General information
This instruction is to be used in conjunction with the Operation Instructions for YORK Centrifugal
chillers furnished with an optional YORK
®
OptiSpeed™ Compressor Drive (OSCD).
OptiSpeed/Harmonic filter component overview
OptiSpeed compressor drive 270, 292, 351, and 424 hp (low horsepower
model)
The OSCD is a liquid cooled, transistorized, pulse- width modulation (PWM) inverter in a highly
integrated package. This package is small enough to mount directly onto the chiller motor, and
small enough to be applied in many retrofit chiller applications. The power section of the drive is
composed of four major blocks: an AC to DC rectifier section with an integrated precharge circuit, a
DC bus filter section, a three-phase DC to AC inverter section and an output suppression network.
An electronic circuit breaker with ground fault sensing connects the AC line to an AC line inductor
and then to the DC converter. The line inductor will limit the amount of fault current so that the
electronic circuit breaker is sufficient for protecting the OSCD. Input fuses to the OSCD are no
longer needed. The following description of operation is specific for the 351 hp OSCD unless
otherwise noted.
The AC to DC converter uses three Silicon Controlled Rectifiers (SCRs) and three diodes. One SCR
and one diode are contained in each module. Three modules are required to converter the three-
phase input AC voltage into DC voltage. The modules are mounted on the bot- tom of the liquid
cooled heatsink.
The use of the SCRs in the converter permits precharge of the DC bus capacitors when the chiller
enters the prelube cycle. It also provides a fast disconnect from the AC line when the chiller
enters the coastdown cycle. At this time, the OSCD is turned off, the SCRs in the converter are no
longer turned on and remain in a turned off condition until the next precharge cycle. The DC bus
capacitors will start to discharge through the bleeder resistors. When the chiller enters the pre-lube
cycle, the OSCD is commanded to precharge and the SCRs are gradually turned on to slowly charge
the DC bus capacitors. This is called the precharge period, which last for 20 seconds. At this time the
SCRs are fully turned on. The SCR Trigger board provides the turn on commands for the SCRs. The
OSCD Logic board provides the command to the SCR trigger board when to precharge.
WARNING
Although many of these parts are similar to the parts used in previous Variable Speed Drive (VSD)
designs, these parts are only compatible with drives having the base part numbers included on
the cover of this form. Failure to use the correct parts may cause major damage to these and other
components in the drive.
For example, the VSD logic board 031-02077-000 used in this drive is not compatible with 031-01433-000
logic board used in previous designs. A new VSD logic board was designed in 2006. The part number
of the new board is 031-02506-002. The part number of the new board for the 575 VAC application
is 031-02506-003. The software is not interchangeable between the 575 VAC version and all other
applications. Also the software is not interchangeable be- tween the 031-01433, 031-02077, or the
031-02506 boards.
The DC Bus filter section of the drive consists of one basic component, a series of electrolytic
filter capacitors. The capacitors provide a large energy reservoir for use by the DC to AC inverter
section of the OSCD. The capacitors are contained in the OSCD Power Unit. “Bleeder” resistors are
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Liquid-Cooled OptiSpeed Compressor Speed Drive
