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Functions
2.1 General
Current transformer saturation
7SD5 contains a saturation detector which largely detects the measuring errors resulting from the saturation of
the current transformers and initiates a change of the measurement method of the distance protection. The
threshold above which the saturation detector picks up can be set in address 1140 I-CTsat. Thres.. This
is the current level above which saturation may be present. The setting ∞ disables the saturation detector. This
parameter can only be altered in DIGSI at Display Additional Settings. If current transformer saturation is
expected, the following equation may be used as a thumb rule for this setting:
P
N
P
i
P'
Note
The parameter is only relevant for distance protection.
Circuit breaker status
Information regarding the circuit breaker position is required by various protection and supplementary functions
to ensure their optimal functionality. The device has a circuit breaker status recognition which processes the
status of the circuit breaker auxiliary contacts and contains also a detection based on the measured currents
and voltages for opening and closing (see also Section 2.25.1).
In address 1130 the residual current PoleOpenCurrent is set, which will definitely not be exceeded when
the circuit breaker pole is open. If parasitic currents (e.g. through induction) can be excluded when the circuit
breaker is open, this setting may be very sensitive. Otherwise this setting must be increased. Usually the pre-
setting is sufficient. This parameter can only be altered in DIGSI at Display Additional Settings.
The residual voltage PoleOpenVoltage, which will definitely not be exceeded when the circuit breaker pole
is open, is set in address 1131. Voltage transformers must be on the line side. The setting should not be too
sensitive because of possible parasitic voltages (e.g. due to capacitive coupling). It must in any event be set
below the smallest phase-earth voltage which may be expected during normal operation. Usually the presetting
is sufficient. This parameter can only be altered in DIGSI at Display Additional Settings.
The switch-on-to-fault activation (seal-in) time SI Time all Cl. (address 1132) determines the activation
period of the protection functions enabled during each energization of the line (e.g. fast tripping high-current
stage). This time is started by the internal circuit breaker switching detection when it recognizes energization
of the line or by the circuit breaker auxiliary contacts, if these are connected to the device via binary input to
provide information that the circuit breaker has closed. The time should therefore be set longer than the circuit
breaker operating time during closing plus the operating time of this protection function plus the circuit breaker
operating time during opening. This parameter can only be altered in DIGSI at Display Additional Settings.
64
= Nominal CT burden [VA]
= Nominal CT internal burden [VA]
= Actual connected burden (protection device + connection cable)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
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