York YK-EP, Operation And Maintenance Manual

Page: 203 / 268

• Serial data communications must be established. Refer to VSD – Serial Communications in this
section. If communications between the VSD Logic Board, Harmonic Filter Logic Board, ACC
Board and Control Center Microboard does not take place during initialization, this message
will be generated. The serial communications can be verified by selecting the VSD DETAILS
Screen from the MOTOR Screen and observing the Full Load Amps value. A zero displayed for
this and other VSD parameters, indicates a serial communications link problem.
• If the Harmonic Filter option is included, make sure the Filter Logic Board is not in continuous
reset. This condition is evidenced by the Filter Logic Board’s LED’s alternately blinking. The
filter can be eliminated as a cause of initialization failure by disconnecting the filter by placing
switch SW1 on the Filter Logic Board in the OFF position and removing the ribbon cable
between the Filter Logic Board and the VSD Logic Boards.
• VSD and Harmonic Filter horsepower ratings do not agree.
VSD – High Phase A Instantaneous Current
This shutdown is generated by the VSD if the motor current in phase “A” exceeds a given limit.
The motor current is sensed by the current transformers on the VSD output pole assemblies and
the signals are sent to the VSD Logic Board for processing. Maximum instantaneous permissible
currents are:
• 351/292 HP equals 771 Amps
• 503/419 HP equals 1200 Amps
• 790/658 HP equals 1890 Amps
If an over current trip occurs, but the chiller restarts and runs without a problem, the cause may
be attributed to a voltage sag on the utility power feeding the VSD that is in excess of the specified
voltage range for this product. Thus is especially true if the chiller was running at, or near full load.
If there should be a sudden dip in line voltage, the current to the motor will increase, since the
motor wants to draw constant horsepower. The chiller Pre-Rotation Vanes cannot close quickly
enough to correct for this sudden increase in current, and the chiller will trip on an over current
fault.
If the chiller will not restart, but keeps tripping on this same shutdown, an output pole problem is
the most likely cause. The VSD would require service under these conditions.
If this cycling shutdown occurs 3 times in 10 minutes, the third shutdown becomes a safety
shutdown.
VSD – High Phase B Instantaneous Current
See High Phase A Instantaneous Current message above.
VSD – High Phase C Instantaneous Current
See High Phase A Instantaneous Current message above.
VSD – Phase A Gate Driver
A second level of current protection exists on the VSD driver boards themselves. The collector-to-
emitter saturation voltage of each IGBT is checked continuously while the device is gated on. If
the voltage across the IGBT is greater than a set threshold, the IGBT is gated off and a shutdown
pulse is sent to the VSD Logic Board shutting down the entire VSD system. A gate driver fault can be
initiated when the VSD is not running.
VSD – Phase B Gate Driver
See Phase A Gate Driver message above.
203 YK-EP Style B Centrifugal Chiller