Emerson 7000, 4000 DelayedTransition Automatic Transfer Switches continued

Delayed–Transition Automatic Transfer Switches continued

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. Tobypass Feature 3A time delay, turn the

Tra n s fe r Con t r o l switchto the Retransfer De lay Bypass position

Atthe conclusion of the Feature3A time delay, the controller is ready to transfer the load

to normal.

Load Retransfer. Toretransfer the load to the normal source in a delayed–transition

modethe controller de–energizesthe ER and ER2relays and energizes the SE2relay. The

transfer switch CE coil energizesand opens the CE transfer switch main contacts. The

load is disconnected f rom both sources. The loa d disconnect time de lay starts. When this

time delay ends the controller energizes the ER relay. The transfer switch CN coil

energizes and closes the CN transfer switch main contacts. 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

TEST MODE

TEST CIRCUIT 5

TD Load Disconnect

__min __s