Parallel OperationInitial Start-UpPreparing a generator for parallel operation requiresspecial attention. Before attempting to parallel units forthe first time, all units must be checked to be sure thefollowing three conditions are met:1. Same phase rotation2. Same alternating current frequency.3. Same voltage adjustmentPhase RotationThe phase rotation must be the same. A set of threelight bulbs is used to determine whether the phaserotation of the incoming unit and the phase rotation ofthe line are the same.1. Connect the light bulbs between the generator leadsand the corresponding line phase, i.e., terminal 1 to line1 across the open circuit breaker.2. Start the units to be paralleled and bring them up tospeed. As they approach the same speed the lights willstart to blink.a. If the lights blink in sequence one of the units isconnected backward. To correct this remove generatorleads 1 and 3 at the circuit breaker and exchange them.This reverses the direction of phase rotation. Line 2should always be connected to line 2.Never attempt to work on electricallyhot wiring. Stop the electric setbefore rewiring generator leads.Open circuit breakers before workingon the equipment which they control.b. If lights blink in unison the phase rotation of bothengines is the same, and condition 1 has been met.Frequency AdjustmentThe 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 enoughfor the internal temperatures to stabilize (about onehour).2. Adjust the governor control to give rated frequency atfull load.3. Remove the load and check the high idle speed; itshould be approximately 3% above full load speed. Ifthese speeds can not be obtained, contact yourCaterpillar dealer.4. For the most consistent results, repeat steps 2 and 3until condition 2 has been met.14
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