Page 174 - Uninterruptible Power Supplies

Rotary UPS Systems
172 Chapter Six

MAINS 3 MAINS 1 MAINS 2

AUTO
BYPASS
~ STATIC
RECTIFIER
= SWITCH

=
INVERTER
~
BATTERY

M
UNIBLOCK
G
CLUTCH DIESEL

ESSENTIAL CRITICAL
Figure 6.3 Rotating transformer system with directly coupled diesel engine.

winding of an asynchronous motor, clearly rotating at the same speed.
The squirrel cage rotor designated in Fig. 6.5 as the Accu rotor turns at
speeds of 1500 rpm relative to the speed of the field winding. Thus, the
Accu rotor is in reality turning at approximately 2600 rpm (allowing for
slippage). The speeds indicated above are for a system operating on a
50-Hz supply. Such sets will operate on a 60-Hz supply, the speeds will
increase pro rata.
On loss of mains supply the incoming breaker is opened and kinetic
energy from the high-speed Accu rotor is utilized to ensure that the main
rotor is kept within tolerance. On opening the mains input breaker, the
diesel is electrically started and within 1 to 2 s the generator has reached
a speed of some 200 to 300 rpm. At this point the electromagnetic clutch

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