York YK-EP B Operation & Maintenance Manual page 172

SECTION 3 - DISPLAY MESSAGES
to detect the loss of any one of the three input phases.
The Trigger will detect the loss of a phase within one
half line cycle of the phase loss. This message is also
displayed every time power to the VSD is removed or
if the input power dips to a very low level.
VSD – High DC Bus Voltage
The VSD's DC Link Voltage is continuously moni-
tored and if the level exceeds 745VDC, a Bus Over-
Voltage shutdown is initiated. If this shutdown occurs,
it will be necessary to look at the level of the 460VAC
applied to the drive. The specified voltage range is 414
to 508VAC. If the incoming voltage is in excess of
508VAC, steps should be taken to reduce the voltage to
within the specified limits.
VSD – Logic Board Power Supply
This shutdown is generated by the VSD Logic Board and
it indicates that the low voltage power supplies for the
Logic Boards have dropped below their allowable op-
erating limits. The power supplies for the Logic Boards
are derived from the secondary of the 120 to 24VAC
transformer, which in turn, is derived from the 480 to
120VAC control power transformer. This message usu-
ally means the power to the VSD has been removed.
VSD – Low DC Bus Voltage
If the DC link drops below 500VDC (or 414VDC for
50 Hz applications), the drive will initiate a system
shutdown. A common cause for this shutdown is a se-
vere sag in the incoming power to the drive. Monitor
the incoming three-phase AC line for severe sags and
also monitor the DC link with a voltmeter.
VSD – Low DC Bus Voltage
(575V/60 Hz applications)
If the DC Link Voltage falls below 600VDC while run-
ning, this shutdown is performed.
VSD – DC Bus Voltage Imbalance
The DC link is filtered by many large electrolytic ca-
pacitors, rated for 450VDC. These capacitors are wired
in series to achieve 900VDC capability for the DC
link. It is important that the voltage be shared equally
from the junction of the center, or series capacitor con-
nection, to the negative bus and the positive bus. This
center point should be approximately ½ of the total DC
Link Voltage. Most actual Bus Voltage Imbalance con-
ditions are caused by a shorted capacitor or a leaky or
shorted IGBT transistor in an output phase bank assem-
bly. This usually indicates the VSD requires service.
172
VSD – DC Bus Voltage Imbalance
(575V/60 Hz applications)
If the Half DC Link Voltage does not remain within
plus or minus 106VDC of the DC Link Voltage divided
by 2 while running, this shutdown is performed.
VSD – Precharge – DC Bus Voltage Imbalance
This message indicates the same as the VSD-DC Bus
Voltage Imbalance message above, except the condi-
tion occurred during the prelube period.
VSD – Precharge-DC Bus Voltage
Imbalance
(575V/60 Hz applications)
If the Half DC Link Voltage does not remain within
plus or minus 106VDC of the DC Link Voltage divided
by 2 during the pre-charge interval, this shutdown is
performed.
VSD – High Internal Ambient Temperature
The ambient temperature monitored is actually the
temperature detected by a component mounted on the
VSD Logic Board. The high ambient trip threshold is
set for 140°F. Some potential causes for this shutdown
are: internal VSD fan failure, VSD water pump failure
or an entering condenser water temperature that ex-
ceeds the allowable limit for the job. Additional causes
for the shutdown are:
• Plugged Strainer – The standard 1.5" Y-strainer
contains a woven mesh element with 20 stainless
steel wires per inch. This has been found to work
adequately on most applications. Some users may
have very dirty condenser water, which can cause
the strainer to plug. Locations with special condi-
tions may want to consider a dual strainer arrange-
ment with quarter turn valves, to permit cleaning
of one strainer with the unit still on line.
• Plugged Heat-exchanger – In cases where the
strainer plugs frequently, the heat-exchanger may
eventually plug or become restricted to the point
of reduced flow. At this point, we suggest you
back-flush the heat-exchanger by reversing the
two rubber hoses which supply condenser water
to-from the heat-exchanger. If the rust cannot be
back-flushed the heat-exchanger might have to be
replaced.
• Low Condenser Flow – The VSD system requires
8 feet of pressure drop across the heat exchanger
to maintain adequate GPM. If the pressure drop is
FORM 160.87-OM1
ISSUE DATE: 8/24/2018
JOHNSON CONTROLS