TSC 7320 Transfer Switch Controller
PM180 REV 0 23/02/10 Thomson Power Systems
16
3.5.2. OPEN TRANSITION (FAST, IN-PHASE) TRANSFER
NOTE: This transfer operation type is applicable to Power Contactor type ATS or those
with spring-charged motor operated breaker types. For specific device settings and
ranges, refer to SECTION 6 Factory Default Programming.
Under normal operating conditions, the transfer switch operates automatically during a
failure and restoration of utility power and does not require operator intervention.
When utility supply voltage drops below a preset nominal value on any phase, an engine
start delay circuit will be initiated. Following expiry of the engine start delay period an
engine start signal (contact closure) will be given.
Once the engine starts, the transfer switch controller will monitor the generators voltage
and frequency levels. Once the generator voltage and frequency rise above preset
values, a warmup time delay will be initiated. Once the warmup timer expires, the transfer
to utility supply signal will be removed (i.e. contact opening) and the transfer to generator
supply signal (contact closure) will be given to the transfer switch mechanism. The load
will then transfer from the utility supply (i.e. opening the utility power switching device) to
the generator supply (closing the generator power switching device) to complete a break-
before-make open transition transfer sequence.
The generator will continue to supply the load until the utility supply has returned and the
retransfer sequence is completed as follows: When the utility supply voltage is restored
to above the preset values on all phases, a utility return delay timer will be initiated.
Following expiry of the utility return timer, the TSC 7320 controller will verify the
difference of voltage, frequency and phase angle between the generator and utility
sources, and once an in-phase condition is detected, the generator power switching
device will open, then the utility power switching device will close within ~150
milliseconds to complete the fast (in-phase) break-before-make re-transfer sequence.
An engine cooldown timer circuit will be initiated once the load has successfully re-
transferred back onto the utility supply. Following expiry of the cooldown delay period
the engine start signal will be removed (remote start contact opened) to initiate stopping
of the generator set.
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