Influence of High Voltage Bundle Configurations on
Human Exposure
Alexandru Salceanu1, Silviu Vornicu1, Eduard Lunca1
1
Marcel Istrate2
Department of Electrical Measurements and Materials
1
“Gheorghe Asachi” Technical University of Iasi
1
Iasi, Romania
asalcean@tuiasi.ro
Abstract—The paper is mainly dedicated to determining the
influence of bundle conductors configurations on the electric and
magnetic field levels determined at the standard height of 1 m
above the ground. The technical-economic advantages are
concisely presented, but also the inherent disadvantages of
implementing such solutions. One of the main advantages is
theoretically analyzed: the reduction of the risk of initiating
corona discharges, as a result of the decrease of the potential
gradient from the conductor surface, implicitly meaning the
increase of the electric field strength near the ground. The
theoretical approaches were reinforced by simulations performed
with the help of ANSYS and EMFACDC software. It was
considered the real case of a 400 kV network through which
phase currents of 1050 A are transported, in three distinct
variants: single conductor, double bundle and triple bundle.
Electric field increases were found by 37% in the case of triple
bundles, taking as reference a single conductor per phase. If the
same total current is considered, the chosen bundle
configurations have no influence on the generated magnetic field.
Keywords—bundle conductors, electric and magnetic fields
I.
GENERAL CONSIDERATIONS ON THE OPPORTUNITY OF
„BUNDLE CONDUCTORS” SOLUTION
There is a general concern about techniques and methods
for reducing human exposure to extremely low frequency
electric fields (50-60 Hz, power frequency), [1], [2]. Due to the
large number of stakeholders, cheap, widely accessible
measurement techniques [3], respecting the European Union
legislation in force, need to be developed [4].
Some of the possible solutions are relatively expensive and
should be used only in special cases, when the values of the
generated fields are critical, [5], [6]. The values of the
generated fields are all higher as the voltage (and implicitly the
currents) have higher values, of over 400 kV and 1000 A,
respectively.
From the point of view of human exposure assessment, the
difficulty lies in establishing the most accurate and rigorous
correspondence between the ambient values of the electric and
magnetic fields (so-called reference values) and the actual
induced electric field in the human body (so-called basic
restrictions), [9], [10], [11].
The use of several sub-conductors (placed parallel to each
other) is an almost mandatory solution, when you want to
2
2
Department of Power Engineering
“Gheorghe Asachi” Technical University of Iasi
2
Iasi, Romania
increase the current capacity (ampere capacity, abbreviated
ampacity) of a High Voltage Overhead Power Transmission
Line (OhHVPL), [12]. Mainly due to the skin effect, the central
part of the cross section of a conductor is not traversed by
power lines, so it is practically unused. One solution
(theoretical, never applied to the transmission of electricity),
would be the use of empty conductors (without any central
area), the so-called hollow conductors. In reality, a completely
different solution with increased economic efficiency is
applied, namely the use of several thinner sub-conductors,
mounted in parallel for the same phase, instead of a single
thicker conductor.
First of all for technological reasons, being easier to bend,
for transport and assembly, these conductors are not massive,
but consist of several twisted wires (stranding wires), on the
same principle of hemp rope woven from several wires. They
have round cross-section and consist of several concentric
layers. The diameter of an Al core wire is (approximately)
between 2 and 4 mm.
We present an edifying example, taking as reference the
standards [13], [14] that applies to conductors which have a
core of zinc-coated steel wires surrounded by aluminum wires,
the so-called ACSR (Aluminum Conductors Steel
Reinforced).The following eloquent comparison could be
extracted. A current of 1050 A (50Hz) might be carried:

using a single conductor ACSR 570/40, having a real cross
section of 571.2 mm2 Al (overall radius 16.1 mm).

using 2 parallel sub-conductors type ACSR 185/30, each
having a real cross section of 183.8 mm2 Al, meaning a
total of 367.6 mm2Al (overall radius 9.5 mm).

using 3 parallel sub-conductors type ACSR 95/15, each
having a real cross section of 94.4 mm2 Al, meaning a total
of 283.2 mm2 Al (overall radius 6.8 mm).
In other words, for the transport of the same alternative
current of more than 1000 A, with a frequency of 50 Hz, as a
result of the application of “double or triple bundle” solutions,
cross sections reduced by 40% and 50%, respectively, can be
used.
This is primarily due to the more efficient use of the entire
cross section, or, in other words, a limitation of the
consequences of the skin effect.
A clarification should be done. Obtaining this very
significant reduction of the cross section (40-50%) required for
the transport of a current over 1000 A was calculated on the
condition of imposing the same maximum conductor
temperature of 80oC. In other words, in the calculation of the
current carrying capacity, the increase of the electrical
resistance per km of conductor was also taken into account.
The three parallel conductors ACSR 95/15 have a resistance
(expressed in Ω/km) approximately twice the resistance of the
conductor 570/40. Also, the surface in direct contact with the
air, which allows the release of heat accumulated due to the
Joule effect is almost double at conductor 570/40 compared to
that of the three parallel sub-conductors 95/15.
In conclusion, taking as a reference for comparison the
same maximum actual carrying current on each of the three
phases, the use of bundle conductors has several definite
advantages:

reduction of Al mass, with significant economic effects, but
also with technological installation facilities;

reduction of inductive reactance of the line [15];

surge impedance reduction (also obtained due to the
increase of the capacitive reactance of the line);

one of the most frequently mentioned advantages of using
bundle conductors is the reduction of the risk of initiating
corona discharges (meaning, implicitly, the reduction of
corona losses, but also of the related radio-frequency
electromagnetic disturbances) [16], [17].
There are also disadvantages, the most important being the
increase of thermal losses due to the Joule effect [18], the
reduction of the heat evacuation surface in the air [19] or the
torsional behavior of the bundle [20]. Last but not least, the
increase of the electric field level generated by OhHVPL at the
standard height of 1 m from the ground level.
As always, the role of the design engineer is to establish the
best compromise, for a certain concrete situation, between the
advantages and the inherent disadvantages of the best chosen
solution.
II. INFLUENCE OF BUNDLE SOLUTION UPON THE GENERATED
ELECTRIC AND MAGNETIC FIELDS
The problem we want to address in this section is the
influence that the adoption of a "conductors bundle"
configuration has on ambient electric and magnetic fields in
general, on human exposure in particular. Of course, the issue
of human exposure concerns everyone, first of all from the
perspective of respecting the maximum limits allowed by the
international standards in force. But, in particular, it is a
separate chapter of the environmental impact studies carried
out for any OhHVPL that is either in operation or at the design
stage which must receive the approval of the various
authorities, including the Environment Agency [21], [22].
Surely the focus must be on the electric field. From the
perspective of reducing the risk of initiating corona type
discharges, it can be demonstrated theoretically that the
adoption of the “bundle” phase conductor solution reduces the
electric field around (or rather, even at the surface) conductors,
precisely in order not to the priming threshold of the corona
discharge is reached. In this situation, it is assumed that the
value of the electric field at ground level (more correctly, at the
conventional height of 1 m imposed by standards) would be
higher.
For our study to be relevant, the electric field values
recorded at this level must be compared, for networks with the
same rated voltage, the same transferred current (hence, the
same power), and of course the same spatial configuration of
the phases given by the use of the same tower type. The
comparison should be done between the single phase conductor
variant and the “bundle” variants, with 2, 3 or even 4 subconductors, using the same type of approved spacers.
The electric field is a vector quantity and represents the
potential gradient (potential is a scalar quantity). The gradient
of a quantity is calculated by applying the differential vector
operator ∇ (partial derivatives on the three coordinate axes). In
other words, by multiplying a vector (the “nabla” or del ∇
operator) by a scalar (in our case the scalar electric potential)
we obtain a vector, the electric field.
In Cartesian coordinates (rectangular) we have the
expression of the electric field:
= −∇ = −
∙
+ ∙
+
∙
(1)
It would be useful to highlight some aspects related to
OhHVPL- associated corona discharges, which we will later
correlate with the effect that a “bundle” phase conductor
configuration might have on the initiation of these discharges.
At first glance, we have an apparent contradiction. The
potential gradient (hence the electric field strength) at the
surface of a conductor with circular cross section will be larger
the smaller the radius of the circular section, which is easy to
explain based on the formula:
=−
(2)
The reduction of the potential gradient and implicitly the
reduction of the risk of initiating a corona discharge must be
explained in the context of the “bundle” type assembly,
consisting of several (sub) conductors at the same potential and
separated by spacers with side 300 or 500 mm.
III.
SIMULATIONS PERFORMED WITH ANSYSAND
EMFACDCSOFTWARE
There are a multitude of factors that influence the value of
the electric and magnetic fields generated by OhHVPL.
In this study we simulated these fields using two
specialized software, ANSYS [23] and EMFACDC [24].
We have considered the concrete case of a deviation tower
(corner tower), in Y, type ICy 400 136, pylon currently used
for simple three-phase 400 kV networks. Due to the maximum
allowable span between two consecutive towers (365 m) and
the corresponding sag of 12000 mm (at the middle of this
distance), we considered the tower height at elevation + 6m.
Glass and Liquid Silicon Rubber insulation chains with a
length of 4000 mm have been considered.
We have simulated for the three cases (equivalent from the
point of view of Ampacity), presented in Section I.
Newer type spacers, with a height of 400 mm, have been
adopted, representing a good balance between the standard
options, having the size of 300 mm and 500 mm, respectively.
Taking into account the conditions previously formulated,
the coordinates of the centers of the cross sections, for the three
cases discussed are summarized in Table I.
TABLE I.
CARTESIAN COORDINATES OF THE CROSS SECTIONS OF CONDUCTORS FOR THE THREE CASES STUDIED.
[mm]
1 cond.
2 subcon.
3 subcon.
R
R-2
R-1
-18100,
12900
-18300,
12900
-18300,
12900
R-3
-17900,
12900
-17900,
12900
S-1
0
12900
-200,
12900
-200,
12900
-18100,
12550
S
S-2
200,
12900
200,
12900
S-3
0,
12550
T-1
18100,
12900
17900,
12900
17900,
12900
T
T-2
T-3
18300,
12900
18300,
12900
18100,
12550
The first simulations have been performed for the electric
field generated at a height of 1 meter from the ground, Fig.1
with ANSYS software.
As expected, the values of the electric field at this
standardized height are the highest near the side phases (i.e.
approx. + / - 18 m from the axis of symmetry of the Y-pole),
for the case of bundle of three conductors, the smallest being
registered for the case of the single conductor. More precisely,
the maximum values recorded for the cases with 2 and 3 subconductors, respectively, are 5679 V/m and 5097 V/m,
representing a slight exceeding of the acceptable limit for
residential exposure, 5000 V/m. In the case of a single
conductor, the maximum value is only 4129 V/m, below the
limit allowed for general public exposure.
In relative terms, the difference between the case with three
sub-conductors and the case of a single conductor is about
37%. The significance of this percentage is considerable
mainly due to the fact that it allows the transition from
acceptable to unacceptable values.
Fig. 2.a. Electric field, lateral profile, 1m height, single conductor,
maximum value 3660 V/m
We performed exactly the same simulation using
EMFACDC software, Fig. 2.
Electric field strength, E(V/m)
ANSYS 1*1050 A
ANSYS 2*525
ANSYS 3*350
6000
5000
4000
3000
2000
1000
0
-50 -40 -30 -20 -10
0
10
20
30
40
50
Lateral distance, d (m)
Fig. 1. Comparative lateral profile of the Electric field generated by a 400 kV
network (1, 2 and 3 conductors per phase)
Fig. 2.b. Electric field, lateral profile, 1 m height, double conductors,
maximum value 4710 V/m
The maximum values are recorded as expected, next to the
phase conductors. For the single conductor, the maximum
electric field has the value of 337887 V/m, for the case with 2
sub-conductors, the maximum value is 228203 V/m and for the
case with three sub-conductors per phase, the maximum value
decreases to 199005V/m.
These results confirm the theory. The smaller is the radius
of the conductor (the sharper the conductor), the higher the
potential gradient at its surface.
In the case of conductors placed in parallel, at distances of
the order of 30-50 cm, a compensating effect occurs.
Specifically, in the case simulated in Fig. 3, the value of the
electric field at the surface of the single conductor is about 70%
higher than the value measured in the immediate vicinity of the
triple-bundle.
Fig. 2.c. Electric field, lateral profile, 1 m height, triple conductors,
maximum value 5430 V/m
The shape of these simulated graphics with the 2 software
is very similar. However, the maximum values are a few
percent lower in the case of simulations performed with
EMFACDC. These differences can be explained by the
different values of soil conductivity assumed for simulation
[25].
An interesting result is the lateral profile of the electric field
measured at a height of 12 meters from the ground, i.e.
practically right on the surface of the conductors that form the
power line, Fig. 3.
The results shown in Fig. 3 are less directly relevant from
the perspective of human exposure (it is very unlikely that the
human subject is 13 m above the ground, just below the high
voltage network). But it has an indirect influence: a larger
electric field near the conductor surface means a smaller field
near the ground (obviously, for the same phase voltage,
measured between the line and ground).
ANSYS 1*1050 A
ANSYS 2*525
ANSYS 3*350
We also performed a necessary simulation for the magnetic
field generated by this network, Fig. 4.
For the relevance of the performed comparisons, we started
from the hypothesis that for each phase, the total current is the
same, 1050 A. The value of the magnetic field depends only on
the current intensity. Naturally, the lateral profile of magnetic
flux density is the same, for any of three cases.
IV.
Bundle conductors are a "sine qua non" solution for
networks over 220 kV and 1000 A.
Significant costs are involved but also the economic
benefits are commensurate. Due to the reduction of the
potential gradient at the surface of the conductors in the
bundles, there is an increase of 30-40% of the electric fields at
the standard height of 1 m above the ground.
Such an increase, in an approximate value of 1000-2000
V/m, may mean exceeding the threshold of 5000 V/m imposed
by the standards for the exposure of the general public,
representing a cause for alarm in the case of residential areas,
which should not be located in the immediate vicinity of
voltage lines.
Magnetic flux density, B(µT)
Electric field strength, E(V/m)
ANSYS 1 metru
20
350000
300000
250000
200000
150000
100000
50000
0
-25
-15
-5
5
15
25
Lateral distance, d (m)
Fig. 3. Lateral profile of the Electric field in the very close vicinity of power
lines (12 meters height).
CONCLUSIONS
18
16
14
12
10
8
6
4
2
0
-50
-40
-30
-20
-10
0
10
20
30
40
Lateral distance, d (m)
Fig. 4. Lateral profile of magnetic field. Identity for all three cases.
50
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