SWITCH AS-LIMIT 6T5925 - Caterpillar

Initial Start-Up
Preparing a generator for parallel operation requires special attention. Before you attempt to parallel units for the first time, check all the units for the following three conditions.
Same phase rotation
Same alternating current frequency
Same winding pitch
Same voltage adjustment
Check the phase rotation. Units that operate in parallel must have the same phase rotation. Two methods may be used to determine if the incoming unit and the unit that is on-line have the same phase rotation. These methods are listed below:
Using a phase rotation meter
Using a set of three light bulbsUse the procedure below to determine the proper phase rotation by using three light bulbs.
Illustration 1 g00695380
When servicing or repairing electric power generation equipment: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. Remove all fuses.
Connect the light bulbs with rated voltage between the generator leads and the corresponding line phase. For example, connect terminal 1 to line 1 across the open circuit breaker.
Start the units that will be in operating in parallel. Bring the units up to speed. As the units approach the same speed, the lights will start to blink.
If the lights blink in sequence, one of the units is connected backward. In order to correct the problem, stop the units. Remove generator leads 1 and 3 at the circuit breaker. Exchange generator leads 1 and 3, thus reversing the direction of phase rotation. Terminal 2 should always be connected to line 2.
Both generators have the same phase rotation when the lights blink in unison. The first condition of "Initial Start-Up" has been met.
Adjust the frequency. The units that will be operating in parallel must operate at the same speed. Speed is proportional to the alternating current frequency. Verify that the generator set is programmed to run at the correct frequency.
Adjust the voltage. Refer to this Operation and Maintenance Manual, "Voltage Regulators".Note: Make sure that the speed droop is identical for all of the engines before adjustments are made to the generator.
Note: Do not change the voltage settings after this step.
Check the winding pitch. The units that operate in parallel must have the same winding pitch to reduce the effect of circulating currents. It is possible to parallel units with different winding pitches after the amount of circulating current flow between each of the units has been determined. Contact your Cat dealer for further information.Starting Multiple Units
Use the procedure for starting single units in order to start multiple units. Refer to Operation Section, "Single Unit Operation".Paralleling Multiple Units
Units may be paralleled at no load. Units may also be paralleled with units under load. After the initial conditions for start-up are satisfied, verify for the following requirements:
One of the governors can be an isochronous governor. Electronic load sharing governors are an exception.
Generators must have voltage droop compensation or cross current compensation.
Start the unit which will be paralleled.
Turn on the synchronizer lights.
After the engine has run a few minutes, bring the engine up to synchronous speed. This means