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The range of voltage and capacity of power transmitted through cables is showing a steady increase over the years. Environmental concerns, aesthetic issues, lack of transmission corridors and difficulty in routing overhead lines in crowded human habitats are some of the reasons for the explosive growth of cable technology well into the extra high voltage range. Due to physical limits on cable lengths for manufacturing and packaging, joints in cable become inevitable, particularly in the context of the utility sector. The cables need to be also terminated at sending and receiving end equipment, a very wide variety of them, in utility as well as industry applications and this calls for appropriate cable termination accessories. Cable terminations and joints form the weakest link in any distribution system. Also, a failed joint in an underground distribution system is much more difficult to locate and repair compared to any similar problem in overhead distribution systems. This means that we should do our upmost to achieve a good joint or termination, which can give years of trouble-free service. The quality of a joint or termination depends to a large extent on the skill of cable jointer. The aim of a cable jointer must therefore be to obtain a joint whose electrical properties are as good as the original cable both in electrical and mechanical terms. The design of cable jointing and termination accessories is based on this perception. Dependence on operator-skill is sought to be reduced to the extent possible by good choice and quality of jointing materials, though such dependence cannot be totally eliminated. We will discuss these issues in this course by looking at the fundamental theoretical aspects involved so that the importance of the correct execution of a termination or joint will be brought home to those who attend the workshop. MORE INFORMATION: http://www.idc-online.com/content/practical-hv-cable-jointing-terminations-engineers-and-technicians-3
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Practical HV cable jointing and termination
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• 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
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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
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Typical overhead line
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Section of typical HV cable
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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
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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
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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)
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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
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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
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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)
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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)
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Straight-through joint
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Making of a T-Joint
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A typical Y-branch joint
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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
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Typical outdoor termination
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