IEC 61000-4-8 pdf download – Electromagnetic compatibility (EMC) – Part 4-8: Testing and measurement techniques – Power frequency magnetic field immunity test

IEC 61000-4-8 pdf download – Electromagnetic compatibility (EMC) – Part 4-8: Testing and measurement techniques – Power frequency magnetic field immunity test
4.7 3.8
decoupling network, back filter
electrical circuit intended to avoid reciprocal influence with other equipment not submitted tothe magnetic field immunity test
34General
The magnetic fields to which equipment is subjected may influence the reliable operation ofequipment and systems.
The following tests are intended to demonstrate the immunity of equipment when subjected topower frequency magnetic fields related to the specific location and installation condition ofthe equipment (e.g. proximity of equipment to the disturbance source).
The power frequency magnetic field is generated by power frequency current in conductorsor，more seldom，from other devices (e.g. leakage of transformers) in the proximity ofequipment.
As for the influence of nearby conductors, one should differentiate between:
– the current under normal operating conditions, which produces a steady magnetic field,
with a comparatively small magnitude;
the current under fault conditions which can produce comparatively high magnetic fieldsbut of short duration,until the protection devices operate (a few milliseconds with fuses,afew seconds for protection relays).
The test with a steady magnetic field may apply to all types of equipment intended for publicor industrial low voltage distribution networks or for electrical plants.
The test with a short duration magnetic field’related to fault conditions,requires test levelsthat differ from those for steady-state conditions; the highest values apply mainly toequipment to be installed in exposed places of electrical plants.
The test field waveform is that of power frequency.
ln many cases (household areas,sub-stations and power plant under normal conditions), themagnetic field produced by harmonics is negligible.However, in very special cases like heavyindustrial areas (large power-convertors,etc.) they occur,and will be considered in a futurerevision of this standard.
5Test levels
The preferential range of test levels，respectively for continuous and short duration applicationof the magnetic field, applicable to distribution networks at 50 Hz and 60 Hz, is given in Table 1and Table 2.
The magnetic field strength is expressed in A/m; 1 Alm corresponds to a free space inductionmagnetic flux density of 1,26 _T.
lnformation on the selection of the test levels is given in Annex C.lnformation on actual levels is given in Annex D.
6 Test equipment
6.1General
The test magnetic field is obtained by a current flowing in an- induction inductive coil; theapplication of the test field to the EUT is by the immersion method.
An example of application of the immersion method is given in Figure 1.
The test equipment includes the current source (test generator), the-induction inductive coiland auxiliary test instrumentation, that are also given in Figure 3.
6.1 6.2Test generator
6.2.1 Current source The current source typically consists of a voltage regulator (connected to the mains distribution network, or other sources), a current transformer and a circuit for the control of short duration application.
The generator shall be able to operate in continuous mode or short duration mode. The connection between the current transformer and the inductive coil input should be as short as possible to avoid that the currents which flow in the connection produce magnetic fields that affect the magnetic field in the test volume. Preferably the cables should be twisted together. The characteristics and performances of the current source or test generator for the different fields and for different inductive coils considered in this standard, are given in 6.1 .1 6.2.2.