Surge Arrestor on Cables Entering an Outdoor Substation 2

[JSLeith]

We have a 100m section of 132kV cable entering into an outdoor substation. At one end the cable is connected to an OHL. Surge arrestors have been installed at the cable sealing ends. The other end the cable terminates into a bay feeder and no surge arrestors have been installed. All other bays connected to the substation are either 132kV OHL’s or transformers, all fitted with surge arrestors. The feeder bay supplying the cable has a line side disconnect switch that may occasionally be open. I will need to confirm that reflections will not cause the voltage to exceed the BIL rating of the cable, with a safety margin.

The question I have is it recommended or normal practice to install surge arrestors at the cable sealing end in the substation to protect the cable against overvoltages from within the substation, say a lightning stike on the busbars etc.

 

[RRaghunath]

Substation by itself would have been protected against lightning strikes through,
- shield wire criss crossing the substation space at top or
- the lightning masts with spikes mounted on top.

This should address the apprehension about the lightning strike in the switchyard that could affect the power cable.

However, I think there should be surge arrestors at the interface between cable and open conductor, irrespective of the availability of surge arrestors in the outgoing OHL feeders. This is important considering that the HV cables are expensive.

Trust the above is helpful.

 

[jghrist]

The surge arresters will probably be required to achieve proper protective margin from reflections for surges at the source end. It is unlikely that the source arresters will have low enough discharge voltage to provide adequate margin at the end when considering voltage doubling by reflections.

 

[RRaghunath]

jghrist,

It is an important point in insulation coordination you touched. Thanks.

 

[jghrist]

The reflections are a point that the original poster says he is going to consider. For a short cable, secondary negative reflections from the source end may get back to the substation end soon enough to reduce the surge voltage. I'd put the arresters at both ends anyway for a 100m length of 132 kV cable even if calculations show an adequate margin. Lightning is a probablistic phenomenon and it may not conform to whatever waveform you use in the analysis.