Annex A (Normative) Induction coil calibration method

(Normative)

A.1. Magnetic field measurement

The magnetic field test is related to free space condition, without the EUT and at 1m minimum distance from the laboratory walls and any magnetic material.

The measurement of the magnetic field may be done with a measurement system comprising of calibrated sensors e.g. a "Hall effect" of multi-turn loop sensor with a diameter of at least one order of magnitude smaller than the test induction coil and a power frequency narrow band instrument.

A.2. Calibration of the induction coil

The calibration shall be carried out by injecting the calibration current at power frequency in the induction coil and measuring the magnetic field by sensors placed at its geometrical centre.

Proper orientation of the sensor shall be selected in order to obtain the maximum value.

The "induction coil factor" shall be determined for each induction coil as the ratio "field strength/current" of injection (H/A).

The "coil factor", determined at a.c current, is not related to the current waveform, because it is a characteristic parameter of the induction coil; it is therefore applicable for the evaluation of magnetic field at power frequency.

For standard dimension coil, the coil factor is determined by the manufacturer of the coil, and can be verified by laboratory measurements before carrying out

(Normative)

B.1. General

This annex considers the problems of generation of the test magnetic fields.

In the first stage, both the immersion and proximity methods were considered.

In order to know the limits of application of such methods, some questions have been emphasized.

In the following the reasons for the values are explained.

B.2. Induction coil requirements

The requirements of the induction coil is "3 dB tolerance of the test field in the volume of the EUT"; this tolerance has been considered a reasonable technical compromise in respect of a test characterized by severity levels in 10 dB steps, due to practical limits in the generation of constant field over a wide range of volumes.

The constancy of the field is a requirement limited to a single direction, orthogonal to the coil plane. The field in different directions is obtainable in successive test steps by rotating the induction coil.

B.3. Induction coil characteristics

The characteristics of induction coils of different dimensions suitable for testing table-top equipment or floor standing equipment are given in diagrams showing:

- Profile of the field generated by a square induction coil (1 m side) in its plane (see figure B.1);

- 3 dB area of the field generated by a square induction coil (1 m side) in its plane (see figure B.2);

- 3 dB area of the field generated by a square induction coil (1 m side) in the mean orthogonal plane (component orthogonal to the plane of the coil) (see figure B.3);

- 3 dB area of the field generated by two square induction coils (1 m side) 0.6 m spaced, in the mean orthogonal plane (component orthogonal to the plane of the coils) (see figure B.4);

- 3 dB area of the field generated by two square induction coils (1 m side) 0.8 m spaced, in the mean orthogonal plane (component orthogonal to the plane of the coils) (see figure B.5);

- 3 dB area of the field generated by a rectangular induction coil (1 m  2.6 m) in its plane (see figure B.6);

- 3 dB area of the field generated by a rectangular induction coil (1 m  2.6 m) in its plane (ground plane as a side of the induction coil) (see figure B.7);

- 3 dB area of the field generated by a rectangular induction coil (1 m  2.6 m), with ground plane, in the mean orthogonal plane (component orthogonal to the plane of the coil) (see figure B.8).

In the selection of the form, arrangement and dimensions of the test coil, the following points have been considered:

- The 3 dB area, inside and outside the induction coil, is related to the shape and dimensions of the induction coil;

- For a given field strength, driving current value, power and energy of the test generator are proportional to the dimensions of the induction coil.

B.4. Summary of characteristics of induction coils

On the basic of the data on the field distribution of coils with different sizes, and in view of adopting the test method given in this standard to different classes of equipment, the conclusions that can be drawn are as follows:

- Single square coil, 1 m side: testing volume 0.6 m  0.6 m  0.5 m high (0.2 m minimum distance from EUT to the coil);

- Double square coils, 1 m side, 0.6 spaced: testing volume 0.6 m  0.6 m  1 m high (0.2 m minimum distance from EUT to the coil); increasing of the separation of the coils up to 0.8 m, extends the maximum high of testable EUT (see the 3 dB area, in the mean orthogonal plane) up to 1.2 m;

- Single rectangular coil, 1 m  2.6 m: testing volume 0.6 m  0.6 m  2 m high (0.2 and 0.3 m minimum distance from EUT to the coil, respectively for the horizontal and vertical dimensions of EUT); if the induction coil is bonded to the GRP, a 0.1 m distance from it is sufficient.



Figure B.1: Characteristics of the field generated by a square induction coil
(1 m side) in its plane.

(Informative)

The test levels shall be selected in accordance with the most realistic installation and environmental conditions.

These levels are outlined in clause 5.

The immunity tests are correlated with these levels in order to establish a performance level for the environment in which the equipment is expected to operate. A survey of power frequency magnetic field strength is given in annex B.

The test level shall be chosen according to:

- The electromagnetic environment;

- The proximity of the disturbances sources to the equipment concerned;

- The compatibility margins.

Based on common installation practices, a guide for the selection of test levels for magnetic fields testing may be the following:

Class 1: Environmental level where sensitive device using electron beam can be used.

Monitors, electron microscope, etc, are representative of these devices.

The environment is characterized by the following attributes:

- Absence of electrical equipment like power transformers that may give rise to leakage fluxes;

- Areas not subjected to the influence of H.V. bus-bars.

Household, office, hospital protected areas far away from earth protection conductors, areas of industrial installations and H.V. sub-stations may be representative of this environment.

Class 3: Protected environment

The environment is characterized by the following attributes:

- Electrical equipment and cables that may give rise to leakage fluxes or magnetic field;

- Proximity of earth conductors of protection systems;

- M.V. circuits and H.V. bus-bars far away (a few hundred metres) from equipment concerned.

Commercial areas, control building, field of not heavy industrial plants, computer room of H.V. sub-stations may be representative of this environment.

The environment is characterized by the following attributes:

- Short branch power lines as bus-bars, etc;

- High power electrical equipment that may give rise to leakage fluxes;

- Ground conductors of protection system;

- M.V. circuits and H.V. bus-bars at relative distance (a few tens of metres) from equipment concerned.

Fields of heavy industrial and power plants and the control room of H.V. sub-stations may be representative of this environment.

Class 5: Severe industrial environment

The environment is characterized by the following attributes:

- Conductors, bus-bars or M.V., H.V. lines carrying tens of kA;

- Ground conductors of protection system;

- Proximity of M.V. and H.V. bus-bars;

- Proximity of high power electrical equipment.

Switchyard areas of heavy industrial plants, M.V., H.V. and power stations may be representative of this environment

Class x: Special environment

The minor or major electromagnetic separation of interference sources from equipment circuits, cables, lines etc., and the quality of the installations may require the use of a higher or lower environmental level than those described above.

It should be noted that the equipment lines of a higher level can penetrate a lower severity environment.


Annex D

(Informative)

Data are limited to available bibliography and/or measurements.

a) Household appliances

A survey on the magnetic fields produced by about 100 different appliances of 25 basic types is given in table D.1. The field strength is related to the surfaces of appliances (it is quite localized) and at greater distances. At a distance of 1 m or more it would vary from the maximum expected field at that distance by only 10% to 20% when measured in any direction from the appliance. Background magnetic field in the homes where appliances were measured ranged from

The faults in domestic low-voltage power lines gives field strength higher than specified, depending on the short circuit current of each installation; the duration is in the order of hundreds ms, depending on the protection devices installed.

Because the magnetic field is dependent on the line configuration, load and fault conditions, the field profile may be more significant to determine the electromagnetic environment to which equipment may be exposed.

General information on the environment produced by high voltage lines is given in IEC 1000-2-3.

The quantitative survey of the actual field measurement is given in table D.2.

The quantitative survey of the actual field measurements related to 220 kV and 400 kV high voltage sub-stations area is given in table D.3.

Measurements were carried out at different areas of a power plant; most of them are comparable, for the kind of power supply lines and electrical equipment, to industrial plants.