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2.5
Voltage Protection 27, 59
Voltage protection has the task to protect electrical equipment against undervoltage and overvoltage. Both op-
erational states are abnormal 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 rejection 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.
2.5.1
Measurement Principle
Connection / Measured Values
The voltages supplied to the device can be either the three phase-to-Ground voltages V
phase-to-phase voltages (V
has been specified during the configuration in address 213 VT Connect. 3ph, see 2.1.3.2.
The following table indicates which voltages can be evaluated by the function. The settings for this are made
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 2-7
Voltage protection, selectable voltages
Function
Connection, three-phase
Overvoltage
Van, Vbn, Vcn
Vab, Vbc, VGnd
Vab, Vbc
Vab, Vbc, Vx
Undervoltage
Van, Vbn, Vcn
Vab, Vbc, VGnd
Vab, Vbc
Vab, Vbc, Vx
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
, V
) and the displacement voltage (ground voltage V
A-B
B-C
(parameter 213)
Vphph (largest phase-to-phase voltage)
Vph-n (largest phase-to-Ground voltage) Phase-to-Ground voltage
V1 (positive sequence voltage)
V2 (negative sequence voltage)
Vphph (largest phase-to-phase voltage)
V1 (positive sequence voltage)
V2 (negative sequence voltage)
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)
Vphph (smallest phase-to-phase voltage) Phase-to-phase voltage
V1 (positive sequence voltage)
Selectable voltage
(parameter 614 / 615)
Functions
2.5 Voltage Protection 27, 59
, V
, V
or two
A-N
B-N
C-N
). The connection mode
N
Threshold to be set as
Phase-to-phase voltage
Positive sequence
voltage
calculated from phase-to-
Ground voltage or phase-
to-phase voltage / √3
Negative sequence
voltage
Phase-to-phase voltage
Positive sequence
voltage
Negative sequence
voltage
Positive sequence
voltage · √3
Positive sequence
voltage · √3
109
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