Functions
2.1 General
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
38
Current Connection
The device features four current measurement inputs, three of which are connected to the set of current trans-
formers. Various possibilities exist for the fourth current input I
4
:
• Connection of the I
4
input to the ground current in the neutral point of the set of current transformers on the
protected feeder (normal connection, see Appendix, A.3a):
Address 220 is then set to: I4 transformer = In prot. line and address 221 I4/Iph CT = 1.
• Connection of the I
4
input to a separate ground current transformer on the protected line (e.g. a summation
CT or core balance CT, see Appendix, A.3):
Address 220 is then set to: I4 transformer = In prot. line and address 221 I4/Iph CT is set:
Example
:
Phase current transformers 500 A/5 A
Core balance CT 300 A / 5AI4/IphCT = 300/500 = 0.6
• Connecting the I
4
input to the starpoint current of a transformer; this is used for the ground fault differential
protection:
Address 220 is then set to: I4 transformer = and address 221I4/Iph CT depends on the transforma-
tion ratio of the starpoint transformer to the transformer set of the protected line.
• If the input I
4
is not required, set:
Address 220 I4 transformer = Not connected,
Address 221 I4/Iph CT is then irrelevant.
In this case, the neutral current is calculated by summing the phase currents.
Rated Frequency
The rated frequency of the system is set at address 230 Rated Frequency. The factory setting of the model
variant must only be changed if the device is to be used for a purpose other than intended when ordering. You
can set 50 Hz or 60 Hz.
System Starpoint
The manner in which the system neutral point is grounded must be considered for the correct processing of
ground faults and double ground faults. Accordingly, set address 207 SystemStarpoint = Grounded,
Peterson-C.Gnd. or Isolated. For low-resistance or high-resistance („impedance grounded“) systems,
set Grounded.
Depending on the setting of this parameter, the ground fault differential protection uses either the measured
ground current (Grounded) or the values calculated from the power values (Peterson-C.Gnd. or
Isolated).
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