Electromagnetic Emission Measurement – Determination of the Test Configuration of Telecommunications Power Rectifier Systems
Marcus Barthus Azevedo
NMi Brasil
℡ +55 19 3845-5965 / ! +55 19 3845-5964
" nmibarthus @ mpc.com.br
José Claudio de Oliveira e Silva
Emerson Energy Systems
℡ +55 12 380-4263 / ! +55 12 380-4555
" claudio.silva @ emersonenergy.com
Victor Vellano Neto
CPqD – Telecom. Research and Dev. Center
℡ +55 19 705-7097 / ! +55 19 705-6699
" vellano @ cpqd.com.br
Mituo Okamoto
Saft Power Systems
℡ +55 11 6100-6350 / ! +55 11 6100-6338
" mituo.okamoto @ saftnife.com.br
Abstract - This paper presents data of investigation of several experiments on the determination of the Minimum Representative System
(MRS) for electromagnetic emission of large Power Rectifier Systems,
which are by nature populated with identical rectifier modules. Two
systems were used as study objects. The work is related to standardization activities in Brazil and trigged by the fact that most of the
EMC test sites are not able to provide enough a.c. current for testing large power systems. The question of the validity of testing
EUT’s populated with small number of rectifiers within the recommendations of the emission standards has arisen in the standardization
commission. The problem of determining a MRS is known - it can be
very time consuming and therefore costly - so for the commission this
work is in essence a feasibility study. The four parties, CPqD, NMi
Brasil, EES and SAFT Power have conducted some tests and studies aiming to provide the commission with solid basis for adopting or not
such practice.
1
Introduction
In the last few years, Brazil significantly extended the development of technical specifications of energy systems and, in special, high frequency rectifying units and systems. Among the new requirements are those related to Electromagnetic Compatibility (EMC) and in there, the electromagnetic
emission that was initially linked to the protection of the radiofrequency spectrum used for broadcast
telecommunication services and that now assumes a more and more important role in complex information technology (ITE) installations.
In general, an electromagnetic emission requirement must define the emission limits and testing procedures. The Brazilian Standard NBR 12304 [2], one of the basic references adopted in the standard
for rectifying systems for telecommunications, comprises most of the items needed, e.g. it establishes
limits, defines appropriate test sites and test equipment, test procedures and a general definition for
the configuration of the Equipment Under Test (EUT). As any general definition, it lacks details, in
our case, on how to define representative configurations of large power systems, what may give rise to
a uncontrolled variety of interpretations and technical judgements, thus jeopardizing the objective of
the standard, interfering with the ability of compare test results and on the settlement of a common set
of rules. In addition to the inherent difficulty associated with the search for the Minimum Representative System (MRS), large power systems impose another test difficulty, that is the high a.c. current
demanded from the test house facility. Trying to solve that, the Brazilian standardization commission
analyzed several other international publications, among which are those generated by: CISPR
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Electromagnetic Emission Measurement - Determination of the Test Configuration of Telecommunications Power Rectifier Systems
J. C. Oliveira e Silva, M. Barthus Azevedo, M. Okamoto,
V. Vellano Neto
(Comité International Special des Perturbations Radioelèctrique), ETSI (European Telecommunication Standardization Institute), CENELEC (Comité Européen de Normalisation Electrotechnique),
and ITU-T (International Telecommunication Union) - Group V, in charge of the recommendations
related to electrical protection and EMC. The relevance of Group V is that it focuses on those requirement applicable to telecommunication equipments, taking into account their electromagnetic environment as well as functional aspects, etc.. Therefore, they actually complement the general and
basic requirements published by IEC/CISPR. Among the documents analyzed on the subject, the most
relevant are listed as references [1], [2], [3], [4], [5], [6] and [7].
CISPR publications are generally considered basic recommendations. CISPR 22 together with the
ITU-T – k38 and ETS - EN 300 127 are the main references for the definition of applicable tests and
procedures of large systems adopted by the telecommunications sector in Brazil.
1.1
Electromagnetic Emissions Requirements
The NBR 12304, based on the first edition of CISPR22, establishes emission limits and test procedures for ITE, and is adopted for rectifying systems for telecommunications. The third edition of
CISPR Publication 22 available today, incorporates details of measurements of telecommunications
lines, validation of test site and test distances, and maintain the core and principles prescribed in NBR
12304.
It is important to understand that, even though a general purpose power system does not fall into the
scope of CISPR 22, it is adopted when it turns to be a system placed in the same electromagnetic environment as telecommunication equipments, where emissions levels allowed by CISPR 11 may be considered too high.
On those standards, Class B is defined for residential environment equipment or equipment connected
to the low voltage public network, where the emission levels must be lower due to the proximity to
radiocommunications, receivers and other communications systems. Class A allows a higher level of
emissions and therefore can cause interference in residential environment, being appropriate for those
equipment installed in business or light industrial environment, where they are not connected to the
low voltage public network and the distance to radiocommunications, receivers and other communications systems is at least 30 meters.
1.1.1
Radiated and Conducted Emissions Limits
Table 1 and Table 2 present the limit lines for conducted and radiated electromagnetic disturbances
respectively, valid for both NBR 12304 and CISPR 22.
CONDUCTED (150 kHz to 30 MHz)
Radiofrequency Disturbance Limits [dB(µV)]
Frequency
Range
[MHz]
0,15 ~ 0,50
0,50 a 5
5 a 30
Class A
QuasiAverage
Peak
79
73
73
66
60
60
Class B
QuasiAverage
Peak
66 ~ 56
56
60
56 ~ 46
56
50
Table 1 – CISPR 22 Conducted Emission Limits
Note:
2
RADIATED (30 MHz to 1 GHz)
Quasi-Peak Limit
Frequency
[dB(µV/m)]
Range
[MHz]
Class A
Class B
30 ~ 230
230 ~ 1000
40
47
30
37
Table 2 – CISPR 22 Radiated Emission Limits
It is important to understand that according to the class definitions in 1.1, equipment to be installed
on telecommunications centers are generally considered Class A, and equipment as outdoor cabinets or those installed in subscriber premises must be considered Class B.
J. C. Oliveira e Silva, M. Barthus Azevedo, M.
Okamoto, V. Vellano Neto
1.2
Electromagnetic Emission Measurement - Determination of the Test Configuration of Telecommunications Power Rectifier Systems
General Disturbance Measurement Test Details
CISPR 22 as well as most of the emissions standards require that the EUT configuration and exercising are such that the maximum emissions are found and recorded to be compared with the limits. For
Power Rectifiers used in Telecommunications, that includes but is not limited to test under all possible output loads and all possible rated input voltages for all ‘typical’ configurations, thus recommending an unaffordable number of measurements.
CISPR 22 establishes limits, defines appropriate test sites and test equipment and test procedures. In
special, it specifies that conducted emission are measured using an Artificial Mains Network (AMN) 1
because it provides the necessary decoupling of the measured noise from the a.c. voltage and provides
a well defined impedance (refer to Figure 1) to the EUT as a noise source. In cases where the current
is too high (say above 100 A, as it is usually the case when measuring conducted disturbances on d.c.
terminals) so that a AMN connection is not possible, the Brazilian committee adopted the voltage
probe method (refer to Figure 2) defined in [1].
Rede de Alimentação
50 µ H
C
250 µ H
Terminação de
50 - Ω
medidor de
perturbação
XC< 1500Ω
Rede de
Alimentação
ESE
0,25 µ F
8µF
1,2 µ F
1000 Ω
5Ω
10 Ω
Figure 1 – Typical AMN schematic
(1500 - R) Ω
X1>R
R
Instrumento
de medição
Figure 2 – Typical Voltage Probe
All other specifications remains according to CISPR 22.
1.2.1
Configuration of the EUT
The definition of the test configuration is as important as the limit settled by a standard. As mentioned
before, [2] and [3] generally defines the configuration of the Equipment Under Test (EUT), allowing
different interpretations and technical judgements. To solve that, other specific references related to
large equipment emission measurement from ITU-T and ETSI was brought to light. It is important to
mention that the recommendations of test configurations may not be feasible or viable since they may
require too many rectifying units and unachievable load requirements. CISPR publications recommends:
•
The EUT shall be configured, operated and its cabling arranged in a way that is consistent with
typical applications and that the maximum emissions be generated;
•
Where not specified, the EUT must be configured, installed, arranged and operated in a manner
consistent with typical applications. Interface cables/loads/devices shall be connected to at least
one of each type of interface port of the EUT, and where practical, each cable shall be terminated
in a device typical of actual usage;
•
Where there are multiple interface ports of the same type, additional interconnecting cables/loads/
devices may have to be added to the EUT depending upon the results of preliminary tests. The
number of additional cables should be limited to the condition where the addition of another cable
does not decrease the margin a significant amount (for example 2 dB) with respect to the limit.
The rational for the selection of the configuration and loading of ports shall be included in the test
report;
•
Where there are multiple interface ports all of the same type, connecting a cable to just one of that
type of port is sufficient, provided it can be shown that the additional cables would not significantly affect the results.
1
AMN are also called Line Impedance Stabilization Network (LISN)
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Electromagnetic Emission Measurement - Determination of the Test Configuration of Telecommunications Power Rectifier Systems
J. C. Oliveira e Silva, M. Barthus Azevedo, M. Okamoto,
V. Vellano Neto
In addition to that, [7] defines a minimum representative system:
•
The minimum representative system is a system which contains the minimum number of units
needed to perform all functions specified for the system.;
The original text of [7] is given in [8], where a procedure for the determination of the minimum representative system is established:
•
Physically large systems are modular in nature, i.e. they will generally be increased in size (and
operational function) by the addition of like units. To ensure that the EUT is representative of installed systems, in terms of function and electromagnetic radiation, tests shall be repeated with the
EUT configured with additional units.
•
If, by adding additional units, which generates synchronized noise, the emission levels do not increase 4 dB or more above the original maximum measured values, independent of frequency,
then a minimum representative system in terms of radiation has been achieved. The additional
units shall be composed to the largest possible extent of highest radiation sources, but they shall
be typical of realistic installation. If, with the increase of additional identical units, the radiation
increases by more than 4 dB, then further additional units shall be added until the increase is less
than 4 dB.
•
After the addition of identical units (as shown in figure 2 of [8]), the measured field levels from
the representative system shall not increase beyond compliance limits.
Another useful source of information is the EMC requirements for UPS [4]:
•
The measurement shall be made in the operating mode producing the largest emission in the frequency band being investigated consistent with normal applications. UPS operating modes, normal mode and stored energy mode shall be investigated covered;
•
An attempt should be made to maximize the emission by varying the test setup configuration of
the test sample;
•
UPS AC outputs shall be loaded with linear load capable of exercising the EUT for any load
condition within its output rating.
2 Proposal
The technical commission responsible for the Brazilian draft standard for switched rectifiers and
power systems up to 2400 A d.c. (project number 03:012.02-027) has considered the introduction of a
procedure to determine the MRS in emission tests. The main problem resides in testing large power
systems.
The flowchart in Figure 3 has been proposed in the draft standard. If the maximum output power that
can be drawn from the EUT is lower than 50 % of its maximum capacity, no matter whether the MRS
was reached or not, the CISPR 22 limits are reduced as indicated in the flowchart.
The proposal implies then on a penalty to the manufacturer, driving then to force test sites to increase
their current capacities. It may in fact happens as one realize that the emission limits can be tougher if
tested in a test house with lower ampacity.
In the other side, even risking to modify a standard, adding a penalty for the extrapolation of results of
a partial test is important to:
•
Have a fixed and reasonable criteria, based on the equipment itself;
•
Use the test resources available to judge the performance of the EUT and still have a good correlation to the reality, without opening a escape channel the to norm;
•
In line with the main objective of the standard, help protecting the electromagnetic environment
in an efficient manner.
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Electromagnetic Emission Measurement - Determination of the Test Configuration of Telecommunications Power Rectifier Systems
J. C. Oliveira e Silva, M. Barthus Azevedo, M.
Okamoto, V. Vellano Neto
FLOWCHART - Determination of minimum representative (power) system for electromagnetic emission test.
n
Nr = Nmax
can be tested?
y
Nr = number of rectifiers composing the system
under test (rectifiers at full power)
Nmax = maximum number of rectifiers that can
equip the system under test
Nr = 1 or Minimum
Check & Record
disturbances with
margin to the limit
< 10 dB
System under test = a power system comprising all
functional parts that can equip the system,
e.g. rectifiers, DC distribution and
supervision units, in a configuration
consistent with practical applications. If the
system can grow by adding more cabinets,
then at least two cabinets shall be tested. If
more than two cabinets are required to permit
that all functional parts be included, then a
sufficient number of cabinets shall be tested
so as to include all functional parts.
According to CISPR22, all ports shall be
connected and exercised.
Nr = Nr+1
∆ > + 20 dB ?
Nmax
n
Nr ≥ Nmax/2
?
n
y
y
y
MRS
Minimum
Representative
System
Test lab
capable of powering
one more rectifier
?
n
(corrected limit)
L - 10 log (Nmax / Nr)
L = specified emission limit
as per CISPR 22
RECORD - Final Measurements
Figure 3 – Proposed flowchart for determination of minimum representative system (MRS) for EMI test.
2.3 Test Samples
The two test samples used for the purposes of this study are defined in Table 3.
EUT 1 (EES)
EUT 2 (Saft)
Manufacturer
Emerson Sistemas de Energia Ltda.
Saft Power Systems Ltda.
Model
Sophia Plus 24V / 25,5kW
SR 1200 / +24V / 2.4.3
Rectifiers
15 x 1700W ( 63 A @ 27 V)
12 x 100 A / +24 V
AC Input
Nominal Voltage
220V, 3 phase
220 V, 3 phase
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Electromagnetic Emission Measurement - Determination of the Test Configuration of Telecommunications Power Rectifier Systems
Frequency
J. C. Oliveira e Silva, M. Barthus Azevedo, M. Okamoto,
V. Vellano Neto
50 – 60Hz
45 Hz a 65 Hz
DC Output
Nominal Voltage
24V
24 V
Current
950 A (@ 27 V)
1200 A
Photo for
reference only
Table 3 – Test sample basic specifications
2.4
Test Conditions and EUT Configurations
In general lines the system configuration started with a small number of rectifiers, three for EUT 1
and just one for EUT 2. The system grew by the addition of rectifiers, one by one, according to the
specified or usual manner these systems grow, so that every step constituted a tested configuration.
Preliminary emission measurements (fixed azimuth) were performed for each configuration. The
maximum emission direction (azimuth and antenna height) was searched in some of the tested configurations.
The system output current was set to a value corresponding to the maximum power that could be provided
by the number of installed rectifiers. Rectifier positions in the cabinets as per Figure 4 and Figure 5.
1
4
2
5
3
6
7
8
9
10
11
12
13
14
15
Figure 4 - Rectifier positions of EES, Sophia+ (EUT1)
6
12
11
10
9
8
7
6
5
4
3
2
1
Figure 5 - Rectifier positions of Saft, SR 1200 (EUT2)
Electromagnetic Emission Measurement - Determination of the Test Configuration of Telecommunications Power Rectifier Systems
J. C. Oliveira e Silva, M. Barthus Azevedo, M.
Okamoto, V. Vellano Neto
2.5
Emission Test Procedure
Two types of radiated emissions measurement was performed, one that is basically a preliminary test,
consisting on recording the measurement on an fixed antenna height and azimuth, used only to compare data, and the standard emissions measurement described on 2.5.1, used for final measurement
according to the standard.
The conducted emissions test procedure is much simpler, being the only remark to the standards that
the 3 phases were always maximized (peak hold) and all data represents the maximum reading. Unless
otherwise specified no reference to phase is noted.
2.5.1
Standard Radiated Emission Maximization Procedure
h = antenna height;
hmax = h respective to maximum emission
θ = azimuth;
θmax = θ respective to maximum emission
•
For θ = 0°, a preview of the emission is done (just visual monitoring on the receiver screen) while
h changes from 1 to 4 m, determining hmax for each antenna
•
With the antenna at hmax , the radiated emission is acquired in peak hold mode so that the maximum emission values are accumulated and recorded while θ changes from 0 to 360°, for both frequency ranges: 30 – 200 MHz and 200 – 1000 MHz. . The emission values recorded are not at a
given fixed θ, so θmax is not determined at this point.
•
For the highest emission frequencies and/or for those close to the emission limit (margin < 6 dB),
a fine search of maximum emission is performed with respect to h and θ. The receiver is set to
zero-span and tuned at the highest emission frequency(ies) for h as well as for θ scanning. The
sweep times (in the order of seconds) are adjusted so as to match the time required for h to move
from 1 to 4 m and then for θ to change from 0 to 360°. Where θmax is achieved, a final antenna
scan is performed, so that a very clear indication of hmax and θmax is obtained on the receiver
screen.
•
The procedure is repeated for horizontal polarization.
hmax and θmax are then well determined for each particular selected high emission frequency.
2.6 Investigation Test Results
The data that follows is also a result of the learning process taken during the test. It was planned that
the data analysis would be performed with all peak measurement and it was noticed, during the process of testing EUT 1, that no coherence was achievable with that approach, requiring the test to be
performed with Quasi-Peak measurement. Since Quasi-Peak measurement is time consuming, decision was taken to perform only on the highest emissions. Tests performed on EUT 2 already took the
EUT 1 findings and all data was planned for Quasi-Peak.
2.6.1
Radiated Emissions
3
4
Measured Frequencies [MHz]
Quasi-Peak Limit
Quasi-Peak
Peak
CISPR22 - A Corrected 1)
84 90 96 129 144 149 152 156 163 176
35,8 31,2 33,6 22,1 23,8 23,8 19,5 19,4 19,3 23,4
40
33,0
35,5 30,6 34,0 18,3 23,4 22,7 18,2 18,3 21,4 22,8
40
34,3
5
6
35,6 31,4 34,2 23,1 22,2 23,8 19,7 18,5 20,3 23,2
35,0 31,6 32,6 21,2 22,1 23,7 18,9 21,3 20,8 25,7
40
40
35,2
36,0
7
34,2 31,6 32,1 22,8 22,3 23,2
40
36,7
Number of
Rectifiers
(NR)
20
19,6 19,2 24,2
7
Electromagnetic Emission Measurement - Determination of the Test Configuration of Telecommunications Power Rectifier Systems
1)
8
9
35,1 31,2 33,2
15
37,7 32,1 34,4
J. C. Oliveira e Silva, M. Barthus Azevedo, M. Okamoto,
V. Vellano Neto
24 26,2 28,3 24,6 31,6 26,1 28,6
22,3 24,8 26,4 22,3 24,3 22,7 26,3
21
27,2 28,9
24
23,3 28,5 26,5
40
40
37,3
37,8
40
40,0
Limit corrected as proposed to 10 log (NR / Total of Rectifiers of the System under Test)
Table 4 – EUT 1 – Highest radiated emissions, vertical polarization
Number of
Quasi-Peak Limit
Measured Frequencies [MHz] (Quasi-Peak Only)
Rectifiers
30
31
32
228
CISPR22 - A Corrected 1)
(NR)
1
33,7
34,3
28,3
17
40
29,2
2
33,8
34,2
28,8
26,6
40
32,2
3
35
35,4
29,8
28
40
34,0
4
35,6
34,5
33,3
28
40
35,2
5
34,5
35,8
33,9
27,8
40
36,2
6
35,1
34,9
33
28,2
40
37,0
7
35,6
34,6
31,9
28,4
40
37,7
8
35,2
34,8
32,8
28,5
40
38,2
9
35,7
35,6
34,1
27,8
40
38,8
12
36,7
35,9
34,8
27,4
40
40,0
1)
Limit corrected as proposed to 10 log (NR / Total of Rectifiers of the System under Test)
Table 5 – EUT 2 – Highest radiated emissions, vertical polarization
EUT 1 - Radiated Emissions (Vertical Polarization) - Peak and Quasi-Peak Measurements
42
QP LIM Cispr22 A
37
Corrected Lim
emission (dBuV/m)
129 MHz
144 MHz
32
149 MHz
152 MHz
156 MHz
27
163 MHz
176 MHz
84 MHz Q-Pk
22
90 MHz Q-Pk
96 MHz Q-Pk
17
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
number of Rectifying Units
Graphic 1– EUT 1 – Highest radiated emissions, vertical polarization
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Electromagnetic Emission Measurement - Determination of the Test Configuration of Telecommunications Power Rectifier Systems
J. C. Oliveira e Silva, M. Barthus Azevedo, M.
Okamoto, V. Vellano Neto
EUT 2 - Radiated Emissions (Vertical Polarization) - Quasi-Peak Measurements
41
40
39
38
QP LIM CISPR 22 A
37
Limite Corrigido
emission (dBµV)
36
35
30 MHz
34
33
31 MHz
32
32 MHz
31
30
228 MHz
29
28
27
0
1
2
3
4
5
6
7
8
9
10
11
12
13
number of Rectifying Units
Graphic 2 – EUT 2 – Highest radiated emissions, vertical polarization
2.6.2
Conducted Emissions
Number of
Rectifiers
(NR)
Average Limit
Measured Frequencies [MHz] (Peak Only)
0,15
0,16
0,55
CISPR22 - A Corrected 1)
3
54,6
54,5
49,9
66
4
57,9
57,8
47,7
66
5
57,9
57,3
46,7
66
6
59,3
59,1
44,6
66
7
57,7
58,3
42,4
66
8
56
57,9
44
66
9
54,9
56
46,8
66
15
53,2
54
44,7
66
1)
Limit corrected as proposed to 10 log (NR / Total of Rectifiers of the System under Test)
59,0
60,3
61,2
62,0
62,7
63,3
63,8
66,0
Table 6 – EUT 1 – Highest conducted emissions
Number of
Rectifiers
(NR)
0,83
0,86
1
49,3
44,6
48,4
60
49,2
2
3
4
5
6
7
8
9
54,4
55,5
55,4
55,4
55,2
56,4
54,8
56,9
50
52,7
53,1
56,3
55,3
56
55,4
55,4
39,5
57,2
53,6
51,7
49,6
48
45,7
44
60
60
60
60
60
60
60
60
52,2
54,0
55,2
56,2
57,0
57,7
58,2
58,8
Measured Frequencies [MHz] (Peak Only)
0,92
54,1
54,8
54
53,5
53,7
54
5,57
Average Limit
7,42
59,3
57,4
55,9
52,5
47
48,1
CISPR22 - A Corrected 1)
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Electromagnetic Emission Measurement - Determination of the Test Configuration of Telecommunications Power Rectifier Systems
12
1)
55,8
J. C. Oliveira e Silva, M. Barthus Azevedo, M. Okamoto,
V. Vellano Neto
55,8
40,8
50,6
60
60,0
Limit corrected as proposed to 10 log (NR / Total of Rectifiers of the System under Test)
Table 7 – EUT 2 – Highest conducted emissions
EUT 1 - Conducted Emissions - Peak Measurements
66
64
emission (dBuV)
62
60
Avg LIM Cispr 22 A
58
Corrected Lim
56
0,1573 MHz
54
0,1615 MHz
52
0,55 MHz
50
48
46
44
42
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
number of Rectifying Units
Graphic 3 – EUT 1 – Highest conducted emissions
EUT 2 - Conducted Emissions - Average Measurements
62
58
Avg LIM Cispr 22A
54
emission (dBµV)
Corrected LIM
0,83 MHz
50
0,86 MHz
46
0,92 MHz
5,57 MHz
42
7,42 MHz
38
34
0
1
2
3
4
5
6
7
8
9
10
11
12
13
number of Rectifying Units
Graphic 4 – EUT 2 – Highest conducted emissions
2.7 Final Test Results
The final test graphic results corresponding to the investigation data (vertical polarization / maximum
emission only) are added below to help identifying each EUT radiated and conducted emission pattern.
10
J. C. Oliveira e Silva, M. Barthus Azevedo, M.
Okamoto, V. Vellano Neto
2.7.1
EUT 1 - Radiated and Conducted Test Results
Graphic 5 – EUT 1 Final Conducted EMI
2.7.2
Electromagnetic Emission Measurement - Determination of the Test Configuration of Telecommunications Power Rectifier Systems
Graphic 6 – EUT1 Final Radiated EMI, Vert. Pol.
EUT 2 - Radiated and Conducted Test Results
Graphic 7 – EUT 2 Final Conducted EMI
Graphic 8 – EUT2 Final Radiated EMI, Vert. Pol.
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Electromagnetic Emission Measurement - Determination of the Test Configuration of Telecommunications Power Rectifier Systems
3
J. C. Oliveira e Silva, M. Barthus Azevedo, M. Okamoto,
V. Vellano Neto
Data Analysis and Discussion
The most relevant findings from the investigation data and from the measuring experiences for those
two study objects, were:
•
The reduction of the limit has to be reconsidered carefully. The two systems passed all tested configurations but would fail if a small number of rectifiers were tested according to the flowchart in
Figure 3, as Graphic 1, Graphic 2 and Graphic 4 shows;
•
To really take advantage of the flowchart, it would be recommended that the emission from the
rectifiers and other non-modular sources, like supervision unit, should be separated in the analysis;
•
The MRS can not be easily found on the receiver screen during the execution of the tests. It was
necessary to tabulate the emission of the frequencies within 10 dB margin to the limit and plot
them so as to get a better view of the emission increase as the number of rectifier increases. A
trend analysis may be helpful. In other words, a rather elaborate assessment of data is required
along the measuring process in order to give directions for the continuation of the tests, turning
the test longer than an ordinary emissions test.
•
Quasi-peak measurements provide better-behaved results and therefore may be necessary if the
MRS is searched for. It also means longer tests.
•
The behavior of the emissions does not follows a trend line like it was predicted by the authors of
this paper. It is in fact highly unpredictable, sometimes even leading to the exit of the flowchart
on a wrong point (points where much higher emissions not yet appeared);
•
There was only one pattern repeated on the two sample tested: the results with 50 % and 100 %
population were somewhat coherent, with differences within the expected values (< 3 dB increase
from 50 % to 100 %). No new or unexpected frequency appeared from one to the other.
The change in the direction of maximum emission as the modules are introduced was not studied in
this work. Such effect can make the data book impossible to analyze. The maximization of the emission as modules are introduced is very time consuming and can by no means be adopted at each step
of the MRS search in ordinary tests.
4 Conclusion
It must be realized that testing large power systems at their maximum configuration may be prohibitive sometimes and that testing poorly equipped systems is not reasonable and may be risky considering that, besides running the risk of spectrum pollution, the test may be rejected by one or another certification agency or customer.
Searching for MRS as proposed is time consuming and may lead to wrong solution. The authors of
this paper recommend that:
a) Emissions test be performed on a System defined as follows:
System under test = a power system comprising all functional parts that can equip the system, e.g.
rectifiers, DC distribution and supervision units, in a configuration consistent with practical applications. If the system can grow by adding more cabinets, then at least two cabinets shall be
tested in order to include the interconnection cable. If more than two cabinets are required to permit that all functional parts be included, then a sufficient number of cabinets shall be tested so as
to include all functional parts.
b) The above system must be tested fully and halfway populated, at full load and other conditions
verified. That is the only way to guarantee full compliance to the standards.
c) When the above is not possible, the test should proceed as close as possible to that balancing between the two extreme (population-wise) test conditions, not being recommended that less than
half a system is tested.
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J. C. Oliveira e Silva, M. Barthus Azevedo, M.
Okamoto, V. Vellano Neto
Electromagnetic Emission Measurement - Determination of the Test Configuration of Telecommunications Power Rectifier Systems
d) If after all, the test can only be performed on systems as defined above less populated then 50%, a
penalty as the one suggested on the flowchart of Figure 3 be adopted.
5 References
[1] CISPR 11 : 1997 – Limits and methods of measurement of radio disturbance characteristics of
ISM equipment
[2] NBR 12304 : 1992 – Limites e Métodos de medição de características radioperturbação de Equipamento de Tecnologia da Informação.
[3] CISPR 22 : 1997 - Limits and methods of measurement of radio disturbance characteristics of
information technology equipment
[4] EN 50091-2 : 1995 – Uninterruptible power systems (UPS) – Part 2: EMC requirements
[5] ITU – K48 – “Product Family EMC Requirements For Each Telecommunication Network Equipment”
[6] ITU-T – k38 – Radiated emission test procedure for physically large systems
[7] Draft EN 300 127 : 1998 – Electromagnetic compatibility and Radio spectrum Matters (ERM) Radiated emission testing of physically large telecommunication
[8] ETS 300 127 : 1994 – Equipment Engineering (EE) - Radiated emission testing of physically
large telecommunication systems
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