Unit Voltage Imbalance; Unit Voltage Phasing - Trane RTXC-XE Series Installation, Operation And Maintenance Manual

Unit Voltage Imbalance

Unit Voltage Phasing

RTXC-SVX003D-EN
Equipment Damage!
Inadequate voltage to the unit may cause control components to malfunction and shorten the
life of relay contact, compressor motors and contactors.
Excessive voltage imbalance between the phases of a three-phase system can cause motors to
overheat and eventually fail for XE(fixed speed) unit. The maximum allowable imbalance is 2
percent. Voltage imbalance is determined using the following calculations:
( �� −�� ) ×100
�� ������
%Imbalance =
��
������
( �� + �� + �� )
1 2 3
�� =
������
3
���� = ��ℎ������ ������ℎ ���������������� �������������������� �������� ��
For example, if the three measured voltages are 375, 389, and 388 volts, the average would be:
375+389+388
�� = = 384 ��
������
3
The percentage of imbalance is then:
( 375 − 384 ) × 100
= 2.34%
384
This exceeds the maximum allowable (2%) by 0.34 percent.
It is important that proper rotation of the compressors be established before the unit is started.
Proper motor rotation requires confirmation of the electrical phase sequence of the power supply
for RTXC-XE/XE-HSE unit. The motor is internally connected for clockwise rotation when viewed
from the motor end with the incoming power supply phases A-B-C. Catastrophic rotor and
housing wear will occur if the compressor is driven in the reverse direction even for a very short
time.
Basically, voltages generated in each phase of a polyphase alternator or circuit are called phase
voltages. In a three-phase circuit, three sine wave voltages are generated, differing in phase by
120 electrical degrees. The order in which the three voltages of a three-phase system succeed one
another is called phase sequence or phase rotation. This is determined by the direction of rotation
of the alternator. When rotation is clockwise, phase sequence is usually called "ABC" , when
counterclockwise, "CBA" .
This direction may be reversed outside the alternator by interchanging any two of the line wires.
It is this possible interchange of wiring that makes a phase sequence indicator necessary if the
operator is to quickly determine the phase rotation of the motor.
Proper compressor motor electrical phasing can be quickly determined and corrected before
starting the unit. Use a quality instrument, such as the Associated Research Model 45 Phase
Sequence Indicator.
1. Check the unit in "Stop" mode from TD7 display.
2. Open the electrical disconnect or circuit protection switch that provides line power to the line
power terminal block(s) in the starter panel (or to the unit mounted disconnect)
3. Connect the phase sequence indicator leads to the line power terminal, as follows:
Phase Sea. Lead
Black (Phase A)
Red (Phase B)
Yellow (Phase C)
4. Turn power on by closing the unit supply power fused-disconnect switch.
5. Read the phase sequence on the indicator. The "ABC" LED on the face of the phase indicator
will glow if phase is "ABC" .
CAUTION
������
Terminal
L1
L2
L3
(������ℎ������ ������������ ���� ��������)
47