POWER
OUTAGE
When commercial power outage occurs,
or
voltage
drop~
lower
than
the
setting
relay
K6, K6
de-
energ1zes and opens the circuit to control relays
K3,
K4,
KS,
and
K7.
De-energizing relay
K3
allows its normally closed
con-
tacts to close and complete the circuit for generator set
start-up. Relay K3 can be either immediate
or
time
delayed
(0.1
to 10 seconds) depending on transfer
switch model.
Upon start-up of the generator set, voltage sensor relay
K9
will energize and close its normally open contacts to
transfer relay
KS
(if equipped). Relay
KS
will then ener-
gize and after its adjustable time delay period (0.3 to 30
seconds) it will close its normally open contacts to
K1
trip coil
(TC)
and
K2
closing coil
(CC)
circuits.
Because transfer switch
K1
had previously been energized closed,
the normally closed
K1
interlock contacts (IC) to K2 closing coll
would now
be
open, and the normaHy open
K1
Interlock contacts (IC)
to
K1
bip
coll (TC) would
be
closed.
Upon closing of
KS
time delay closed (TDC) contacts,
the
K1
trip coil (TC) would then energize to open
K1.
By
opening transfer switch
K1,
the normally closed inter-
lock
contacts
(IC)
would then close and complete the
circuit
to
energize K2 closing coil (CC). Energizing
K2
closing coil (CC) then closes its normally open contacts
to
complete the transfer
of
power, and the generator set
is
connected to the load.
GENERATOR
SET
STARTING
CIRCUITS
Sending start and stop signals
to
the generator set is a
basic function
of
the transfer switch. The starting circuit
function
of
the
transfer switch must be compatible with
that
of
the generator set control. The transfer switch will
be either a
two-wire
or three-wire starting circuit, des-
cribed as follows:
2-7
Two-Wire Starting
In
a
two-wire
starting circuit, battery voltage
(B+)
is
connected by
K3
to the remote (RMT) terminal. When
commercial power fails
or
falls below the holding volt-
age
of
voltage sensor relay
K6,
it de-energizes. This
removes power from
K3;
and after any time delay,
K3
closes the contact between
B+
and RMT terminals to
initiate generator set starting.
For periodic exercise of the generator set, M2 exerciser
clock
will close its normally open contacts between
B+
and RMT terminals to initiate start and run command of
the generator
set
The generator set will start and run at
no load for the time set by the exercise clock
M2.
Three-Wire Starting
Normally closed contacts
of
generator voltage sensor
relay
K9,
and cranking limiter relay K10 are in series in
the generator set starting circuit. During a power outage
of normal commercial power supply, generator set start-
ing will be initiated by de-energizing relay
K3;
the nor-
mally open contacts for stop command will open, and
the normally closed contacts for start command will
close.
When the generator voltage sensor relay
K9
detects
proper
generator
voltage,
the
contacts
open and
remove ground from relay cranking limiter coil
K10.
If
ground is not removed within 60 seconds,
K1
O will time
out and remove the start signal from the generator
set by
opening its time delay to open
(TOO)
normally closed
contacts. The cranking limiter (K10) is used only with
three-wire starting systems.
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