GE Industrial Solutions ZBTSCTH SERIES 100 - 4000 AMPS - Manual (Page 8)

ZBTSCTH Operation and Maintenance Manual (46R-7000) 6 Zenith Controls, Inc.
SECTION II - OPERATION AND FEATURES
1. SEQUENCE OF OPERATION
Figure 4 is a typical schematic diagram of a
Zenith closed transition transfer switch. The
information supplied with the transfer switch
includes a schematic diagram and description of
operation of all accessories provided.
Transfer of the load to the Emergency source
begins automatically when any phase of the
Normal source falls below the preset dropout
point and this undervoltage failure condition is
detected by solid state phase relays B1, B2, B3.
The phase relays drop out, de-energizing the
Normal control relays CR & CR2, 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 the Normal source voltage returns
above the phase relays’ pickup setting, the P1
timing cycle is reset to zero by re-energizing the
CR relay.
If the normal source 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. An Emergency voltage and
frequency sensing relay (VFSM) monitors the
voltage and frequency of the Emergency source.
When both the voltage and the frequency of the
Emergency source reach the preset pickup
points, the VFSM relay initiates transfer to the
Emergency source and timer W begins it timing
cycle. The W timer provides an adjustable
transfer delay to the Emergency source as
required.
When the W time is completed, the Emergency
control relay RT energizes and picks up the
CCNO relay. The CNO solenoid is then
energized to open the transfer switch from
normal position to neutral position. The switch
remains in the neutral position for the duration of
the DW time delay. After the DW time delay is
completed, the CCE relay energizes the CE
solenoid to close the transfer switch into the
emergency source. The SE limit switch activates
to de-energize the CCE relay.
The sequence for retransfer to the Normal
source begins automatically when the voltage on
all phases of the Normal source reach the preset
pickup point and this condition is detected by the
solid state phase relays, B1, B2, B3.
When the Normal source restores and if the
transition mode selector switch is in CT (Closed
Transition), the transfer switch will return to the
Normal source in a make-before-break sequence
(this is described in the Testing section of this
manual).
If the transition mode selector switch is in OT
(Open Transition), the transfer switch will return
to the normal source in a break-before-make
sequence. When the Normal source restores, the
solid state phase relays, B1, B2, B3 pick up and
switching to the Normal source is initiated by
energizing timer T, beginning its timer cycle. The
T timer provides an adjustable delay to insure
that the Normal source has stabilized before
reconnection to the load. If the Normal source
fails before the T time delay completes, the
phase relays drop out and the T timing cycle is
reset to zero.
When the T time delay is completed, the Normal
control relay CR energizes and picks up the
power relay CCEO. This energizes the CEO
solenoid opening the transfer switch out of the
emergency source. The SEO-1 limit switch
activates to energize the DT time delay and
de-energize the CCEO relay. After the DT time
delay is completed, the CCN relay energizes the
CN solenoid to retransfer the switch into the
normal source. The SN limit switch activates to
de-energize the CCN relay. The SN limit switch
also energizes the engine over-run timer U and
begins its timing cycle. This 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.
NOTES:
1.
The transition mode selector switch on the
front door enables the user to operate the
unit in Open Transition mode, if so desired.
2. When in Closed Transition mode, if the
transfer switch does not open the first source
within 100 milliseconds, an alarm will sound,
the transfer switch will open the last source it
closed in to and will lock out the control
circuit from any transfer operation. After the
condition has been corrected the control
circuit should be reset by turning the Failed
to Open Lockout Reset switch to the right.
3. The controls will provide a signal to shunt trip
the generator breaker if the transfer switch
remains closed into both sources for more
than 325 ms. The load will then be fed by the
utility source. The maximum time that the
two sources would be parallel, under these
conditions, is less than 0.5 sec. Before
operating the closed transition transfer
switch the condition must be corrected and
the shunt trip reset. Refer to the procedure
for servicing the switch after shunt tripping
occurs. The shunt trip reset switch is
provided on the front door. Alarm and lights
on the front door provide indication of failure
conditions.