ABB Relion 670 Series Technical Reference Manual page 211

Line differential protection ansi

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1MRK505222-UUS C

Technical reference manual

The polarizing voltage is a memorized positive sequence voltage. The memory is

continuously synchronized via a positive sequence filter. The memory is starting to run

freely instantaneously when a voltage change is detected in any phase. A non-

directional impedance measurement is used to detect a fault and identify the faulty

phase or phases.

At a three phase fault when no positive sequence voltage remains (all three phases are

disconnected) the memory is used for direction polarization during 100 ms.

The memory predicts the phase of the positive sequence voltage with the pre-fault

frequency. This extrapolation is made with a high accuracy and it is not the accuracy of

the memory that limits the time the memory can be used. The network is at a three

phase fault under way to a new equilibrium and the post-fault condition can only be

predicted accurately for a limited time from the pre-fault condition.

In case of a three phase fault after 100 ms the phase of the memorized voltage can not

be relied upon and the directional measurement has to be blocked. The achieved

direction criteria are sealed-in when the directional measurement is blocked and kept

until the impedance fault criteria is reset (the direction is stored until the fault is cleared).

This memory control allows in the time domain unlimited correct directional

measurement for all unsymmetrical faults also at voltage reversal. Only at three phase

fault within the range of the set impedance reach of the criteria for control of the

polarization voltage the memory has to be used and the measurement is limited to 100

ms and thereafter the direction is sealed-in. The special impedance measurement to

control the polarization voltage is set separately and has only to cover (with some

margin) the impedance to fault that can cause the voltage reversal.

The evaluation of the directionality takes place in Directional impedance quadrilateral,

including series compensation (ZDSRDIR,21D) function. Equation

are used to classify that the fault is in forward direction for phase-to-ground fault and

phase-to-phase fault.

EQUATION2005 V2 EN

For the AB element, the equation in forward direction is according to:

Impedance protection

and equation

(Equation 22)

Relion red670