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2.19 Second harmonic O/C stage If2 >
(51F2)
2 Protection functions
Technical description
88
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VM50.EN004
Measured and recorded values of single-phase
undervoltage stages U<, U<<, U<<< (27):
Parameter Value
Unit
Description
Measured
value
Umin V
Minimum value of line
voltages
SCntr -
Start counter (Start)
reading
TCntr
-
Trip counter (Trip) reading
Flt
%Un The min. fault value
Recorded
values
EDly %
Elapsed time as compared
to the set operating time,
100% = tripping
2.19.
Second harmonic O/C stage I
f2
>
(51F2)
This stage is mainly used to block other stages. The ratio
between the second harmonic component and the fundamental
frequency component is measured on all the phase currents.
When the ratio in any phase exceeds the setting value, the
stage gives a start signal. After a settable delay, the stage gives
a trip signal.
The start and trip signals can be used for blocking the other
stages.
The trip delay is irrelevant if only the start signal is used for
blocking.
The trip delay of the stages to be blocked must be more than 60
ms to ensure a proper blocking.
&
t
&
&
Im1
Im2
Im3
MAX
2nd
H
arm
t
s
t
r
>
Start
Trip
Register
event
Register
event
Setting
2.
H
arm
Block
Delay
Enable events
Figure 2.19-1 Block diagram of the second harmonic stage.