4--4 Description of Operation

Closed–Transition Automatic Transfer Switches continued

Closed–Transition Load Transfer to Emergency Source

due to Transfer Test

The sequence for closed–transition load transfer to the emergency source begins
automaticallywhen the controller detects a transfer test signal.
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 transfer sequence by de–energizing the SE, SE2, and NR
relays. Feature1C engine starting time delay is bypassedduring transfer test.
Engine Start Signal. When the NR relay de–energizes it 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 sourceis accepted. Usually about 10 seconds elapse from dropout of the NR
relay to acceptance of t he emergency source. Thi s interval occurs because the
engine–generatormust crank, start, and run up to nominal pickup points. If the emergency
sourceis 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 ontransf er toemergency (if desired). If the emergency source fails while Feature 2B
time delay is running, the controller again waits for the emergency source to become
acceptableagain and restarts Feature 2B.
At the conclusion of theFeature 2B time delay, the controller starts the synchronization
time delay which allowsboth sources to stabilize. After the synchronization time delay,
the controllerstarts the in–sync monitor. Threecriteria mustbe met for the sources to be
consideredin–sync. The phase difference between the sources must be less than 5 degrees,
thefrequencydifferencemustbelessthan0.2Hz,andthevoltagedifferencemustbeless
than5%. Theseparameters are displayed. The controllerwaits for the sources to become
in–sync. Atthe same time, thefailure to sync time delay is runni ng. Ifthe failure to sync
time exceeds the user selected time, the failure to sync output is activated and remains
active untili t is resetvia the alarm reset. The controllercontinues the transfer sequence
even after the failure to synchronizealarm becomes active.
Whenthe sources becomein–sync the controller is ready to transfer theload to emergency.
LoadTransfer. To transferthe load to the emergency source the controllerenergizes the
ER2 relay. The transfer switch CE coil energizes, and all CE transfer switch contacts
(mains, controls,auxiliaries) reverse position. Theload is connected to both the Normal
and Emergencysources. The extended parallel time delay is started and the controller
energizes the ER relay. Thetransfer swit ch CN coil energizes, and all CN transfer switch
contacts (mains, control,auxiliaries) reverse position to disconnect the Normal source.
The load is now only connected t ot he Emergency source. If the sources are p aralleled
longerthan the extended paralleltime setting the controller activates an extended parallel
output. Italso deenergizesthe ER and ER2 relays, energizes the SE and SE2 relays, and
it locksout any further transfer operations. Thislock–out condition is resetvia the alarm
reset.
TEST MODE
TEST CIRCUIT 5
Waiting for Emerg
Acceptable
TEST MODE
TEST CIRCUIT 5
Load on Emerg