Voltage Restrained Overcurrent Protection For Generator And Step-Up Transformer - ABB REG670 Applications Manual

Section 12
Multipurpose protection
12.1.3.5
12.1.3.6
458
Voltage restrained overcurrent protection for generator and 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, GF05)
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 StartCurr_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 UHighLimit_OC1 to value 100%
14. Set ULowLimit_OC1 to value 25%
Proper operation of the CVGAPC function made in this way can easily be verified by
secondary injection. All other settings can be left at the default values. Furthermore
the other built-in protection elements can be used for other protection and alarming
purposes.
Loss of excitation protection for a generator
Example will be given how by using positive sequence directional overcurrent
protection element within a CVGAPC function, loss of excitation protection for a
generator can be achieved. Let us assume that from rated generator data the following
values are calculated:
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
1MRK 502 071-UEN -
Application manual