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4--2 Description of Operation
Open–Transition (2–position) Automatic Transfer Switches continued
Load Retransfer To Normal
Thesequenceforloadretransfertothenormalsourcebeginsautomaticallywhenthe
controller detects a restored normal source or a cancelled transfer test signal.
Normal Source Restoration. The Normal source is considered acceptable again when
all
six voltage, frequency, or phase rotation conditions occur (see page 3–1).
Cancel Transfer Test. Removal of the test transfer signal can be by the Tra ns fe r C on tr ol
switch (Feature 5), engine–generator exerciser clock (Feature 11C), or via serial port
(Feature 72A). When using the Tr an sfe r C on tr ol switch, it must be released
from the
Transfer Test position.
The controller begins the load retransfer sequence by starting the Feature 3A time delay.
Feature 3A time delay on retransfer to normal allows the normal source to stabilize. If the
normal source fails while the Feature 3A time delay is running, the controller waits for the
normal source again to become acceptable and restarts the Feature 3A time delay. If the
emergency source fails while Feature 3A is running, the controller bypasse s the time delay
for immediately load retransfer. To bypass Feature 3A ti me delay, turn the Tr an sfe r
Control switch to the Retransfer Delay Bypass position.
At the conclusion of the Feature 3A time delay, the controller is ready to transfer the load
to normal. If Feature 27 inphase monitor control is enabled, the controller will inhibit
transfer until the sources are in phase.
Load Retransfer. To re transfer the load to the normal source the controller de–energizes
ER relay and energizes SE relay. The transfer switch TS coil energizes, and all transfer
switch contacts (mains, controls, auxiliaries) reverse position. The transfer switch is now
supplying the load from the normal source again
Engine Cooldown & Stop. After load retransfer to the normal source, the controller
starts Feature 2E time delay. Feature 2E time delay provi des an unloaded cooldown
running period for the engine–generator. At the end of the time delay, the controller
energizes the NR relay and the engine–generator is signalled to shutdown.
NORMAL OK
TD Engine Cooldown
__min __s
NORMAL OK
TD Emerg>Normal
__min __s
NORMAL OK
Load on Emerg
NORMAL OK
Load on Normal