4--5Description of Operation

Closed–Transition Automatic Transfer Switches continued

Closed–Transition 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
emergency source fails during while Feature 3A is running, the controller bypasses the
time delay for immediately load retransfer. To bypass Feature 3A time delay, turn the
Tra n s fe r Con t r o l switchto the Retransfer De lay Bypass position.
At the conclusion of the Feature 3At ime delay, the controller starts the synchronization
timedelay which allowsboth sources to stabilize. Afterthe synchronizationtime delay the
controllerst arts the in–sync monitor and the failure to sync time delay. When the sources
become in–syncthe controller is ready to transfer the load to normal.
LoadRetransfer. To retransfer the load to the normal source the controller de–energize
the ERand ER1 relays and energizes the SE relay. The transfer switch CN coil energizes,
and all CN transfer switch contacts (mains, controls, auxiliaries) reverse position to
connect the Normal sou rce. The load is now connected to both sources. The extended
paralleltime delay is started and the SE2 relay is energized.The transfer switch CE coil
energizes, and all CE transfer switch contacts (mains, controls, auxiliaries) reverse
positionto disconnect the Emergency source. The transf er switch is now supplying the load
from the normal source again. If the sources are paralleled longer than the extended
parallel time setting the controller activates an extended parallel output. It also
deenergizesthe SE and SE2 relays, energizes the ER and ER2 relays, and itlocks out any
further transfer operations. This lock–out condition is reset via the alarm reset.
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.

Bypass Closed–Transition Load Transfer

A pending closed–transition load transfer can be bypassed by using the Closed Transition
Bypass switch. Depending upon the configuration of the controller, bypassing the
closed–transition load transfer sequence will result in either an open or delayed–
transition transfer.
NORMAL OK
TD Engine Cooldown
__min __s
NORMAL OK
TD Emerg>Normal
__min __s
NORMAL OK
Load on Emerg
NORMAL OK
Load on Normal