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Practical HV cable jointing and termination


• Need for high voltage cables• Advantages of using cables over overhead

transmission lines• Disadvantages of cables • Various types of high voltage cables• Need for cable jointing • Need for termination • Various types of jointing kits and termination

kits

Topics


Function of electrical lines

• Transmitting power from generating source to load centers

• Distributing power from main substations to individual consumers

• Lines can be overhead conductors or underground cables

• Long transmission lines and rural distribution by overhead lines

• Shorter/urban feeders by cables


Typical overhead line


Section of typical HV cable


Why high voltage?

• The higher the voltage, the lower the current for a given value of power

• More energy transmitted for a given conductor section

• Lower conductor losses


Relation between voltage and load rating

Motor rating in kw Operating voltages in Volts

Up to 200kw 415V

Between 200 to 500kw 3300V

Between 500kw to 2500kw

6600V

Above 2500kw 11000V


Cables: Advantages

• Less space compared to overhead lines• No visual intrusion (also called visual

pollution)• Not susceptible to atmospheric activity

(wind/lightning)• Higher surge impedance reduces severity of

switching over voltages• Ideal way to transmit power across a water

body (e.g., supply to an island)


Cable-drawbacks

• Fault location is difficult and time consuming• Expensive• More monitoring (for certain types of cables)• Jointing/termination require persons with high

skill levels• Joints/terminations become weak points• Testing is difficult and time consuming


Common types of HV cables

• Low pressure oil filled cables• High pressure oil filled cables (Common for

EHV)• Paper insulated cables• Cross linked polyethylene (XLPE) cables


Need for jointing (Splicing)

• Cables are heavy and difficult to transport• Fixed drum lengths (e.g.,500m) are typical

packaging norm• Longer feeder lengths need joints• Joints are needed for partial replacement (in

case of a cable fault)• Joints are also needed for specific purposes

(next slide)


Types of joints

• Straight through – Long routes and repaired sections

• Branch Y joints– For branching of a feeder

• T joints– For branching of a feeder

• Transition joints– Special joints between two different types of

cables (Oil filled/XLPE)


Straight-through joint


Making of a T-Joint


A typical Y-branch joint


Need for termination

• A cable needs to be connected to an equipment or another cable

• A connection between two cables is called a joint

• A connection to an equipment is called a termination

• Termination can be indoor type or outdoor type• End sealing kits are used to cover the cut end of

a cable against moisture entry


Typical outdoor termination


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