As seen in the setting examples above the sensitivity of HZPDIF function is normallyhigh, which means that the function will in many cases operate also for short circuitsor open current transformer secondary circuits. However the stabilizing resistor canbe selected to achieve sensitivity higher than normal load current and/or separatecriteria can be added to the operation, like a check zone. This can be either anotherIED, with the same HZPDIF function, or be a check about the fault condition, whichis performed by an earth overcurrent function or neutral point voltage function.For such cases where operation is not expected during normal service the alarm outputshould be used to activate an external shorting of the differential circuit avoidingcontinuous high voltage in the circuit. A time delay of a few seconds is used before theshorting and alarm are activated. Auxiliary relays with contacts that can withstandhigh voltage shall be used, like RXMVB types.The metrosil operating characteristic is given in the following figure.IEC05000749 V1 ENFigure 66: Current voltage characteristics for the non-linear resistors, in the range 10-200 V, the averagerange of current is: 0.01–10 mA7.3 Generator differential protection GENPDIF7.3.1 IdentificationFunction description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberGenerator differential protection GENPDIFId>SYMBOL-NN V1 EN87G1MRK 502 071-UEN - Section 7Differential protectionGenerator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 167Application manual
