Belted Cable

 

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. 

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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