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:
•
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
– After counting a faulty C-element
– 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 7-22).
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.
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
. Phase A component of the current I
c
flowing into the
capacitor bank is used as the reference for the normalization. When using the parameter Normalization
with Ic, normalization is enabled or disabled.
I
c
Lower than Current Thresh. CB Open
If any phase current of 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 (see Figure 7-22). This deactivates the protection stages that work with compen-
sated values.
This condition will be indicated (indication
I>-stage(cmp) blk.(Ic<)
).
In this case, normalization with current I
c
will no longer work properly either. Normalization is canceled. This
means that the non-normalized value will be used instead of the normalized value (see Figure 7-22).
Charging/Energizing the Capacitor Bank or a Phase of the Bank
Charging of the bank takes place when the discharged bank is switched on to the network. Charging of a
phase can occur in case of network faults. If a phase-to-ground voltage drops to 0 V due to a network fault,
Capacitor Bank Protection
7.5 Current-Unbalance Protection for Capacitors, 1-Phase
SIPROTEC 5, Overcurrent Protection, Manual 1005
C53000-G5040-C017-8, Edition 07.2017
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