lightning protection for gas- pipelines installed under the ground · 2010-11-02 · lightning...

Lightning Protection for Gas- Pipelines installed under the Ground

HITOSHI KIJIMA、KOJI OCHI

Electrical Department Polytechnic University

4-1-1 Sagamihara Kanagawa 229-1196 JAPAN [email protected]

Abstract: - Lightning Protection for Buried Gas-pipelines has not yet being studid. Gas-Pipelines usually are covered with polyethylene sheath. When there is a high tower nearby a pipeline, polyethlene’s insulation may be destroyed by earth potential rise caused by lightning surge. In this study, we can evaluate possibilities of insulatin breakdown of polyethren sheath using electric current distribution and electrical field analysis.

As there is no rule on countermeasures in the world, we have to investigate the phenomenon when a lightning strikes the pipelines. Even the gas company normally use aditional hard steel pipes or iron plates to protect gas pipelines from lightning surge current, the effectiveness of these counter measure methods have not been evaluated. In addition to these methods, we have also investigated on the effectiveness of buried shielding wire normaly used for burial telecommunications lines.

In this study, we have simulated various methods such as hard steel pipes, iron plates and buried shielding wire by using computer software so that called JMAG.

Key-Words: - pipeline, dielectric breakdown, sheath pipe, protection griddle, counterpoise, JMAG 1 Introduction

Lightning protection for power installations and telecommunications installations have being studied [1].[8]. However, it was not yet investigated on the lighting protection of burial gas-pipelines. Polyethylene is widely adopted as a pipeline's outside corrosive protection material. When a power transmission steel tower etc. is installed near the pipeline route, when earth potential rise caused by a direct lightning strike to the tower, dielectric breakdown of polyethylene occurs. As there is no rule on countermeasures in the world, we have to investigate the phenomenon when a lightning strikes the pipelines. Even the gas company normally use aditional hard steel pipes or iron plates to protect gas pipeliness, the effectiveness of these counter measure methods have not been evaluated. In addition to these methods, we have also investigated on the effectiveness of buried shielding wire normaly used for burial telecommunications lines. In this research we used JMAG which is magnetic-field analysis software applying the finite element method[9].. 2 Several lightning protection measures

The following can be considered as measures against lightnig damage.

Table 1 Lightning protection measures Measures View

(1) Cover by sheath pipe protection

covered with a steel sheath pipe.

(2) Cover by a protection griddle

covered and equalized by a protection griddle.

(3) Cover by counterpoise A counterpoise is laid 30cm upper partof the pipeline

Fig.1 Lightning Protection measure (cover nothing, a sheath pipe, a protection griddle, an counterpoise)

SELECTED TOPICS in POWER SYSTEMS and REMOTE SENSING

ISSN: 1792-5088 171 ISBN: 978-960-474-233-2

3 Examination items 3.1 Parameter selection

In analyzing by JMAG, parameters were selected as follows. (1) Make a pipeline's burial depth into 1.5 general below ground. * Quality of the material -- Steel Inside diameter 387.4×10-3ｍ Outer diameter 406.4×10-3ｍ Steel pipe thickness 9.5×10-3ｍ Pipeline length 20.0m Volume specific resistivity 1.5×10-7Ω･m Relative permeability 280 (2) Quality of the Polyethylene Outer diameter 411.4×10-3ｍ thickness 2.5×10-3ｍ length 20.0ｍ Volume specific resistivity 1.0×1014Ω･m Specific inductive capacity 2.3 (3) Make the burial depth of a sheath pipe into 1.4m below ground. * Quality of the material -- Steel Sheath pipe inside diameter 589.0×10-3m Sheath pipe outer diameter 609.6×10-3m Sheath pipe thickness 10.3×10-3m Sheath pipe length 20.0ｍ Volume specific resistivity 1.5×10-7Ω･m Relative permeability 280 (4) Make a protection griddle and the burial depth of counterpoise into 1.2m below ground. Upper part (side) protection griddle width w3 (w4) 1.0m Upper part (side) protection griddle thickness 6.0×10-3m Upper part (side) protection griddle length 20.0ｍ Distance of a side protection griddle and a steel pipe

0.3m Radius of counterpoise 1.0×10-2m Counterpoise length 20.0ｍ Volume specific resistivity 1.5×10-7Ω･m Relative permeability 280 (5) Soil Soil specific resistivity ρs 30～1000Ω･m

3.2 Dielectric breakdown of polyethylene

(a) Fig.2 Voltage in which polyethylene causes a dielectric breakdown [3] .

Since thickness of polyethylene was set to

2.5×10-3m in this model, figure 2 shows that the dielectric breakdown voltage of polyethylene is 200kV(2.0E+5V). This value is compared with the value computed by the simulation.

3.3 Model (b) A direct lightning surge peak current is 100kA. (c) A pipeline's burial depth is 1.5 m under the

ground. (d) In order to examine the screening effect by the

difference in soil resistance, soil specific resistivity was made into 30, 100, and 1000 Ω･m.

(e) Model radius is 3 m. (f) Model total length is 20 m.

Fig.3 Cross section view


ISSN: 1792-5088 172 ISBN: 978-960-474-233-2

Fig.4 Outside cubic diagram 4 Simulation

The electric field up to 1.5m below ground is examined in the case with and without cover. Moreover, it examines what kind of change takes place in the case where soil specific resistivity is changed. In this study, we have simulated various methods

such as hard steel pipes, iron plates and buried shielding wire by using computer software so that called JMAG which is magnetic-field analysis software applying the finite element method[9] .

4.1 With no cover

The analyzed result at the time of changing soil specific resistivity is shown in Table 2.

Fig.5 Flow of the current when not covering

Table 2 Field strength at gas pipe burial position Electric field [V/m] ( ρs=30Ω･m) 1.729E+2（100％）

Electric field [V/m] ( ρs=100Ω･m) 1.665E+3（100％）

Electric field [V/m] (ρs=1000Ω･m) 2.434E+0（100％）

From now on, field strength in the case of having no cover will be made into 100%.

Next, it takes into consideration about the dielectric breakdown (ρs=100Ω･m) of polyethylene.

Since voltage integrates with the field strength up to 1.5m,

2.64E+7 V ≫ 2.0E+5V （１） It became clear from the result of (1) that the

voltage exceeding the breakdown voltage value of polyethylene is added. It turned out that polyethylene will cause a dielectric breakdown in the case of no cover.

4.2 Cover using a sheath pipe (whole part)

The gas company normally uses aditional sheath steel pipe (whole part) to protect gas pipelines from lightning surge current.

The analyzed result at the time of changing soil specific resistivity values is shown in Table 3.

When a sheath pipe (whole part) is used, compared with the case where there is no cover, electric field strength has fallen sharply.

It tured out that the current from all the direction was able to be covered by the sheath pipe (whole part).

Fig.6 Flow of the current when using a sheath pipe (whole part)

Table 3 Field strength at gas pipe burial position Electric field [V/m] (ρs=30Ω･m) 2.116E-4（0.00012%）

Electric field [V/m] ( ρs=100Ω･m) 1.602E-5（0.000019%）

Electric field [V/m] (ρs=1000Ω･m) 4.422E-8（0.0000018%）


ISSN: 1792-5088 173 ISBN: 978-960-474-233-2

When it takes into consideration about the dielectric breakdown (ρs=100Ω･m) of polyethylene, it is at voltage.

1.90E+3 V ≪ 2.0E+5V （２）

The result of (2) showed that it was less than the

breakdown voltage value of polyethylene. It is thought that it can become a protection measure very effective when a sheath pipe (whole part) is used.

4.3 Cover using a sheath pipe (only upper part)

Even the gas company has not yet used sheath steel pipe having only upper part, we investigated this model.

The analysis result at the time of changing soil specific resistivity ρs is shown in Table 4. Fig.7 Flow of current covered with sheath pipe (Only upper part)

Table 4 Field strength at gas pipe burial position Electric field [V/m] (ρs=30Ω･m) 5.130E-3 (0.0029%)

Electric field [V/m] (ρs=100Ω･m) 3.518E-4 (0.000021%)

Electric field [V/m] ( ρs=1000Ω･m) 3.282E-5 (0.000013%)

It turned out that electric field strength has fallen

sharply compared with the case where there has no cover even when a sheath pipe (upper part) is used.

When it takes into consideration about the dielectric breakdown (ρs =100Ω･m) of polyethylene, it is at voltage.

5.84E+3 V ≪ 2.0E+5V （３）

The result of (3) showed that it was less than the breakdown voltage value of polyethylene. By this,

when a sheath pipe (upper part) is used, it becomes a very effective protection measure.

4.4 Cover using a protection griddle

The gas company normally use iron plates to protect gas pipelines from lightning surge current, The analyzed result at the time of changing soil

specific resistivity ρs is shown in Table 5.

Fig.8 Flow of the current at the time of covering by a protection griddle


Electric field [V/m] (ρs=100Ω･m) 1.032E-1（0.0062%）

Electric field [V/m] (ρs=1000Ω･m) 6.026E-1（24%）

It turned out that compare having no cover and

electric field strength has fallen from Table 5. The protective barrier of the upper part and left-hand side shows intercepting current. However, since the pipeline's whole surface is not enclosed like a sheath pipe, it is assumed that the current from a right-hand side and a lower part side without a protective barrier was not able to be covered.


4.01E+4 V ≪ 2.0E+5 V （４）

The result of (4) showed that it was less than the breakdown voltage value of polyethylene. Even when a protection griddle is used, it can be said that it can become an effective protection measure.


ISSN: 1792-5088 174 ISBN: 978-960-474-233-2

4.5 Cover using counterpoise (whole part)

Even the gas company des not use counterpoise, we have investigated on the effectiveness of buried shielding wire normaly used for burial telecomm. lines.

The analyzed result at the time of changing soil specific resistance ρs is shown in Table 6.

Fig.9 Flow of the current at the time of covering with an counterpoise (whole part)




It turned out that compare having no cover and

electric field strength has fallen extremely from table 6.


3.31 E+3 V ≪ 2.0E+5V （５）

The result of (5) showed that it was much less than the breakdown voltage value of polyethylene. The screening effect was excellent as a measure.

4.6 Cover using counterpoise (10cm of iron bar interval of 1m)

The analyzed result at the time of changing soil specific resistance ρs is shown in Table 7.

Even if it installs a 1m stick at intervals of 10cm, it is thought that it can cover almost as well as what laid one iron stick underground.

Fig.10 Flow of the current at the time of covering with an iron bar (10cm interval)

Table 7 Field strength at gas pipe burial position Electric field [V/m] (ρs=30Ω･m) 5.413E+0 (3.1%)

Electric field [V/m] ( ρs=100Ω･m) 1.660E+0 (0.099%)

Electric field [V/m] (ρs=1000Ω･m) 1.631E-1 (6.7%)

When it takes into consideration about the dielectric

breakdown (ρs=100Ω･m) of polyethylene, it is at voltage.

3.56E+3 V ≪ 2.0E+5V （６） The result of (6) showed that it was much less than

the breakdown voltage value of polyethylene. 5 Comparisons

The analyzed result of the voltage is shown in Table 8. Table 8 Voltage evaluation of various measures

With no cover

Voltage (ρs=30Ω･m)

Voltage (ρs=100 Ω･m)

Voltage (ρs=100 Ω･m)

With no cover

2.17E+8 ×

2.64E+7 ×

6.60E+6

× Sheath pipe protection (whole)

1.95E+4

1.90E+3

5.85E+2

Sheath pipe protection

(upper part)

1.95E+4

5.84E+3

5.84E+2

Protection griddle

2.22E+5

× 4.01E+4

1.70E+4

Counterpoise

(whole) 1.04E+4

3.31 E+3

3.13E+2

Counterpoise (1m interval)

1.84E+4

3.56E+3

5.53E+2


ISSN: 1792-5088 175 ISBN: 978-960-474-233-2

Order of the screening effect is in the case of ρs =100Ω･m is as follows.

1. Cover by Counterpoise (whole part) 2. Cover by Counterpoise (1m Interval) 3. Cover with Sheath Pipe (Whole part) 4. Cover with Sheath Pipe (Upper Part) 5. Cover by Protection Griddle

The electric field distribution by the counterpoise

(whole) having the best screening effect is shown in figure 11.

Fig.11 Electric field distribution by counterpoise 6 Conclusion

The following results were obtained by analyzing electric field distribution of the lightning surge which flows into a burial pipeline by JMAG. (1) If nothing copes with it, polyethylene will cause a dielectric breakdown, and a hole will open. Thereby, a gas leak may be caused. (2) By enclosing a pipeline's whole surface by the high substance (steel) of conductivity and relative permeability, the current from all can be covered and it can be said that it is the outstanding measure against lightning. (3) Using a griddle, a screening effect is acquired from a pipeline because at least a part covers the 0.3-m-away place. (4) By laying an iron bar under the 0.3m upper part from a pipeline, most current concentrates on an iron bar and a very effective screening effect is acquired. (5) Table 9 shows comprehensive evaluation of various measures.

Table 9 Comprehensive evaluation of various measures

Screening effect

Construction expense and time

evaluation

With no cover × ×

Sheath pipe protection (whole)

Sheath pipe protection

(upper part)

Protection griddle ×

Counterpoise (whole)

Counterpoise (1m interval)

References: - [1] H. Kijima, M. Shibayama, Circuit breaker type

disconnector for SPD, WSEAS Transactions on power systems, Issue 5, vol. 4, pp167-176, 2009

[2] H. Kijima, T. Hasegawa, Electrical force analyzed on switchgear of disconnector, WSEAS Transactions on power systems, Issue 1, vol. 5, pp32-41, 2010

[3] IEC 61643-1, Surge protective devices connected to low voltage power distribution systems Part 1: Requirements and test methods, 2005

[4] H. Kijima, Overvoltage protective device and method of overvoltage protection, 8th electrical conference WSEAS, pp155-160, 2009

[5] H. Kijima, Experimental results on earth potential rise when arrestor operating, 12th WSEAS conferences, pp311-315, 2008

[6] K. Takato H. Kijima, Transmission degradation in the frequency band of PLC, 12th WSEAS conferences, pp.300-305, 2008

[7] H. Kijima “Earthing system and lightning protection,” Corona Co. Published, ISBN4-88552-147-C3055, 2002

[8] H. Kurosawa, H. Kijima “Recent lightning protection design,” Japanese Standard Association Published, ISBN4-542-30397-7-C3054, 2006

[9] Japan Research Institute, Inc. "JMAG-Studio version8.4" and Vol.1, 2006


ISSN: 1792-5088 176 ISBN: 978-960-474-233-2

lightning protection for gas- pipelines installed under the ground · 2010-11-02 · lightning...

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