Guide Specification – 3-Phase Static Uninterruptible Power Supply
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5.3.5 Overload Capacity:
The Inverter output shall be capable of providing an overload current of 125% for 2 min.
and 150% for 1 min. A message on the control panel shall indicate this condition. If the
time limit associated with the overload condition expires, or the overload is in excess of
the set current limit, the load power shall transfer to the bypass source without
interruption.
5.4
Static Bypass Circuit:
5.4.1 General:
An integral static bypass circuit shall be provided to supply an alternate source of power
to the critical load in the event the inverter cannot supply rated output power. The bypass
circuit shall be capable of supplying the UPS rated load current and accommodate fault
clearing.
The 100% duty rated static bypass panel shall be composed of a thyristor switch with a
wrap-around contactor. The thyristor switch shall be a high-speed transfer device. The
wrap-around contactor shall be electrically connected in parallel to the thyristor switch
and shall, at the same time as the thyristor switch, be energized and, upon closure,
maintain the bypass source to the load to improve the efficiency and reliability of the
system. The thyristor switch shall only be utilized for the time needed to energize the
contactor closure.
The UPS system logic shall employ sensing which shall cause the thyristor switch to
energize and provide an uninterrupted transfer of the load to the bypass source when any
of the following limitations are exceeded:
Inverter output undervoltage or overvoltage.
Overloads exceeding 125% for 2 min., or 150% for 1 min.
DC circuit undervoltage or overvoltage.
Final discharge voltage of system battery is reached and the bypass source is
present, available, and within tolerance range
Transferring the output from the inverter to the bypass source and vice versa shall be
performed by pressing “START/STOP” icon on the touchscreen display.
Operating Mode
Transfer mode
Transfer Type
Synchronized
Unsynchronized
Automatic
Inverter to Bypass
(Overload, Internal Fault)
Uninterrupted
Interrupted
“BYPASS”
switch operated
Inverter to Bypass
Uninterrupted
Interrupted
(forced transfer)
Automatic
Bypass to Inverter
(Auto-Retransfer Mode)
Uninterrupted
Transfer inhibited
“UPS”
switch operated
Bypass to Inverter
Uninterrupted
Transfer inhibited
