Trane RTWB Helical-Rotary Installation Operation & Maintenance page 30

Unit voltage power supply
Voltage to the unit must meet the
criteria given in Table 7. Measure
each phase of the supply voltage at
the unit main-power, fused
disconnect. If the measured voltage
on any phase is not within the
specified range, notify the supplier
of the power and correct the
situation before operating the unit.
C C A A U U T T I I O O N N
Inadequate voltage to the unit can
cause control components to
malfunction and shorten the life of
relay contacts, compressor motors,
and contactors.
Unit voltage imbalance
Excessive voltage imbalance
between the phases of a three-phase
system can cause motors to
overheat and eventually fail. The
maximum allowable imbalance is
2%. Voltage imbalance is determined
using the following calculations:
% imbalance =(Ux - U average)
U average
U average = (U1 + U2 + U3) / 3
Ux = phase with greatest difference
from U average (without regard
to sign).
For example, if the three measured
voltages are 401, 410, and 407 volts,
the average would be:
401 + 412 + 417 = 410
3
The percentage of imbalance is
then:
100 * ( 410 - 401) = 2.2%
410
This exceeds the maximum
allowable (2%) by 0.2%.
30
Unit Start-Up
Procedures
Unit voltage phasing
W W A A R R N N I I N N G G
It is imperative that L1-L2-L3 in the
starter be connected in the A-B-C
phase sequence, to prevent
equipment damage due to reverse
rotation.
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. The motor is
internally connected for clockwise
rotation, with the incoming power
supply phased A,B,C.
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.
Water system flow rates
Establish a balanced chilled-water
flow through the evaporator. The
flow rates should be between the
minimum and maximum values
given in Table 4.
The flow rates through the
condenser must also be balanced
according to the flow rates table
(Table 4).
Water system pressure drop
Measure the water pressure drop
through the evaporator and
condenser at the field-installed
pressure taps, on the system water
piping. Use the same gauge for each
measurement. Do not include
valves, strainers, or fittings in the
pressure drop reading.
RTWB-SVN01B-E4