IEEE C57.113-2010 EEERecommended Practice for Partial Discharge Measurement in L iquid-Filled Power Transformers and Shunt Reactors.
4.4.3 Display unit In addition to the measurement of the apparent charge level by means of analog or digital meters it is strongly recommended to display the phase-resolved PD patterns by means of a suitable display unit, such as an oscilloscope or a computer. This may assist not only the identification and classification of harmful PD defects but also the discrimination of disturbing electromagnetic interferences, which are often not phase-correlated. 4.4.4 Basic sensitivity The basic sensitivity should be determined by means of calibrating pulses specified in 4.6, which are injected into the input of the measuring impedance connected to the PD measuring instrument via the associated measuring cable. A calibrating charge of 50 pC should cause a minimum deflection of 50% of the full reading of the indicating instrument or of the optional display unit. 4.4.5 Linearity The linearity should be determined by means of calibrating pulses specified in 4.6, which should be injected in the measuring impedance connected via the associated measuring cable to the PD measuring instrument. The measuring sensitivity should be adjusted such that the full reading (100%) is obtained for an injected calibrating charge of 500 pC. After that the magnitude of the calibrating charge should be reduced stepwise by 100 pC. Under this condition the values indicated by the PD measuring instrument should not deviate by more than ±10% from the true magnitudes of the injected pulse charges.
4.6 Maintaining the specified parameters of PD measuring circuits To verify the specified technical parameters of the PD measuring circuits including the PD calibrator, performance checks should be performed at least once a year and after repair. The scale factor, S f , of the PD measuring circuit and the values of the pulse charges, q 0 , created by the PD calibrator shall be kept in a record of performance established and maintained by the user. Additionally, type tests, routine tests, and performance tests should be performed in compliance with the recommendations of IEC 60270.
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