Lightning Surge Arrestors

[Khonwan]

I have just had two high voltage lightning surge arrestors replaced by PEA (cost me over Bt5,000) after they blew within a few days of each other (direct lightning strikes).

I pay the 22-33kV rate for my electricity and therefore assume that the high voltage is not less than 22kV. I was therefore surprised to see that both arrestors are rated at 21kV (Ur) / 17kV (Uc).

The arrestors did their job in that the transformer was undamaged and my power was not interrupted. But, could it be that this apparent mismatch is causing the arrestors to blow?

Rgds

Khonwan

[Crossy]

Do you know your actual incoming voltage (should be marked on the transformer)?

Those numbers do seem low for a 22kV supply

[Khonwan]

Hi Crossy

I’ve climbed the 6 metres or so in the past to examine the transformer, but that was before it was connected to the high voltage – I don’t think I’ll be doing so again.

From memory, I’m pretty sure it is rated at >22kV. I’ll ask PEA.

Assuming the transformer IS rated at >22kV, and the supply IS >22kV, could this discrepancy be to blame for the short life of the arrestor? Should the arrestor be expected to survive a direct lightning strike? The first strike was witnessed by villagers.

Rgds

Khonwan

[Crossy]

I am no lightning expert, IIRC :-

1. Uc is the maximum RMS that the unit is designed to handle (ie your mains voltage).
   
2. Ur is the 'clamp' voltage, ie the maximum voltage that will be developed when a strike occurs (once it's triggered).
   

This suggests that your units with a Uc of 17kV and a Ur of 21kV are possibly on the edge of triggering under normal conditions and are certainly being overdriven which can't be helping them

As to whether they should survive a direct strike it depends on a huge number of variables, they are normally expected to handle several strikes before they fail but a biggie nearby may dump enough energy into the MOV to fry it in one

EDIT

This document suggests that the units you have are the normal ones used by PEA http://www.itee.uq.edu.au/~aupec/aupec03/p...20Klairuang.pdf

EDIT 2

It's just occured to brain here that your units are NOT being over driven, the MOVs are connected phase-ground so there are effectively two in series between the phases giving a rated voltage phase-phase of 34kV

[Khonwan]

Thanks Crossy. An interesting article (despite the difficult ‘English’). My arrestors certainly have not enjoyed a life of 30+ years so I guess something must be wrong. The local manager was saying that he was just learning that areas of frequent strikes may have a concentrated mineral geology that is attracting the lightning (or something like that).

Rgds

Khonwan

[Pink Mist]

The ones I deal with have a life span of one hit and need replacing after that (usually a cartridge)

[Khonwan]

The ones I deal with have a life span of one hit and need replacing after that (usually a cartridge)

Hi bronco

Mine are made by Cooper Power Systems - USA. They are apparently tested to 20 impulses (http://www.cooperpower.com/library/pdf/95062.pdf). No easily replaced cartridges.

Rgds

Khonwan

[Pink Mist]

we build ours into switchboards and are supplied by Schneider, they are providing protection to the electronics within the switchboard.

having said that we supply these boards to Broadcast Australia and they have MOV protection on their masts and antenna's which are sometimes cartridge and sometimes completely replaceable as indicated by LED or other device.

I could get some info for you from the BA engineers if you want.

[Khonwan]

Hi bronco

Are you referring to high voltage arresters? These arrestors are attached to the high voltage cables as they terminate at the transformer. If yes, I could be interested in them were they cheaper than Bt2,370 (the cost of the American product as charged by PEA before labour).

Rgds

Khonwan

[Pink Mist]

Will ring the Schneider rep tomorrow (Monday)