Emerson 400A manual Sequence of Operation, Transfer To Emergency, Retransfer to Normal

SECTION 2 SEQUENCE OF OPERATION

	Lights show position of transfer switch.				Lights show the sources accepted.
Transfer To Emergency						Light for built–in
The sequence for load transfer to						engine exercise timer:
						³ blinks rapidly when
emergency source begins automatical-
						button is held 5 sec.
ly when normal source voltage falls						while being set
below the preset dropout point or						³ blinks slowly when
when Transfer Test button is pressed.						button is released (set)
An under voltage condition on any						and during 20 min.
phase of the normal source is de-						exercise period.
						³ stays on after engine
tected by the sensor.
When the normal						stops (exerciser is
						enabled for weekly
source voltage fails or						operation)
the Transfer Test						See page 5–1
button is pressed, the	Hold 15 sec. to	Press to cancel the		Hold 5 sec. to set		for complete
SE relay de-energizes						instructions
	start the engine	active exercise period		20 min. engine exercise
and relay NR begins
	generator and to	(stops engine now or		period immediately (engine
its timing cycle (1 or 3	transfer the load	after cooldown) See		starts) and weekly thereafter.
seconds, momentary	to emergency.	page 5–1.	Figure 2–1. Membrane controls and indicator lights.
normal source outage					Retransfer to Normal
delay). The NR relay is provided with a time delay on
dropout to override momentary outages and prevent			The sequence for load retransfer to the normal source
nuisance starting of the engine-driven generator. If the			automatically begins when the voltage sensor detects
normal source voltage returns above the sensor dropout			restoration of the normal source. The voltage level
setting before the time delay expires, the NR relay timing			must rise above the preset pickup point on all phases
cycle is reset to zero and relay SE energizes.			before the sensor will accept the normal source.

If the normal source voltage does not return above the sensor dropout setting before the time delay expires, the NR relay de-energizes and signals the engine-driven gen- erator to start. At the same time, a voltage and frequen- cy sensor begins monitoring the emergency source. The sensor will accept the emergency source only when both voltage and frequency reach preset pickup points. Usual- ly about ten seconds elapse from dropout of the NR relay to acceptance by the sensor. This time span occurs be- cause the engine-driven generator must crank, start, and run up to nominal pickup points. For this reason, if the Transfer Test button is pressed it must be held for 15 sec- onds. If the emergency source is available immediately, the sensor may accept it as soon as NR relay drops out.

When the emergency source is accepted by the sensor, relay ER begins its timing cycle (transfer to emergency delay). ER relay is provided with an adjustable (0 to 5 minutes) time delay on pickup to delay transfer of the load to the emergency source. For immediate transfer press Bypass Time Delay button.

ER relay energizes, the TS coil is energized, the transfer switch operates, and all switch contacts (mains, controls, auxiliaries) reverse position. The transfer switch is now supplying the load from the emergency source.

The transfer switch will remain in the Emergency position until the normal source is restored. If the Transfer Test button is used, the transfer switch will remain on emergency until the retransfer to normal delay times out.

When the normal source is accepted by the sensor, relay SE begins its timing cycle (adjustable 1 sec. to 30 min., retransfer to normal delay). For immediate retransfer press Bypass Time Delay button. SE relay is provided with a time delay on pickup to prevent immediate load retransfer to the normal source. The delay insures that the normal source has stabilized before reconnection of vital loads. If the normal source voltage falls below the present dropout point before the time delay expires, the timing cycle is reset to zero. If the emergency source fails for more than 4 seconds during the timing cycle, ER relay drops out and the load is immediately retransferred to the normal source, if that source is acceptable.

SE relay energizes and ER relay is dropped out. The TS coil is energized, the transfer switch operates, and all switch contacts (mains, controls, auxiliaries) reverse position. The transfer switch is now supplying the load from the normal source again.

Upon retransfer to the normal source, NR relay begins its timing cycle (unloaded running delay, engine cooldown). NR relay is provided with a 5 min. time delay on pickup to keep the engine running for a cool-down period.

NR relay energizes after the time delay and signals the engine-driven generator to shut down. All circuits are reset for any future normal source failure.

Activation of standard control features shown in Section 5 will alter the sequence of operation and introduce additional time delays during transfer operations.

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