ABB Relion Technical Manual page 146

Generator protection

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Differential protection

currents in this section can be tolerances of the current transformers used on both sides of

the protected generator. Slope in section 1 is always zero percent. Normally, with the

protected machine at rated load, the restrain, bias current will be around 1 p.u., that is,

equal to the machine rated current.

In section 2, a certain minor slope is introduced which is supposed to cope with false

differential currents proportional to higher than normal currents through the current

transformers.

The more pronounced slope in section 3 is designed to result in a higher tolerance to

substantial current transformer saturation at high through-fault currents, which can be

expected in this section.

Temporarily decreased sensitivity of differential protection is activated if the binary input

DESENSIT is (temporarily) set to 1 (TRUE). In this case, a new, separate limit is

superposed to the otherwise unchanged operate-bias characteristic. This limit is called

TempIdMin and it is available as a setting. The value of the setting TempIdMin must be

given as a multiple of the setting IdMin. In this case no trip command can be issued if all

fundamental frequency differential currents are below the value of the setting

AddTripDelay: If the input DESENSIT is activated also the operation time of the

protection function can be increased by using the setting AddTripDelay.

1MRK 502 048-UUS A

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