Solution
The distance function is based on impedance loop calculation between the phases and phases to the ground. There is a minimum current requirement in order to start an accurate impedance calculation. This is defined with the following parameters:

For phase to phase faults (given as percentage of the rated CT secondary)

- IPh Base Sens is the minimum phase current

For phase to ground faults (given as percentage of the rated CT secondary)

- IRes Base Sens is the base sensitivity for residual current detection

- IRes Bias is the biasing current, which is applied for the detection of zero sequence current in the case of increased phase currents.

Note, that Protecta offers different distance functionblocks for solidly grounded and for isolated/compensated networks. By solidly grounded applications the biasing current is determined by the highest phase current, while by isolated/compensated applications the biasing current is determined by the sum of the phase currents.

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