Siemens 7SJ85 - Page 1035

[dw_voltage_measurement_isolated, 2, en_US]
Figure 7-40 Voltage Measurement for an Isolated Capacitor-Bank System
The following formula is used to calculate the differential voltage V
diff.
of phase A:
V
diff,A
= |(V
BB,A
- V
N
) - k
A
⋅ (V
tap,A
- V
N
)|
V
BB,A
Busbar voltage, phase A
V
tap,A
Tap voltage, phase A
k
A
Voltage matching factor, phase A
V
N
Neutral-point-to-ground voltage
This calculation also applies to the calculation of the V
diff.
of phase B and phase C.
The voltage V
N
is measured via a 1-phase measuring point V-1ph. The measuring point V-1ph must be
connected with the V
unbalance
(voltage unbalance) interface of the function group.
[Sc_isolate_ground, 1, en_US]
Figure 7-41 Connecting Measuring Points to the Capacitor Bank Function Group for the Isolated Capacitor-
Bank System
Both the capacitor-bank tap voltage and the calculated differential voltage are displayed as measured values of
the function.
General Notes on the Compensation
An operational differential voltage is added to a differential voltage resulting from faulty capacitor elements.
This corrupts the measuring result.
The operational differential voltages can result from the following factors:
•
Manufacturing tolerances of the capacitor
•
Aging of the capacitor
•
Environmental influences, for example, temperature
Capacitor Bank Protection
7.7 Voltage Differential Protection for Capacitors
SIPROTEC 5, Overcurrent Protection, Manual 1035
C53000-G5040-C017-8, Edition 07.2017