Different Screen Arrangements of Distribution Insulated Cables

Abstract

The distribution cables can be operated with their metallic screens in solid bonding (bonded and earthed at both ends) or in single-point bonding (bonded and earthed only at secondary station earthing grid). Each arrangement has pros and cons and the final choice depends upon the cable line length and the earth potential rise of the primary substation. If the distribution network is operated with neutral earthed by an arc suppression coil (or Petersen coil), a first phase-to-ground short circuit gives a low current value (depending on the degree of Petersen coil tuning). In these systems, the sound phases can experience high overvoltages during the fault clearing time so that a second phase-to-ground short circuit can occur in a different phase from the first faulted one. This occurrence is very redoubtable since the short circuit current can be several thousand of amps. The single-point bonding (if applicable) avoids that a great part of the screens is interested by high currents and by their associated I2t. On the contrary, solid-bonded cables suffer from high double phase-to-ground short circuit currents, which could damage the outer jacket of the cables and lead to the failure with time.