SECTION I
Theory of Operation
Page 1.2
BP+ 10-150
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1.3
Inverter
The inverter changes dc voltage to precision ac voltage through pulse width
modulation (PWM) inversion. Output isolation transformers and an output filter
provide “clean”, computer grade ac which is then sent to the critical load. When
utility power is available, the rectifier supplies power to the inverter. Should the
utility power fail, the inverter is powered by the batteries for a predetermined length
of time.
1.4 Static Bypass Switch
The static bypass switch connects the UPS bypass input to the load in the
event of the loss of the inverter output or an overload condition. During normal
conditions, the static bypass switch is in the open or disconnected mode which
isolates the bypass input from the load.
If the inverter output becomes unavailable or exceeds its specified tolerance,
the static bypass switch will close and transfer the load directly to ac power
without interruption. This transfer is automatically inhibited in the event the UPS
bypass input is not within specified tolerance.
As soon as the inverter becomes available, returns to within tolerance or the
overload clears, the static bypass switch will disconnect and retransfer the load to
the inverter. Note, however, that so long as the inverter is out of specification, the
static bypass switch will automatically inhibit retransfer of the load.
1.5 Batteries
The optional battery pack supplies 216 VDC (10-30 kVA) or 360 VDC (37.5-
150 kVA) nominal. It can be attached to the UPS module to form a single unit or
may stand alone to accommodate space restrictions. It is the energy reservoir of the
UPS and provides dc power to the inverter in case of loss of UPS input power or
rectifier malfunction. The DC Disconnect (Battery) Circuit Breaker electrically
isolates the battery pack from the UPS module for maintenance purposes and
provides overcurrent protection at the battery output.
