7/31/2019 Directional Over Current Relay Working Principle

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Directional Over current relay working principle.

Directional phase protection equipment is used on a radial network

for substations supplied simultaneously by several sources.

In order to obtain good continuity of service, it is important that a

fault affecting one of the sources does not cause all the sources to

trip.

The required selectivity is achieved by installing phase directional

protection equipment on the incomer of each of the sources.

A phase element connected Ia VbcB phase element connected Ib VcaC phase element connected Ic Vab

7/31/2019 Directional Over Current Relay Working Principle

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Directional Over current relay working principle

Directional overcurrent

This type of directional relay is made by combining

overcurrent protection equipment with an equipment

to measure the phase displacement between the

current and the polarisation variable Vbc.

Tripping is subject to the two following conditions:

- the current is greater than the threshold &

- the phase displacement between the current and thepolarising Volage Vbc, defined by the

characteristic angle, is in the zone between +90 and -

90.