The Online Journal on Electronics and Electrical Engineering (OJEEE)
Vol. (3) – No. (1)
An Experimental Study on Corona
Losses in Conductors
A. Ersoy
A. Kuntman
Department of Electrical-Electronics Engineering, Faculty of Engineering,
Istanbul University, Istanbul, Turkey
Abstract- In this paper, the corona inception voltage,
extinction voltage and hence the corona power loss
associated with bare conductors which are used for
overhead energy transmission and distribution lines is
experimentally studied. To simulate the corona process, a
smooth surfaced corona cage is built. Test measurements
were carried out to determine whether the corona losses
are more dependent on conductor type or conductor
diameters. Aluminum, copper and steel conductors are
investigated according to conductor diameters. Test
results reveal that for the same conductor type, the corona
losses show linearity with conductor diameter.
Keywords- Corona inception voltage, Corona extinction
voltage, Corona losses.
I. INTRODUCTION
Corona is a type of electrical conduction that generally
occurs at or near atmospheric pressure in gases. Coronas can
generate audible and radio-frequency noise, particularly near
electric power transmission lines. They also represent a power
loss, and their action on atmospheric particulates, along with
associated ozone and NOx production, can also be
disadvantageous to human health where power lines run
through built-up areas [1]. Therefore, it is one of the most
important factors when designing high voltage equipments.
Corona’s long term effect results damages in motors,
transformers, capacitors by destroying their insulation [2].
In transmission lines, it causes power loss, audible noise,
electromagnetic interference, purple glow, ozone production,
etc. Hence to minimize this negative effects, the conductor
surface condition, size, distance to ground and other
conductors has to be considered when planning and
construction of overhead power lines [3-4]. In transmission of
electricity ac voltages are used to transmit electric power
because of their efficiency against dc voltage. The basic
difference between ac and dc coronas is the periodic change
in direction of the applied field under ac, and its effect on the
residual space charge left over from the discharge during
preceding half-cycles. In an ac corona trichel pulses, negative
glow and positive glow and streamer coronas can be
observed.
Reference Number: W10-0047
This study investigates the effect of ac corona on different
type and size of conductors. To do this an ideal corona cage is
built. Tests are performed on aluminum, copper and steel
conductors. For each bare conductor, the corona inception
voltage, extinction voltage and currents at this voltage levels
are reported. Moreover corona power loss is calculated by
using common experimental formulas.
II. EXPERIMENTAL PROCEDURE
The AC source was a generator with maximum output
voltage of 400 kV. In the tests an ideal cage made of steel
which has a smooth surface (in figure 1) is used. The corona
cage is 25 cm long and has a diameter of 10 cm. Its thickness
is measured as 1 mm. For current measurements a ring is
placed on the centre of corona cage. The ring was fit to
corona cage and the conductor taken from this ring is
connected to a measuring device. Current measurements are
done by using an oscilloscope which is connected to cage by
the conductors fitted to cage with a 102.6 Ω measuring
resistor in series also with a Fluke 187 digital multimeter.
Principle scheme for corona measuring system is given in
figure 2.
To evaluate corona inception voltage, the applied voltage is
gradually increased and the lowest voltage at which
continuous corona occurs is noted. When measuring corona
extinction voltage, applied voltage is raised % 10 up to the
voltage level which corona inception voltage is recorded.
Then the applied voltage started to decrease until the corona
noise can not be heard and the harmonics were started to
decline while monitoring from oscilloscope and control unit.
Therefore to see the exact value of corona inception and
extinction voltage levels, the rate of rise is chosen 500 V/s.
All the experiments were done in the same outdoor
conditions at room temperature (22 oC) and 756 mmHg
ambient pressure. One single conductor is used in each
experiment for clearance. The diameters for aluminum
conductors are selected as 2.1 mm and 4.25 mm. For steel
conductors, conductor diameters are 2.20 mm and 4.23 mm.
For copper conductors which has a diameter of 1.72 mm and
2.68 mm is used.
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The Online Journal on Electronics and Electrical Engineering (OJEEE)
Figure (1): Corona cage used in experiments
Vol. (3) – No. (1)
Figure (2) : Principle scheme for corona measuring system
III. EXPERIMENTAL RESULTS
Experimental results for different type of conductors are
done for each conductor diameter independently. The
experimental results for aluminum, steel and copper
conductors are concluded in Table 1. Corona inception
voltage and corona extinction voltage values are increased
with increasing conductor diameter. For all type of
conductors, currents measured at this voltage levels increased
with increasing conductor diameter. Also for each type of
conductor, corona extinction voltages measured lower than
the corona inception voltage. Currents measured at corona
inception and extinction levels increased with increasing
conductor diameter for aluminum and copper conductors.
However for steel conductors currents measured at corona
inception and extinction levels decreased with increasing
conductor diameter.
For the same conductor diameter for aluminum and steel
conductors corona inception and extinction voltage measured
quite differently
IV. CALCULATION OF CORONA POWER LOSS
For calculating ac corona power losses several empirical
formulas have been suggested. To calculate the fair weather
corona losses of transmission lines the very common
experimental formula is Peterson’s;
Pc 
3.73K
(D / r ) 2
f .V 2 kW/km
(1)
where f is the frequency, V the line voltage, and D and r the
phase conductor separation and radius. K is a factor
depending on the ratio of the operating voltage V to the
corona onset line voltage V0 .
Table (1): Corona measurements for different type of conductors.
Conductor Type
Aluminum (r=2.1 mm)
Aluminum (r=4.25 mm)
Steel (r=2.1 mm)
Steel (r=4.25 mm)
Copper (r=1.72 mm)
Copper (r=2.68 mm)
Reference Number: W10-0047
Uiv (İnception
Voltage, kV)
9.05
10.03
6.94
13.52
8.62
10.49
Iiv (Current, μA)
10.10
45.73
56.93
27.12
13.41
44.80
Uev (Extinction
Voltage, kV)
8.19
8.96
6.31
11.36
7.61
9.93
Iev (Current, μA)
33.77
40.61
47.77
25.14
9.30
42.30
353
The Online Journal on Electronics and Electrical Engineering (OJEEE)
Corona onset voltage is calculated as,
VI. CONCLUSION
V0  E 0 .r ln(D / r ) kVpeak
(2)
Here E0 is calculated by the empirical formula

E 0  30 1  0.3
r

kVpeak/cm
(3)
where r is the conductor radius in cm. At standard
temperature and pressure,   1 [3].
Using the experimental results given in Table 1, for
corona inception voltage value and corona extinction
voltage, corona power loss values are calculated. The
results are given in Table 2.
Corona power loss
calculations reveal that increasing the conductor diameter
increases the power loss. As it is seen from equation (1)
power loss is experimentally increased with the applied
voltage to the conductor. And from Table 1, corona
inception and extinction voltage depends on the conductor
diameter and increase with it. So for the same phase
conductor separation, corona power loss is increased with
the applied voltage and conductor diameter.
In this experimental study it has been tried to show how
corona inception and extinction voltage change with
conductor type and conductor diameter under AC
voltages. The results show that corona inception and
extinction voltage increase with increasing conductor
diameter. Also it is reported that the change in corona
inception and extinction voltage depend not only
conductor size also depend on conductor type. Regardless
of the conductor diameter corona start at higher values of
applied voltage compared to extinction voltage.
By using the Peterson’s empirical formula the corona
power loss is calculated. The results show that corona
losses are increased with conductor diameter and applied
voltage.
REFERENCES
[1]
[2]
Table (2): Corona power loss calculations
[3]
Conductor Type
Aluminum (r=2.1mm)
Aluminum (r=4.25mm)
Steel (r=2.1 mm)
Steel (r=4.25mm)
Copper (r=1.72mm)
Copper (r=2.68mm)
PCloss (at Uiv)
983,886
6202,534
754,494
8360,744
570,060
2088,645
Reference Number: W10-0047
Vol. (3) – No. (1)
PCloss (at Uev)
890,389
5540,848
686,002
7025,004
503,267
1977,145
[4]
F.W. Peek, Dielectric Phenomena in High Voltage
Engineering, McGraw-Hill, 1929.
N.H. Malik, A. Al.Qureshi, M.I. Qureshi, Electrical
Insulation in Power Systems, 1st ed., Marcel Dekker,
New York, 1998.
M. Khalifa, High-Voltage Engineering, Theory and
Practice, Marcel Dekker, Inc., New. York, 1990
A. Akses, O. Kalenderli, A.I. Yurekli, H. Kumbasar,
Design and construction of a 12 kV Impulse
generator, EMC Europe 2002, Int. Symp. on
Electromagnetic Compatibility, Sorrento, Italy, pp.
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