
TS
850 TRANSFER SWITCH
5.
GENERAL THEORY OF OPERATION
5.1. STANDARD AUTOMATIC TRANSFER SWITCH
5.1.1.
NORMAL OPERATION
When utility supply voltage drops below a preset nominal value (adjustable from
70%
to 1
00%
of nominal)
on
any phase,
an
engine start delay circuit will
be
initiated
and
the transfer to utility supply signal
will
be
removed (i.e. contact opening). Following
expiry of the engine start delay period (adjustable from 0 to
60
sec.)
an
engine start
signal (contact closure) will
be
given.
Once the engine starts, the transfer switch controller will monitor the generator
voltage and frequency levels. Once the generator voltage
and
frequency rises above
preset values (adjustable from
70%
to
100%
of nominal), the engine warmup timer
will
be
initiated. Once the warmup timer expires (adjustable from 0 to
60
sec.
),
the
Transfer to Generator Supply signal (contact closure) will
be
given to the transfer
switch mechanism. The load will then transfer from the utility supply to the generator
supply
via
the motor driven mechanism. Note:
An
optional neutral delay timer circuit
will delay the transfer sequence
in
the neutral position (i.e. both breakers open) until
the selected time expires (adjustable from 0 to
60
sec.).
The generator will continue to supply the load until the utility supply has returned.
The retransfer sequence
is
completed
as
follows: when the utility supply voltage
is
restored to above the preset values (adjustable from
70%
to 100% of nominal)
on
all
phases, a transfer return delay circuit
will
be
initiated. Following expiry of the
Transfer Return Timer (adjustable from 0 to
30
min.), the Transfer to Generator
Supply signal will
be
removed (contact opening), then the Transfer to Utility Supply
signal (contact closure)
will
be
given to the transfer switch mechanism. The load will
then retransfer the load from the generator supply back to the utility supply. Note:
An
optional neutral delay timer circuit will delay the transfer sequence
in
the neutral
position (i.e. both breakers open) until the selected time expires (adjustable from 0 to
60
sec.).
An
engine cooldown timer circuit will
be
initiated once the load
is
transferred from the
generator supply. Following expiry of the cooldown delay period (adjustable from 0
to
30
min.), the engine start signal will
be
removed (contact opening) to initiate
stopping of the generator set.
·
PM042
Rev!
·
01110!17
4
Thomson
Technology
Inc
. ·