Powerware 5075 kVA - Manual (Page 52)

44 Powerware BPIII Harsh Environment UPS 50--75 kV Installation and Operation
164291261 Rev. F 111503
Maintenance Bypass Mode
The UPS can be manually switched to Maintenance Bypass mode allowing the
UPS to be electrically isolated from the critical load. The bypass source supplies
the commercial AC power to the load through an internal circuit breaker.
CAUTION:
Critical load is not protected while the UPS is in Maintenance Bypass mode.
Figure 21 shows the path of electrical power through the UPS system when the UPS
is operating in Maintenance Bypass mode.
Bypass
Rectifier
K4
Input
Input
K3 CB1
(closed)
BATTERY
Path of electrical power
RECTIFIER INVERTER
Output
TRANSFORMER
BYPASS
DC/DC
CONVERTER
CB2
(closed)
(MBP)
(closed)
Input
Isolation
Transformer
(BIB)
(open)
(MIS)
(open)
OUTPUT
Figure 21. Path of Current Through the UPS in Maintenance Bypass Mode
The wrap---around maintenance bypass is useful during routine UPS maintenance
or repairs, by suppling utility power to the critical load while the UPS inverter and
bypass are de-energized.
The major components of the Maintenance Bypass are described in the following
paragraphs.
Maintenance Bypass (MBP) Circuit Breaker
This breaker is normally open. When closed, it feeds utility power to the critical load
when the MIS breaker is opened.
Maintenance Isolation (MIS) Circuit Breaker
This circuit breaker is normally closed, feeding UPS power to the critical load. This
breaker is opened to isolate the UPS after the MBP breaker is closed.
Maintenance Bypass (MBP) Circuit Breaker
This circuit breaker is normally closed feeding bypass power to the UPS internal
bypass circuit. This breaker is opened to isolate the UPS bypass after the load is
transferred to maintenance bypass.
The MBP and MIS breakers are electrically interlocked to limit the possibility of UPS
system damage from improper operation.