Application - ABB RELION 620 Series Technical Manual

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1MAC504801-IB E

620 series ANSI

Technical Manual

TRIP output is not activated. The activation of the output of the second harmonic

blocking signal BLK2H deactivates the TRIP output.

Application

A ground-fault protection using an overcurrent element does not adequately protect the

transformer winding in general and the 87LOZREF winding in particular.

The restricted ground-fault protection is mainly used as a unit protection for the

transformer windings. 80LOZREF is a sensitive protection applied to protect the

87LOZREF winding of a transformer. This protection system remains stable for all the

faults outside the protected zone.

87LOZREF provides a higher sensitivity for the detection of ground faults than the overall

transformer differential protection. This is a high-speed unit protection scheme applied to

the 87LOZREF winding of the transformer. In 87LOZREF, the difference of the

fundamental component of all three phase currents and the neutral current is provided to

the differential element to detect the ground fault in the transformer winding based on the

numerical stabilized differential current principle.

Connection of current transformers

The connections of the main CTs are designated as "Type 1" and "Type 2". In case the

groundings of the current transformers on the phase side and the neutral side are both

either inside or outside the area to be protected, the setting parameter CT connection type

is "Type 1".

If the grounding of the current transformers on the phase side is inside the area to be

protected and the neutral side is outside the area to be protected or vice versa, the setting

parameter CT connection type is "Type 2".

Protection functions

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