Belted cable ( Multi core cable )
- The multi core cable is used for voltage rating up to 11,000 V.
- It is belted type cable consists of circular shaped / oval shaped / sector shaped.
- Each core of multi core cable is wrapped by impregnated paper insulation.
- The space between core / conductor is filled with packing to make the cable circular cross section.
- There is insulating belt of impregnated paper is provided surrounding all the cores.
- The impregnated paper is covered by lead sheath in order to protect paper against moisture.
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Why belted cable is not used above 22 kV?
- The belted type cable construction is not suitable for voltage rating above 22 kV because of radial and tangential stress development in the cable.
- The tangential stress acts along the insulation.
- The electric resistance, dielectric strength of the impregnated paper is higher across the layer than along the layer.
- The leakage current causes power loss due to tangential stress along the impregnated paper insulation and it may be breakdown it.
- As cables are belted together, one / two core of the cable is over stress whereas remaining core is under stress under loading and unloading condition.
- This may result in formation of voids between cores.
- The spaces between cores are ionized during loading of cable and it may deteriorate cable insulation.
- In order to protect insulation against leakage current, screened cables are used in which leakage current is earthed through metallic screen.
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