Configure across the stages whether the unbalanced current must be normalized with the current I
c
that flows
into the capacitor bank. Phase A component of the current I
c
flowing into the capacitor bank is used as the
reference for the normalization. You can find more information in this chapter under Normalization with I
c
,
Page 1005.
The method of measurement used processes the sampled unbalanced-current values and filters out the funda-
mental component numerically. The protection stages evaluate the fundamental component of the unbal-
anced current.
General Notes on the Compensation
An operational unbalanced current is added to an unbalanced current resulting from faulty capacitor
elements. This corrupts the measuring result.
Operational unbalanced currents can result from the following causes:
•
Manufacturing tolerances of the capacitor
•
Aging of the capacitor
•
Environmental influences, for example, temperature
The compensation eliminates operational unbalanced currents by calculation. For this purpose, the phasor of
the operational unbalanced current I
unbal.,op.
is stored at specific times. The stored phasor (compensation
phasor), is subtracted from the actually measured unbalanced-current phasor:
[fo_compensatied unbal., 1, en_US]
The following indications describe the status of the compensation:
Indication
Description
Alg. not
compensated
The algorithm is not compensated. The compensated values are not available under
the following conditions:
•
After initial startup of the device before any compensation is carried out
•
After activating the binary input
>Reset comp. val.
•
After change of I
rated,obj
Protection stages that are working with compensated values are inactive.
Compens.
succeeded
This indication is issued (as transient indication with a pulse duration of 10 ms) if the
existing unbalance has been compensated manually or automatically. In case of auto-
matic compensation, the signal is issued at each event-based situation where full
compensation is carried out.
Comp. via BI
blk.(Ic<)
If a manual compensation has been initiated and the current I
c
(current flowing into
the capacitor bank) at this time is less than the threshold Current threshold CB
open, the manual compensation is not executed. This is signaled via the
Comp. via
BI blk.(Ic<)
indication.
2 different methods are available for the compensation:
•
Manual compensation via binary input signals
•
Automatic compensation
Manual Compensation via Binary Input Signal
If the binary input signal
>Compensate
is activated, the manual compensation starts. This will fully compen-
sate any unbalance that exists at this time. This means, the value I
unbal.,comp.
will then become 0. You can also
use the manual compensation in parallel with the automatic compensation.
For the reliability of manual compensation, the binary input signal
>Compensate
has a preset software
filtering time (configurable in DIGIS) of 20 ms.
Capacitor Bank Protection
7.5 Current-Unbalance Protection for Capacitors, 1-Phase
1004 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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