Design of power and communication cable installations to minimise interference in tunnels

A 220 kV XLPE 1×1000 mm2 Al cable was installed by ENDESA in a cable tunnel along the Barcelona inner ring road. The tunnel section is 2.5 m×2.0 m rectangular or 2.5 m diam circular, one side being occupied by power cables and the other side by communication circuits (both copper and optical fibre cables). This forced parallelism implied the risk of inducing considerable voltages in the weak current circuits, as well in the auxiliary circuits. The electromagnetic compatibility (EMC) between the power cable and the communication cables laid nearby was thoroughly considered. The first estimation shows that the induction created by the power cable could exceed the maximum allowable longitudinal voltage level of 650 V (CCITT Directives). In order to evaluate the possibility of co-existence of both systems and the necessary measures for it, a study for the precise evaluation of the induced voltage was made. That study, in turn, required the development of a sophisticated computer program. The program is able to cope with most of the common installations and allows identifying means to reduce the induced voltage to acceptable levels