IEC 61000-4-7:2002 pdf download

IEC 61000-4-7:2002 pdf download.Electromagnetic compatibility(EMC)-Part 4-7: Testing and measurement techniques – General guide on harmonics and interharmonicsmeasurements and instrumentation, for powersupply systems and equipment connected thereto.
4.4 General structure of the instrument
New designs of instrument are likely to use the discrete Fourier transform (DFT), normally using a fast algorithm called fast Fourier transform (FFT). Therefore this standard considers only this architecture but does not exclude other analysis principles (see clause 6).
The general structure is represented in figure 1. An instrument may or may not comprise all the blocks and outputs given.
4.4.1 Main instrument
The main instrument comprises
— input circuits with anti-aliasing filter,
— A/D-converter including sample-and-hold unit,
— synchronisation and window-shaping unit if necessary,
— DFT-processor providing the Fourier coefficients a,77 and b,,1 (“OUT 1”).
It is complemented by the special parts devoted to current assessment and/or voltage assessment.
NOTE 1 For further details, see 5.5.
NOTE 2 For the analysis of harmonics and interharmonics, the signalf(i) which has to be analysed is pre-treated to eliminate frequencies higher than the operating range of the instrument.
For full compliance with this standard, the window width shall be 10 (50 Hz systems) or 12 (60 Hz systems) periods with rectangular weighting (see also clause 7). Hanning weighting is allowed only in the case of loss of synchronisation. This loss of synchronisation shall be indicated on the instrument display and the data so acquired shall be flagged.
The time window shall be synchronised with each group of 10 or 12 cycles according to the power system frequency of 50 Hz or 60 Hz. The time between the leading edge of the first sampling pulse and the leading edge of the (A’f+l )th sampling pulse (where Mis the number of samples; see 3.5.1) shall be equal to the duration of the specified number of cycles of the power system, with a maximum permissible error of ±0,03%. Instruments including a phase- locked loop or other synchronisation means shall meet the requirements for accuracy and synchronisation for measuring at any signal frequency within a range of at least ±5% of the nominal system frequency. However, for instruments having integrated supply sources, so that the source and measurement systems are inherently synchronised, the requirement for a working input frequency range does not apply, provided the requirements for synchronisation and frequency accuracy are met.
The output (OUT 1, see figure 1) shall provide the individual coefficients am and bm of the DFT, for the current or voltage, i.e. the value of each frequency component calculated.
The instrument shall be able to accept input signals with a crest factor up to 4 for the ranges
up to 5 A r.m.s., 3,5 for the 10 A r.m.s. range and 2,5 for higher ranges.
An overload indication is required.
The overall accuracy requirements are stated in table 1.
For other requirements, see clause 8.
NOTE A d.c. component is often associated with the distorted current to be measured; such a d.c. component may produce large errors in input current transformers. The manufacturer should indicate in the instrumentation specifications the maximum allowed d.c. component so that the additional influence error does not exceed the stated accuracy.
5.2 Voltage input circuit
The input circuit of the measuring instrument shall be suitable for the maximum voltage and the frequency of the supply voltage to be analysed and shall keep its characteristics and accuracy unchanged up to 1,2 times the maximum voltage. A crest factor of at least 1,5 is sufficient for measurements, except for highly distorted voltages in industrial networks, for which a crest factor of at least 2 may be necessary. An overload indication is required in any case.
Stressing the input for I s by an a.c. voltage of four times the input voltage setting or 1 kV r.m.s., whichever is less, shall not lead to any damage in the instrument.
Many nominal supply voltages between 60 V and 690 V exist, depending on local practice. To permit a relatively universal use of the instrument for most supply systems, it may be advisable for the input circuit to be designed for the following nominal voltages:
Unom 66 V, 115 V, 230 V, 400 V, 690 V for 50 Hz systems
Unom 69 V, 120 V, 240 V, 277 V, 347 V, 480 V, 600 V for 60 Hz systems.