4.2.4.5 Operation principleThe function can be enabled and disabled with the Operation setting. Thecorresponding parameter values are "on" and "off".The operation of EFPADM can be described using a module diagram. All the modulesin the diagram are explained in the next sections.OPERATENeutraladmittancecalculationBLOCKSTARTIRES IoUoRELEASEtTimerURESBlockinglogicOperationcharasteristicsFAULT_DIRGUID-80220F27-4046-4345-83AB-5CD6E091E01C V1 ENFigure 246: Functional module diagramNeutral admittance calculationWhen the residual voltage exceeds the set threshold Voltage start value, an earth faultis detected and the neutral admittance calculation is released.To ensure a sufficient accuracy for the Io and Uo measurements, it is required that theresidual voltage exceeds the value set by Min operate voltage. If the admittancecalculation mode is "Delta", the minimum change in the residual voltage due to a faultmust be 0.01 × Un to enable the operation. Similarly, the residual current must exceedthe value set by Min operate current.The polarity of the polarizing quantity Uo can be changed, that is,rotated by 180 degrees, by setting the Pol reversal parameter to "True"or by switching the polarity of the residual voltage measurementwires.As an alternative for the internal residual overvoltage-based start condition, theneutral admittance protection can also be externally released by utilizing theRELEASE input.When Admittance Clc mode is set to "Delta", the external logic used must be able togive RELEASE in less than 0.1 s from fault initiation. Otherwise the collected pre-fault values are overwritten with fault time values. If it is slower, Admittance Clc modemust be set to “Normal”.Neutral admittance is calculated as the quotient between the residual current andresidual voltage (polarity reversed) fundamental frequency phasors. The AdmittanceClc mode setting defines the calculation mode.Admittance Clc mode = "Normal"1MRS759142 C Section 4Protection functionsREX640 455Technical Manual
