HV cable systems - Cross bonding + transposition 1

[Foudrette]

Hello,

I would like to know in which laying cases (trefoil, flat formation),transposition of HV cables has to be used additionnally to cross bonding of screens. Are there any cases where transposition is not really necessary and we can then use only the cross bonding of screens (when for example cables are laid in symetrical trefoil formation)?

Thank you very much for your help,
Foudrette

 

[cuky2000]

Question: Are there any cases where transposition is not really necessary and we can then use only the cross bonding of screens (when for example cables are laid in symmetrical trefoil formation)?

Yes, for example in trefoil cable configuration and short flat transmission line, transposition may not be required since the mutual impedance is null or small enough that could be neglected.

COMMENT
<sub>Line transposition is desirable to obtain uniform inductance (reactance) in the three phase. When the line is completely transposed, the mutual impedance represented by the off-diagonal elements of the impedance matrix is very nearly balanced. With non-transposed lines, the imaginary portion (reactance) of the off-diagonal terms varies greatly, leading to unbalanced voltages between the three phases.

Cross bonding of screen (Line Shielding) is done for different reason for safety reasons and to improve the operating performance of the line such as to reduce EMF, limit communication interference, reduce the hazard of shock, obtain uniform radial voltage, mitigate excessive voltage stress between conductor and insulation, etc.</sub>