Hitachi Relion 670 Series Applications Manual page 181

1MRK511407-UUS Rev. N
protection against all unbalance faults (phase-to-phase faults as well). Care shall be taken that the
minimum pickup of such protection function shall be set above natural system unbalance level.
An example will be given, how sensitive-ground-fault protection for power lines can be achieved by using
negative-sequence directional overcurrent protection elements within a CVGAPC function.
This functionality can be achieved by using one CVGAPC function. The following shall be done to ensure
proper operation of the function:
1. Connect three-phase power line currents and three-phase power line voltages to one CVGAPC
instance (for example, CVGAPC:4)
2. Set CurrentInput to NegSeq (please note that CVGAPC function measures I2 current and NOT 3I2
current; this is essential for proper OC pickup level setting)
3. Set VoltageInput to -NegSeq (please note that the negative sequence voltage phasor is intentionally
inverted in order to simplify directionality
4. Set base current IBase value equal to the rated primary current of power line CTs
5. Set base voltage UBase value equal to the rated power line phase-to-phase voltage in kV
6. Set RCADir to value +65 degrees (NegSeq current typically lags the inverted NegSeq voltage for
this angle during the fault)
7. Set ROADir to value 90 degree
8. Set LowVolt_VM to value 2% (NegSeq voltage level above which the directional element will be
enabled)
9. Enable one overcurrent stage (for example, OC1)
10. By parameter CurveType_OC1 select appropriate TOC/IDMT or definite time delayed curve in
accordance with your network protection philosophy
11. Set PickupCurr_OC1 to value between 3-10% (typical values)
12. Set tDef_OC1 or parameter "TD" when TOC/IDMT curves are used to insure proper time
coordination with other ground-fault protections installed in the vicinity of this power line
13. Set DirMode_OC1 to Forward
14. Set DirPrinc_OC1 to IcosPhi&U
15. Set ActLowVolt1_VM to Block
•
16. Set EnRestrainCurr to On
17. Set RestrCurrInput to PosSeq
18. Set RestrCurrCoeff to value 0.1
If required, this CVGAPC function can be used in directional comparison protection scheme for the power
line protection if communication channels to the remote end of this power line are available. In that case
typically two NegSeq overcurrent steps are required. One for forward and one for reverse direction. As
explained before the OC1 stage can be used to detect faults in forward direction. The built-in OC2 stage
can be used to detect faults in reverse direction.
However the following shall be noted for such application:
Phasor measurement unit RES670
Application manual
In order to insure proper restraining of this element for CT saturations during three-phase
faults it is possible to use current restraint feature and enable this element to operate only
when NegSeq current is bigger than a certain percentage (10% is typical value) of measured
PosSeq current in the power line. To do this the following settings within the same function
shall be done:
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Section 11
Multipurpose protection
175