Are surge arresters required on underground networks?

[electrical429]

Imagine an AIS substation with 132 kV outdoor busbar system, 132/33 kV transformer and 33 kV underground incomer cables, 33 kV indoor metalclad switchboard, 33 kV underground feeders etc. You would normally install surge arrestors on 132 kV side of 132/33 kV transformer. But would you need surge arrestors anywhere on 33 kV side (132/33 kV transformer bushings or 33 kV switchboard terminations) assuming that there will not be any 33 kV or downstream LV overhead lines? My understanding is that no surge arrestors are required on 33 kV as any potential voltage surges on 132 kV side, whether its lightning or switching surges will be drained through 132 kV surge arrestors so no voltage surges will make it into 33 kV side. And considering that there are no overhead lines or AIS busbars on 33 kV side there cannot be any voltage surges coming from 33 kV side.

 

[cranky108]

Yes you need surge arresters on underground. If you don't you will see conductor failures near the end of the line (reflection of surges, and such).

 

[Kiribanda]

From the travelling wave theory, we need to install a surge arrester wherever there is a change
in the surge impedance (Z0). From your description, there is such surge impedance change at the
junction of transformer 33kV bushings & the underground 33kV cable feeder to swgr. Therefore, it
is always advisable to install a set of 33kV surge arresters at this junction. Whatever the surges
not clamped by the 138kV primary side arresters and transmitted to the 33kV secondary side,
will be clamped by the 33kV set of arresters. If the 33kV cable is very long, you need to install
these arresters because of the cable capacitance.

Unless you model your system accurately on an EMT program such as PSCAD or EMTP, you cannot quatify
the transmitted surge to the 33kV side from 132kV primary. Therefore, always it is a good engineering practice
to install a set of surge arresters at the junction of 33kV underground cable.

 

[cuky2000]

Sheath voltage limiters (SVL), is a type of surge arrester used in UG network to protect the outer jacket of the cable from electrical overvoltage stresses caused during transient by switching, short circuit or lightning event. See an example below.

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[stevenal]

Think of it this way: Air insulation is self healing, UG cable insulation is not. You want to protect that UG insulation.
You speak of 33kV switchgear, which could be a source of switching surges.

 

[RRaghunath]

I don't think you need surge arresters on 33kV side (assuming the 3kV bushings of transformer are inside cable box and not exposed).
I haven't seen that in my service of over 35 years.