2018/10 10 VPX-MAN002-E REV4.DOCX4
5. TRANSFER SWITCH OPERATION SEQUENCE
5.1.TRANSFER TO
ALTERNATE POWER
SOURCE
The Transfer to Alternate Power Source
starts automatically when at least one of the
following conditions applies:
-Normal Power voltage falls below 85%
of nominal voltage,
-Normal Power Phase Reversal is
detected,
-‘Reset-Test’push button (located on the
front display) is maintained depressed
for over 10 seconds.
When an under voltage condition on any
phase of the Normal Power source is
detected by the sensor the 3 second normal
power source outage delay timer starts
counting.
If the normal source voltage rises above the
sensor dropout setting before the 3 second
time delay expires, the transfer sequence is
cancelled.
If the Normal Power source voltage is still
below the sensor dropout setting (85%)
when the time delay expires, the relay is
deactivated to start the generator set. At the
same time, a voltage and frequency sensor
begins monitoring the Alternate Power
Source. The sensor will accept the alternate
power source only when both voltage and
frequency reach pre-set pickup value. An
approximate 15 second time span occurs
because the engine-driven generator
cranks, starts, and runs up to nominal
pickup value. For this reason, if the Transfer
switch ‘Reset-Test’ push button is pressed, it
must be held until transfer is initiated.
When the Alternate Power Source is within
acceptable limits (above 90% of the nominal
voltage), the transfer to alternate power
source is initiated.
The transfer switch will remain in the
alternate power source position until the
normal source is restored. If the ‘Reset-
Test’ button is used, the transfer switch will
remain on alternate power source until the
retransfer to normal delay times out (5
minutes).
5.2.RETRANSFER TO
NORMAL
Important: the transfer switch stays in
alternate position if motor is running.
Retransfer sequence is enabled if motor is
not running.
The Retransfer to the Normal Power source
starts when the voltage sensor detects
restoration of the Normal Power Source
within acceptable limits. The voltage level
must rise above the pre-set pickup value
(90%) on all phases before the sensor will
accept the normal source.
When the normal source is accepted by the
sensor, the retransfer to normal delay timer
starts counting (factory set at 5 minutes).
This delay prevents immediate load
retransfer to the normal source. The delay
insures that the normal source has stabilized
before reconnection of Fire Pump Motor. If
the normal source voltage falls below the
pre-set dropout value before the time delay
expires, the timing cycle is reset to zero. If
the alternate power source fails during the
timing cycle, the load is immediately
retransferred to the normal source, if that
source is acceptable.
The Automatic Transfer Switch is now
feeding the Fire Pump Motor from the
Normal Power Source again.
Upon retransfer to the normal source, the 5
minute cooling timer starts counting to keep
the engine running for a cool-down period.
After the time delay, the relay is re-activated
to shut down the engine-driven generator.
All circuits are reset for any future normal
source failure.
