15
When a pole short-circuit occurs on a generator
provided with a static excitation system the
generator voltage and the excitation rapidly
decrease so much, that the short-circuit current
falls below the set start current of the overcur-
rent relay.
By capturing the start signal of the overcurrent
relay with a drop-off delayed auxiliary relay,
which controls the external blocking input of
the undervoltage relay, the protection arrange-
ment can be made to operate, even though the
overcurrent relay resets without tripping. The
undervoltage stage is normally blocked and it is
deblocked by the starting signal of the low-set
stage of the overcurrent relay. The undervoltage
stage trips the circuit breaker after the set oper-
ate time t<.
When required, the undervoltage stage can be
blocked when the miniature circuit breaker of
the energizing voltage circuit operates.
The start signal of the undervoltage stage can be
used for preventing the generator from being
connected to the network during undervoltage
or for alarming on undervoltage.
The selector switches of the voltage relay SPAU
130 C can be set as follows:
Switch
SG1/SPCU 3C14
SGB/SPCU 3C14
SGR
1
0 three-phase
0 not in use
1 blocking signal from the
drop-off delayed relay
2
1 U> start time = 30 s
0 not in use
1 start signal of stage U<
to output relay D
3
1 U> inverse charact.
0 not in use
0 no start signal of stage U>
to output relay D
4
1
0 not in use
0 no trip signal of stage U<
curve B
to output relay D
5
0
1 blocking of stage t<
1 trip signal of stage U<
to output relay C
6
0 U< no block., when
0 not in use
1 trip signal of stage U<
U < 20% x U
n
to output relay A
7
0 U< start time = 0.1 s 0 not in use
1 trip signal of stage U>
to output relay C
8
0 t< = 1…12 s
0 not in use
0 no trip signal of stage U>
to output relay B
Σ
14
When the switches are set as above, the output
relays of the voltage relay SPAU 130 C provide
the following signals:
Switch
Function
65-66
Tripping of the generator circuit breaker and the excitation circuit breaker on
pole short circuit (stages U< and I>) or on overvoltage (stage U>)
68-69
Prime mover shut down on pole short circuit (stages U< and I>)
80-81
Signal on operation of the overvoltage stage or pole short circuit protection
77-78
Start signal of the undervoltage stage U<
70-71-72
Self-supervision signal
The output contacts of the relay SPAJ 131 C can
be given the following functions:
Switch
Function
65-66
Tri'of generator circuit breaker, stages I> and I>>
68-69
Tripping of excitation circuit breaker and shut down, stage I>>
80-81
Signal on operation of stage I> and I>>
77-78
Start signal from stage I> to the drop-off delayed auxiliary relay
70-71-72
Self-supervision alarm signal
