Specifications

1. Set the generator to always run five minutes longer than the unit start-to-start timer, which could be set from
15 to 60 minutes. The actual setting can be viewed on the operator interface panel on the Setpoint/Timer
screen.
2. Configure the transfer switch, provided with the generator, to automatically shut down the chiller before
transfer is made. This function can be accomplished through a BAS interface or with the “remote on/off”
wiring connection shown in Figure 15. A start signal can be given anytime after the stop signal since the
three-minute start-to-start timer will be in effect.
Chiller Control Power: For proper operation on standby power, the chiller control power must remain as
factory-wired from a unit-mounted transformer. Do not supply chiller control power from an external power
source because the chiller may not sense a loss of power and do a normal shutdown sequence.
System Pumps
Operation of the chilled water pump can be to 1) cycle the pump with the compressor, 2) operate continuously,
or 3) start automatically by a remote source.
The cooling tower pump must cycle with the machine. The holding coil of the cooling tower pump motor starter
must be rated at 115 volts, 60 Hz, with a maximum volt-amperage rating of 100. A control relay is required if the
voltage-amperage rating is exceeded. See the Field Wiring Diagram on page 23 or in the cover of control panel
for proper connections.
All interlock contacts must be rated for no less than 10 inductive amps. The alarm circuit provided in the
control center utilizes 115-volts AC. The alarms must not draw more than 10-volt amperes.
VFD Line Harmonics
Despite their many benefits, care must be taken when applying VFDs due to the effect of line harmonics on the
building electric system. VFDs cause distortion of the AC line because they are nonlinear loads, that is, they
don't draw sinusoidal current from the line. They draw their current from only the peaks of the AC line, thereby
flattening the top of the voltage waveform. Some other nonlinear loads are electronic ballasts and
uninterruptible power supplies.
Line harmonics and their associated distortion can be critical to ac-drives for three reasons:
1. Current harmonics can cause additional heating to transformers, conductors, and switchgear.
2. Voltage harmonics upset the smooth voltage sinusoidal waveform.
3. High-frequency components of voltage distortion can interfere with signals transmitted on the AC
line for some control systems.
The harmonics of concern are the 5
th
, 7
th
, 11
th
, and 13
th
. Even harmonics, harmonics divisible by three, and high
magnitude harmonics are usually not a problem.
Current Harmonics
An increase in reactive impedance in front of the VFD helps reduce the harmonic currents. Reactive impedance
can be added in the following ways:
1. Mount the drive far from the source transformer.
2. Add line reactors. They are standard equipment on WMC chillers.
3. Use an isolation transformer.
4. Use a harmonic filter.
Voltage Harmonics
Voltage distortion is caused by the flow of harmonic currents through a source impedance. A reduction in
source impedance to the point of common coupling (PCC) will result in a reduction in voltage harmonics. This
can be done in the following ways: