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REF 610
4.1.4.3.
20
Feeder Protection Relay
Technical Reference Manual
Stage I>>> can be set out of operation in SGF3. This state will be indicated by
dashes on the LCD and by "999" when the set start value is read via serial
communication.
Stages I>> and I>>> will be reset in 50 ms after all three phase currents have fallen
below the set start value of the stage.
Note!
Stages I> and I>> can be set to be blocked by the auto-reclose function.
Earth-fault protection
The non-directional earth-fault current protection detects phase-to-earth currents,
caused by insulation failure due to ageing and thermal cycling, for instance.
When the earth-fault current exceeds the set start value of the low-set stage, I
stage will generate a start signal after a ~ 60 ms' start time. When the set operate time
at definite-time characteristic or the calculated operate time at IDMT characteristic
elapses, the stage will generate a trip signal. The low-set stage can be given an
instantaneous characteristic by setting the operate time to the minimum, i.e. 0.05 s.
Stage I
> has a settable resetting time (both at definite-time and IDMT
0
characteristics), t
, for reset coordination with existing electromechanical relays or
r0
for reducing fault clearance times of recurring, transient faults. If stage I
started and the earth-fault current falls below the set start value of the stage, the start
of the stage will remain active for the set resetting time. If the earth-fault current
exceeds the set start value again, while the timer is being reset, the start of the stage
will remain active. Consequently, the set resetting time ensures that when the stage
starts because of current spikes, it will not be immediately reset. However, if stage
I
> has already tripped, the stage will be reset in 50 ms after the earth-fault current
0
has fallen below 0.5 times the set start value of the stage.
The inverse-time function of stage I
starts. In this case, the operate time will be determined by stage I
is made in SGF4.
When the earth-fault current exceeds the set start value of the high-set stage, I
the stage will generate a start signal after a ~ 40 ms' start time. When the set operate
time at definite-time characteristic elapses, the stage will generate a trip signal. The
high-set stage can be given an instantaneous characteristic by setting the operate
time to the minimum, i.e. 0.04 s. The stage will be reset in 50 ms after the earth-fault
current has fallen below the set start value of the stage.
The set start value of stage I
situation, i.e. when the object to be protected is being connected to a network.
Consequently, a set start value below the connection inrush current level can be
selected for the stage. A start situation is defined as a situation where the earth-fault
current rises from a value below 0.12 x I
than 60 ms. The start situation ends when the current falls below 1.25 x I
remain below for at least 200 ms. The selection is made in SGF4.
Stage I
>> can be set out of operation in SGF3. This state will be indicated by dashes
0
on the LCD and by "999" when the set start value is read via serial communication.
> can be set to be inhibited when stage I
0
>> can be set to be automatically doubled in a start
0
> to a value above 1.5 x I
0
1MRS 755310
>, the
0
> has
0
>>
0
>>. The selection
0
>>,
0
> within less
0
> and
0
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