Jul,04

IEC 61083-1 pdf – Instruments and software used for measurements in high-voltage and high-current tests – Part 1: Requirements for instruments for impulse tests

6 Requirements for impulse measurements

6.1 Requirements for digital recorders used in approved measuring systems The expanded uncertainty of a digital recorder used in an approved measuring system according to IEC 60060-2 shall be not more than (at a level of confidence of not less than 95 %)

• 2 % in the voltage (current) measurement of full and standard-chopped (tail chopped) lightning voltage impulses, switching voltage impulses, exponential current impulses and rectangular current impulses;

• 3 % in the voltage measurement of front-chopped lightning impulses;

• 4 % in the measurement of the time parameters (front time, time to chopping, etc.) of the impulse. Digitiser can be qualified for measurement of one, or more, or all types of impulses. These uncertainties shall be estimated according to ISO/IEC Guide 98-3:2008. NOTE The estimated uncertainty of the digitiser is used as a component of uncertainty of the complete measurement system according to IEC 60060-2 or IEC 62475. The digital recorder shall allow storage of the raw data.

6.2 Individual requirements

6.2.1 General In order to stay within the limits given in 6.1 , the limits for individual contributions given in 6.2 should usually be met. In some cases, it is permissible that one or more of these limits be exceeded provided that it is demonstrated by estimation in accordance with ISO/IEC Guide 98-3:2008 that overall uncertainty specified in 6.1 is not exceeded.

6.2.2 Sampling rate The sampling rate shall be not less than 30/T x where T x is the time interval to be measured. NOTE T x = 0,6 T 1 is the time interval between T 30 and T 90 of the lightning impulse to be measured.

For a 1 ,2/50 lightning impulse, the permitted lower limit of front time T 1 is 0,84 µs. Therefore, a sampling rate of at least 60 × 1 0 6 s –1 is normally used for full and tail chopped lightning impulses. Similarly, a sampling rate of at least 1 00 × 1 0 6 s –1 is normally used for front chopped impulse and a sampling rate of at least 1 ,5 × 1 0 5 s –1 is normally used for the standard switching impulse.

6.2.3 Rated resolution A rated resolution of 8-bit (0,4 % of the full-scale deflection) or better is required for tests where the impulse parameters are to be evaluated. NOTE For tests which involve spectrum analysis or waveform transformation other than impulse parameter evaluation, a rated resolution of 9-bit (0,2 % of the full-scale deflection) or better is normally used.

6.2.4 Impulse scale factor The impulse scale factor determined by one of the methods as specified in 5.1 shall be constant within ±1 % over the nominal epoch. The impulse scale factor, determined by either 5.2 or 5.3, shall be determined with an expanded uncertainty of not more than 1 %. If the impulse scale factor is only determined by the step calibration method specified in 5.3, the step response level shall be constant within ±1 % over the time intervals specified in 5.4.

The non-linearity of the impulse scale factor determined in 5.4 as the measure of an uncertainty component u B1 , either by the impulse voltage method or the step voltage method, shall not

exceed 0,5 %.

6.2.5 Errors of time parameters

The errors of time parameters determined by the impulse calibration described in 5.2 shall be less than:

• 3 % for the front time T 1 of all relevant types of impulses,

• 2 % for the time to half-value T 2 of all relevant types of impulses,

• 3 % for the time to chopping T c of the standard chopped (tail chopped) lightning voltage impulse,

• 5 % for the time to chopping T c of the front chopped lightning voltage impulse,

• 3 % for the peak time T p of switching voltage impulse,

• 3 % for T d and T t for the rectangular current impulse.

If the impulse calibration as specified in 5.2 is not performed, the digitiser is approved for measuring time parameters if the digitiser meets the requirement of constancy of impulse scale factor specified in 6.2.4 and the requirement for error of time base specified in 6.2.6.

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