4--6 Description of Operation
Delayed–Transition Automatic Transfer (4ADTS, 7ADTS, 7ADTB)Load Transfer To Emergency
The sequence for load transferto the emergency source begins automaticallywhen the
controller detects a normal source failure or a transfer test signal.
Normal Source Failure. The Normal source is considered unaccep table 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 Tra n s f e r Co n t r o l switch
(Feature 5), the engine–generatorexerciser clock (Feature 11C), or via the serial port
(Feature72A). Whenusing the Tr a n s fe r Cont r o l switch,itmustbeheldintheTransferTest
position until the emergencysource becomes available (within 15 seconds).
The controller begins the load transfe r sequence by de–energizing the SE and SE2 relays
andstarting the Feature 1C timedelay. Feature 1C time delay on engine startingprevents
nuisance starting of the engine–generator set and load transfer to emergency due to
momentaryfai luresof t he normalsource. Ifthe normal source is restored (voltage returns
above the dropout point) while Feature 1C time delay is running, the SEand SE2 relays
are re–energizedand the transfer sequence is terminated. (Fortransfer test the Feature
1C time delay is bypassed.)
Engine Start Signal. Whenthe Feature1C time delay ends, the controller de–energizes
the NR relay which signals the engine–generator to start. The controller monitors the
emergencysource, waiting for it to become acceptable. Bothvoltage and freq uency must
reach preset pickup points before the emergencysource is accepted. Usually about 10
seconds elapse from dropout of the NR rela y toa cceptance of the emergency source. This
interval occurs becausethe engine–generator must crank, start, and run up to nominal
pickuppoi nts. Ifthe emergency source is available immediately, the controller willaccept
it as soon as the NR relay drops out.
When the emergency source becomes a cceptable, the controlle r starts the Feature 2B time
delay on transfer to emergency (if desired). Feature 2B time delay allows the emergency
sourceto stabilizebefore load transfer.If the emergencysource fails while Feature2B time
delay is running, the cont roller again waits for the e mergency source to become a cceptable
again and restarts Feature2B.
Atthe conclusion of the Feature2B time delay, the controller is ready totransfer the load
to emergency.
Load Transfer. To transfer the load to the emergency sourcein a delayed–transition
mode the controllerenergizes ER relay first. Thetransfer switch CN coil energizesand
opens the CN transfer switch contacts. The load is disconnected from both sources. The
loaddisconnect time delay starts. When this time delayends, the controller energizes the
ER relay. The transfer switch CE coil energizes and closes the CE transfe r switch main
contacts. The transfer switch is now supplying the load from emergency source.
NORMAL FAILED
TEST MODE
TEST CIRCUIT 5
Waiting for Emerg
Acceptable
TEST MODE
TEST CIRCUIT 5
Load on Emerg
TEST MODE
TEST CIRCUIT 5
TD Load Disconnect
__min __s