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Type COV Voltage
Controlled Overcurrent Relay
2.3
INDICATING INSTANTANEOUS TRIP UNIT
(IIT)
The instantaneous trip unit is a small ac operated
clapper type device. A magnetic armature, to which
leaf-spring mounted contacts are attached, is
attracted to the magnetic core upon energization of
the switch. When the switch closes, the moving con-
tacts bridge two stationary contacts completing the
trip circuit. Also during the operation two fingers on
the armature deflect a spring located on the front of
the switch which allows the operation indicator target
to drop. The target is reset from the outside of the
case by a push rod located at the bottom of the
cover.
A core screw accessible from the top of the switch
provides the adjustable pickup range.
2.4
VOLTAGE UNIT (V)
The voltage unit is an induction cylinder type unit.
Mechanically, the voltage unit is composed of four
basic components: A die-cast aluminum frame, an
electromagnet, a moving element assembly, and a
molded bridge.
The frame serves as the mounting structure for the
magnetic core. The magnetic core which houses the
lower pin bearing is secured to the frame by a locking
nut. The bearing can be replaced, if necessary, with-
out having to remove the magnetic core from the
frame.
The electromagnet has two pairs of voltage coils.
Each pair of diametrically opposed coils is connected
in series. In addition; one pair is in series with an
adjustable resistor. These sets are paralleled as
shown in Figure 1 (page 2). The adjustable resistor
serves not only to shift the phase angle of the one
flux with respect to the other to produce torque, but it
also provides a dropout adjustment.
Locating pins in the electromagnet are used to accu-
rately position the lower pin bearing, which is
mounted on the frame, with respect to the upper pin
bearing, which is threaded into the bridge. The elec-
tromagnet is secured to the frame by four mounting
screws.
The moving element assembly consists of a spiral
spring, contact carrying member, and an aluminum
cylinder assembled to a molded hub which holds the
shaft. The shaft has removable top and bottom jewel
bearings. The shaft rides between the bottom pin
bearing and the upper pin bearing with the cylinder
rotating in an air gap formed by the electromagnet
and the magnetic core. The stops for the moving ele-
ment contact arm are an integral part of the bridge.
The bridge is secured to the electromagnet and
frame by two mounting screws. In addition to the
holding the upper pin bearing, the bridge is used for
mounting the adjustable stationary contact housing.
The stationary contact housing is held in position by a
spring type clamp. The spring adjuster is located on
the underside of the bridge and is attached to the
moving contact arm by a spiral spring. The spring
adjuster is also held in place by a spring type clamp.
With the contacts closed, the electrical connection is
made through the stationary contact housing clamp,
to the moving contact, through the spiral spring out to
the spring adjuster clamp.
3.0 CHARACTERISTICS
To prevent the relay from operating for currents above
the overcurrent unit pick-up, the voltage unit contact
is connected in the shading coil circuit of the overcur-
rent unit. The voltage contact is held open at voltages
above the set point, to prevent torque from being pro-
duced in the overcurrent unit. This arrangement
yields a tripping characteristic as shown in Figure 3
(page 4).
3.1
OVERCURRENT UNIT
The relays are generally available in the following
overcurrent unit current ranges:
RANGE
0.5 - 2.5
0.5
0.6
2 - 6
2
2.5
4 - 12
4
5
These relays may have either single or double circuit
closing contacts for tripping either one or two circuit
breakers.
The time vs. current characteristics are shown in Fig-
ures 4 to 8 (page 13 to page 17). These characteris-
tics give the contact closing time for the various time
dial settings when the indicated multiples of tap value
current are applied to the relay.
3.2
IIT UNIT
Current ranges available for this unit are: 2-8, 4-16,
10-40, 20-80, and 40-160.
3.3
VOLTAGE UNIT
The contact can be adjusted to close over a range of
80 to 100 volts. The contact opens if the voltage is
41-116K
TAPS
0.8
1.0
1.5
2.0
2.5
3
3.5
4
5
6
6
7
8
10
12
3
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