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5.1.2 Static Transfer Switch
The circuit blocks labeled Static Switch in Figure 27 contain electronically controlled switching cir-
cuits that enable the critical load to be connected to either the inverter output or to a bypass power
source via the static bypass line. During normal system operation the load is connected to the
inverter; but in the event of a UPS overload or inverter failure, the load is automatically transferred
to the static bypass line.
To provide a clean (no-break) load transfer between the inverter output and static bypass line, the
static switch activates, connecting the load to bypass. To achieve this, the inverter output and bypass
supply must be fully synchronized during normal operating conditions. This is achieved through the
inverter control electronics, which make the inverter frequency track that of the static bypass supply,
provided that the bypass remains within an acceptable frequency window.
A manually controlled, maintenance bypass supply is incorporated into the UPS design. It enables the
critical load to be powered from the utility (bypass) supply while the UPS is shut down for routine
maintenance.
5.1.3 Battery Temperature Compensation
For 10-30kVA UPS with internal batteries, a standard temperature probe is installed to measure the
internal battery temperature to optimize battery management. The measured temperature can be
displayed from the UPS front panel.
For UPS with external batteries, an optional battery temperature interface equally optimises the
external battery management by connecting up to four external temperature sensors from the battery
cabinet(s) to a control unit inside the UPS.
Figure 28 Multiple battery temperature sensors
NOTE
When the UPS is operating in bypass mode or on maintenance bypass, the connected
equipment is not protected from power failures or surges and sags.
Temperature
Sensor
TMP-2
+
IN
-
NC
12V
GND
OUT
BCB Box
BCB Control
Board – C2
+12V
GND
OUT
X103
X105
X104
X106
X108
UPS
Monitor
Board
– U2
X7
-12V
GND
BAT-T
Temperature
Sensor
TMP-2
+
IN
-
NC
12V
GND
OUT
Temperature
Sensor
TMP-2
+
IN
-
NC
12V
GND
OUT
Temperature
Sensor
TMP-2
+
IN
-
NC
12V
GND
OUT