STUDY ON 500kV AC INTERFERENCE ON THE … ON 500kV AC INTERFERENCE ON THE BURIED GAS PIPELINE Ir. Noradlina Abdullah TNB Research Sdn Bhd, Malaysia ... • Substation Earthing Resistance

STUDY ON 500kV AC INTERFERENCE ON THE BURIED GAS PIPELINE

Ir. Noradlina Abdullah TNB Research Sdn Bhd, Malaysia

21st Conference of the Electric Power Supply Industry, Bangkok, Thailand 23 – 27 October 2016

2Copyright©2016TNBResearch

•  A pipeline, railway or telecommunication cable (referred to as victim line) sharing a common corridor with ac power transmission or distribution lines captures a portion of the electromagnetic field energy surrounding the power lines in the air and soil.

•  This captured energy, often designated as ac interference, can result in an electrical shock hazard for people touching the victim lines or metallic structures connected to them.

•  Excessive stress voltages across rails, telephone pairs or pipe walls and coating surfaces can result in degradation or damage to equipment and puncture of pipe coating, leading to accelerated corrosion and can damage insulation flanges and rectifiers.

Introduction


•  Objective of this study: –  to analyse proximity effect from TNB proposed 500kV

double circuit transmission lines in different scenarios, which are steady state, fault conditions and lightning strike.

–  Induced voltage and currents on a gas pipeline to be d e t e r m i n e d u s i n g C u r r e n t D i s t r i b u t i o n , Electromagnetics and Soil Structure Analysis (CDEGS) software.

Study Objective


•  Network Description •  Soil Structure Modelling & Analysis •  Results & Analysis

– Steady state conditions – Fault condition at Substation – Fault condition due to Lightning

•  Conclusions

Contents


•  NACE SP0177-2007 (formerly RP0177): Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems –  Touch voltages at these installations to be verified less than 15V

during worst case steady state conditions –  Section 4: Design Considerations for Protective Devices, –  Section 5: Personnel Protection, –  Section 6: AC and Corrosion Considerations –  Section 7: Special Considerations in Operation and Maintenance

of CP System and Safety Systems.

Standard References


Network Description

GASPIPELINE

1.  The 36” diameter pipeline enters the right-of-way in a near perpendicular direction, 11.44 km from Substation No. 1 (Terminal 1 - JMJG).

2.  There is no other crossing of pipeline within the right-of-way of the transmission line.


Network Description (cont.)

33.06km

It consists of the following four major components: •  A power system network consisting of a 500kV overhead transmission lines

crossing at angle of 88.67o. •  Two substations (terminals) from which power is fed to the transmission line

network. •  A buried 36ʺ diameter (about 2.6m below ground) high pressure gas pipeline. •  The characteristics of the soil along the right-of-way under study.


•  Phase conductor –  Bundle of four, 523.7 mm2 (1033.5 kcmil),

54/7, ACSR Curlew per phase •  Shield wire: 60 mm2, 12/7, ACSR Skunk •  Span length: Avg. of 450m •  Load Currents (from NLDC)

–  min of 840A, max 1317A •  Fault Currents (from Protection)

–  Single phase to earth fault of 26KA •  Lightning Peak Current (2004 – 2013, TNBR)

–  min 2kA, average 22kA, max 252kA •  Soil resistivity (measured by TNBR)

–  58 Ωm, Wenner method •  Substation Earthing Resistance (measured by

Asset Maintenance) –  Janamanjung (0.50Ω), Ayer Tawar (0.43 Ω)

Input Parameters •  Burial depth: 2.6m •  Steel Pipe diameter: 91.44 cm (36ʺ) •  Wall thickness: 10.88 mm •  Coating type: Fusion Bonded Epoxy

(FBE) electrical strength (3-5kV) •  Coating resistance: 5000 Ωm2


•  One of the major variables affecting AC interference study is the soil resistivity profile of the site.

•  Soil resistivity measurements were performed using the Wenner four-electrode method.

•  Multiple soil resistivity tests were carried out within the vicinity of the gas pipeline crossing.

•  The soil resistivity measurements were analyzed using computer simulation and the resulting composite multilayer soil model is shown in Table 1.

Soil Structure Modelling & Analysis

SoilLayer SoilModelResisFvity(Ωm) Thickness(m)

Top 156.52 0.4348 Middle 58.59 14.88 BoKom 94.68 ∞

Table1:ElectricalSoilModel


•  The SESTLC software package is a transmission and distribution line analyser for rapid line parameter (constants), EMF and steady-state or fault induced voltage estimates (whether inductive and conductive).

•  Estimate line parameters, electric fields, and magnetic fields associated with arbitrary configurations of parallel transmission and distribution lines.

•  It also estimates voltages and currents generated by electromagnetic interference on other neighbouring metallic utilities, such as pipelines, railways and communications lines.

CDEGS Software Module (SESTLC)


Results & Analysis: Steady State Condition

Note:FusionbondedepoxycoaDngselectricalstrengths3-5kV[NACESP0177-2007,Para4.13.2]

0.03795V at 160m (both sides)



0.03795V at 160m (both sides)

Note:FusionbondedepoxycoaDngselectricalstrengths3-5kV[NACESP0177-2007,Para4.13.2]



0.02073 A


•  Pipeline (both sides) from tower center will experience a maximum inductive voltage and coating stress voltage of 0.03795 V which is expected to occur at 160 m from tower center.

•  Test post located at about 198.662m from the right of pipeline center will experience possible induced voltage of 0.03771V and induced current of 18.25mA.

•  Induced voltages at these locations are below the safety limit 15V given in NACE Standard SP0177-2007 (Section 5.2.1.1).

•  Maximum longitudinal current is 20.72mA at the pipeline directly below the overhead line.



•  The probability of AC corrosion is primarily a function of the AC current density at the steel / earth interface and is delineated with regard to the following current density thresholds: –  AC-induced corrosion does not occur at AC densities less

than 20 A/m2 –  AC corrosion is unpredictable for AC densities between 20 to

100 A/m2 –  AC corrosion occurs at current densities greater than 100 A/

m2



•  For a circular coating holiday, the AC current density is related to the induced AC voltage by the following equation:

where; i = AC current density, VAC = induced AC voltage with respect to remote earth, ρ = soil resistivity at steel/earth interface, d = diameter of circular holiday

•  For a worst case condition of 1cm2 surface area of circular coating holiday (i.e. diameter of 0.0113m),

•  Current densities for calculated for maximum possible inductive voltage of 37.95mV during steady state condition is 0.1475 A/m2.

•  Thus, there is no risk of AC-induced corrosion on the pipeline.



•  AC interference on the pipeline caused by the 500kV transmission line during a single-phase-to-earth fault (26kA, 0.5s) occurring at Ayer Tawar 275kV substation is investigated.

•  The distribution of the currents in the faulted phase and earth wires are calculated.

Results & Analysis: Fault Condition (Substation)



Maximum inductive voltage occurs at pipeline distance of 1020m away from overhead line with magnitudes of 2.24V.



Maximum conductive voltage occurs at pipeline crossing with magnitude of 1.14183V



Maximum coating stress voltage occurs at 765m to the right of pipeline crossing with magnitude of 3.04167V.


3.9A at center crossing



•  Maximum inductive voltage occurs at pipeline distance of 1020m away from overhead line with magnitudes of 2.24V.

•  Maximum conductive voltage occurs at pipeline crossing with magnitude of 1.14V

•  Maximum coating stress voltage occurs at 765m to the right of pipeline crossing with magnitude of 3.042V.

•  The maximum pipeline voltages are within the 15V steady-state touch voltage safety limit given in NACE Standard SP0177-2007 (Section 5.2.1.1).

•  For a worst case condition of 1cm2 surface area of circular coating holiday (i.e. diameter of 0.0113m),

•  Current densities for calculated for maximum possible inductive voltage of 2.24V during steady state condition is 8.7067 A/m2.


Summary: Fault Condition (Substation)


•  The proximity effect on the pipeline caused by the 500kV transmission line during a fault due to lightning strike occurring at tower closest (worst case condition) to the pipeline is investigated.

•  The interference levels on the pipeline such as induced potentials (inductive) and coating stress voltages are computed.

Results & Analysis: Fault Condition (Lightning)


•  Lightning activity profile for the proposed transmission line was plotted using available data from 1st January 2004 until 31st December 2013 collected by TNBR Lightning Detection System Network.

•  There was a total of 37,640 lightning strikes detected within 5km radius from center of the transmission line during this period with peak current minimum, average and maximum of 2kA (2%, 752 occurrences), 22kA (50%, 18,820 occurrences) and 252kA (0.01%, 4 occurrences) respectively.

Results & Analysis: Fault Condition (Lightning)


Theproposedtransmissionlineresideswithintheareaswhichexperiencebetween8and9lightningstrokesperkm2peryear(i.e.yellowboundedareas).

Results&Analysis:FaultCondiFon(Lightning)


Results & Analysis: Fault Conditions (Lightning)

FaultCondiFonduetoLightning(22kA)attowertop:VicFmLinePotenFalMagnitude(InducFve)

0.2724 V



FaultCondiFonduetoLightning(22kA):VicFmLineCoaFngStressMagnitude

395.1 V



FaultCondiFonduetoLightning(22kA):VicFmLineLongitudinalCurrentMagnitude

0.4425 mA


•  For average lightning peak current of 22kA, strike at tower nearest to the pipeline: 1.  Maximum inductive voltage occurs at pipeline distance of 1036m away from

overhead line with magnitudes of 0.2724V. 2.  Maximum conductive voltage and coating stress voltages occur at pipeline

crossing with magnitude of 395.1V 3.  Maximum longitudinal current at pipeline crossing is 0.4425mA

•  The maximum inductive pipeline voltages are within the 15V steady-state touch voltage safety limit given in NACE Standard SP0177-2007 (Section 5.2.1.1).

•  Maximum coating stress voltages is below the FBE electrical strength

•  Current densities for calculated for maximum possible inductive voltage of 3.12V during fault due to lightning condition is 1.058 A/m2.


Summary:FaultCondiFon(Lightning)


•  The 500kV transmission line was completed and energized in March 2015.

•  The Close Interval Potential Survey (CIPS) method on coated pipeline with Impressed Current Cathodic Protection (ICCP) was carried out from 29th until 30th December 2015.

•  The survey covers the total length of 1km; with 0.5km upstream and downstream from the center of transmission line crossing the buried pipeline.

•  The survey activities include measurement of cathodic protection level (pipe to soil potential) at three meters interval along the pipeline, transformer rectifiers check and overall CP facilities assessment.

On-Site Measurement Results


PipelineMeasured TotalSurvey(meter) CPProtected CPUnderprotecFon

Area

KP155 1,005 100% 0%

Table 3: Survey results


1.  Simulation results for steady-state conditions and fault conditions have shown that the maximum pipeline voltage is within the 15V steady-state touch voltage safety limit given in NACE Standard SP0177-2007 (Section 5.2.1.1). There is no risk of AC-induced corrosion on the pipeline.

2.  On-site Close Interval Potential Survey results has shown 100% of the pipelines were found fully protected by the present Impressed Current Cathodic Protection current.

3.  The 500kV transmission line crossing the buried gas pipeline at an angle close to 90o is allowable and no risk of AC-induced corrosion on the pipeline.

Conclusions


THANK YOU

Prepared by :

Ir. Noradlna binti Abdullah Technical Expert (Lighting Protection)

Office address:

TNB Research Sdn. Bhd. No. 1, Lorong Air Hitam

Kawasan Institusi Penyelidikan 43000 Kajang, Selangor Darul Ehsan

MALAYSIA

Tel: +603-8922 5000 / Fax: +603-8926 8828/9 Email: [email protected] / Website: www.tnbr.com.my


Disclaimer. All information contained herein are solely for the purpose of this presentation only and cannot be used or referred to by any party for other purposes without prior written consent from TNB. Information contained herein is the property of TNB and it is protected and confidential information. TNB has exclusive copyright over this information and it is prohibited to disseminate, distribute, copy, reproduce, or use and /or disclose this information

Documents

STUDY ON 500kV AC INTERFERENCE ON THE … ON 500kV AC INTERFERENCE ON THE BURIED GAS PIPELINE Ir. Noradlina Abdullah TNB Research Sdn Bhd, Malaysia ... • Substation Earthing Resistance