Factors to be considered for High Voltage Cable Joint Design

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Presented by : Shahab KhanMSc Electrical Power Systems

Contents

Introduction

Importance of Cable Joint Design

Design Factors for HV Cable Joints

Conclusion

References

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IntroductionCable Joints and their Use

An integral part of Cable systems Joins up the individual sections of power cables to obtain desired cable

lengthUsed in the event of cable failure

Used to tap into an existing cable (T or Y joints) [1]

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Importance of Cable Joint DesignWhy good Cable Joint Design is so important?

Majority of Faults are in cable Joints (52%) [2]

Reduction of highly skilled Jointers

Economic pressures to reduce Joint installation times as no live jointing is done on high voltages

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Factors for HV Cable Joint DesignTypes of Cables to be joined (Paper, XLPE, Oil, and Gas

filled)

Transition Joints are required for cables with different insulation

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Oil Filled Paper Insulated Cable

XLPE Insulated Cable

Factors for HV Cable Joint Design

What voltage transient levels a Joint may experience?

Transient Overvoltages in cable system through switching surges and faults.

Transients leads to Insulation Coordination issues.

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Factors for HV Cable Joint Design

The Voltage level for which the cable is designed Insulation requirement will increase with voltage level Also different voltage level requires different level of electrical

stress control.

Number of Phases 3Φ and 1Φ cable have different number of cores. Therefore,

Joint design is different.

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Factors for HV Cable Joint DesignDielectric Strength of Cable and Joint body interface

Interface pressure and surface smoothness affects the interface dielectric strength [3]

Better dielectric strength of interface is attained by having high pressure and perfect smoothness.

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Factors for HV Cable Joint Design

Choice of Material for Manufacturing of Joint

Material chosen should lead to easy and quick joint installation No or less sophisticated installation tool requirement Should be reliable and safe as well

Manufacturing and installation costs

Joint manufacturing and installation should be economical

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Factors for HV Cable Joint Design

Design must cater for Straight, Branched and Transition Joints.

Straight Joint for Identical cables

Transition Joint for different insulation cables

Branched Joints to tap into existing cables.

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Factors for HV Cable Joint Design

Location of Cable installation

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Underground Above the ground Inside tunnel

Factors for HV Cable Joint Design

Thermal performance

Thermal performance affects cable ampacity.

Joint must exhibit good thermal performance.

Joint should have continuous temperature monitoring sensors for preventive replacement [4].

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Factors for HV Cable Joint DesignElectrical Stress Control

Fundamental requirement in construction of shielded cable Joint [5].

High electrical stress in dielectric, much higher than the design stress, might lead to permanent cable damage.

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Factors for HV Cable Joint DesignElectrical Stress Control

Control of electrical stress can be done by stress cone or high permittivity material.

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Factors for HV Cable Joint DesignEnvironmental protection

Joint design must prevent the water ingress into cable joint from surrounding.

Mechanical protection

Joint design must have sufficient mechanical strength. Important for cables vulnerable to damage.

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ConclusionCable Joints are the weakest links in Cable Systems.

Joint’s design must have high degree reliability, good thermal performance.

Easy and quick to install yet reliable and safe.

Joint’s manufacturing and installation should be economical.

Types of cable to be joined, cable-joint body interface, cable system voltage and voltage transients greatly influence cable joint designing.

Electrical stress control problem is more pronounced at higher voltages and must be addressed for good joint design.

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References1. R. Goodman, I. Osborn. ”3M Power cable splicing and terminating”.

http://multimedia.3m.com/mws/mediawebserver?mwsId=SSSSSu7zK1fslxtUNx_UlxMSev7qe17zHvTSevTSeSSSSSS--

2. E. Gulski, F. J. Wester, W. Boone, et al, “Knowledge rules support for CBM of power cable circuits”, CIGRE, Paris, 2002

3. S. Ansorge, B. Arnold, ”Jointing of high voltage cable systems”. http://pfisterer.com/download_download/d_3630.pdf

4. D. Fournier and N. Amyot, “Diagnostic of overheating underground distribution cable joints,” IEE Conf. Electricity Distribution, vol. 1,no. 482, June 2001, pp. 18-21

5. Moore, G.F (1997). Electric Cables Handbook. 3rd ed. Cornwall: Blackwell Science. p401-418.

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Thank you for your Time & Attention

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Questions

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