Nidec 4P10, Instruction Manual, Page: 25 / 46

Page 25
Parallel Operation
For the generator to operate in parallel with a system in operation,
the phase sequence of the generator must be the same as that of the
system. Use transformers to reduce the voltage to an acceptable level,
and then use a phase rotation meter or incandescent lamp method,
described in electrical machinery handbooks, for a phase sequence
check.
The output voltage at the paralleling point must be the same each
instant, which requires that the two voltages be of the same frequency,
same magnitude, same rotation, and in coincidence with each other.
Voltmeters indicate whether the voltage magnitude is the same, and
frequency meters indicate whether the frequencies are the same.
Whether the voltages are in phase and exactly at the same frequency is
indicated by a synchroscope or by synchronizing lamps.
A synchroscope can be used to indicate the difference in phase angle
between the incoming machine and the system. The generator can
be paralleled by using incandescent lamps connected as shown in
Figure 17. The voltage rating of the series lamps must equal the voltage
rating of the transformer-low voltage winding.
Each prime mover in the system must have the same speed regulating
characteristics, and the governors must be adjusted to give the same
speed regulation as determined by applying load that is proportional
to the full load rating of the generator.
The voltage regulator must include paralleling circuitry. In addition,
the voltage, droop settings and the V/Hz regulation characteristics
must be the same for all the voltage regulators. This will allow the
generators to properly share reactive loads.
Figure 17 Synchronizing Paralleled Generators with Test Lamps
If cross-current compensation is used, paralleling current transformers
must give the same secondary current.
System Bus
Synchronizing
Lamps
Load
Switch
Load Lines From the Incoming Generator