4--2 Description of Operation

Open–Transition (2–position) Automatic Transfer Switches continued

Load Retransfer To Normal

Thesequenceforloadretransfertothenormalsourcebeginsautomaticallywhenthe
controllerdetects a restored normal source or a cancelled transfer test signal.
Normal Source Restoration.The Normal source is consideredacceptable again when
all six voltage, frequency, or phase rotation conditions occur (see page 3–1).
Cancel TransferTest. Removal of the test transfer si gnal can be by the Tr a n s fe r Con t ro l
switch (Feature 5), engine–generator exerciser clock (Feature 11C), or via serial port
(Feature 72A). When using the Tr a n s f e r Con t r o l switch, it must be released fromthe
TransferTestposit ion.
The controllerbegins the load retransfer sequenceby starting the Feature 3A time delay.
Feature3A time delay on retransfer to normalallows the normal sourceto stabilize. If the
normalsource fails while the Feature 3A time delay is running, the controller waits for the
normalsource again to become acceptable andrestarts the Feature 3A time delay. Ifthe
emergencysource fails while Feature 3A is running, the controller bypasses the time delay
for immediately load retransfer. To bypass Feature 3A time delay, turn the Tran s f e r
Control switch to the Retransfer Delay Bypass position.
Atthe conclusion of the Feature3A 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 untilthe sources are in phase.
LoadRetransfer. To retransfer the load to the normal source the controllerde–ene rgizes
ER relay and energizesSE relay. The transfer switch TS coil energizes, and all transfer
switchcontacts (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 normalsource, the controller
starts Feature 2E time delay. Feature 2E time delay provides 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