Conductive clothing

ICOUM 2014 ·11th International Conference on Live Maintenance· 21-23 May 2014· Budapest, Hungary





Conductive clothing for live line working



R. Malgesini, C. Valagussa, A. Villa, R. Carrara, R. Carrara, G. De Dona, C. D. Milanella and A. A.
Parizia





Abstract-Conductive clothing are a mandatory tool to assure
the safety of live line working when the bare hand technique is
used. This is particularly true for the maintenance of UHV lines.
In this work we discuss some tests performed to determine the
shielding characteristics of facial masks. Some numerical
simulations have been performed to assess how much of the tests
prescribed by the IEC 60895 standard are cautionary.
Figure I: two examples of a facial screen. On the left a thin mesh and on the
Index Terms-Conductive clothing, live line working.
right a large copper mesh are considered.
I. INTRODUCTION
The dumping factor of the whole configuration (mask plus
N this work we analyze some experimental results regarding suit) is tested and results are displayed in Table I.
Ithe shielding capabilities of conductive clothing. In
particular we are interested in characterizing the electric field
attenuation factor of a complete suit when a facial mask is
used. Conductive clothing are a key element to perform live
line working [I]: nearly 2500 live maintenance works take
place in Italy every year. 400 of these are performed at the
same potential of the line and, therefore, require conductive
clothing. We review the clothing performances for possible
applications to UHV lines (above 750 kV): in this case a
proper shielding for the face must be added.
We discuss some of the standard tests prescribed by IEC
60895 (now under revision). We show, using some
electrostatics simulations, that the shielding properties are
influenced by the object that must be shielded and by the wire
spacing.
The paper is divided in two sections: we first present the
experimental results of a complete suit using some different
Figure 2: a sword mask.
mask configurations. Then we interpret the results using finite
element analysis to evaluate the conservativeness of the tests.
The revision the IEC 60895 standard for applications to
UHV lines prescribes a minimum attenuation factor of 50 dB
II. EXPERIMENTAL RESULTS
for the full suit. Without a facial mask that prescription cannot
We have considered three different types of masks that are be met. All the mask configurations comply with the desired
depicted in Figure 1 and Figure 2. The first type is made of a screening characteristics. The sword mask obtains the best
very thin metallic mesh, the second is made of a few large
result and in addition it provides a sufficient visibility for the
copper wires and the last closely resembles a sword mask
operator.
made of several medium-size wires. The last configuration can
be seen as a compromise between the first two solutions. TABLE 1: THE ATTENUATION FACTOR OF THE VARIOUS
CONFIGURATIONS
Facial screning Screening efficiency
type (dB)
R. Malgesini, C. Valagussa, A. Villa are with RSE - Department of
Technologies for Transmission and Distribution (TTD), Via Rubattino 54, Without screening 46,42
20134, Milano, Italy (e-mail: [email protected]. Thin metallic mesh 64,05
Claudio. [email protected], Andrea. [email protected] ). Large copper mesh 60,86
R. Carraro, R. Carraro, are with Carraro S.r.1., Via Sareia 7, Paruzzaro,
Italy (e-mail: [email protected]. Sword mask 7 1 , 76
[email protected] ).
G. De Dona, C. D. Milanello and A. A. Parizia are with Terna Rete Italia Since the suit attenuation results are global measures and
S.p.a, Strada del Drosso 75, Torino, Italy (e-mail: [email protected].
Carlodante. M i [email protected], Alessandroandrea. [email protected] ). give no information about the local strength of the electric



978-1-4799-5993-8/14/$31.00 ©2014 IEEE

R. Malgesini et al.· Conductive clothing for live line working
2

field on the face we have also carried out some tests on the
mask only to evaluate its screening factor. We have treated the
1
mask net as if it is a material of the suit and we have tested it
according lEe 60895 standard.

TABLE 2· SHIELDING EFFICENCY OF DIFFERENT NETS
Type Wire Spacing Screening 3 3
diameter (mm) (db)
(mm)
Sword mask-l 0.6 2.5 25.7
Sword mask-2 0.5 1 . 5 35.8 2
Thin metallic 0.2 l.5 1 9
mesh
Figure 3: the computational domain.
Three different kinds of nets have been tested and the The computational domain is a rectangle with sides of
results are included in Table 2. We have considered two types length of 220 mm and 1 2 0 mm. Inside we have placed a
of nets for the sword mask and the thin metallic mesh. The variable number of circles with a diameter of 2mm. They
large copper mesh has been discarded because, although represent the wire sections. We have placed them on a circle
providing a satisfactory overall shielding, it provides very low of30mm in diameter.
local attenuation. We have applied a unit potential ( 1 V) on the top boundary
It is interesting to note that though the mean shielding of
(part I) of Figure I. The bottom part of the boundary is
the suit is always satisfactory, see Table 1 , the net of mask,
grounded (part 2), on the two lateral boundaries (part 3) we
tested alone, always provide a lower screening than the suit
have imposed that the normal component of the electric field
fabric.
vanishes. On the wires we have applied the same floating
potential.
III. NUMERICAL SIMULATION An example of the results is shown in Figure 4 where the
The conductive clothing must have many characteristics shielding properties of this configuration can be observed.
such as: good electrical conductivity, good shielding
properties and a good comfort. These characteristics are
obtained properly choosing the diameter of the wires, that
compose the clothing, and the wire density. A suit too thick
may lead to a poor comfort while a too thin suit may have an
unsatisfactory shielding.
Also the mask faces similar challenges as the producer
have to strike a balance between the shielding characteristics
and the visibility of the operator.
The miscrosopic structure of the screen can be simulated.
In this case we have used the geometry depicted in Figure 1 .
Though it is a considerable simplification of the complex
structure found in modern suits, this kind of simulation
represents their main physical aspects. In fact, the electric field
lines are forced to arrive perpendicular to the metallic wires
and this creates a sharp decrease of the electric field in the
space enclosed by the wires.













Figure 4: an example of electrostatic solution. The whole domain (up) and a
zoom of the shielded region (down).

To analyze the effects of a closer spacing we have varied

ICOUM 2014 ·11th International Conference on Live Maintenance· 21-23 May 2014· Budapest, Hungary
3

the number of wires from 8 to 32 and we have plotted the
modulus of the electric field on an inner circle of diameter 24
mm. The configurations corresponds to a wire - void ratio of
.0
1 l .7 and 2.94 with 8 and 32 wires respectively.
-H.Wlrl"�
10


80
E 0,001
� 0.1 -tIIWlr'�'
."
� -16 �<:ni�lmm)
Figure 7: plot of the modulus of the electric field with water in the shielded
region.
0.00'
We have also tried to emulate the real conditions under
which conductive clothing are used. In particular they are used
-- Lenllht(mm)
Figure 5: plot of the modulus of the electric field with air in the shielded to shield a human body whose relative pennittivity is close to
region. that of water. Therefore we have substituted the metallic circle
of the former case with a circle characterized by the relative
The results are presented in Figure 2. As expected, the
permittivity of water. The results are reported in Figure 4 and
shielding characteristics depend on the number of wires, being
we can see that they are intermediate between the two fonner
the denser configuration the best in terms of shielding.
cases. This effect is due to the polarization charges that tend to
Another important aspect that determines the shielding
enhance the electric field outside the water region and tend to
properties of the suit are the physical characteristics of what is strongly weaken it inside that region.
inside the shielded region. Till now we have considered air or
another material with a weak relative permittivity. However in IV. CONCLUSIONS
many tests prescribed by the IEC 60895 standard the object to
We have evaluated the shielding characteristics of a
be shielded is represented by a metallic object. For instance, to
conductive clothing and we have evaluated how these can be
test a full scale suit, a metallic dummy is used.
linked to the wire spacing. Moreover we have evaluated how
These cases can be represented by a slight variation of the
the shielding varies as a function of the characteristics of the
geometry already depicted in Figure 1 just introducing a circle
object to be shielded. In general, shielding a metallic object
with a diameter of 24mm in the shielded area. We have
will lead to the worst case scenario.
applied a floating potential to this latter circle.
We have outlined that the shielding value of the complete
I. suit does not provide a clear indication of the screening of the
mask. Therefore it is interesting to evaluate directly the
characteristics of the face screen. This device, in fact, protects
a very sensitive area of the human body and should be
E 0 , 1 optimized to guarantee a sufficient comfort and visibility.
2: -8Wlres
:l1
� 0,01
-.u.w�e$ V. ACKNOWLEDGMENT
This work has been financed by the Research Fund for the
Italian Electrical System under the Contract Agreement
between RSE and the Ministry of Economic Development.
0,0001
The authors wish to thank L. Barbareschi for her useful
l@nght{mm)
contribution and suggestions.
O,"OXII �-
Figure 6: plot of the modulus of the electric field with a metallic object in the
shielded region. VI. REFERENCES
[1] C. Valagussa, U. Leva, G. De Dona, C. D. Milanello, R. Carraro, and R.
In this case the electric field lines are forced to be Carraro, "Laboratory test for the verification of the screening
perpendicular both to the wires and to the circle we have just perforruance of protective conductive clothing used in Live Line
added. This has the effect of increasing considerably the Working," presented at the Icolim 2011, 2011.
[2] "IEC 60895 - Live Working, conductive clothing for use at nominal
electric field inside the shielded region. In Figure 3 we have
voltage up to 800 kV a.c and 600 kV d.c." 2008-2002.
shown the modulus of the electric field on the metallic object
so that results can be directly compared with Figure 2. We can
appreciate a strong weakening of the shielding properties: with VII. BIOGRAPHIES
32 wires the electric field is an order of magnitude stronger.
Roberto Malgesini was born in Cosio Valtellino (Italy) on March 21, 1968.
He received his high school qualifications in Electrotechnical Sciences from

R. Malgesini et al.· Conductive clothing for live line working
4

E. Mattei specialization school (Sondrio, Italy) in 1987. He currently has a
permanent research position at Ricerca Sistema Energetico (RSE) in Milan,
Italy. His research areas include the overvoltage protection of power lines and
the health monitoring of insulating devices.
Claudio Valagussa was born in Milan (Italy) on June 26, 1959. He received
the master degree in Electrotechincs from Politecnico di Milano (Milan, Italy)
in 1986. He currently has a permanent coordination position at Ricerca
Sistema Energetico (RSE) in Milan, Italy. Valagussa is member of the Italian
Electrotechnical Committee (CEI) TC78 and member or expert in some WG
of International Electrotechnical Commission (lEC) TC78.
Andrea Villa was born in Milan (Italy) on September 11, 1981. He received
the master degree in Aerospace Engineering from Politecnico di Milano
(Milan, Italy) in 2006 and the Phd in applied mathematics from Universita'
degli Studi di Milano (Milan, Italy) in 2010. He currently has a permanent
research position at Ricerca Sistema Energetico (RSE) in Milan, Italy. His
research areas include numerical analysis, numerical simulation, plasma
physics and the development of high performance codes.

Giorgio De Dona received his master degree in communication science from
the University of Torino in 2003. He joined ENEL in 1981 and then TERNA
in 1999, where he is in now responsible for conventional and live-line
working methods on overhead lines and substations. De Dona is secretary of
the Italian Electrotechnical Committee (CEI) TC78, project leader of IEC-TC
78 and convenor of WG 11-TC78 for the International Electrotechnical
Commission.
Carlo Dante Milanello received his certificate in Industrial Electronic in
1984. He joined ENEL in 1986 and then TERNA in 1999, where he is now
responsible for tool tests in conventional and live-line working methods on
overhead lines and substations. Milanello is member of the Italian
Electrotechnical Committee (CEI) TC78 and member in several WG of
International Electrotechnical Commission (lEC) TC78.