ABB SPAJ 111 C User Manual page 11

The earth-fault relay provides two-stage earth-
fault protection. The fault current can be mea-
sured with a core-balance transformer or three
phase current transformers in parallel.
The earth-fault relay SPAJ 111 C is used in
applications, where a high accuracy is required.
By using core-balance current transformers the
disadvantage with the three phase current trans-
formers connected in parallel can be avoided.
The core-balance transformer ensures a stable
and sensitive earth-fault protection.
The above application can be used in isolated
neutral networks and in networks earthed over
a resistor, in which case the reproduction capa-
bility of the core-balance transformer is suffi-
cient.
In isolated neutral networks and in networks
which are earthed over a high-value resistor the
magnitude of the earth-fault current is rather
limited. At an earth-fault the healty network
supplies fault current to the faulty feeder. There-
fore non-directional earth-fault relays like SPAJ
111 C are best suited for the earth-fault protec-
tion of networks with rather short feeders, as for
instance motor and transformer feeders of an
industrial switchgear.
Switch SG1/SPCJ 1C7
1 1 t> = 0.5...10 s
}
2 1
I > = 0.2...2% x I
0
3 0
4 0 no latching
5 0 not in use
}
6 1
I >> = 1...8% x I
0
7 0
8 0 t>> = 0.05...1.00 s
Σ
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When the switches are set as above, the output
contacts of relay SPAJ 111 C provide the follow-
ing signals:
Contact Function
65-66 Circuit breaker trip signal, stage I
68-69 Signal on tripping, stage I
80-81 Signal on tripping, stage I
77-78 Start signal, stage I
73-74-75 Start signal, stage I
70-71-72 Self-supervision signal
The earth-fault relay is provided with two stages,
a high-set stage and a low-set stage. The low-set
stage satisfies the sensitivity requirements of the
protection and the high-set stage the operate
time requirements. The two-stage relay also
enables selective protection arrangements to be
made in such cases, where the fault current
generated by the feeder during a fault some-
where else in the network exceeds the set start
current of the low-set stage but not the high-set
stage.
The operation of a non-directional neutral over-
current relay can be stabilized with a residual
voltage relay. During a no-fault situation the
residual voltage relay provides a blocking signal
which is routed to the non-directional earth-
fault relays. At an earth-fault the residual voltage
relay starts, the blocking signal disappears and
the neutral overcurrent relays are allowed to
operate.
Both earth-fault stages trip the CB. In the above
example the start signal of the low-set stage
blocks the earth-fault relay of the incoming
feeder, also see Example 2.
The selector switches of the earth-fault relay
SPAJ 111 C can be set as follows:
SGB/SPCJ 1C7
0 not in use
0 not in use
n
0 not in use
0 stage t> not blocked
0 stage t>> not blocked
0 not in use
n
0 not in use
0 not in use
> and stage I
0
>>
0
>
0
>>
0
>. Blocking signal for the e/f relay of the incoming feeder
0
SGR
0 no blocking signal
1 I >> start signal to relay D
0
0 no I > start signal to relay D
0
0 no I >> trip signal to relay D
0
0 no I >> trip signal to relay C
0
1 I >> trip signal to relay A
0
1 I > trip signal to relay C
0
0 no I > trip signal to relay B
0
>>
0
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