ABB Zenith
23
ZTSCT / ZBTSCT Operation & Maintenance Manual
Sequence of Operation
Open 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 2Timer (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.
Table 3
Timer Designations as they appear in the SET menu
ATS Type
P
W
DW
T
DT
U
Open
Time Delay
Time Delay
ATS Open
Time Delay
ATS Open
S2 Stop
Transition
S2 Start
S2 Stable
Time to S2
S1 Stable
Time to S1
Delay
Source 1
Transfer to Source 2
Source 1
Transfer to Source 1
Engine
Fails
Returns
Cooldown
