Voltage Restrained Overcurrent Protection For Generator And Unit Step-Up Transformer - Hitachi Relion 670 Series Applications Manual

Section 11
Multipurpose protection
1. Connect three-phase currents from the protected object to one CVGAPC instance (for example,
CVGAPC:3)
2. Set CurrentInput to value UnbalancePh
3. Set EnRestrainCurr to On
4. Set RestrCurrInput to MaxPh
5. Set RestrCurrCoeff to value 0.97
6. Set base current value to the rated current of the protected object in primary amperes
7. Enable one overcurrent step (for example, OC1)
8. Select parameter CurveType_OC1 to value IEC Def. Time
9. Set parameter PickupCurr_OC1 to value 5%
10. Set parameter tDef_OC1 to desired time delay (for example, 2.0s)
Proper operation of CVGAPC function made in this way can easily be verified by secondary injection. All
other settings can be left at the default values. However it shall be noted that set values for restrain
current and its coefficient will as well be applicable for OC2 step as soon as it is enabled.
Furthermore the other built-in protection elements can be used for other protection and alarming
purposes. For example, in case of generator application by enabling OC2 step with set pickup to 200%
and time delay to 0.1s simple but effective protection against circuit breaker head flashover protection is
achieved.
11.1.4.5 Voltage restrained overcurrent protection for generator and unit step-up
transformer
Example will be given how to use one CVGAPC function to provide voltage restrained overcurrent
protection for a generator. Let us assume that the time coordination study gives the following required
settings:
• Inverse Time Over Current TOC/IDMT curve: ANSI very inverse
• Pickup current of 185% of generator rated current at rated generator voltage
• Pickup current 25% of the original pickup current value for generator voltages below 25% of rated
voltage
This functionality can be achieved by using one CVGAPC function. The following shall be done in order
to ensure proper operation of the function:
1. Connect three-phase generator currents and voltages to one CVGAPC instance (for example,
CVGAPC:5)
2. Set CurrentInput to value MaxPh
3. Set VoltageInput to value MinPh-Ph (it is assumed that minimum phase-to-phase voltage shall be
used for restraining. Alternatively, positive sequence voltage can be used for restraining by selecting
PosSeq for this setting parameter)
4. Set base current value to the rated generator current primary amperes
5. Set base voltage value to the rated generator phase-to-phase voltage in kV
6. Enable one overcurrent step (for example, OC1)
7. Select CurveType_OC1 to value ANSI Very inv
8. If required set minimum operating time for this curve by using parameter tMin_OC1 (default value
0.05s)
9. Set PickupCurr_OC1 to value 185%
10. Set VCntrlMode_OC1 to On
11. Set VDepMode_OC1 to Slope
12. Set VDepFact_OC1 to value 0.25
13. Set VHighLimit_OC1 to value 100%
14. Set VLowLimit_OC1 to value 25%
180
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1MRK511407-UUS Rev. N
M13088-158 v5
Phasor measurement unit RES670
Application manual