Research on the Anti-corona Coating of the Power Transmission Line Conductor

doi:10.4236/epe.2013.54B028

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Energy and Power Engineering, 2013, 5, 148-150

doi:10.4236/epe.2013.54B028 Published Online July 2013 (http://www.scirp.org/journal/epe)

Research on the Anti-corona Coating of the Power

Transmission Line Conductor

Ziqiang Xu, Ren Li

Hebei Provincial Key laboratory of Power Equipment Security Defense, North China Electric Power University, Baoding, China

Email: [email protected]

Received April, 2013

ABSTRACT

An anti-corona method for the power transmission lines is proposed in this paper. The RTV coating is used as the an-

ti-corona coating, which is spaying onto the surface of the wearing conductor. The corona characteristic of the conduc-

tor test was done, and the corona onset voltage in crease after the spraying of the anti-co ro na layer, the coron a lo ss in the

same voltage decrease, which could prove the excellent effect of improving the corona characteristic of the conductor.

This anti-corona method will have great prospect, based on the background of the construction of UHV power trans-

mission lines.

Keywords: Corona Loss; EHV/UHV Power Transmission; RTV Coating; Anti-corona

1. Introduction

Corona discharge is a discharge phenomenon that the

surface electric field strength exceeds the breakdown

electric field strength. The breakdown electric field

strength is generally 2 0-30 kV/cm, when the electric field

strength exceeds this value, the discharge sound could be

heard, and the smell of ozone, and the bluish velvet light

could be seen in the surrounding of the conductor. The

ions generated by corona discharge move fro and to the

conductor by the alternating electric field, and light and

radio interference will be generated in the meantime. The

above effect will cause a consumption of energy, which

is called corona loss. The calculation of corona loss is the

primary work in the optimum transmission line design.

Especially the UHV long distance power transmission in

the high altitude areas, the calculation of the corona loss

plays a decisive role [1-3].

Nowadays, the research on UHV and EHV power

transmission is in the studying the characteristic step.

Measures like enlarging the diameter of the conductor,

enlarging the bundle space or raise the height of the

tower can reduce the corona loss of power transmission

line, but on the other hand, the measures themselves will

cause a lot of money. And for the conductors with de-

fects, it is really unrealistic to replace the original con-

ductors in large scale. It is urgently need to find a new

way to reduce the corona loss of the UHV/EHV power

transmission lines. The application object of the an-

ti-corona coating is the windings of the power generator,

which is different from the high voltage level power

transmission line [4-5].

2. Selection of the Coating

The research on the an ti-corona coating is relatively l ittle,

the research mainly aims at the anti-corona of the wind-

ings of the power generator. After overall consider of the

performance of the coating and the cost, the anti-corona

coating should have the following characteristics: low

cost, the easy availability and no harm to the environ-

ment.

RTV coating is a widely used coating for its good heat

and cold resistant and electric insulation property. The

good hydrophobicity and migration of hydrophobicity

make it have the performance of pollution flashover cha-

racteristics, which is the best plan in solving the problem

of pollution flashover of the outer insulation of the power

equipment.

How to put the coating on the surface of the conductor

is another problem, because the shape of the coating will

greatly influence the effect of anti-corona. The methods

in GBT4585.2-91 artificial po llution test of the high vol-

tage insulators in AC systems: quantitative brush method,

pouring method, spray dyeing method, etc. the quantita-

tive brush method and pouring method could not make

the surface of the conductor un iform, so in the end spray

dyeing method is taken. The conductor with and with no

coating are shown in Figure 1 and F igure 2.

The surface electric field strength is calculated with

the finite element method with the software ANSYS, the

electric field strength decrease with the increase of the

thickness of the layer, the relative dielectric constant is 3 ,

and the electric field strength condition is much im-

proved after spraying the anti-corona coating. The di-

Z. Q. XU, R. LI 149

ameter of the conductor is 22.28 mm. The calculation

results are shown in Figure 3 and Figure 4.

Figure 1. Conductor with no coating

Figure 2. Conductor with coating

0.0 0.5 1.01.5 2.0

17.5

18.0

18.5

19.0

19.5

20.0

20.5

E/kV/cm

Thickness of the la

er/m

Figure 3. Electric field calculation result.

Figure 4. Electric field distribution of the conductor with

1mm coating.

3. Corona Characteristic Test

3.1. Test Arrangement

Corona loss experiments based on the small corona cage

is done in North China Electric Power University, key

laboratory Hebei Provincial key laboratory of power

transmission equipment security defense, the cross-sec-

tional structure size of the corona cage is 1.8 × 1.8 m,

and the length is 6 m. With a rated voltage of test trans-

former is 250 kV, which can satisfy the requirement of

corona experiment. The corona loss measurement system

through hybrid light-powered electronic current sensors to

achieve safe and reliable measurement of the corona cur-

rent in corona cage; outdoor high-precision capacitive

voltage divider can achieve accurate and reliable meas-

urement of the voltage; using the coaxial cable to trans-

mit voltage signals and the optical fiber is used to trans-

mit current signals, combined with modern digital signal

processing technology and virtual instrument technology,

voltage and current signals are accurately measured.

Based on the software Labview, the voltage and current

signals are collected and corona loss is calculated. The

sketch of the measurement system is shown in F igure 5.

Instantaneous power method is used to calculate the

corona loss, curren)sin()( im tIti





 , voltage

im , I is the current effective value, U

is the voltage effective value, the power factor angle.

)sin()( tUtu





1-measuring segment; 2-shielding segment; 3-support insulation; 4-resis-

tance switch box; 5-OPCT upper module; 6-OPCT local module; 7-capaci-

tive voltage d ivider; 8-v oltage regulator; 9-test transformer; 10- optical fiber

Figure 5. Sketch of the electrical-optical measurement sys-

tem structure.



 nT

dtuti

IUP 0)()(

cos



(1)

After the discretization,







1

)()(

1Tnf

sjuji

Tnf

P (2

where, fs is sampling frequency, N is computing cycles

3.2. Test Procedure

The first experiment is done on corona loss without

coating material wire. In order to damage in the surface,

grinding the wire surface with coarse sandpaper, then

Z. Q. XU, R. LI

150

4. Conclusions

spray dyeing coating on the wire and the thickness of the

layer is measured by vernier caliper, coating thickness is

about 1 mm, and the experiment is done on the conductor

with coating and without coating.

An anti-corona method is proposed in this paper by

spaying the RTV coating on the wear conductor.

The electric field strength with the coating is less than

that with no coating, and the thicker the coating is, the

less the electric field strength becomes.

The measurement results are shown in Figure 6. As

can be seen, conductor corona loss decreases with the

increase of coating thickness. From the point of the co-

rona loss changes, the corona inception voltage value can

be seen roughly, in the corona inception voltage can be

found to increase with the wire thickness. The anti-co-

rona coating effect is obvious; the thickness of the coat-

ing should depend on the practical situation of the con-

ductor.

The corona loss of the conductor with RTV coating is

less than that with no coating, which means the method

proposed in this paper is effective.

REFERENCES

[1] Z. Y. Liu: “Ultra-high Voltage Grid”, Beijing: China

Economic Publishing House, 2005, pp. 253-256.

[2] J. J. Clade and C. H. Gary: “Predetermination of Corona

Losses under Rain: Experimental Interpreting and Check-

ing of a Method to Calculate Corona Losses,” IEEE

Transactions on PAS, Vol. 89, No. 5, 1970, pp. 853-860.

[3] P. S. Maruvada: “Corona performance of high-voltage

transmission lines”, London, UK: Research Studies Press

Ltd, 2000.

[4] Y. P. Liu, S. H. You, Q. F. Wan, et al., “Design and Re-

alization of AC UHV Corona Loss Monitoring System,”

High Voltage Engineering, Vol. 34, No. 9, 2008, pp.

1797-1801.

[5] F. C. Lu, S. H. You, Y. P. Li u, Q. F. Wan and Z. B. Zhao,

“AC Conductors’ Corona-loss Calculation and Analysis,”

IEEE Transactions on Power Delivery, Vol. 27, No. 2,

2012, pp. 877-885.doi:10.1109/TPWRD.2012.2183681

Figure 6. Measurement results.