ABB COQ Instruction Leaflet

Effective: May 1997
Supersedes I.L. 41-161H Dated July 1984
( | ) Denotes Change Since Previous Issu
!
CAUTION
Before putting protection 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 prop-
erly. Operate the relay to check the settings
and electrical connections.
1. APPLICATION
The COQ is used to prevent a synchronous machine
from being damaged due to negative sequence fault
currents. Two varieties are available, as shown in
Figures 2 and 3, depending upon whether the neutral
can be formed at the COQ or whether the neutral
must be formed elsewhere. (See external schematic,
Figures 8 and 9.)
2. CONSTRUCTION AND OPERATION
The COQ consists of an induction disc overcurrent
unit, a negative sequence filter, and an indicating
contactor switch (ICS).
2.1. Overcurrent Unit
This is an induction-disc type unit operated by nega-
tive sequence quantities supplied to an electromag-
net in the rear of the relay. A voltage is induced in the
secondary coil of this electromagnet by transformer
action of the main coil. Both coils are located on the
center leg of the electromagnet. Current flow is from
the secondary coil to coils on the outer legs of the
All possible contingencies which may arise during installation, operation or maintenance, and all details and
variations of this equipment do not purport to be covered by these instructions. If further information is desired
by purchaser regarding this particular installation, operation or maintenance of this equipment, the local ABB
Power T&D Company Inc. representative should be contacted.
Printed in U.S.A.
ABB Power T&D Company Inc.
Relay Division
Coral Springs, FL 33065
Negative Sequence Generator Relay
e
electromagnet. The reaction between the outer leg
coil fluxes and the main coil flux creates an operating
torque on a spiral shaped aluminum disc mounted on
a vertical shaft.
2.2. Indicating Contactor Switch Unit (ICS)
The dc indicating contactor switch is a small 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 contacts bridge
two stationary contacts, completing the trip circuit.
Also during this operation two fingers on the arma-
ture 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.
The front spring, in addition to holding the target, pro-
vides restraint for the armature and thus controls the
pickup value of the switch.
3.
3.1. Overcurrent Unit
The COQ negative sequence relay is available with
the following negative sequence current taps:
3
These tap values represent the current transformer
secondary amperes which correspond to one per unit
generator current. At these values of negative
sequence current, the moving contact will leave the
time dial stop and reach the stationary contacts in a
time as determined by the time dial setting and is as
shown by Figure 7. For example, with a time dial
Type COQ
(50/60 Hertz)
CHARACTERISTICS
3.25 3.5 3.8
Instruction Leaflet
I.L. 41-161J
4.2 4.6 5.0