generators, the voltage droop of each generator must be the same to satisfactorily divide reactive load.

5. Readjust the voltage droop control to obtain desired voltage with full load at .8 power factor.

6. Repeat Steps 3, 4 and 5 for each generator to be paralleled until line voltage is equal to desired level at .8 power factor and no load voltage is approximately 5% above rated voltage.

7. Parallel generators and apply the driven load (see the topic Operation/Paralleling). If the sum of the amps of the individual generator amperes exceeds the total amps going to the load by 10% at full load, adjust voltage droop controls to share current proportionally between generators.

8. Tighten the locknuts on all controls and install the access cover. Condition 3 has been met.

Starting Multiple Units

Starting-Units are started the same as single units.

Paralleling

Units may be paralleled at no load or paralleled with units under load. To parallel two or more units the following conditions must be met:

1. Same phase rotation.

2. Same voltage level.

3. Same voltage droop.

4. Same frequency.

5. Voltages must be in phase.

The first three conditions have been met in the initial start-up for parallel operation.

1. Start the unit to be paralleled according to the procedure in the engine operation section.

2. Turn the synchronizer lights on.

3. After the engine has run long enough to warm up, bring it up to synchronous speed (the same frequency as the unit on the line). The synchronizing lights will begin to blink.

4. Using the governor control adjust the speed until the lights blink very slowly.

5. The lights are off when the voltages of the two units are in phase. At this point very quickly close the breaker while the lights are out.

6. Use governor controls to share KW load between engines

7. After generator temperature has stabilized (1 hr.), adjust the droop control of each generator so as to share the reactive load and to limit the circulating currents. Less droop (moving control CCW) increases the reactive current carried by the generator.

The frequency of the incoming unit should be slightly greater than the line frequency. This will allow the incoming unit to assume some of the load rather than add to the system load.