Onan LT II User manual

t>C8 ASSY-TRANSFER SWITCH CONTROL
CAUTIOH:
HIGH
Off OFF VOLTAGE
30J
20
1
AETRANSFERD
11151 DSTOPPING
BYPASS AiS2 BYPASS
li 4
9 7
<:> K9
Wl
K6
I VOLTAGE SENSOR
1t>GENERATOA S1DE
§ PHASE SENSOA RELAY
. rg:-; :.iiSENSOR 30
• ~m-ET~~ $ENSOR 10
K8
§TRANSFER RELAY
• TfME DELAY TRANSFER
AANGE: 0.3 lo 30
SECONDS ON
ENERGfZAT~OH
NORM: 2 SECONDS
"TtME DEL.AV STOPPING
AfTER RETRANSFEA
RANGE 3 TO 300
SECONDS ON
~NERGIZAllON
NOAU' 300SECONDS
K5
ON ON
K7
f INST ANT TRANSFER
TOUNE
"TIME OELAY BETRANSFER
RANGE' 21'0 301lllNUT£S
ON ENERGIZATION
NORM: 15MINUTES
K4
00
3 1
6 4
9 7
oP11
START RE.LAY
. nue DELAY STARTING
~: 0.1 to 10SECONDS
NORM: 2 SECONDS
K3
C1
H--
FIGURE 2-4. CONTROLLER PCB ASSEMBLY
NORMAL OPERATION
During normal operation, the commercial power line is
connected to the Load terminals by the transfer switch
contacts K1. The following briefly describes the
required interaction of control componentsto closethe
K1 contacts. Refer to Figure 2-S when reviewing this
informationtogainan understandingofcontrol
compo-
nentinteraction.Then refertowiringdiagramspecificto
your transfer switch to identify where your transfer
switch may differ.
When commercial
power isfirst applied, line voltage is
transformed to 120 volts AC and supplied to voltage
sensor relay
K6. Energizing the coil of K6 will close its
normally open contacts to complete the circuit to relay
coils K3, K4, KS, and K7. Relay K7 energizes imme-
diately,and ifthecommercial (Normal) linecontactsare
not closed,the K1 closingcoil (CC) isenergized. With K1
closingcoilenergized,thenormallyopen contactsof K1
between Line and Load will close.
' 2-6
Once the transfer switch is closed to the normal line
side, it is held in that position and the closing coil is
de-energized
by opening of the K1 cutout switch (CS).
The cutout switch is activated bythe mechanical inter-
lock.Contactoperation differsonlyin
how theyareheld
in position, eitherelectrically
or mechanically.
Relay K6 can
be eithera voltagesensorwithan adjusta-
ble pickup voltage, or a phase loss sensor, when the
voltage feeding the relay coil
drops below the relay
holding voltage.
During normal operation when K3 relay isenergized, it
opensitsnormallyclosed contacts
of thegeneratorstart
circuit,andpreventsautomaticstartingofthegenerator
set
Relays K4 and KS (ifequipped) function as described in
the Restoration
of Commercial Power section.

POWER OUTAGE
When commercial power outage occurs, or voltage
drop~ lower than the setting relay K6, K6 de-
energ1zesandopensthecircuittocontrol relays K3, K4,
KS, and K7.
De-energizing relay K3 allowsits normally closed con-
tactsto close and complete the circuitfor generatorset
start-up. Relay K3 can be either immediate
or time
delayed
(0.1 to 10 seconds) depending on transfer
switch model.
Upon start-up ofthegeneratorset, voltage sensor relay
K9 will energizeandclose itsnormallyopen contactsto
transfer relay
KS (ifequipped). Relay KS will then ener-
gizeand after its adjustable time delayperiod (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
wouldnow
be open,andthenormaHyopen K1 Interlockcontacts(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 openingtransferswitch K1, thenormallyclosed inter-
lock contacts (IC) would then close and complete the
circuit
to energize K2 closing coil (CC). Energizing K2
closing coil(CC) then closesitsnormallyopencontacts
to completethetransfer of power,andthegeneratorset
is connected to the load.
GENERATOR SET STARTING CIRCUITS
Sending startand stop signals to the generator set is a
basicfunction
of thetransferswitch.Thestartingcircuit
function
of the transferswitch mustbe compatible with
that
of thegeneratorsetcontrol.Thetransferswitchwill
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.
Forperiodicexerciseofthegeneratorset, M2exerciser
clock will close its normally open contacts between B+
and RMTterminals to initiate startand run command of
thegenerator
set Thegenerator setwill startand 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
thegeneratorsetstarting circuit. During a poweroutage
ofnormalcommercial powersupply, generatorsetstart-
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 isnotremoved within 60seconds,
K1 Owill time
outandremovethestartsignal from thegeneratorsetby
opening its time delay to open
(TOO) normally closed
contacts. The cranking limiter (K10) is used only with
three-wire starting systems.