Voltage Imbalance; Motors) - Trane Foundation GCC180-300 Installation Operation & Maintenance

Figure 29. Typical unit gas train configuration

Voltage Imbalance

Three phase electrical power to the unit must meet
stringent requirements for the unit to operate properly.
Measure each leg (phase-to-phase) of the power supply.
Each reading must fall within the utilization range stamped
on the unit nameplate. If any of the readings do not fall
within the proper tolerances, notify the power company to
correct this situation before operating the unit.
Excessive three phase voltage imbalance between phases
will cause motors to overheat and eventually fail. The
maximum allowable voltage imbalance is 2 percent.
Measure and record the voltage between phases 1, 2, and
3 and calculate the amount of imbalance as follows:
% Voltage Imbalance = (100 x AV - VD) / AV where;
• V1, V2, V3 = Line voltage readings
• AV (Average Voltage) = (V1 + V2 + V2) / 3
• VD = Line voltage reading that deviates the farthest
from the average voltage
Example:
The supply power line voltage readings (V1, V2, V3) are
221, 230, and 227 respectively.:
• AV (Average Voltage) = (221 + 230 + 227) / 3 = 226
Avg.
• VD (reading farthest from average) = 221
• % Voltage Imbalance = (100 + 226 + 221) / 226 = 2.2%
The 2.2 percent imbalance in this example exceeds the
maximum allowable imbalance of 2.0 percent. This much
imbalance between phases can equal as much as a 20
RT-SVX51L-EN
percent current imbalance with a resulting increase in
motor winding temperatures that will decrease motor life.
If the voltage imbalance is over 2 percent, notify the proper
agencies to correct the voltage problem before operating
this equipment.
Electrical Phasing (Three Phase Motors)
The compressor motor(s) and the supply fan motor are
internally connected for the proper rotation when the
incoming power supply is phased as A, B, C.
Proper electrical supply phasing can be quickly determined
and corrected before starting the unit by using an
instrument such as an Associated Research Model 45
Phase Sequence Indicator and following the steps below:
WARNING
Hazardous Voltage!
Failure to disconnect power before servicing could
result in death or serious injury.
Disconnect all electric power, including remote
disconnects before servicing. Follow proper lockout/
tagout procedures to ensure the power can not be
inadvertently energized. Verify that no power is
present with a voltmeter.
1. Turn the field supplied disconnect switch that provides
power to the main power terminal block or to the "Line"
side of the optional factory mounted disconnect switch
to the "Off" position.
2. Connect the phase sequence indicator leads to the
terminal block or to the "Line" side of the optional
factory mounted disconnect switch as follows:
• Black (phase A) to L1
• Red (phase B) to L2
• Yellow (phase C) to L3
3. Close the field supplied main power disconnect switch
or circuit protector switch that provides the supply
power to the unit.
WARNING
Live Electrical Components!
Failure to follow all electrical safety precautions when
exposed to live electrical components could result in
death or serious injury.
When it is necessary to work with live electrical
components, have a qualified licensed electrician or
other individual who has been properly trained in
handling live electrical components perform these
tasks.
4. Observe the ABC and CBA phase indicator lights on
the face of the sequencer. The ABC indicator light will
glow if the phase is ABC. If the CBA indicator light
glows, open the disconnect switch or circuit protection
switch and reverse any two power wires.
Installation
27