ABB Relion 670 Series Technical Reference Manual page 129

Line differential protection ansi

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1MRK505222-UUS C

Technical reference manual

ANSI05000040 V2 EN

Example of application on a three-terminal line with breaker-and-a-half

breaker arrangements

The current differential algorithm provides high sensitivity for internal faults, at the

same time as it has excellent stability for external faults. Current samples from all CTs

are exchanged between the IEDs in the line ends (master-master mode) or sent to one

IED (master-slave mode) for evaluation.

A restrained dual biased slope evaluation is made where the bias current is the highest

phase current in any line end giving a secure through fault stability even with heavily

saturated CTs. In addition to the restrained evaluation, an unrestrained high differential

current setting can be used for fast tripping of internal faults with very high currents.

A special feature with this function is that applications with small power transformers

(rated current less than 50 % of the differential current setting) connected as line taps

(that is, as "shunt" power transformers), without measurements of currents in the tap,

can be handled. The normal load current is here considered to be negligible, and

special measures need only to be taken in the event of a short circuit on the LV side of

the transformer. In this application, the tripping of the differential protection can be

time delayed for low differential currents to achieve coordination with down stream

over current IEDs.

Protected zone

Communication Channel

Differential protection

ANSI05000040_2_en.vsd

Relion red670