Application; Principle Of Function - ABB SPAJ 111 C User Manual

Application

Principle of
function
The sensitive earth fault relay SPAJ 111 C is
designed to be used as neutral current measuring
feeder earth fault relay, as generator interturn
fault protection, as capacitor bank unbalance
protection and rotor earth-fault protection.
The sensitive earth fault relay suits as both
primary and back-up earth fault protection re-
lay. The input impedance of the energizing
The sensitive earth-fault relay SPAJ 111 C is a
secondary relay which is connected to the cur-
rent transformers of the object to be protected.
When an earth-fault occurs, the relay delivers an
alarm signal, trips the circuit breaker or starts an
external auto-reclose relay, depending on the
application and the configuration of the relay.
When the energizing current exceeds the set
start value I > of the low-set stage, the earth fault
0
relay starts. When the set operate time t> ex-
pires, the relay operates. In the same way the
Io
BLOCKING
*) Definite time only
Fig. 1. Protection functions of the sensitive earth-fault relay SPAJ 111 C. The encircled numbers
refer to the ANSI (=American National Standards Institute) number of the concerned protection
function.
SENSITIVE DEFINITE TIME
OVERCURRENT STAGE Io>
DEFINITE TIME OVERCURRENT
STAGE Io>>
BLOCKING OF ONE OVER-
CURRENT STAGE OR BOTH
SERIAL COMMUNICATION PORT
circuit of the earth-fault relay is extremely low
which means that the relay can also be energized
from low output core-balance current trans-
formers. Core-balance current transformers can
be recommended when an extremely sensitive
earth-fault protection is required. The earth-
fault relay can also be energized from a set of
three phase current transformers connected in
parallel, the so called residual current connection.
high-set stage starts once its set start value I
is exceeded and, when the set operate time t>>
expires, the relay operates.
The start signal from the sensitive earth-fault
relay is received as contact function. The start
signal can be used, for instance, for blocking
cooperating protection relays.
The relay contains one optically isolated logic
input for incoming external control signals,
generally blocking signals.
51N*)
50N
>>
0
TRIP 1
TRIP 2
SIGNAL 1
START 1
START 2
IRF
SERIAL I/O
3