Operation Principle - ABB RELION 620 Series Technical Manual

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1MAC504801-IB E

620 series ANSI

Technical Manual

The fundamental components of the currents are used for calculating the residual current

of the phase currents, the neutral current, differential currents and stabilizing currents. The

operating characteristics are according to the definite time.

87LOZREF contains a blocking functionality. The neutral current second harmonic is

used for blocking during the transformer inrush situation. It is also possible to block

function outputs, timers or the function itself, if desired.

Operation principle

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

parameter values are "Enable" and "Disable".

The operation of 87LOZREF can be described using a module diagram. All the modules

in the diagram are explained in the next sections.

GUID-F8C2915F-CA7B-4830-B748-3E19E26803CC V1 EN

Functional module diagram

Ground-fault detector

The operation is based on comparing the amplitude and the phase difference between the

sum of the fundamental frequency component of the phase currents (ΣI, residual current)

and the fundamental frequency component of the neutral current (IG) flowing in the

conductor between the transformer or generator's neutral point and ground. The

differential current is calculated as the absolute value of the difference between the

residual current (the sum of the fundamental frequency components of the phase currents

I_A, I_B and I_C) and the neutral current. The directional differential current

ID_COSPHI is the product of the differential current and cosφ. The value is available in

the monitored data view.

Protection functions

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