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ISSN 1843-6188
Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 1 (12)
RADIOFREQUENCY DISTURBANCES RADIATED AND INJECTED
IN A POWER LINE BY A HIGH VOLTAGE EQUIPMENT
Marian COSTEA, Ileana BĂRAN
Politehnica University of Bucharest
E-mail: [email protected]
connected to them: insulators strings, line fittings,
switching equipment, surge arresters etc. For medium
voltage lines having low values of the surface voltage
gradient on phase conductors, the disturbing
radio-frequency level of the line is practically determined
only by the equipment connected to them. Basically,
equipment connected to the line act as high-frequency
current sources. The superposition of high-frequency
currents injected by each of the n-contributors
(conductors and equipment) determines the overall
disturbing effect of the line. As the individual emissions
are independent, the resulting interference current can be
computed by applying the law of quadratic summation of
non-correlated signals. If the disturbing level of an
overhead line can be measured by means of the radiated
radiofrequency field, the estimation of each component’s
contribution (e.g. insulation string) is not easy to perform.
CISPR 18-2 standard establishes the general framework
for making such a determination and IEC 60437 standard
specifies the method for insulator strings. Contribution to
the overall overhead line radio-frequency disturbing level
of given equipment is assessed measuring the conducted
disturbances generated by this in a standard circuit that
simulates the wave impedance of the line and in a
shielded laboratory, which can provide a low background
noise. The solution is subject to question in several
respects. In addition, the test implies a number of
precautions that make it expensive (not only because of
the requested time to perform it).
This paper aims to investigate the correlation between the
radiated and the injected disturbances generated by
equipment connected to a line. Rationale of this approach
lies not only in knowing how a given equipment
contributes to the overall disturbance level of the
overhead line, but also to propose a simple experimental
method for its evaluation.
Finding a correlation between electrical quantities due of
corona discharge and other not yet standardized quantities
or physical records (such as UV images) was a concern
also for other works [2-3] in order to offer new tools for
investigation or diagnosis.
Abstract: The paper attempts to identify correlations between
radiated disturbances generated by high-voltage equipment
and the conducted disturbances injected by the same
equipment into an overhead line to which it is connected.
Nowadays, according to relevant standards, the radio
frequency disturbances caused by such an equipment are
evaluated by means of a specified voltage across a resistor
which simulate the wave impedance of the line although the
overall effect is evaluated in the vicinity of the overhead line
by means of radiated disturbances. This voltage is measured
using an EMI receiver with quasi-peak detector. Rigorous
experimental arrangement is described by the standards and
measurements must be done in a shielded high voltage
laboratory. Because RIV measurement procedure specified
above, is relatively complicated, the authors try to determine
the correlation between the conducted and radiated
disturbances of two insulator sets in order to identify a new
method of measuring the radiofrequency disturbance level of
high voltage equipment or at least one pre-test methods,
useful for comparing equipment of the same type.
Keywords: radio interference voltage, insulator string, quasipeak detector, high frequency electric field probe
1. INTRODUCTION
Overhead lines are sources of low frequency radiated
disturbances represented by power frequency electric and
magnetic fields in normal operation conditions and also
radio frequency disturbance sources due to corona
discharge and associated phenomena (micro-sparks in
areas of contacts between insulating materials and metal
fittings or discharges due to imperfect contacts).
High frequency disturbing level of an overhead line is
theoretically estimated through calculations and then
evaluated by measurements as described in CISPR 18-1
Publication [1]. To perform measurements in situ, a
magnetic field antenna is used and its location is also
specified versus the position of lateral conductors. Use of
these antennas is justified by the fact that the magnetic
field component near the line is more stable, while the
electric field component varies quickly, due to primary
source character (electric dipole type). This source is the
discharge on the conductor surface or between different
components of the equipment.
Radio-frequency magnetic field component is determined
by adding the contributions of all high-frequency currents
travelling along conductors. These currents are injected
by phase conductors themselves and by equipment
2. CONDUCTED RADIO-FREQUENCY
DISTURBANCES GENERATED BY STRING
INSULATORS
Various national standards set limits, expressed in dBµV,
for the radio-frequency disturbances generated by
equipment. The total interference current responsible for
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Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 1 (12)
the radio frequency disturbances caused by the
equipment, fittings and phase conductors (Ioverall) is
adequately expressed as quadratic summation of high
frequency (HF) currents, Ii , individually injected into the
line by each of the overhead line’s components, [4]:
I overall 
 m   n   p 
kmnp  k x2  k y2  k z2  
 
 

 w   h   l 
2
f mnp 
n
 I i2 .
kmnp
2
2
c0 
2
2
c0  m   n   p 
     
2  w h  l 
2
(5)
2
(6)
where, in addition to previously defined geometric
dimensions, c0 is the wave propagation speed in air. If in
expression (5) c0 = 300 m/μs and geometric dimensions
are given in meters, resonant frequencies result in MHz.
The modes spectrum in terms of cavity’s natural
frequencies is represented in Figure 1. For the TE-mode
m and n are allowed to be 0 but p is not allowed; for
TM-mode neither m nor n is allowed to be zero but p is
allowed to be 0.
Standing waves that occur in the resonant cavity will be
characterized by the maximum electric field in the center
of symmetry of the enclosure and maximum values of
magnetic field close to metal walls.
(1)
i 1
Assuming that the total interference current of a line
span is determined by a relationship as follows,
2
2
,
I overall  I span
 I string
ISSN 1843-6188
(2)
where Ispan is the interference current due to conductors
and Istring the current generated by insulator strings, the
condition that the overall disturbance level of the line
expressed as
PLoverall  20  log 10 I overall I ref  1 µA  [dB], (3)
to be only slightly modified by the presence of insulator
sets is given by the condition
I string  1 3I span
(4)
in which case the additional contribution of the insulator
string (for a given disturbing level due to conductors) is
only approx. 0.5 dB. Medium voltage overhead lines
have very low values of electric field on the conductors’
surface, making it practically impossible the occurrence
of corona discharge. In this case, the disturbing of the line
is determined solely by the contribution of equipment
connected to the line.
Figure 1. Natural frequencies for the first 16 TE and
12 TM modes of the testing hall.
3. THE EXPERIMENTAL ARRANGEMENT
Theoretically, there are an infinite number of resonant
frequencies, but only some of them (usually having the
lowest frequencies) may present technical interest. For
the testing hall, the lowest TE-mode or dominant mode is
TE101 with a wavelength of 36.1 m (frequency 8.3 MHz).
The next mode is TM110 (the lowest TM-mode) with a
wavelength of 24.0 m (frequency 12.5 MHz).
Both frequencies are greater than the measuring
frequencies (0.5 MHz and 1 MHz) recommended by
CISPR 18-2 for RIV tests. Therefore, the occurrence of a
resonance phenomenon on the measuring frequencies
specified above is not to be expected. Moreover, the
modes of propagation in the laboratory are surely affected
by the presence of other existing equipment, not only the
high-voltage AC installation used during the experiments.
Experimental arrangement was build as for classical radio
interference voltages (RIV) test but simultaneous and
comparative measurements were performed using both an
EMI receiver, to measure the conducted disturbances and
a high frequency electric field probe. The last measuring
system was placed in different positions in respect to the
source of disturbance, i.e. insulator string. Measurements
were made in a shielded laboratory, having the
dimensions: length l = 42 m, width w = 20 m and height
h = 15 m. As known, within a shielded enclosure
resonance phenomena may occur, depending on the
geometry of the enclosure. Thus, a parallelepiped
enclosure with width w (placed parallel to the x
direction), height h (parallel to y), and length l (parallel to
z) h < w < l, can be regarded as a rectangular cavity. In a
rectangular cavity, harmonic electromagnetic fields can
exist only as standing waves in all the three directions of
the space, with angular wave numbers kx = m/w,
ky = n/h, kz = p/ℓ m, n and p being integers (0 included)
which customize the propagation modes for the
transverse electric-TE or transverse magnetic-TM field.
The natural angular wave number of the cavity and the
natural (or resonant) frequency are given by
3.1. The standardized RIV measuring circuit
The structure of RIV measuring circuit according to
CISPR 18-2 Publication can be seen in Figure 2. The
requirements for the main components of the circuit are:
 the resistive load RL which simulate the surge
impedance of the line must have 300 Ω and it is divided
into two resistors. In order to adapt the transmission line
to the input resistance of the receiver, Rm (= 50 ) the
condition R1 = Rm = Zc must be fulfilled (Zc is the surge
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Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 1 (12)
ISSN 1843-6188
impedance of the coaxial cable). Consequently,
RL = R2 +R1/2;
 the impedance of the high voltage arm of the
measuring circuit, ZS, could be either an L–C series
circuit, tuned to fm the measuring frequency
recommended by the above specified standard, or a
coupling capacitor. This last solution (a most practical
one), was adopted in the High Voltage Laboratory of
UPB where the experiments were performed. If the
solution with coupling capacitor is adopted its
capacitance must be at least five times greater than the
capacitance to earth of both EUT and high voltage
connections;
 the total impedance of the measuring circuit must have the
magnitude Z s  RL  300  40  , and the phase   200 ;
the resistor R1 is transmitted through the coaxial
measuring cable, adapted at both ends, to the measuring
set. The circuit characteristics are chosen such as the
largest part of disturbance currents id to be forced to pass
through the impedance Zs and therefore through the
measuring resistance. Finally, the measuring values (Vm)
must be reported considering that the interference current
id is injected only in the simulated surge impedance of the
line and through the self-capacitance of the tested
equipment, Ce , to the ground.
Consequently, the final result of such a test must be
calculated using the expression [4]:
 in order to suppress the high frequency currents to
the high voltage test transformer, a rejection filter, F,
must be installed. It could be either an L – C parallel
circuit, tuned to fm or an inductor damped by parallel
resistors. It’s insertion attenuation at fm must be greater
or at least equal to 35 dB, in both directions;
where Vm and V are voltage values corresponding to the
reference measuring voltage Ur at EUT terminals. The
term A expressed in [dB/μV] represents the attenuation
due to the testing circuit. The term must eliminate the
influence of the real testing circuit compared to the ideal
one which contains only the resistive load RL. Regarding
the correction factor R, it expresses the fact that the read
voltage Vm is not the drop voltage value across the
resistance RL = 300 Ω, as stipulates the standard, but
across the equivalent resistance R1/2. It is computed as:
R
(8)
R  20 log 10 L [dB].
R1 /2
is
V [dB/μV/300Ω] = Vm[dB/μV] + A[dB/μV] + R[dB]
Co.
F
im
ZS
Cd
EUT
id
ie
Tr.
D
Ce
Measuring
receiver
R2
MS L3
R1
Cc.
(Zc)
(7)
Rm
If the term R is easy to calculate, the attenuation A
due to the testing circuit must be evaluated
experimentally following a prescribed procedure. The
procedure involve two steps: in the first one, a
constant current of about 50 μA, at the measuring
frequency fm, is injected in the whole non-energized
testing circuit (as presented in Figure 2). The value of
voltage, expressed in [dB/µV] and recorded by the
measuring set is denoted as V1. In the second step, the
same current is injected only in the EUT and the
measuring resistance, all others elements being
disconnected. The new value of disturbance level, V2
is recorded. Now, the attenuation of the testing circuit
could be calculated as the difference between the two
measured values:
(Vm )
AC voltage test
measuring system
Figure2. RIV measuring circuit: EUT – equipment under
test, Tr. – high-voltage test transformer, D –a.c. voltage
divider, Co. – corona free connection, simulating the line
conductor, Cc. – coaxial cable; F – low pass filter; Zs –
coupling impedance (high pass filter).
 in the shielded box containing the resistors R1 and R2
an inductance L3 is also disposed, which play the role of
a final short-circuit to earth for the residual power
frequency component. His value must be equal or greater
than 1 mH, at frequency fm .
For the measuring frequency, CISPR 18-2 Publication
stipulates a reference value f0 of 0.5 MHz or 1 MHz, with
a margin of ± 10 % for the actual measuring frequency
fm , in order to find the lowest background noise.
The measuring set, a receiver with a quasi-peak detector,
must comply with the specifications of CISPR 16-1
Publication.
The voltage reference value Ur , for which the RIV level is
reported at the final of test procedure is equal to
1.1  U n / 3 , where Un is the rated voltage of the
equipment under test (EUT).
A [dB/ μV] = V2 [dB/ μV] – V1 [dB/ μV]
(9)
The attenuation A reaches a value of only few dB/μV,
generally depending on the testing circuit’s dimensions.
The classical testing procedure consists of the following
steps, [4]:
 first, the voltage applied to EUT is increased up to
1,1·Ur and this value is kept at least 5 minutes;
 then the voltage is decreased in steps of about 0,1·Ur ,
up to 0,3·Ur;
 after that the voltage is increased in steps, up to
1,1·Ur , and this value is kept for one minute;
 follows a new decrease of the voltage in steps of
about 0,1·Ur , up to 0,3·Ur;
For each value of the applied voltage the Vm value of RIV is
recorded. The last series of measurements is used to evaluate the
RIV level (V) at the voltage reference value Ur .
3.2. Circuit calibration
As it can be seen in Figure 2, the interference current id ,
generated by the corona discharge and other micro
discharges at the EUT, is divided into three components:
a current through the measuring impedance, im , a current
to ground through the self-capacitance Ce of the EUT, ie ,
and a current through the testing voltage transformer, is
(limited by the rejection filter F). The voltage drop across
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Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 1 (12)
insulator set. In this case the electric field probe was
located in different positions (P0 to P4 in figure 4).
4. EXPERIMENTAL RESULTS
y
The classical procedure to asses the radio interference
voltage of a high voltage equipment following CISPR
publications, described above, is a time consuming one,
first of all because of the circuit calibration procedure.
Other difficulties, except the costs of measuring
system, are:
 to read the values of RIV (numerical or analogical
displayed) for certain voltages where the corona
discharge is very unstable;
 to ensure a low background noise level during the tests.
Regarding the radiofrequency emissions, the behavior of
the equipment under service conditions could differ from
that evaluated, in reproducible conditions, in the high
voltage laboratory.
An alternative and simple method which could be
adopted in order to asses the radiofrequency emissions
of high voltage equipment is the recording of high
frequency electric or magnetic field radiated in their
neighborhood. The experimental arrangement could
be the same used for a classical RIV test, in order to
ensure the same impedance for high frequency
currents or could be even simplified. For the
experiments described in this paper, the high voltage
circuit was kept as for a classical RIV test. The main
dimensions of the simulated line and the distances
where the field probe was disposed are presented in
Figure 3.
Corona free
connexions
(U)
High voltage
measuring system
Unlike overhead line-conductors which have their
elementary sources of interference distributed over very
great length, a piece of substation equipment, an
insulator string or different metallic fittings, can be
considered as a localized generator of interference.
During an indoor test, the HF current injected by the
EUT in the testing circuit is governed by the number
and amplitude of the elementary pulses generated per
unit time, while his form depends mostly on the
characteristics of the testing circuit.
The HF current generated by the EUT and collected
by the corona-free connection is the source of the
radiated field. The frequency spectrum of the emitted
field depends on the HF-current spectrum but it is
difficult to establish a direct relation based on the
antennas and propagation theory due to the nonlinear
aspects of the emission and the stochastic character of
the HF-current. When judging the results we must
keep in mind the fact that the electric field probe used
in this research is an isotropic probe. For a
monochromatic incident electric field expressed as the
sum of three orthogonal components
High frequency electric
field measuring system
d
7.5 m
P1
Figure 4. Locations of the electric probe (P0 …P4).
Cb = 1.85 nF
(Vm)
P4
P2
P0
5m
Insulator set (EUT)
Zm = 300 
x
45
6.2 m
2× 600 kV
P3
insulator set
Rejection filter
(L = 20 mH)
148 pF
ISSN 1843-6188
h

Ei r , t  
RIV measuring
system
n x, y , z
Figure 3. The main components of the experimental
arrangement for combined measurements, RIV and
radiated electric field.
Eni  r  cos t  n  r   nˆ 
(10)
  E  r ,   e nˆ  Re E n  r ,   e jt
i
jt
i
n
n
n
an isotropic probe placed in P( r ) will have a response
proportional to the Hermitian magnitude (or effective
value) of the complex vector field defined in [6] as:
The measurements were performed using a high
frequency electric field probe, in a 300 kHz-3 GHz range
and parallel records (RIV and radiated electric field) were
recorded. The radiated field measuring systems was
adjusted to display the average or maximum average
value of electric field (in a time period of 4 sec.).
The testing objects were a 110 kV composite insulator
set and then a toughened glass insulator set both having
the same rated voltage. The experimental arrangement
was carried out according to IEC 60383-2 Publication
[5]. The length of the conductor used to simulate the
line was 6 m and the clearance from the floor of
laboratory was 6.2 m.
The electric probe was placed at 1 m above the laboratory
floor at different locations denoted as P0 to P4 in figure 4.
The first series of tests were performed on the composite
insulator set. The electric field probe was located in P1.
The second series of tests were performed on the glass
i
E  Ex Ex  Ey Ey  Ez Ez
i
i*
i
i*
i
i*
(11)
In the relations above, the subscripts indicate rectangular
components and the character (*) the complex conjugates.
The Hermitian magnitude is independent of the orientation
of the probe with respect to the field thus, the probe is
isotropic. Note that the Hermitian magnitude of the
complex field is an upper bound on the instantaneous field:
Ei  r , t   E r , 
i
(12)
On the other hand, for frequencies up to 1 MHz, an object
placed up to about 10 m from an electromagnetic field
source is located inside “near electromagnetic field” zone
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Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 1 (12)
(the wavelength corresponding to the frequency of
1 MHz is 300 m). In the near-field zone, the electric
component of the electromagnetic field contains the
electrostatic term (~1/R3) the induction term (~1/R2) and
the radiation term (~1/R), meanwhile the magnetic
component contains only induction and radiation terms.
Therefore, the radiation pattern eventually established for
the electric field can not be directly used to determine the
magnetic field radiation pattern.
The parallel measurements (RIV and radiated high
frequency electric field) were performed for two
frequencies, 500 kHz and 1 MHz and for the same steps
of voltage recommended in [4].
4.1 RIV measurements
RI level (given by the average value detector of the EMI
receiver) versus the applied voltage is plotted in Figure 5
for the composite insulator set and in Figure 6 for the
glass insulator set.
For the composite insulator set, the RIV exhibits an
exponential growth with the applied voltage, starting
from a constant level (35.2 dB for 500 kHz and 26.7 dB
for 1 MHz) and increasing quickly as the voltage
overcomes the threshold for the initiation of corona or
micro discharges on metallic parts of the insulator set.
The voltage dependency of RI level for the glass
insulator set follows a different pattern, the curve fitting
the experimental results being a sigmoid 4 parameter
function, an S-shaped function which displays a RI level
progression from a small, stable value (26.2 dB at
500 kHz and 23.6 dB at 1 MHz) to an other higher stable
value (30.0 dB at 500 kHz and 28 dB at 1 MHz).
For tests performed at the same measuring frequency on
both insulator sets, the lower stable level, which is due
mainly to the inherent electromagnetic noise existing
even inside a shielded hall such as the HV Laboratory,
differs, pointing out the noise variability.
But, each of the two insulators sets exhibits a specific
pattern of RIV growth when the applied voltage reaches
and than goes beyond the threshold for corona and/or
micro-discharges.
Figure 6. Glass insulator set RIV curves.
The mentioned pattern plotted using the fitted curves
displayed on Figure 5 and 6 can be observed in Figure 7.
For both measuring frequencies, the RI level generated by
the composite insulator set increases with the applied
voltage without limitation, suggesting that the interference
current, which is the source of the disturbing
electromagnetic field, increases as the applied voltage is
increased. The glass insulator set pattern, for both
measuring frequencies, exhibits a bell-shape growth
pattern similar to those presented in [7] for different
substations equipments. This pattern suggests the
presence of a single source becoming active after
exceeding the threshold voltage and reaching a saturation
value for the interference current.
Figure 7. Growth pattern for RI level.
The HF electric field (EF) was measured as average value
over 4 seconds for both series of RIV measurements (at
500 kHz and 1 MHz) with the probe placed in point P1.
The values show the same type of voltage dependency,
exponential growth of the electric field with applied
voltage. The results are presented in Figure 8.a for the
composite insulator set and 8.b for the glass insulator set.
As it can be seen, the influence of the measuring
frequency, which is evident in RIV values, is difficult to
asses when analyzing electric field values.
Figure 5. Composite insulator set RIV curves.
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Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 1 (12)
ISSN 1843-6188
seen in Figure 10 (points P1, P2, P3).
The data series for each of the 5 locations under study
have in common the RIV which, for a given value of the
applied voltage, should be the same, regardless the
measuring point location.
The data set containing all the available RIV-values is
represented in Figure 11 together with the fitted model
and the 95% prediction boundaries.
(a)
Figure 9. HF Electric Field versus applied voltage measured
in different location (P0 to P4).
(b)
Figure 8. HF electric field (isotropic values) for composite
(a) and glass (b) insulator sets – 500 kHz and 1 MHz data.
For example, in the case of the composite insulator set
(Figure 8.a) the EF measured at 1 MHz rises faster with
the applied voltage than the EF measured at 500 kHz. In
the same time, for the glass insulator set (Figure 8.b) the
HF EF seems to be frequency-independent. This behavior
can be related to the structure of the electric field in the
“near-field” zone, and the presence of the electrostatic,
induction and radiation terms each of them exhibiting a
different frequency-dependence. This issue will be
approached in a further research. The results that will be
presented below come from measurements done at the
same frequency (500 kHz or 1 MHz).
Measurements performed in point P0 to P4 with the glass
insulator set, were designed to check the space
distribution of the EF, as the insulator set together with
the line model form a source of emission with a
complicated 3D geometry. The results are illustrated in
Figure 9 for the 500 kHz measurements. The points being
scarce, we can only highlight some tendencies. For
example, using the fitted curves we have compute the
predicted values and the 95% confidence interval for the
EF at 80 kV; the obtained values were represented in
Figure 10 versus the distance between the center of the
emission source and the measuring point. For the same
applied voltage, the EF decreases as the distance between
the emission source and the measuring point increases
but, for the same distance the values depend on the
azimuth and elevation of the measuring point as it can be
Figure 10. EF predicted values for the same applied voltage
(80 kV) at different locations around the emission source
Figure 11. 500 kHz RIV, glass insulator string, all series.
Using this results we looked at the correlation between
RIV values and EF values measured in the locations P0 to
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P4, disposed around the tested equipment. The scattering
plot for 500 kHz measuring frequency is displayed in
Figure 12. A summary of correlation coefficients and
their 95% confidence intervals are given in table 1.
6. REFERENCES
[1] * * * C.I.S.P.R. Publ. 18-1 (1982): Radio interference
characteristics of overhead power lines and high voltage
equipment. Part 1: Description of phenomena.
[2] Cardoso J., Filho O., Levy, A., Correlating Digital
Measurements of Electrical Quantities and Related
Images on Micro Discharges, 2008 Intl. Conf. on High
Voltage Engineering and Application, Chongqing,
China, November 9-13, 2008.
[3] da Frota Mattos, M. A, Biagioni, P. H., Bassi, W., Electric
field measurement on time domain generated by corona on
insulators on distribution systems, 1996 IEEE Intl. Symp. on
Electrical Insulation, Montreal, Canada, June 16-19,1996.
[4] * * * C.I.S.P.R. Publication 18-2 (1986), Am. 1 (1993):
Radio interference characteristics of overhead power lines
and high voltage equipment. Part 2: Methods of
measurement and procedure for determining limits.
[5] * * * IEC 60383-2 (1993): Insulators for overhead
lines with a nominal voltage above 1 000 V –Part 2:
Insulator strings and insulator sets for a.c. systems –
Definitions, test methods and acceptance criteria.
[6] Wacker F, Bowman RR, Quantifying hazardous
electromagnetic fields: Scientific basis and practical
considerations, IEEE Trans. Microwave Theory Tech.,
1971, 19(2): 178-187.
[7] CIGRE SC36-WG01, Interferences produced by
corona effect of electric systems. TR 20, 1974.
Table 1 RIV – Electric Field correlation, 500 kHz data
Correlation
Lower
Upper
Test
Point
Coefficient
Limit
Limit
Value
P0
0.9580
0.7797
0.9926
0.0023
P1
0.9769
0.8736
0.9960
0.0002
P2
0.9669
0.8229
0.9942
0.0001
P3
0.9860
0.9218
0.9976
0.0001
P4
0.9759
0.8682
0.9958
0.0001
The last column contains the probability of getting a
correlation as large as the observed value by random
chance when the true correlation is zero.
The high values for the correlation coefficients and the
very low test values confirm the existence of an important
deterministic component when evaluating the
dependency between the electric field and the RIV.
Due to the anisotropy of the emission source, this
dependency is also a function of the position in space
and will be investigated in further researches.
Figure 12. Correlation between RIV and HF electric field.
5. CONCLUSIONS
The measurement procedure which must be applied to
asses the radio interference voltage due to high voltage
equipment and described in the CISPR standards is with
no doubt expensive and time-consuming. On the other
hand the instability of displayed results for certain values
of applied voltage make difficult the task to record them
and to conclude about the behavior of the object under
test. A simple, cheaper and saving time method could be
the recording of radiated field components around tested
object using high frequency field probes in a well defined
electromagnetic environment such as a shielded high
voltage laboratory. The first results are promising, the
correlation between radio interference voltage and
radiated electric field was proved, but more experiments
are still necessary to refine this alternative method.
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