Westinghouse CO Instructions Manual

Types CO and COH Overcurrent Relays
CAUTION
Before putting protective relays into service
remove all blocking which may have been inserte
for the purpose of securing the parts during ship­
ment. Make sure that all moving parts operate
freely. I nspect the contacts to see that they are
clean and can cl ? se properly. . Operate the relay
to check the settmgs and electncal connections.
APPLICATION
These induction-overcurrent relays are used to
disconnect circuits or apparatus when the current
in them exceeds a given value.
�
battery (48 volts or over) is available the circuit
c osi r: g type relays are normally used
circuit breaker. Where low voltage or no station
bat � ery � xists the circu . it opening type relay in
•
.
conJ unctiOn with a-c senes trip coils can be used
to open the breaker.
. The inverse time (low-energy) type relay is used
111
preference to the definite minimum time (stand­
a _ rd energy) relay where the requirements neces­
sitate ( 1 ) a lower burden on the current trans­
former, or (2) a more inverse curve for selectivity,
or (3) a very low current range as for example
ground protection of transmission systems.
. �he very-in- y erse time (low-energy) relay is
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 (40 second) relay is designed to
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
_
tiOn type relay is desired. It 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-Closing Relay
T e circuit-closing types CO and COH relays
� on . sist of an overcurre � t element, an operation
md1cator, a contactor switch, and an instantaneous
trip attachment where required.
�stin g house
INSTRUCTIONS
d
Where a station
'
to trip the
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. A small set
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
the statiOnary contact set screws permit adjust­
ment so that both circuits will be made simul­
taneously.
. The moving disc is rotated by an electromagnet
m 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 1 . The main pole coil
This can be
of the relay acts as a transformer and induces a
voltage in a secondary coil .
secondary coil flows through the upper pole coils and
a
thus produces torque on the disk by the reaction
high speed induc­
between the fluxes of the upper and lower poles.
teristic curve because of a small saturating trans­
fo � mer that is interposed between the secondary
coil and the upper pole coils.
torque compensator and it slows down the disk
movement to such an extent that no gearing 1s
required. (See Figure 2) .
For
torque compensator.
out a torque compensator.
Contactor Switch
solenoid type switch. A cylindrical plunger with
a silver disc mounted on its lower end moves in the
core o
the disc bndges three silver stationary contacts.
1
Overcurrent Element
Thi � 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
aux1hary shaft geared to the disc shaft in the
geared type relays. The electrical connection is
m � de fro � the moving contact through the arm and
spiral spnng. One end of the spring is fastened to
the arm , and the other to a slotted spring adjuster
disc which in turn fastens to the element frame.
The stationary contact assembly consists of a
�
s mounted on the rigid moving arm . Then
The definite-time relay obtains its flat charac­
The long time relay is a geared relay with a
The type COH relay is a non-geared relay with­
The d-e. contactor switch in the relay is a small
f �
the s ? lenoid. As t e plunger travels upward ,
L. 41-280-C
I.
Current from this
This is called the