The 4th International Power Engineering and Optimization Conf. (PEOCO2010), Shah Alam, Selangor, MALAYSIA: 23-24 June 2010

LIGHTNING FLASHOVER TEST ON PIPELINE: EFFECT TO CONDUCTING MATERIAL

F.Z.Ab.Latif, F.Hanaffi, A.Nazmin, Aziah Khamis, A.A.Rahman

Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka, Durian Tunggal, 76109 Melaka, Malaysia

Email: farhan@utem.edu.my

Abstract - It is generally known that power system outages caused by lightning flashover present a serious engineering problem. Most of the industrial company take serious action in order to protect their equipment from damage by natural causes such as lightning. It will be the necessary precautions to keep the lightning channel far away from the immediate neighbourhood of flammable and explosive materials. Protection of electric equipment against this power of nature is one objective of high voltage engineer-ing and testing. The aim of this study is to investigate flashover in gap between industrial pipeline and any con-ducting material around the pipe. Impulse voltage test are used to simulate the lightning and tested on prototype of pipeline. The influence of the spark gap discharge on the statistics of the air breakdown processes has been investi-gated in a wide range of gap lengths from 1.0cm to 3.0cm under impulse conditions. The results were discussed base on its breakdown voltage affected by the length of the gap. Keywords: flashover, industrial pipeline, spark gap dis-charge, high voltage testing, Impulse conditions

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I. INTRODUCTION

deally, the lightning protection for pipeline industry is designed in order to provide an effective discharge of direct or indirect strike of lightning and avoid flashover from the pipeline to other material surround it. In practice, however the efficiency of the protection decrease cause by lack of maintenance on the connection or on the earthing of the system. The lightning frequently happens at pipeline industry and do affect the flashover between the material and environment around it. From the previous tragedy, the lightning flashover incident had been occurred at south of peninsular Malaysia. The bolt came during an evening thunderstorm, which striking a tank that held nearly 90,000 litres of petrol. When the sparks flew, two bigger tanks with a total capacity of about 700,000 litres also went up in flames [1]. The Hazard of lightning strike on oil refineries industries at Indonesia and Oklahoma has been reported [2]. Industrial area have more frequent lightning strike compare to other area due by more space charge arise in the area. The flashover from the pipeline to explosive or instrument can create disaster to the

industry. The flashover characteristic can be explained by the breakdown of air as the insulator medium. As insulator medium, the flashovers occur due to break-down in the air are influenced by temperature, humidity, pressure and the shape of the electrode [3]. Thus, changes from one of the characteristic would influence the flashover between the material used and the pipeline. One of the tested that can be used to measure the flashover between the materials is impulse voltage test. Impulse voltage test are generate in laboratory are used to simulate direct lightning strike in positive and negative polarity. It used standard of IEEE STD 4-1995 [4] as a reference.

In this paper, flashovers due to impulse voltage are in-vestigated on gap between industrial pipe and conductive plate depending on the length of the gap. Testings are conducted in room temperature and pressure with power frequency impulse voltage. As a result, the breakdown voltage characteristics shown are affected by the length of the gap.

II. THEORETICAL BACKGROUND

Most of the electrical apparatus use air as the insulating medium. When the applied voltage is low, small currents flow between the electrodes and the insulation retains its electrical properties. On the other hand, if the applied voltages are large, the current flowing through the insula-tion increases very sharply, and an electrical breakdown occurs. A strongly conducting spark formed during break-down practically produces a short circuit between the electrodes. There are two types of breakdown mechanism under different conditions where the mechanism of air breakdown can be explained by Streamer theory and Townsend theory [5]. The Townsend mechanism explains the phenomena of breakdown only at low pressure, corre-sponding to p x d (gas pressure х gap distance) values of 1000 torr-cm and below. While, Streamer theories predict the development of a spark discharge directly from a single avalanche in which the space charge developed by the avalanche itself is said to transform the avalanche into a plasma transfer.

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The 4th International Power Engineering and Optimization Conf. (PEOCO2010), Shah Alam, Selangor, MALAYSIA: 23-24 June 2010

III. EXPERIMENTAL SETUP AND TEST PROCEDURE

The configuration of the experiments was shown in Fig 1. The experiments were performed on gap between stainless steel plate and pipe with the specification of the pipe are 1m length, 4 inch outer diameter and 3.05mm thickness. The length of gap between the plate and pipe are varies from 1.0cm to 3.0 cm with 0.5cm interval. The test is setup with impulse test circuit as illustrated in Fig 1.

Fig1 Impulse Test Circuit

To control and measure the impulse, testing had been conducted at the control room of high voltage laboratory. The high voltage KIT is supplied with two separate instru-ments which is the control unit OT276 and impulse meas-urement unit DM1551. Operating terminal of OT276 is used to control the regulating of (rating transformer) of transformer. The state of contactors as well as the current and voltage on the secondary side of the regulating trans-former are clearly indicated on the front plate which display by LED. The measuring instrument unit DM155 is required in order to measure impulse voltages at the same time. Therefore, the DM1551 is equipped with three independent measuring which is impulse, ac and dc data where it can display all three values simultaneously.

IV. FLASH OVER IN TEST DISTANCE

From the testing, general impulse voltage waveform can be generated as shown in Fig 2. This is according to Stan-dard Impulse Wave shape [IEC public. 60-1(1989)] where the rating is given by 1.2±30% µs for front time and 50±20% µs for the tail time. Front time is measured when the rise voltage increase 90% of maximum voltage and tail time when the voltage decrease to 50% from the peak.

Fig 2 Impulse waveform

Waveform for flashover occurs between the pipeline and the plate is capture as shown in Fig 3. The waveforms pattern is same for different distance but the maximum flashover voltage and the transient time are proportional with the increase of the distance.

Fig3 Flashover waveform

Breakdown voltage results for the test are presented in Table 1. The breakdown voltage result between impulse positive and negative are slightly difference depend on the distance of the flashover occurs. As the result compared with the IEEE STD 4-1995, the impulse voltage between plat-cylinder is much lower than sphere-sphere gap. This is because with 1cm sphere-sphere gap would give 31.9KV while with 1cm plat-cylinder gap tested it gives 16.15KV. As the distance between the plat-cylinder gap are varying with 0.5cm the value of impulse voltage also increased proportionally with the distance gap as shown in Table 1. Breakdown voltage for Impulse positive at distance 1.5cm is 20.83kV which is 2.13kV lower than Impulse negative. Other than that, difference as much as 0.46kV of breakdown voltage at distance 2.0cm between Impulse positive and negative. 31.43kV breakdown voltage for Impulse negative which is 1.25kV higher than Impulse positive at distance 2.5cm and at distance 3.0cm the break-down voltage for Impulse positive is 39.7kV which is 0.88kV higher than Impulse negative.

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The 4th International Power Engineering and Optimization Conf. (PEOCO2010), Shah Alam, Selangor, MALAYSIA: 23-24 June 2010

Table 1 Flashover for different distance Distance

(cm) Impulse Posi-

tive (KV) Impulse Negative

(KV)

1 16.15 16.69 1.5 20.83 22.96 2 27.55 28.01

2.5 30.18 31.43 3 39.7 38.82

The different effect of impulse polarity is presented in

Fig 4 with the flashover voltage under negative impulse are higher for 2.5cm and 3cm. Thus, the flashover voltage under impulse test is proportional with the distance of the gap either using positive or negative impulse.

Fig 4 Effect of positive and negative impulse

V. CONCLUSION

It was shown that due to the industrial pipeline where process plants were belong to the largest and most sophisti-cated structures to be protected against lightning. Special measures must be taken to insure the reliability, the quality and the efficiency of this peculiar industry. In a high danger zone, the pipelines are more exposed to the hazards of lightning direct strike. Base on the test results, the break-down due of impulse voltage on pipeline are lower than breakdown on sphere gap. It shown, the possibility of flashover from the pipeline is high due of the shape of the pipe.In order to avoid the flashover, lightning protection and grounding system must be monitor in the best condition to provide the lowest resistance path for the lightning strike.

VI. ACKNOWLEDGMENT

The author would like to express gratitude to the Faculty Members of Electrical Engineering Universiti Teknikal Malaysia Melaka for giving the opportunity to carry ex-perimental work in their high voltage laboratory and also giving technical support for this project.

VII. REFERENCES

[1] Bernama “Lightning Strikes Petronas Depot” , Inde-pendent National Newspaper Of East Malaysia, April 2006

[2] Christian Bouquegneau, “Lightning Protection of Oil and Gas Industrial Plants”, IX International Sympo-sium on Lightning Protection, November 2007, Brazil

[3] M.S Naidu and V.Kamaraju, “High Voltage Engineer-ing”, 3rd Ed, Mc Graw Hill, 2004, pp 27-39

[4] IEEE Standard technique for High Voltage Testing, IEEE Std 4-1995

[5] J. Kuffel , E. Kuffel, W. S. Zaengl ,”High Voltage Engineering Fundamental”, 2 Ed, Butterworth-Heinemann, 2000

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