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A single core cable is graded by using three dielectrics with relative permittivity 5,4,3 respectively. The diameter of the conductor is 2cm and the overall diameter is 8 cm. If the three dielectric work at the same maximum stress of 40kV/cm, then the safe working rms voltage of cable is ______ kV

A single core cable is graded by using three dielectrics with relative permittivity 5,4,3 respectively. The diameter of the conductor is 2cm and the overall diameter is 8 cm. If the three dielectric work at the same maximum stress of 40kV/cm, then the safe working rms voltage of cable is ______ kV Correct Answer 57.72

d=2cm, d1 = ?, d2= ?, D = 8cm Ԑ1 = 5; Ԑ2 = 4; Ԑ3 = 3 gmax =40 kV/cm Ԑ1d1 = Ԑ2d2 = Ԑ3d3 d1 = 2.5cm, d2 = 3.33 cm Rms value of the peak voltage = 81.63/√2 = 57.72 kV.

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