Figure 3-20.Parallel operation connection diagram.
SYNCHRONIZING LIGHTS (fig. 3-19) will bring the
phase and frequency into exact agreement. As the phase
and frequency approach the same value, the
SYNCHRONIZING LIGHTS will gradually turn on
and off. When the blinking slows to a rate of once per
second or slower, close the main circuit breaker of the
incoming set while the SYNCHRONIZING LIGHTS
are at a point of being dark. The phase sequence relates
to the order in which the generator windings are
connected. If the phase sequence is not correct, the
SYNCHRONIZING LIGHTS will not blink on and off
together. When the incoming set is first connected to
the load through the appropriate switchgear (fig. 3-20).
you should observe one of four occurrences. When the
phase sequence, voltage, frequency, phase, and engine
performance are the same, the changeover will be
smooth with only the slightest hesitation in engine
speed; if each output is slightly out of phase, one of the
engines will shudder at the point of changeover; if the
phase sequence or voltage levels are incorrect, the
reverse power relay will trip on one of the generator sets
and open its main circuit breaker contactors; if the
incoming generator set loses speed significantly or
almost stalls, the incoming engine may be defective.
Should either generator set lose speed,
buck, or shudder when the incoming set is
connected to the distribution feeder lines,
immediately flip the CKT BRK switch of the
incoming set to open, and then recheck the
paralleling set-up procedures.
Refer to figures 3-19 and 3-20 to set up the
generator sets for parallel operation.
When performing step 1, make certain that
the incoming set is shut down and that there are
no voltages at the switchgear terminals being
connected to the incoming set. Do not take
anybodys word for it! Check it out for
yourself! Dangerous and possibly deadly
voltages could be present. Take extreme care
not to cross the LO (neutral) with any of the
other phases (L1, L2, or L3).
1. Connect the incoming set, as shown in figure
2. Make certain that the voltage change board
(reconnection board) (fig. 3-12) of the incoming
generator is set up for the same output voltage as the on-
3. Set CKT BRK switch on the incoming set to
OPEN. When the incoming set circuit breaker is open
(CKT BRK indicator light will be out), operate the load
switchgear so that the on-line output voltage is present
at the voltage change board of the incoming set.
4. Set the PARALLEL OPERATION-SINGLE
UNIT operation switch on both sets to PARALLEL