4--3Description of Operation
Closed–Transition Automatic Transfer (4ACTS, 7ACTS, 7ACTB)The 4ACTS, 7ACTS, and 7ACTBprovides load transfer in either closed (make–befo-
re–break)or open (break–before–make) transition modes depending uponthe condition
ofthe two power sources. Controllogic automatically determines whether the load trans-
fer should be open or closed transition. If both sources are acceptable, such as during a
transfer test or when retransferring back to Normal, closed–transition transfer occurs
withoutinterrupting the electrical loads. If either source is not present, such as when nor-
mal fails, open–transitionload transfer occurs in the break–before–make mode.
Open–Transition Load Transfer to Emergency Source
due to Normal Source Failure
The sequence for open–transition load transfer to the emergency source begins
automatically whenthe controller detects an unacceptable normal source. The Normal
source is considered unacce ptable when any one of six volt age, frequency, or ph ase
rotation abnormal conditions occur (see page 3–1).
Normal Source Failure. Anunder voltage condition on any phase of the normal source
means that the voltagehas fallen below the preset dropout point.
The controller begins the load tra nsfer sequence by de–energizin gthe S Ean d SE2r elays
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 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.
Atthe conclusion of the Feature2B time delay, the controller is ready to transfer the load
toemergency. Ifenabled,Feature 31F time delaywill run prior to transfer and theFeature
31F output willbe active while the time delay runs.
LoadTransfer. To transferthe load to the emergency source the controllerenergizes the
ER relay. The tra nsfer switch CN coil energizes, and all CN transfer switch contacts
(mains,controls, auxiliaries) reverse position to disconnectthe Normal source. Thenthe
controller energizes the ER2 relay. The transf er switch CE coil energizes, and all CE
transfer switch contacts (mains, controls, auxiliaries) reverse position to connect the
Emergencysource. Thet ransfer switch is now supplyingt he load from emergency source.
Ifenabled, Feature 31M time delay willrun after the transfer and the Feature31M output
will be active while the time dela y runs.
NORMAL FAILED
TEST MODE
TEST CIRCUIT 5
Load on Emerg