Parallel Operation
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.
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.
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