Radiative Energy Measurements of Pulsed High-Current Arcs
J.M. Bauchire1, D. Hong1, H. Rabat1 and G. Riquel2
1
GREMI, UMR6606 CNRS/Université d’Orléans, 14 rue d’Issoudun, BP 6744, 45067 Orléans Cedex 2, France
2
EDF R&D, Avenue des Renardières – Ecuelles, 77818 Moret-sur-Loing Cedex, France
Abstract: Workers operating near power lines can be injured by radiation from
high-current electric arcs that can accidentally occur. In order to improve worker
protection, it is necessary to evaluate this radiation in the optical range
(ultraviolet, visible, infrared). To this purpose we have performed experimental
measurements using optical energy sensors. The results show that for highcurrent arcs a large amount of the electrical input energy is dissipated by
radiation. When the arc is 10 cm long, this radiation is mainly in the visible and
UV spectral ranges, and metallic vapors play an important role in radiative
transfer, whereas for longer arcs (2 m), the arc radiation is more characteristic of
that of air, with high radiation in the visible and infrared spectral ranges.
Keywords: Electric arcs, radiation, air, copper, iron, aluminum.
1. Introduction
The so-called “arc default” is an electric
discharge that occurs accidentally in electrical
installations. An arc fault dissipates a large amount
of energy into its surroundings within a short time.
Radiation is intense, potentially causing serious
damage. Thus, an operator working near arcs should
wear appropriate personal protective equipment
(PPE). A recent modification in the French labor
code [1], based on a European directive [2] and a
technical report [3], has defined the maximum
permissible exposures to incoherent optical radiation
in each radiation band (from UVC to IRC) i.e. from
180 nm to 1 mm.
In order to compare these permissible
exposures with plasma radiation, a collaboration has
been set up between the EDF group (which supplies
electricity), and two laboratories (LAPLACE and
GREMI). LAPLACE is responsible for calculating
the high-current arc emission, while EDF and
GREMI conduct the experimental determination of
radiative emission to provide data that can be
compared to theoretical calculations.
This paper presents the first part of the
experimental study. Two configurations of highcurrent arcs were created. The first one is a short
length – short duration arc, and the second one a
long length – long duration arc. For both
configurations, we have measured the radiative
energy emitted by the arc, thanks to joulemeters
equipped with adapted filters. Prior to these
quantitative measurements, a time-resolved imaging
study was conducted to determine the dynamics of
the arc. These measurements were performed
depending on the electrode material and on the
current intensity.
In the first part of this paper, we describe the
experimental setup of the two configurations. In the
second part, results are presented and discussed.
2. Experimental set-up
2.1.Configuration 1
The experimental setup consists of two
vertical opposed round metallic rod electrodes,
each18 mm in diameter. As shown in figure 1, the
upper electrode is connected to the power supply. It
faces the lower electrode connected to the base of
the framework. Electric current goes back via the
return conductors (20 cm from the axis) to the upper
plate, and then to the outer cylinder connected to the
power supply. The distance between the electrode
tips was 10 cm. Given this wide gap, the electrodes
were joined by a thin wire allowing arc ignition in
open air.
equipped with different filters so as to obtain the
radiative energy emitted by the arc for 4 spectral
ranges: UVA-B (UVA + UVB), Visible, IRA and
UVC*-IRB-C* which is part of the UVC range +
IRB + part of IRC, as shown in figure 2.
Time resolved imaging of the arc was also
performed using an Andor ICCD camera with an
exposure time of 10 µs.
2.2.Configuration 2
The shape of this configuration is almost the
same as the previous one except that the dimensions
of the device are larger, with an electrode gap, i.e.
the arc length, of 2 m. The electrodes were rods 25
mm in diameter. The power source was also
“enlarged” since it supplies 5 periods of a 50 Hz
sinusoidal current. The experiments were performed
for current intensities of 4, 10, 20 and 40 kA RMS.
IRMS (kA)
Figure 1. Experimental setup of configuration 1.
4
10
20
40
Copper
0.75 1.67 3.27 5.38
Steel
0.73 1.81 3.09 6.04
Aluminum 0.69 1.84 3.64 5.74
The power source supplied a positive halfwave current of a 50 Hz sine waveform, with a 10
kA peak amplitude. The discharge current and
voltage were recorded during each run, and their
product was integrated on the total arc duration to
estimate the input electric energy of the discharge,
which was found to be about 15 kJ with a good
reproducibility shot-to-shot.
Figure 2. Illustration of spectral ranges for which arc radiation was
measured.
Table 1. Mean input electric energies (MJ) as a function of RMS current
and electrode materials.
As shown in table 1, input energies were much
higher than those of configuration 1, mainly because
of longer arc length, and hence higher arc voltage,
and longer discharge time duration.
The joulemeters were, in this case,
positioned 9.4 m from the electrodes axis, and aimed
at the center of the arc in a slightly low-angle shot.
3. Results
3.1.Configuration 1
Arc radiation measurements were done with
two joulemeters from Gentec Electro-Optics. They
were positioned 1780 mm from the electrodes axis,
on the horizontal plane defined by the middle of the
electrodes gap, and aimed at the center of the arc.
Preliminary measurements for different positions of
the joulemeters confirmed that radiation coming
from the arc is isotropic. The joulemeters were
Figure 3 shows the part of energy lost by
radiation in the UVA-Visible-IRA spectral ranges
compared to the input electric energy (100%), for
different electrode materials. It can be seen that for
steel electrodes a very large amount of arc energy is
lost by this radiation. For copper or aluminum
electrodes, the loss is lower but still represents 40 %
of the input energy. These results indicate that the
presence of metallic vapors in the arc has a nonnegligible influence on radiative transfer.
Figure 4. Contribution of each spectral range (UVA+B, visible, IRA) to
the radiative losses (UVA to IRA), for different electrode materials.
Figure 3. Percentage of radiative energy (UVA to IRA) compared to the
input electric energy (100%), for different electrode materials. “Others”
means all energy losses except radiative energy from UVA to IRA.
Figure 4 shows the contribution of each spectral
range to the radiative losses. For all electrode
materials, the main contribution seems to come from
the UVA-B range, while the visible and IRA ranges
contribute the same proportion. The calculation by
Cressault et al [4] showed that for air plasmas,
radiation is significant in the visible and IRA ranges.
These results compared to our measurements
confirm the strong influence of metallic vapors in
the arc radiation for configuration 1, meaning that
radiative transfer in this plasma is driven by metallic
vapors.
These metallic vapors come from electrode erosion,
but they should be present throughout the plasma to
have the significant role previously mentioned.
Photos of the arc (figure 5) show that after the wire
has blown completely over its entire length between
the two contact points, directed jets coming from the
electrodes interact with each other, creating large
transient plasma and hot gas volumes, spreading the
metallic vapors.
However, calculations [4] have also shown that the
radiation of air plasma with metallic vapors is
mainly in the UVC and visible ranges. These results
are in contradiction with our measurements where
the UVA-B range predominates. As a large volume
of warm gas surrounds the arc, it can be assumed
that this gas absorbs most of the UVC radiation.
Figure 5. Photos of the arc at 4.5 ms (left) and 8.5 ms (right) for a
current discharge with a5kA peak.
3.2.Configuration 2
The proportion of radiative losses, in configuration
2, compared to the total input energy is shown in
table 2. It can be seen that the percentage is lower
than in configuration 1.
IRMS (kA)
4
10
20
40
Copper
27 % 33 % 50 % 64 %
Steel
66 % 73 % 82 % 72 %
Aluminum 43 % 55 % 70 % 79 %
Table 2. Proportionof the radiative energy (UVC* to IRC*) in percent of
input electric energy, for different electrode materials.
It can thus be considered that the mean concentration
of metallic vapors in the plasma is lower. In
comparison with configuration 1, steel electrodes
still produce the highest plasma radiation, but
aluminum electrodes produce higher plasma
radiation than the copper ones. This can be
explained by a higher electrode erosion in the case
of aluminum, leading to a higher metallic
concentration in the plasma. This is corroborated by
measurements on electrode length after each shot.
radiation. In this case, even if the absolute quantity
of metallic vapors is undoubtedly higher because of
higher currents and therefore of higher electrode
erosion, the concentration of metallic vapor seems to
be lower because of a larger volume of plasma. As a
result, the global influence of metallic vapors in
radiative transfer is weaker.
4. Conclusion
In summary, we have measured the radiative energy
in several optical bands from 280 nm to 0.2 mm,
emitted by two configurations of high-current pulsed
arcs, and for different electrode materials. The
results show that for high-current arcs a large
amount of the electric input energy is dissipated by
radiation. When the arc is 10 cm long this radiation
is mainly in the visible and UV spectral ranges, and
metallic vapors play an important role in radiative
transfer. For longer arcs (2 m), in contrast, the arc
radiation is more characteristic of that of air, with
high radiation in the visible and infrared spectral
ranges. Further measurements will be performed in
particular to determine the metallic vapor
concentration and plasma temperature.
This work was supported by the EDF (Electricité de
France) group.
References
Figure 6. Contribution of each spectral range (UVA-B, visible, IRA,
UVC*+IRB-C*) to the radiative losses (UVC* to IRC*), for different
electrode materials. From inner circle to outer circle: 4, 10, 20 and 40
kA. Orange (top): copper electrodes, green (center): steel electrodes and
blue (bottom): aluminum electrodes.
Contrary to configuration 1, UVA-B radiation is not
the predominant one. Visible and IRA seem to be the
most radiative ranges, as for pure air plasma
[1] Décret n°2010-750 du 2 juillet 2010 relatif à la
protection des travailleurs contre les risques dus
aux rayonnements optiques artificiels, Ministry
of employment, France
[2] Directive 2006/25/CE of European parliament
and council (2006)
[3] IEC, “Part 9 - Compilation of maximum
permissible exposure to incoherent radiation”,
TR 60825-9 (1999)
[4] Y. Cressault, A. Gleizes, G. Riquel, “Calculation
of the radiation emitted by isothermal arc
plasmas in air and air-metal mixtures”, ISPC 20,
25th-29th July 2011, Philadelphia, USA