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Agilent AN 1319
Compliance Testing to IEC/EN 61000-4-8
Application Note
Compliance Testing to the IEC/EN 61000-4-8 Standard
"The magnetic fields to which equipment is subjected may influence the reli-
able operation of equipment and systems."
The statement above is taken directly from the IEC/EN 61000-4-8 standard,
and is the premise upon which the standard is based. Electronic equipment
can encounter magnetic fields at power line frequencies in a variety of
places. As such, it is wise to ensure that the equipment will operate reliably
when exposed to these power line frequency magnetic fields. The IEC/EN
61000-4-8 standard describes how equipment should be tested for immunity
to power line frequency magnetic fields. This application note provides a
discussion of the standard, including interpretation of the requirements,
and suggestions for equipment selection.
Table of Contents
2 Introduction
3 Selecting a test level
5 Generating a test field
5 The induction coil
8 The test generator
13 Current measurement
14 Transformers
16 Performing a test
17 Evaluating test results
18 Appendix
18 References
Agilent Technologies
Introduction
Magnetic fields generated at power which electronic equipment is sub- short duration if a protection device
line frequencies are all around us. jected to ensure the equipment con- like a fuse, circuit breaker, or other
The electronic equipment we use is tinues to operate reliably. Stated protection circuitry interrupts the
subjected to these fields in a variety another way, it ensures that electronic flow. High current can also temporar-
of places: residential and commercial equipment is immune to certain com- ily exist during initial power turn-on
locations, industrial installations and monly occurring magnetic fields, of some electronic equipment. A com-
power plants, and medium and high fields that the equipment is likely to paratively high magnetic field will
voltage sub-stations. The source of encounter during operation. The spe- result while the current is flowing,
the magnetic fields is typically the cific fields are those occurring at the but again, for only a short duration.
power line current flowing in conduc- power line frequencies. Although The standard addresses both types of
tors, or occasionally, transformers in immunity limits are not specified in fields (continuous and short dura-
nearby equipment. As such, it is wise this standard, generic immunity stan- tion) by specifying field strengths for
to ensure that electronic equipment dards or product standards state spe- continuously applied fields and even
will operate reliably when exposed to cific limits. The standard also does higher field strengths for short peri-
these power line frequency magnetic not address fields produced at fre- ods of time that could occur under
fields, namely, 50Hz or 60Hz, depend- quencies other than 50Hz and 60Hz, fault or ac turn-on conditions.
ing on the country. The fields may be nor does it address magnetic fields
present continuously, or for short resulting from dc current flow. The method for testing equipment for
duration, so equipment may have to Although it is recognized that the immunity to magnetic fields is to pro-
be tested by being exposed to either current producing the power line duce a controlled magnetic field of
type of field. The proximity of the frequency magnetic fields contains known field strength by driving a
equipment to the source of the mag- harmonics of the line frequency, the large coil with a test generator, and
netic disturbance will also significantly resultant harmonic magnetic fields placing the equipment in the center
affect the equipment's behavior within are thought to be negligible and are of the coil, thereby subjecting the
the magnetic field since the field therefore not considered in the pres- equipment to the magnetic field.
strength is dependent on the distance ent revision of the standard. Proper operation of the equipment is
from the magnetic disturbance. evaluated during the application of
Under normal operating conditions, the field. For equipment that will be
The IEC/EN 61000-4-8 standard power line frequency current flows tested, the IEC/EN 61000-4-8 stan-
addresses these phenomena. Part 4 continuously in conductors, produc- dard provides guidelines for selecting
of the 61000 series refers to "Testing ing continuous or steady power line a magnetic field strength test level,
and measurement techniques," while frequency magnetic fields. When test generator specifications, induc-
Section 8 addresses the "Power fre- some type of fault occurs, the fault tion coil specifications, as well as test
quency magnetic field immunity test." condition can cause comparatively set-up, procedure, and reporting
This standard describes an immunity high current to flow in the conductor. information.
test. It specifies the magnetic fields to This high current may exist for only a
2
Selecting a test level
The IEC/EN 61000-4-8 standard speci- Most household appliances generate Taking these commonly occurring
fies five test levels for testing products magnetic field strengths in the range field strengths for various operating
as shown in Table 1. The level labeled of 0.03 A/m to 10 A/m, with a maxi- environments into consideration,
"X" is an open level that can be called mum of around 20 A/m, all at a dis- Annex C of IEC/EN 61000-4-8 pro-
out in the product specification. tance of 0.3 m from the surface of vides guidance for selecting an appro-
the appliance. At a distance of 1.5 m priate test level. Equipment is classi-
Table 1. Test levels for continuous and from the appliance surface, the field fied based upon the environment in
short duration (pulsed) fields strengths are typically below 0.1 A/m, which it will be operating, and the
with a maximum of 0.4 A/m. corresponding test level is then
Level Continuous Pulsed (1 to 3 sec.) selected. The environments in which
field strength field strength Directly under high voltage lines, field equipment can operate are as follows:
strengths in the range of 10 to 16 A/m
1 1 A/m Not applicable
for every 1000 A flowing in the lines Class 1:
2 3 A/m Not applicable
are encountered. At a lateral distance Environment where a device using an
of 30 m from the lines, the field electron beam is used. Examples
3 10 A/m Not applicable strength range is reduced to 3 to 5 A/m include environments containing CRT
for every 1000 A flowing in the line. monitors or an electron microscope.
4 30 A/m 300 A/m
High voltage sub-stations (220 and
5 100 A/m 1000 A/m 400 kV) can produce field strengths Class 2:
of 9 to 14 A/m near a line carrying Well protected environment.
X Special Special 500 A. In the relay room, 1 to 7 A/m Examples include household, office,
field strengths are encountered, while and hospitals.
Selection of a test level depends on in the equipment room, 0.7 A/m can
the expected operating environment be found. Class 3:
of the equipment under test (EUT). Protected environment. Examples
An appropriate test level for an EUT In power/industrial plants, bus- include commercial areas, small
should be chosen based upon the bars carrying 2200 A produce field industrial plants, or a computer room
magnetic field strengths the EUT is strengths of 6 to 85 A/m, depending of a high voltage sub-station.
likely to encounter in its typical oper- on the distance from the bus-bar
ating environment. In choosing a test (roughly 0.3 m to 1.5 m, with the
Class 4:
level, it is useful to note some com- higher field strength encountered
Industrial environment. Examples
monly occurring magnetic field closer to the bus-bar). Other magnetic
include heavy industrial plants,
strengths for various environments as field sources in this environment pro-
power plants, or the control room of a
reported in Annex D of the standard, duce field strengths from 4 to 30 A/m,
high voltage sub-station.
and as described in the following four depending on the source.
paragraphs. Note that the field
strength decreases as the distance Class 5:
from the source of the field increases; Severe industrial environment.
the amount by which it decreases Examples include the switchyard of
depends upon the configuration of heavy industrial plants, or medium
the source of the magnetic field and voltage and high voltage power sta-
the proximity to the source. tions.
3
Note that the information presented As an example, consider testing an
from both Annex C and Annex D of appliance such as a digital alarm
the standard is labeled as "informa- clock. Since the environment in
tive" information in the standard. which this piece of equipment will
As such, it is considered to be useful typically operate is "household", the
in applying the standard, but not a environment would be a Class 2 envi-
compliance requirement. Information ronment. Corresponding to this class,
labeled "normative" would include a Level 2 field strength from Table 1
requirements that must be met for is shown as 3 A/m continuous, while
compliance. The techniques, proce- a short duration, pulsed test is not
dures, and instrumentation character- required. This is assuming that the
istics specified in IEC/EN 61000-4-8 product is not covered by a more spe-
are considered normative. Specific cific product standard that specifies
limits would be determined by prod- different test criteria.
uct committees and specified in the
corresponding product standard. Once the required field strength to
Additional immunity test information which the EUT must be subjected is
is contained in EN 50082-1 (1997), selected, it is necessary to generate
"Generic immunity standard for resi- this field according to the standard.
dential, commercial, and light indus- For the alarm clock example, proper
try environments," and in EN 50082-2 operation of the clock would have to
(1995), "Generic immunity standard be verified with the clock immersed
for industrial enviroments." in a 3 A/m magnetic field.
4
Generating a test field
The overall purpose of the IEC/EN The induction coil field is developed that varies by no
61000-4-8 standard is to describe a Annex B of the standard (a normative more than