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UNDERGROUND TRANSMISSION SYSTEM - Coggle Diagram
UNDERGROUND TRANSMISSION SYSTEM
GENERAL
underground transmission systems can be either underground cables or submarine cables.
underground transmission systems can cost 4-10 times more than an equivalent distance overhead line.
despite the high cost and operational limitations, underground transmission systems are still sometimes necessary in urban areas or sensitive locations.
CHARACTERISTICS
electric power can also be transmitted by underground power cables instead of overhead power lines.
underground cables take up less right of way than overhead lines, have low visibility, and are less affected by bad weather.
however, costs of insulated cable and excavation are much higher than overhead constructions.
underground cables are strictly limited by their thermal capacity, which permits less overload or re-rating than overhead lines.
long underground AC cables have significant capacitance, which may reduce their ability to produce useful power to loads beyond 50 miles (980km).
long underground DC cables have no such issue and can run for thousands of miles.
UNDERGROUND CABLE
cable is a conductor which is
insulated electrically
and
protected mechanically
.
the cable design complexity increases with voltage level.
in low voltage (LV) cable design, the basic criteria are to provide insulation and mechanical protection.
for medium voltage (MV) and high voltage (HV) cables, besides insulation and mechanical protection, electric field stress management must be considered together with other parameters that may affect the safe operation of the cable.
EXTERNAL PROTECTION
underground transmission systems require trenches to be dug to lay cables, either directly buried in-ground or in ducts. ducts can either be concrete encased or plastic pipes.
CABLE ACCESSORIES
Cable joints/splice
purpose
used to link individual sections of power cables to achieve the desired length.
to replace failed section of a cable.
to tap into existing cables (Y or T joints).
the joints/splices are designated according to the voltage level, number of cores and insulation.
Cable termination
the electrical cable termination is the physical and electrical connection of a cable end that connects to another cable, or to the terminal of the equipment.
the methods used to terminate the cables vary according to the type of cable, type of connector, and application
basic electrical and mechanical requirements for joints and terminations
there must be sufficient contact area between the two current-carrying surfaces (e.g. between wire and terminal) this ensures that heat is not generated on such surfaces on account of increased resistance.
there must be adequate mechanical strength this will avoid cables from being pulled apart.
should be easy to connect and disconnect (although electrical joints are made permanent by crimping or soldering).