The compensation eliminates the operational differential voltage by adjusting the voltage matching factors.
The adjusted phasors of the matching factor are calculated at the compensation moment, with the following
formula (for phase A):
•
Grounded capacitor-bank system
k
cp,A
= V
BB,A
/ V
tap,A
•
Isolated capacitor-bank system
k
cp,A
= (V
BB,A
- V
N
) / (V
tap,A
- V
N
)
With
V
BB,A
Busbar voltage, phase A
V
tap,A
Tap voltage, phase A
k
cp,A
Calculated matching factor at the compensation moment, phase A
V
N
Neutral-point-to-ground voltage
The calculation also applies to the calculation of the voltage matching factors of phase B and phase C.
The phasors of the calculated voltage matching factors k
cp
are stored and used for calculation of the differen-
tial voltage until the next compensation is applied or until the compensation is reset.
The phasors of the calculated voltage matching factors k
cp
are displayed as functional measured values after
the compensation is applied. In addition, the compensated differential voltage Vdiff.cp is available as func-
tional measured value. Vdiff.cp is the differential voltage at the moment of the compensation compared to
the not compensated status. The compensated differential voltage Vdiff.cp is calculated with the following
formula (for phase A):
•
Grounded capacitor-bank system
V
diff.cp,A
= | (
V
BB,A
- V
N
) - k
cp,A
⋅ (V
tap,A
- V
N
)|
•
Isolated capacitor-bank system
V
diff.cp,A
= | V
BB,A
- k
cp,A
⋅ V
tap,A
|
With
k
cp,A
Calculated matching factor at the compensation moment, phase A
V
BB,A
Voltage from the busbar, phase A
V
tap,A
Voltage from the tap, phase A
V
N
Neutral-point-to-ground voltage
This calculation also applies to the calculation of the compensated differential voltage of phase B and phase C.
Manual Compensation via Binary Input Signal
Manual compensation via binary input signals is available.
The following indications describe the status of the compensation:
Indication
Description
Alg. not compensated
The algorithm is not compensated. Compensated values are not available.
Compens. succeeded
If the existing unbalance has been compensated manually, this indication is
issued (as transient indication).
By activation of the binary input signal
>Compensate
, the manual compensation is started and the differen-
tial voltage that exists at that moment is compensated to 0. The value of V
diff.
becomes 0.
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
7.7 Voltage Differential Protection for Capacitors
1036 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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