TS 880 TRANSFER SWITCH
PM064 REV8 10/01/25 15 Thomson Technology
Note: The standard closed transition transfer switch does not contain an automatic
synchronizer to control the generators frequency or voltage to bring it within limits of
the sync check relay. For correct closed transition transfer operation, the system
requires the generators frequency to be set within 0.25% of nominal frequency and
the generators voltage to be set within 0.5% of nominal voltage.
3. Closed Transition Time Period: The time period in which both sources of supply
are paralleled together during the closed transition transfer sequence is 50-100
milliseconds (maximum). The time period is inherently controlled by operation of
auxiliary contacts from the power switching devices (i.e. when one switching
devices closes, its aux contact closes to initiate tripping of the opposite switching
device).
4. Closed Transition Failure Mode Operation: A control logic circuit and timer (CFT)
continually monitors the closed transition operation time period. The CFT timer
is factory set for 100 milliseconds that allows normal closed transition operation
(i.e. both power switching devices remain closed for less than 100 milliseconds).
The timer and alarm circuit is not activated under normal operation. Should the
closed transition operation time exceed 100 milliseconds (i.e. both power
switching devices remain closed for longer than the normal closed transition time
period plus the setting of timer CFT), the following sequence of events will occur:
q CFT time delay period will expire and will activate auxiliary trip relay.
q If the transfer switch was transferring power from the generator source to the
utility source and the generator switching device failed to open, an auxiliary
trip relay will trip open the utility power switching device to immediately
separate the two power sources. If the transfer switch was transferring
power from the utility source to the generator source and the utility switching
device failed to open, an auxiliary trip relay will trip open the generator power
switching device to immediately separate the two power sources.
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