Emerson 7000, 4000 Delayed-Transition Automatic Transfer 4ADTS, 7ADTS, 7ADTB, Normal Failed

4--6 Description of Operation

Delayed–Transition Automatic Transfer (4ADTS, 7ADTS, 7ADTB)

NORMAL FAILED

TEST MODE

TEST CIRCUIT 5 Waiting for Emerg Acceptable

TEST MODE

TEST CIRCUIT 5

TD Load Disconnect

__min __s

TEST MODE

TEST CIRCUIT 5

Load on Emerg

Load Transfer To Emergency

The sequence for load transfer to the emergency source begins automatically when the controller detects a normal source failure or a transfer test signal.

Normal Source Failure. The Normal source is considered unacceptable when any one of six voltage, frequency, or phase rotation conditions occur (see page 3–1).

Transfer Test Signal. Test transfer signal can be from the Transfer Control switch (Feature 5), the engine–generator exerciser clock (Feature 11C), or via the serial port (Feature 72A). When using the Transfer Control switch, it must be held in the Transfer Test position until the emergency source becomes available (within 15 seconds).

The controller begins the load transfer sequence by de–energizing the SE and SE2 relays and starting the Feature 1C time delay. Feature 1C time delay on engine starting prevents nuisance starting of the engine–generator set and load transfer to emergency due to momentary failures of the normal source. If the normal source is restored (voltage returns above the dropout point) while Feature 1C time delay is running, the SE and SE2 relays are re–energized and the transfer sequence is terminated. (For transfer test the Feature 1C time delay is bypassed.)

Engine Start Signal. When the Feature 1C time delay ends, the controller de–energizes the NR relay which signals the engine–generator to start. The controller monitors the emergency source, waiting for it to become acceptable. Both voltage and frequency must reach preset pickup points before the emergency source is accepted. Usually about 10 seconds elapse from dropout of the NR relay to acceptance of the emergency source. This interval occurs because the engine–generator must crank, start, and run up to nominal pickup points. If the emergency source is available immediately, the controller will accept it as soon as the NR relay drops out.

When the emergency source becomes acceptable, the controller starts the Feature 2B time delay on transfer to emergency (if desired). Feature 2B time delay allows the emergency source to stabilize before load transfer. If the emergency source fails while Feature 2B time delay is running, the controller again waits for the emergency source to become acceptable again and restarts Feature 2B.

At the conclusion of the Feature 2B time delay, the controller is ready to transfer the load to emergency.

Load Transfer. To transfer the load to the emergency source in a delayed–transition mode the controller energizes ER relay first. The transfer switch CN coil energizes and opens the CN transfer switch contacts. The load is disconnected from both sources. The load disconnect time delay starts. When this time delay ends, the controller energizes the ER relay. The transfer switch CE coil energizes and closes the CE transfer switch main contacts. The transfer switch is now supplying the load from emergency source.