Sequence Of Operation - GE ZTS Series Operation And Maintenance

Sequence of Operation

The information package supplied with the transfer
switch includes a schematic diagram and description
of operation of all accessories provided.
The sequence for load transfer to Source 2 begins
automatically when any phase of Source 1 falls below
the preset "fail" or dropout point and this undervoltage
failure condition is detected by the solid state phase
relays B1, B2, B3.
The phase relays drop out, de-energizing Source 1
control relay CR, and engine start timer P1 begins its
timing cycle. The P1 time delay is provided to override
momentary outages and to prevent nuisance starting
of the engine generator. If Source 1 voltage returns
above the "restore" or pickup setting of the phase
relays, the P1 timing cycle is reset to zero by the
re-energization of the CR relay.
If Source 1 voltage does not return before the P1 time
delay is completed, the P1 timer drops out and sends a
starting signal to the engine generator. Source 2 voltage
and frequency sensing relay VFSM monitors the voltage
and frequency of Source 2. When both the voltage and
the frequency of Source 2 reach the preset "restore"
or pickup points, the VFSM relay initiates the transfer
to Source 2 and timer W begins its timing cycle.
The W timer provides an adjustable transfer delay
to Source 2 as required.
When the W time delay is completed, Source 2 control
relay RT energizes and picks up the power relay, CE1 or
CCE. The power relay connects voltage from Source 2
to the Source 2 switch operating circuit causing the
switch to transfer its main contacts to Source 2.
The switch is mechanically locked in Source 2 position.
The power relay and Source 2 operator are de-ener-
gized when the SE limit switch is activated by the
operator. The SN limit switch is deactivated at the
same time, readying Source 1 control circuit for
retransfer when Source 1 is restored.
36 ZTS/ZTSD/ZTSH/ZTSDH/ZTSDL/ZTSHL/ZTSDHL Operation and Maintenance Manual (71R-3000)
The sequence for retransfer to Source 1 begins automat-
ically when the voltage on all phases of Source 1 reach
the preset "restore" or pickup point and this condition
is detected by the solid state phase relays.
When Source 1 restores, the solid state phase relays B1,
B2, B3 pick up and initiate retransfer of the switch to
Source 1 by energizing timer T and beginning its timing
cycle. The T timer provides an adjustable delay to
ensure that Source 1 has stabilized before reconnection
to the load. If Source 1 fails before the T time delay is
completed, the phase relays drop out and the T timing
cycle is reset to zero.
When the T time delay is completed, Source 1 control
relay CR energizes and picks up the power relay, CN1 or
CNN. The power relay connects voltage from Source 1
to Source 1 switch operating circuit causing the retransfer
of the main switch contacts to Source 1. The switch is
mechanically locked in Source 1. The power relay and
Source 1 operator are de-energized when the SN limit
switch is activated by the operator. The SN limit switch
also energizes the engine over-run timer U and begins
its timing cycle. The timer provides a period of time
for the engine generator to run without load and cool
down before shutdown. After the U time delay is
completed, the P1 timer is energized and the engine
generator is shutdown.
GE Zenith Controls