power cables operation, maintenance, location and fault detection
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Technology training that works
Power cables: Operation, Maintenance, Location and Fault Detection
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Topics
• 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
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What is a CABLE?
• Cable: Denotes a bundle of wires– e.g: A wire rope is a type of cable
• Electrical cable is a bundle of electrical conductors used for carrying electricity– Bare conductors– Insulated conductors
• In electro-technology, cable means an insulated electrical conductor used for transmitting electrical energy
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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
Technology Training that Workswww.idc-online.com/slideshareSlide 6
Section of typical HV cable
Alum inum conductorSem icon XLPE(C onductor sh ie ld)XLPE insula tion
Sem icon XLPE(Insula tion screen)
C opper tape
PVC S t2O uter sheath
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Why high voltage?
• Higher the voltage, 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 overvoltages• Ideal way to transmit power across a water
body (Ex: supply to an island)
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Cable-drawbacks
• Fault location is difficult and time taking
• 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 cables
• PVC insulated cables
• VIR insulated cables
• Low pressure oil filled cables
• High pressure oil filled cables
• Paper insulated cables
• Polyethylene (PE) 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 (ex: 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
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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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Installation steps
• Preparation of installation site• Arranging cable supports• Unwinding of cable from the cable drum• Laying along the supports and clamping to
prevent dislocation• Threading through pipes where a cable duct is
used• Jointing/Termination• Testing
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DO YOU WANT TO KNOW MORE?
If you are interested in further training or information, please visit:
http://idc-online.com/slideshare
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