Liebert® Series 610™ UPS - Jonweb.net
Liebert® Series 610™ UPS - Jonweb.net
Liebert® Series 610™ UPS - Jonweb.net
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2.2.5 Static Bypass<br />
Theory of Operation<br />
A static bypass is an integral part of the <strong>UPS</strong> System Control Cabi<strong>net</strong> (SCC). Refer to Figure 7. The<br />
static bypass consists of two reverse-paralleled SCRs (silicon-controlled rectifiers) per phase and<br />
solid-state switching devices working in conjunction with the motor-operated System Bypass Breaker<br />
(SBB). An automatic transfer control circuit senses the status of the operator controls, <strong>UPS</strong> logic signals<br />
and alarm messages and critical bus operating conditions. If the <strong>UPS</strong> modules can no longer supply<br />
the critical load, the static bypass switch (in conjunction with the SBB and <strong>UPS</strong> Output Breaker)<br />
automatically transfers the critical load to the bypass source without interruption.<br />
Figure 7<br />
System Control Cabi<strong>net</strong> block diagram<br />
Gate<br />
Driver<br />
Static<br />
Bypass<br />
Switch<br />
Static Switch<br />
Disconnects<br />
Bypass Line<br />
Static Bypass Breaker<br />
Sync &<br />
Transfer<br />
<strong>UPS</strong><br />
System<br />
Modules<br />
Control<br />
Power<br />
Supply<br />
System<br />
Monitor<br />
Transfer<br />
Control<br />
Voltage<br />
Adjust<br />
Alarms<br />
<strong>UPS</strong> Output<br />
To Critical<br />
Load<br />
Fuse Protection<br />
The static bypass switch path uses two back-to-back SCRs per phase. Each phase is individually protected<br />
by a fuse sized to clear only in the event of a catastrophic fault (with the exception of the continuous<br />
duty static switch used in the SCCC control cabi<strong>net</strong>). This is a more reliable method than<br />
depending on external protection devices. The fuses are in the circuit to protect the critical bus distribution<br />
equipment against catastrophic faults. The static switch SCRs are oversized to easily handle<br />
any current surges that may blow the fuses.<br />
Shorted SCR Monitoring<br />
In all SCCI and SCCC control cabi<strong>net</strong>s, and all SCCT control cabi<strong>net</strong>s 1600A and larger, the static<br />
bypass system has redundant shorted SCR sensing circuits and disconnects. This will prevent <strong>UPS</strong><br />
output power backfeed to the distribution system even if two component failures exist simultaneously.<br />
If a shorted SCR is detected, the static bypass switch is isolated and annunciated at the SCC<br />
control panel, and the critical load remains on <strong>UPS</strong> output power.<br />
In all SCCT control cabi<strong>net</strong>s smaller than 1600A, the static bypass system is equipped with redundant<br />
disconnect circuits that prevent backfeed of lethal voltage to a de-energized bypass input in the<br />
event of a shorted static switch SCR. If the bypass input power is interrupted, the static switch disconnect<br />
devices will open, preventing backfeed of inverter voltage to the bypass input terminals.<br />
16