25
Zenith Automatic Transfer Switch | new.abb.com/low-voltage
Sequence of Operation -
Automatic Mode - Isolation ATS
Standard Transition
Source 1 Power Failure:
When Source 1 voltage or frequency has fallen below the preset
“Fail” values, the controller initiates the Time Delay Source 2
Start Timer (Engine Start Timer “P”) cycle. Upon completion
of the (P) time delay, an Engine start Signal is sent to Source
2. When Source 2 voltage and frequency reach the preset
“Restore” Values, the time delay to Source 2 Timer (W) begins
its timing cycle to ensure voltage and frequency stabilization
before transfer. A manual pushbutton BYPASS is provided
to bypass the “W” time delay if desired. After the (W) time
delay, the MX controller initiates a transfer signal through the
SCR-E to operate the main transfer operator. The load is now
transferred to Source 2 line. The transfer switch is mechanically
locked. SN limit switch awaits the next operation to Source 1.
Restoration of Source 1 Power:
When Source 1 power reach the preset “Restore” values,
the controller initiates re-transfer to Source 1 sequence.
The delay to Source 1 Timer (T) begins its timing cycle to
ensure voltage and frequency stabilization before retransfer.
A manual pushbutton BYPASS is provided to bypass the “T”
time delay if desired. After the (T) time delay, the MX controller
initiates a transfer signal through the SCR-N to operate the
main transfer operator. The load is now transferred to Source
1 line. The transfer switch is mechanically locked. SE limit
switch awaits the next operation to Source 2. Immediately
after re-transfer, the S2 Stop Delay Timer (Delay to Engine
Stop “U”) begins its cycle to allow Source 2 Engine to run
unloaded. A manual pushbutton BYPASS is provided to
bypass the “U” time delay if desired. Upon completion of the
(U) timing cycle, the controller sends an Engine stop signal.
Delayed Transition
Source 1 Power Failure:
When Source 1 voltage or frequency has fallen below the preset
“Fail” values, the controller initiates the Time Delay Source 2
Start (Engine Start Timer “P”) cycle. Upon completion of the (P)
time delay, an Engine start Signal is sent to Source 2. When
Source 2 voltage and frequency reach the preset “Restore”
values, the time delay to open Source 1 timer (W) begins its
timing cycle to ensure voltage and frequency stabilization
before re-transfer. A manual pushbutton BYPASS is provided
to bypass the “W” time delay if desired. After the (W) time
delay, the MX controller initiates a transfer signal through
the SCR-NO to operate the main transfer operator. The load
is now transferred to the Open position. The time delay to
Source 2 timer (DW) begins its timing cycle. After the (DW) time
delay, the MX controller initiates a transfer signal through the
SCR-E to operate the main transfer operator. The load is now
transferred to Source 2 line. The transfer switch is mechanically
locked. SN limit switch awaits the next operation to Source 1.
Restoration of Source 1 Power:
When Source 1 power reach the preset “Restore” values,
the controller initiates re-transfer to Source 1 sequence. The
delay to open Source 2 Timer (T) begins its timing cycle to
ensure voltage and frequency stabilization before retransfer.
A manual pushbutton BYPASS is provided to bypass the “T”
time delay if desired. After the (T) time delay, the MX controller
initiates a transfer signal through the SCR-EO to operate the
main transfer operator. The load is now transferred to the
Open position. The time delay to Source 1 timer (DT) begins
its timing cycle. After the (DT) time delay, the MX controller
initiates a transfer signal through the SCR-N to operate
the main transfer operator. The load is now transferred to
Source 1 line. The transfer switch is mechanically locked.
SE limit switch awaits the next operation to Source 2.
Immediately after re-transfer, the S2 Stop Delay Timer (Delay
to Engine Stop “U”) begins its cycle to allow Source 2 Engine
to run unloaded. A manual pushbutton BYPASS is provided to
bypass the “U” time delay if desired. Upon completion of the
(U) timing cycle, the controller sends an Engine stop signal.
