Functions
2.6 Voltage Protection 27, 59
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
140
2.6
Voltage Protection 27, 59
Voltage protection has the task to protect electrical equipment against undervoltage and overvoltage. Both op-
erational states are unfavorable as overvoltage may cause for example insulation problems or undervoltage
may cause stability problems.
There are two elements each available for overvoltage protection and undervoltage protection.
Applications
• Abnormally high voltages often occur e.g. in low loaded, long distance transmission lines, in islanded
systems when generator voltage regulation fails, or after full load shutdown of a generator from the system.
• The undervoltage protection function detects voltage collapses on transmission lines and electrical ma-
chines and prevents inadmissible operating states and a possible loss of stability.
2.6.1
Measurement Principle
Connection / Measured Values
The voltages supplied to the device may correspond to the three phase-to-ground voltagesV
A-N
, V
B-N
, V
C-N
or
two phase-to-phase voltages (V
A-B
, V
B-C
) and the displacement voltage (ground voltage V
N
) or, in case of a
single-phase connection, any phase-to-ground voltage or phase-to-phase voltage. Relays 7SJ623/624 and
7SJ64 provide the option to detect three phase-to-ground voltages and additionally the ground voltage. With a
multiple-phase connection, the connection type was specified during configuration in address
213
VT
Connect. 3ph
.
If there is only
one
voltage transformer, the device has to be informed of this fact during configuration via
address
240
VT Connect. 1ph
(see also Section 2.24).
The following table indicates which voltages can be evaluated by the function. The settings for this are carried
out in the
P.System Data 1
(see Section 2.1.3.2). Furthermore, it is indicated to which value the threshold
must be set. All voltages are fundamental frequency values.
Table 2-11
Voltage protection, selectable voltages
Function
Connection, three-phase
(address213)
Selectable voltage
(address614 / 615)
Threshold to be set as
Overvoltage
Van, Vbn, Vcn
Van,Vbn,Vcn,VGn
Van,Vbn,Vcn,VSy
Vphph (largest phase-to-phase voltage)
Phase-to-phase voltage
Vph-n (largest phase-to-ground voltage)
Phase-to-ground voltage
V1(positive sequence voltage)
Positive sequence voltage
V2 (negative sequence voltage)
Negative sequence voltage
Vab, Vbc, VGnd
Vphph (largest phase-to-phase voltage)
Phase-to-phase voltage
V1(positive sequence voltage)
Positive sequence voltage
V2 (negative sequence voltage)
Negative sequence voltage
Undervoltage Van, Vbn, Vcn
Van,Vbn,Vcn,VGn
Van,Vbn,Vcn,VSy
Vphph (smallest phase-to-phase voltage) Phase-to-phase voltage
Vph-n (smallest phase-to-ground voltage) Phase-to-ground voltage
V1(positive sequence voltage)
Positive sequence voltage ·
√
3
Vab, Vbc, VGnd
Vphph (smallest phase-to-phase voltage) Phase-to-phase voltage
V1 (positive sequence voltage)
Positive sequence voltage ·
√
3
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