Westinghouse CO Instructions Manual

Types Co, Coh And Coa Overcurrent Relays
CAUTION
Before putting protective relays into
service, remove all blocking which may
have been inserted for the purpose of
securing the parts during shipment, make
sure that all moving parts operate
freely, inspect the contacts to see that
they are clean and can close properly.
Operate the relay to check the settings
and electrical connections.

INSTALLATION

The relays should be mounted on
switchboard panels or their equivalent
in a location free from dirt, moisture,
excessive vibration and heat.
the relay vertically by means of the
two mounting studs. Either of these
studs may be utilized for grounding the
metal base. The electrical connections
may be made direct to the terminals by
means of screws for steel panel mounting
or to terminal studs furnisbed with the
relay for ebony-asbestos or slate panel
mounting. The terminal studs may be
easily removed or inserted by locking
two nuts on the studs and tl1en turning
the proper nut with a wrench.
Because the circuit-opening relay con­
tacts short circuit the trip coil, it is im­
portant that the relay be mounted where
it will not be subjected to sbocks wl1ich
may jar the contacts open and thereby
allow current to flow tl1rough the trip
coil. Trouble of tl1is kind can be avoided
by preventing jars to the switchboard
and. also by setting tl1e trip coil l1igh
enough so tlmt it will not operate on
normal load current. This is an extra
safe-guard so that there is no danger
from even an excessive sbock unless tl1e
current is also heavy.
Typical external connections
shown in Figures 12 to 16. When using
the circuit-opening relays for phase pro­
tection, ground protection may be se­
cured by using a low-energy circuit­
closing relay operating on a-c. voltage
trip coil, as shown in Figure 16.
Stalianar y
/
Contact Oper Jnd;cator
Contaclor Switch
For trip cur. less
connect and de
end lh1s lead
·Connector Block
--
FRO.::\ T VIEW
'''·· � Torque Compensator
FIG. 2-INTERNAL CoNNECTIONS
SINGLE-TRIP, DEFINITE TIME, S
CLOSING TYPE co RELAY IN THE
AND FouR-SECOND Low-ENERGY,
ENERGY.
CIRCUIT
STANDARD CASE.
*Supersedes I.L. 3295
'-'kstin g house
INSTRUCTIONS*
Mount
\
.'--- -- - - - -- - -----
FIG.
1-lNTEILl\I"AL CoNNECTIONS
DounLE-TRIP, INVERSE AND VERY-INVERSE,
Low-ENERGY CIRCUIT CLOSING
LAY AND TilE TYPE COH
ARD CASE WITH Instantaneous Trip AT-
TACHMENT

APPLICATION

These induction-overcurrent relays are
used to disconnect circuits or apparatus
when the current in them exceeds a
given value.
The low-energy type relay is used in
preference to the standard-energy relay
where the requirements necessitate (1) a
lower burden on the current transformer,
or (2) a more inverse curve for selectivity,
or (3) a very low current range as for
example, ground protection of trans­
mission systems.
The very-inverse relay is similar to
the low-energy relay and is used where a
still more inverse curve is desired. The
are
term "low energy" refers to the burden
that is placed on the current transform­
ers and does not refer to the current
rating.
tfovinq Contact
Terminal
Z?5
acJ
amp d;s-
.
Punchinqs
OF THE
FIG.
T A NDARD ENERGY, CIRCUIT CLOSING TYPE CO RELAY IN THE RoUND
DEFINITE TIME, STANDARD
EvERY HousE NEEDS WEsTINGHousE
A
40-second relay is specially designed
to protect motors against overloads.
This can be equipped with an instan­
taneous attachment that will operate,
Ol'ti!I'ITt0/'1
If'JDJCIITQR.S
if a short-circuit occurs in the motor.
The type COH relay finds application
for phase and ground protection where
the type CO is considered too slow and
the instantaneous-type relay, such as
the type SC, too fast or not applicable.
CONSTRUCTION
i

CIRCUIT-CLOSING RELAYS-

i
circuit-closing relays consist of an in­
duction-disk element operating on over­
)
current, an operation indicator, a con­
tactor switch, and an instantaneous trip
attachment where required.
OF THE
The operating torque is obtained by
CO RE­
TYPE
the circuit arrangement shown in Figure
RELAY IN THE STAND­
1.
The main pole coil of the relay acts
as a transformer and induces a voltage
in a secondary coil. Current from this
secondary coil flows through the upper
pole coils and thus produces torque in
the disk by the reaction between the
fluxes of the upper and lower poles.
The inverse and very inverse relays
operate on this principle. The definite­
time, standard-energy relay obtains its
flat characteristic curve because of a
small saturating transformer that is
interposed between the secondary coil
and the upper pole coils. This is called
the torque compensator and it slows
down the disk movement to such an
extent that no gearing is required.
(See Fig. 2).
The 40-second relay is a geared relay
with a standard definite time electro­
magnet and torque compensator.
Upper Stationary
When insfantaMous trip
is used,
wire per
Rear View.
3-INTERNAL CoNNECTIONS oF THE
ENERGY, AND FouR-SECOND Low­
CASE.
I. L. 41-280-A
AND
OPERATION
The
Contact
Punchinqs
lead,!
omit this
dotted lines.,
DouBLE-TRIP,