TUBE 1572397 - 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 voltage adjustment
Check the phase rotation. The phase rotation of the paralleled units must be the same. There are two methods that are used to determine whether the phase rotation of the incoming unit and the phase rotation of the on line unit(s) are the same. These methods are listed below.
Using a phase rotation meter
Using a set of three light bulbsHow to determine the proper phase rotation by using three light bulbs is described below.
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 which are going to be paralleled. 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 these generator leads. This reverses the direction of phase rotation. Terminal 2 should always be connected to line 2. Go to 5.
If the lights blink in unison, the phase rotation of both generators is the same. The first condition of 1 has been met.
Adjust the frequency. The speed of the units that will be paralleled must be the same. Speed is proportional to the alternating current frequency.
Allow each electric set to run under load for about 30 minutes.
Adjust the governor control to give rated frequency at full load.
Remove the load and check the high idle speed. The high idle speed should be approximately 2 to 5 percent above full load speed for governors that are equipped with droop. If these speeds can not be obtained, contact your Caterpillar dealer.
For the most consistent results, repeat 2.b and 2.c until the second condition of 1 has been met.
Adjust the voltage. There are two fundamentally different methods for reactive power equalization.
Reactive droop compensation (also known as individual compensation)
Cross current compensation (also known as differential compensation)In the reactive droop compensation the voltage regulator causes an individual generator output voltage to change in proportion to the reactive current. The reactive current is measured with a current transformer (CT).The reactive current can be either lagging or leading. As the lagging reactive current increases, the voltage regulator will cause the generator output voltage to lower (droop) proportionally. As the leading reactive current increases, the voltage regulator will cause the generator output voltage to rise proportionally.This method will tend to reduce the reactive current for better KVAR sharing with other units. The reactive droop compensation is a standard