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2.6 Voltage Protection 27, 59
134
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
2.6 Voltage Protection 27, 59
Voltage protection has the function to protect electrical equipment against undervolt-
age and overvoltage. Both operational states are unfavourable as overvoltage may
cause, for example, insulation problems or undervoltage may cause stability prob-
lems.
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 machines and prevents from inadmissible operating states and
a possible loss of stability.
2.6.1 Measurement Principle
Connection The voltages supplied to the device may correspond to the three phase-to-ground volt-
ages V
AN
, V
BN
, V
CN
or two phase-to-phase voltages (V
AB
, V
BC
) and the displacement
voltage (V
N
) or, in case of a single-phase connection, any phase-to-ground voltage or
phase-to-phase voltage. Relay 7SJ64 provides the option to detect three phase-
ground voltages and the ground voltage in addition. With multiple-phase connection
the connection mode was specified during the 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).
With three-phase connection , the overvoltage protection requires the phase-to-
phase voltages and, if necessary, calculated from the phase-to-ground voltages. In
case of phase-to-phase connection, two voltages are measured and the third one is
calculated. Depending on the configured parameter setting (address
614 OP.
QUANTITY 59
), the evaluation uses either the largest of the phase-to-phase voltages
Vphph
or the negative sequence component
V2
of the voltages.
With three-phase connection , undervoltage protection relies either on the positive
sequence component
V1
or the smallest of the phase-to-phase voltages
Vphph
. This
is configured by setting the parameter value in address
615 OP. QUANTITY 27
.
The choice between phase–ground and phase–phase voltage allows voltage asym-
metries (e.g. caused by a ground fault) to be taken into account (phase–ground) or to
be unconsidered (phase–phase).
With single-phase connection a phase-ground or phase-phase voltage is connected
and evaluated (see also Section 2.24) dependent on the type of connection.
Current Supervi-
sion The primary voltage transformers are arranged, depending on the system, either on
the supply side or the load side of the associated circuit breaker. These different ar-
rangements lead to different behavior of the voltage protection function when a fault
occurs. When a tripping command is issued and a circuit breaker is opened, full
voltage remains on the supply side while the load side voltage becomes zero. When
voltage supply is absent, undervoltage protection, for instance, will remain picked up.
If pickup condition must reset, the current can be used as an additional criterion for
pickup of undervoltage protection (current supervision CS). Undervoltage pickup can
only be maintained when the undervoltage criterion is satisfied and a settable