RTAD-SVX01F-E4 69
Pre-Start Checkout
CAUTION! Provide adequate voltage
to the unit. Failure to do so can
cause control components to
malfunction and shorten the life of
relay contact, compressor motors
and contactors.
CAUTION! Power supply with TT or
TN earthing arrangement is not
compatible with IT (Insulated
Neutral) earthing arrangement.
Unit Voltage Imbalance
Excessive voltage imbalance
between the phases of three-phase
system can cause motors to
overheat and eventually fail. The
maximum allowable imbalance is
3 percent. Voltage imbalance is
determined using the following
calculations:
% Imbalance = [(Vx - V ave) x
100]/Vave
V ave = (V1 + V2 + V3)/3
Vx = phase with the greatest
difference from V ave (without
regard to the sign)
For example, if the three measured
voltages are 221, 230, and 227 volts,
the average would be:
(221+230+227)/3 = 226
The percentage of the imbalance is
then:
[100 * (221-226)] / 226 = 2.2%
This exceeds the maximum
allowable (2%) by 0.2 percent.
Unit Voltage Phasing
WARNING! 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.
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.
Unit Voltage Power Supply
Voltage to the unit must meet the
criteria given in the Installation-
Electrical Section. Measure each leg
of the supply voltage at the unit's
main power fused- disconnect. If the
measured voltage on any leg is not
within specified range, notify the
supplier of the power and correct
the situation before operating the
unit.
To Next Page
Loading...
Need help?
General
