IEC 61083-1:2021 pdf free download – Instruments and software used for measurements in high-voltage andhigh-current tests
5.2lmpulse calibration
lmpulse calibration is the reference method to establish the impulse scale factor of approveddigital recorders. lt is also the reference method to determine the errors of the impulse timeparameters caused by the digital recorders.Requirements on reference calibration impulses forcalibrating approved digital recorders are given in Table 2.The wave shapes shall be chosenfrom Table 2 according to the type and polarity of the high-voltage or high-current impulses thatthe digitiser is approved to measure.The uncertainties of the peak value and time parametersof the applied calibration impulses shall be within the limits given in Table 2,and the actualvalues shall be entered in the record of performance.
The number of calibration impulses to be applied shall be sufficient for obtaining sufficiently lowtype A uncertainties for all relevant parameters.
The impulse scale factor is the ratio of the peak value of the input calibration impulse and thepeak value of its corresponding impulse recorded by the digitiser.The assigned impulse scalefactor is the mean of impulse scale factors determined from a set of individual calibrationimpulses.
The error of a time parameter is the mean of the time parameter errors determined fromindividual calibration impulses.
This impulse calibration shall be made in each range of each channel that the digitiser isapproved for use in impulse tests.
NOTE A digital recorder can be calibrated for exponential current impulses(IEC 62475) using either a lightningimpulse generator or a switching impulse generator that best matches the waveform of the current impulse,
5.3Step calibration
The step calibration is the alternative method for establishing the impulse scale factor of anapproved digital recorder. To qualify an approved digitiser for measuring impulse timeparameters, the scale factor constancy test specified in 5.4 and the calibration of time base asspecified in 5.5 shall also be performed if the impulse calibration as specified in 5.2 is notperformed.
A direct voltage VcAL, with an uncertainty less than 0,1 % and within the assigned measurementrange of the instrument,is applied to the input and then short-circuited to ground by anappropriate switching device，preferably based on a mercury-wetted relay. The resultanttransition to zero level is recorded as the output o(t)(an example is shown in Figure 1) andevaluated within the time interval of the step calibration epoch.A number of records (e.g.10)of the response shall be averaged to reduce the random noise.The deviation of the samplevalues o(t) in the time interval of the step calibration epoch from their mean Osm shall be withinthe uncertainty limits specified for the assigned impulse scale factor.The value of osm shall beevaluated as the mean of all o(t) values within the step calibration epoch (IEC 60060-2:2010).The impulse scale factor is the quotient of the input voltage VcAL and osm. The rise time of thestep shall be less than 10 % of the lower limit of the step calibration epoch.
This voltage calibration shall be made in each range of each channel that the digitiser approvedfor use in impulse tests.This test shall be performed using both voltage polarities. lf the scalefactors determined with the two polarities agree to within ±0,5 %, then the impulse scale factordetermined by this method is valid. Otherwise，impulse calibration according to 5.2 ofappropriate polarity shall be used.