With the circuit breaker open, the total capacitance will be smaller compared to normaloperating conditions. This means that the neutral point 3rd harmonic voltage will bereduced compared to the normal operating condition. Therefore, there is a possibility toreduce the sensitivity of the protection when the generator circuit breaker is open.With the setting CBexists change of the sensitivity is enabled. If the binary input signal 52ais activated the set sensitivity is valid. If the generator circuit breaker is opened the binaryinput 52a is deactivated and the sensitivity is changed. This is done by changing the factorBeta which is multiplied with a set constant FactorCBopen.In addition to the binary outputs also some analog outputs are available from theprotection function in order to enable easier commissioning:E3: the magnitude of the 3rd harmonic voltage induced in the stator given in primary voltsVN3: the magnitude of the 3rd harmonic voltage measured in the neutral point of thegeneratorVT3: the magnitude of the 3rd harmonic voltage measured in the terminal point of thegeneratorANGLE: the angle between the phasors VN3 and VT3 given in radiansDV3: the magnitude of the 3rd harmonic differential voltageBV3: the magnitude of the 3rd harmonic bias voltageV_N: the fundamental frequency voltage measured in the neutral point of the generator9.5.8 Technical dataTable 183:STEFPHIZ (59THD) technical dataFunction Range or value AccuracyFundamental frequency level UN(95% Stator EF)(1.0–50.0)% ofVBase ± 0.5% of VnThird harmonic differential level (0.5–10.0)% ofVBase ± 5.0% of VnThird harmonic differential blocklevel(0.1–10.0)% ofVBase ± 5.0% of VnTimers (0.020–60.000) s ± 0.5% ± 25 msFilter characteristic:FundamentalThird harmonicReject third harmonic by 1–40Reject fundamental harmonic by1–40-Section 9 1MRK 502 048-UUS AVoltage protection318Technical manual
