Automatic Compensation
When using the parameter Automatic compensation , this automatic compensation function can be
enabled or disabled.
The automatic compensation consists of 2 different mechanisms:
•
The event-based compensation of any existing unbalance.
This compensation is performed in the following situations:
– After energizing the capacitor bank or a phase of the bank (phase-selective compensation)
– After counting a faulty C-element (phase-selective compensation)
– After each startup of the device
– After specific parameter changes:
– Switching on the automatic compensation
– Changing the rated current of the capacitor bank
In order to avoid transient inrush-current effects, the compensation is delayed by 250 ms after energizing
has been detected.
Full compensation after bank energization can be avoided in case of only short de-energization by means
of parameter De-energ.time w/o comp.. If the de-energized duration is less than the setting of
parameter De-energ.time w/o comp., the full compensation is not carried out after energizing a
phase or the whole bank.
•
Cyclic, slow and thus gradual compensation of an existing unbalance in small increments.
This permits, for example, the automatic compensation of environmental influences.
Resetting the Compensation
The algorithm can be reset to the non-compensated status. Compensated values are not available in this case.
Protection stages that work with compensated values are rendered inactive. The binary input signal
>Reset
comp. val.
of the function or function group resets the compensation (see also Figure 7-8).
For the reliability of manual compensation, the binary input signal
>Reset comp. val.
has a preset soft-
ware filtering time (configurable in DIGIS) of 20 ms.
NOTE
When operating with manual compensation, changing the value of parameter capacitor reference
current will reset the compensation values.
Normalization with I
c
The threshold for the unbalanced current is usually set by assuming the rated capacitor current I
c,rated
. The
current I
c
flowing into the capacitor bank determines the amount of the unbalanced current. A lower I
c
also
means a lower unbalanced current. If I
c
< I
c,rated
, the protection becomes less sensitive. This influence can be
compensated via the normalization. Normalization keeps the sensitivity of the protection function constant by
normalizing the unbalance value with the current I
c
. When using the parameter Normalization with Ic ,
normalization is enabled or disabled.
I
c
Lower than Current Thresh.CB Open
If the current I
c
is lower than the threshold Current Thresh.CB Open, the compensated value can no
longer be computed with sufficient accuracy. To avoid a malfunction, the compensated unbalanced value
I
unbal.,comp.
is set to 0 A in a phase-segregated way (see Figure 7-8). This deactivates the affected phase meas-
uring components of the protection stages that work with compensated values.
This condition will be indicated in a phase-segregated manner (indication
I>-stage(cmp) blk.(Ic<)
).
Capacitor Bank Protection
7.4 Current-Unbalance Protection for Capacitors, 3-Phase
980 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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