ABB COQ Instruction Leaflet

ABB Power T&D Company Inc.

Relay Division
Coral Springs, FL 33065

Instruction Leaflet

I.L. 41-161J

Type COQ

Negative Sequence Generator Relay

Effective: May 1997

Supersedes I.L. 41-161H Dated July 1984
( | ) Denotes Change Since Previous Issue

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 prop­erly. 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 nega­tive sequence quantities supplied to an electromag­net 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

(50/60 Hertz)

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 leaf­spring 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 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.

The front spring, in addition to holding the target, pro­vides restraint for the armature and thus controls the
pickup value of the switch.

3. CHARACTERISTICS

3.1. Overcurrent Unit

The COQ negative sequence relay is available with
the following negative sequence current taps:

3 3.25 3.5 3.8 4.2 4.6 5.0

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

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.

I.L. 41-161J

TABLE 1

Typical Overcurrent Unit Burden And Thermal Rating

Input Continuous One Second Watts at Volt Amps Circuit Impedance

Condition Phase Rating Amps Rating Amps 5 Amps At 5 Amps Z ∠θ (R+jX)

Three A 5 100 8.3 8.3 0.33 ∠0° (0.33+j 0.00)

Phase B 5 100 1.3 3.8 0.15 ∠110° (-0.05+j 0.14)

C 5 100 2.9 4.7 0.19 ∠52° (0.11+j 0.15)

PHASE-TO-PHASE FAULT CONDITION

Phase A-B 5 100 6.1 6.5 0.26 ∠−161.7° (-0.24-j 0.08)

To B-C 5 100 3.4 8.0 0.32 ∠65° (0.13+j 0.29)

Phase C-A 5 100 10.2 11.5 0.46 ∠−152° (-0.41-j 0.22)

PHASE-TO-NEUTRAL FAULT CONDITION

Phase A-N 5 100 5.1 5.2 0.21 ∠8.70° (0.20+j 0.03)

To B-N 5 100 3.5 3.8 0.51 ∠24.3° (0.14+j 0.06)

Neutral C-N 5 100 4.8 5.5 0.22 ∠29.0° (0.19+j 0.11)

setting of “4” the relay will close its contacts in 30
seconds with the above tap currents applied to the
relay.

As shown by the curves of Figure 5, the relay’s char­acteristic is defined by a generator characteristic
I22T = K. The relay characteristic is such that it coin­cides with the generator characteristic at 1 per unit
negative sequence current but at higher values of
negative sequence current, the relay characteristic is
substantially parallel and slightly less than the gener­ator characteristic. In this manner, a suitable margin
of safety is obtained between the two characteristics.

Figure 5 defines the relay characteristics for two gen­erators – one with a permissible constant of “30” and
the other with a constant of “90”. The time dial set­tings for these constants are “4” and “11” respec­tively. Similar protection for other generators with
I22T constants between “30” and “90” is obtained by
settings of the time dial. Figure 4 shows the neces­sary time dial settings for various I22T constants. By
referring to this figure, the time dial can be set so the
relay protects different generators whose I22T con­stants range from “30” to “90”.

contact spacing. For this figure a tap setting of 3 is
used with a machine full load current of 4.

Typical time-current curves of the relay are shown in
Figure 7. Minimum pickup is approximately 0.6 of the
tap value current. See Table 1 for burdens and termi­nal ratings.

3.2. Trip Circuit

The main contacts will safely close 30 amperes at
250 volts dc and the seal-in contacts of the indicating
contactor switch will safely carry this current long
enough to trip a circuit breaker.

The indicating contactor switch has two taps that pro­vide a pickup setting of 0.2 or 2 amperes. To change
taps requires connecting the lead located in front of
the tap block to the desired settings by means of a
screw connection.

3.3. Indicating Contactor Switch (ICS)

0.2 ampere tap 6.5 ohms dc resistance

2.0 ampere tap 0.15 ohms dc resistance

4. SETTING CALCULATIONS

Figure 6 demonstrates the use of a tap setting lower
than the full load current of the machine to accommo­date I22Tlimits from 5 to 10 while still providing wide

Determine from the machine manufacturer the per­missible I22T constant. From Figure 4, find the
required time dial setting.

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