Westinghouse CO Instructions Manual

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Before puttin� protective relays into service,
remove all blockmg which may have been inserted
for the purpose of securing the parts during ship­
ment. Make sure that all moving parts operate
freely. Inspect the contacts to see that they are
clean and can cl?se properly .
to ch�k the settmgs and electrical connections.
. These ind � cti � m-overcurrent relays are used to
disconnect circLuts or appatatus when the current
in them exceeds a given value.
(48
bat�ery
c�osi�g type relays are normally used to trip the
CircUit breaker . vVhere low voltage or no station
bat � ery : ·xists,
conJunCion with a-c senes trip coils can be used
to open the breaker.
The inverse time (low-energy) type relay is used
.
m preference to the definite minimum time (stand­
a : d energy) relay where the requirements neces­
(1)
Sitate a lower burden on the current trans­
(2)
former, or
or (3) a very low current range as for example,
ground protection of transmission systems.
. �he very-in � erse time
similar to the mverse relay and is used where a
still more inverse curve is desired. The term " low
energy" refers to the burden at tap value that is
placed on the current transformers and does not
refer to the current rating.
The long time
protect motors against overloads.
equipped with an instantaneous attachment that
will operate, if a short-circuit occurs in the motor.
The type COH relay finds application for phase
a_nd ground protection where a high speed induc­
tiOn type relay is desired. I t is sometimes used in
differential protective schemes.
The above relays can be supplied with the sec­
ondary electromagnet circuit brought out to sepa­
rate terminals. This variety is known as the type
CO or COH Torque Control Relay. Thus the con­
tacts of a separate relay can be used to control
the operation of the torque control relay.
example, a three phase directional relay can be
used to directionally control three torque control
relays.
CONSTRUCTION AND OPERATION
Circuit-Closin� Relay
.T�e "circuit-dosing types CO and COH relays
�on:>tst of an overcurrent element, an operation
mdtcator, a contactor switch, and an instantaneous
trip attachment. where required.
,
\\iestin g house
'
�
es CO and COH Overcurrent Relays
CAUTION
Operate the relay
APPLICATION
Where a station
volts or over) is available, the circuit
the circu_it opening type relay in
_
a more inverse curve for selectivity,
(low-energy) relay is
(40
second) relay is designed to
This can be
INSTRUCTIONS
Overcurrent Element
This . element is an induction-disc type element
operatmg on overcurrent. The induction disc is a
thin four-inch diameter, aluminum disc mounted
on a vertical shaft. The shaft is supported on the
lower end by a steel ball bearing riding between
concave sapphire jewel surfaces, and on the upper
end by a stainless steel pin.
The moving contact is a small silver hemisphere
fastened on the end of an arm. The other end of
this arm is clamped to an insulated section of the
disc. � haft in the non-geared type relays, or to an
auxthary shaft geared to the disc shaft in the
geared type relays.
made from the moving contact through the arm and
spiral spring. One end of the spring is fastened to
t�e arm_, an_d the other to a slotted spring adjuster
dtsc whtch m turrt fastens to the element frame.
The stationary contact assembly consists of a
silver contact attached to the free end of a leaf
spring. This spring is fastened to a M icarta block
and mounted on the element frame.
screw permits the adjustment of contact follow.
When double trip is required , another leaf spring
is mounted on the M icarta block and a double
contact is mounted on the rigid moving arm. Then
the stationary contact set screws permit adjust­
ment so that both circuits will be made - simul­
taneously.
. The moving disc is rotated by an elec;tromagnet '
1n the rear and damped by a permanent magnet in
the front. The operating torque of the inverse or
very inverse relays is obtained by the circuit ar­
rangement shown in Figure
of the relay acts as a transformer and induces a
voltage in a secondary coil.
secondary coil flows through the upper pole coils and
thus produces torque on the disk by the reaction
between the fluxes of the upper and lower poles.
The definite-time relay obtains its flat charac­
teristic curve because of a small saturating trans­
former that is interposed between the secondary
coil and the upper pole " c oils.
torque compensator and it slows down the disk
movement to such an extent that no gearing is
required. (See Figure
For
The long time relay is a geared relay with a
torque compensator.
The type COH relay is a non-geared relay with­
out a torque compensator.
Contactor Switch
The d-e. contactor switch in the relay is a small
solenoid type switch.
a silver disc mounted on its lower end moves in the
core o� the s ? lenoid. As t�e plunger travels upward,
the dtsc bndges three silver stationary contacts.
1
41-280-C
I .L.
The electrical connection is
A small set
1 .
The main pole coil
Current from this
This is called the
2) .
A cylindrical plunger with
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