20210257 MV Cable Jointing Termination

7/30/2019 20210257 MV Cable Jointing Termination

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PRINCIPLES

of

M.V. CABLE JOINTING AND TERMINATING


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CONSTRUCTION OF XLPE

CABLES


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Filler

Bedding

Armour

Outer sheath

Binder tape

Conductor

Conductor Screen

XLPE insulation

Copper ScreenInsulation Screen

Construction of XLPE cables


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Conductor

Carries the load current.

Conductor screenEnsures smooth and void free interface with insulation

InsulationPrevents the flow of electricity from the energized conductors to

the ground or an adjacent conductor

Withstands the electrical stresses produced by the alternatingvoltage

Withstands superimposed transient voltage stress on the

conductor



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Insulation screenEnsures that the electrical field is confined within the

polymeric insulation

Copper ScreenKeeps the insulation screen at Earth potential.

Carries the charging current.

Serves as a path for earth fault currents.

FillerFills gaps between cores

Rounds up the cable


Strippable type and bonded type.


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Binds the cores & filler together and separates the cores

from the next layer

Binder Tape

BeddingServes as a cushion for the armour


Extruded bedding protects ingress of water


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Protects against mechanical stresses

Armour

Serves as a path for earth fault currents.

Steel Tape Armour (STA)

Galvanized Steel Wire (GSW) or (SWA)

Types of armour:


Galvanized Steel StripAluminum wire armour (single core cables).


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OversheathProtects against external impact or pressure

Protects against corrosion

Protects from water ingress


Types of outer sheath

PVC PE LSF(LSZH)

Conducting Coating on the outer sheath

Graphite coating

Extruded semi-conducting layer (For HV

cables)

Enables to check sheath integrity


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BASIC CONCEPTS


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What is Electrical Stress?

Basic Concepts


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Potential Distribution within XLPE insulation

Max stress

11kV ---- 2.2kV/mm

33 kV---- 3.5kV/mm

132kV--- 8 kV/mm

Basic Concepts

V

Uo


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Break Down Voltage (BDV)

Air 3 kV/mm

PVC 20-30 kV/mm

XLPE - 40-50 kV/mm

Voltage Insulation

Basic Concepts


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Air void in solid insulation

Voltage

t

V

t

V

Stress across air void = V/ t

Basic Concepts


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Eliminating air voids in cables

Triple extrusion

Super clean XLPE

Dust proof extrusion area

Smooth interface between conductor screen and XLPE

insulation

Basic Concepts


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Nick on XLPE insulation

U0

Conductor

XLPE Insulation Conductor

Screen

Insulation screen

Basic Concepts


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Deep Cut on XLPE insulation

U0

Conductor


Screen

Insulation screen

Basic Concepts


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Lifting of semi-conductingscreen

Basic Concepts

U0Conductor


Screen

Insulation screen


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Stress concentration at the screen termination

Equipotential lines

15%

35%

55%

75%

95%

U0

Conductor


Screen

Insulation screen

Basic Concepts

Flux lines


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Stress control layer at the screen termination

Equipotential lines without control

Basic Concepts

Flux lines

95%

75%

55%

15%

35%

Insulation screen

Conductor

Screen

U0

15%

35%

55%

75%

95%

Equipotential lines with control

Stress Control Layer


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STRESS GRADING BY GEOMETRICAL PROFILE


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STRESS GRADING IN M-SEAL PUSH-ON


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QS-1000 Field Plot

E1 : 1.45 kV / mm Max. Electrical Stress in Connector Area

E2 : 1.66 kV / mm Max. Electrical Stress in the Insulation

E3 : 2.07 kV / mm Max. Electrical Stress at Semi-con Edge

E4 : 2.32 kV / mm Max. Electrical Stress in the Original Cable


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After removing the semi-conducting layer,polish the insulation

surface with Al. oxide cloth and cleaned with cleaning fluid.

IMPORTANT

While preparing the cable:

Take care to avoid any damage on insulation

The end of semi-conducting screen is the most stressed areaof a joint or termination. Take care to avoid any damage or nick

on the insulation in this area.

Basic Concepts

While removing strippable type semi-conducting screen, take

care not to lift up the edge of the screen termination.


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REQUIREMENTS OF JOINTS AND

TERMINATIONS


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Requirements of Joints

Conductor connection

Stress grading

Insulation

Screen continuity

Interfacepressure(Elasticity)

Earth continuity

Sealing Mechanical strength

Requirements of Joints & Terminations


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Requirements of Terminations

Conductor connection

Stress grading Interface pressure (Elasticity)

Creepage Insulation

Earth continuity

Sealing Resistance against UV light (for Outdoor)

Requirements of Joints & Terminations

Documents

20210257 MV Cable Jointing Termination