ABB Relion 670 Series Applications Manual page 129

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1MRK 511 401-UUS F

T-feeder protection

In many busbar arrangements such as breaker-and-a-half, ring breaker, mesh corner, there will be

a T-feeder from the current transformer at the breakers up to the current transformers in the

feeder circuit (for example, in the transformer bushings). It is often required to separate the

protection zones that the feeder is protected with one scheme while the T-zone is protected with

a separate differential protection scheme. The 1Ph high impedance differential HZPDIF (87)

function in the IED allows this to be done efficiently, see Figure 53.

Bay control REC670

Application manual

That the settings of U>Alarm, U>Trip and SeriesResistor must be chosen such that

both U>Alarm/SeriesResistor and U>Trip/SeriesResistor are >4% of IRated of the

used current input. Normally the settings shall also be such that U>Alarm/

SeriesResistor and U>Trip/SeriesResistor both gives a value <4*IRated of the used

current input. If not, the limitation in how long time the actual current is allowed to

persist not to overload the current input must be considered especially during the

secondary testing.

Differential protection