Operation Principle - ABB RELION 620 Series Technical Manual

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Protection functions

Operation principle

The function can be enabled and disabled with the Operation setting. The corresponding

parameter values are "Enable" and "Disable".

The operation of 78 can be described using a module diagram. All the modules in the

diagram are explained in the next sections.

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Functional module diagram

Impedance calculation

This module calculates the positive-sequence impedance (Z1) using positive-sequence

voltage and current. For the module to calculate impedance it is required that the positive-

sequence current is above Min Ps Seq current setting and the negative-sequence current

is below the Max Ng Seq current setting.

The calculated positive-sequence impedance amplitude Z1_AMPL and angle

Z1_ANGLE are available in ohms and degrees, respectively, in the Monitored data view.

The calculated impedance is converted to ohms as the operating

characteristics are defined with the ohm settings.

Out of step detection

The operating characteristic is a circular offset mho on the impedance plane with two pair

of blinders. The mho characteristic is defined with the Forward reach, Reverse reach, and

Impedance angle settings. Forward reach defines the impedance from the origin to the

edge of circle on the top side. Reverse reach defines the impedance from the origin to the

edge of the circle on the bottom side. The diameter of the mho characteristics is the sum of

Forward reach and Reverse reach settings. Two sets of blinders are defined by Inner

1MAC504801-IB E

620 series ANSI

Technical Manual

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