Pole mounted lightning arrestors

[gtwy]

Hello,

I'm more of a low voltage, instrumentation type and was curious about how the power company's pole mounted lightning arrestors work- say at the 14 kv level. I'm used to the gas filled or MOV type down here at the lo voltage level.
Can they fail in such a manner that a visual inspection can't catch?

 

[cranky108]

They are sort of MOV type, at least the newer ones. The older ones had a spark gap at the top. The polymer skined arresters typically fail by generation of gas, either from partial melting, or from water inside. The ground lug will typically be forced away from the body, or the polymer skin will tear. It's usually noticable. The older porclian arresters also developed gas, then exploded. A few would leak and would not be notacable.

Very few power companies use 14 kV arresters in the US, as the typical distribution voltage is 8 kV phase to ground on the primary. The secondary maybe a different story, as some utilities don't put arresters on the secondary (that's why customers should carry insurance).

Why would you think the utility companies arrester failed?

Sags and surges happen all the time, and these are typically not arrested because the magnitude is to small. And most sags and surges are caused by the customers, not the utility company.

 

[dpc]

Failures are generally dramatic and obvious. Arrestors can generate a fair amount of RF energy if there is small leakage current or the outer insulating surface gets dirty and tracks, or there is a loose connection. Corona problems can be detected by both RF and acoustic detectors, but this is almost never done unless someone is complaining.

Very few power companies use 14 kV arresters in the US

A bit of an overstatement. Out west at least, higher voltage distribution systems are pretty common. A lot of 20.8, 24.9 and now even 34.5 distribution feeders are in service.

 

[gtwy]

Thank you for the responses- I periodically visit outdoor custody water metering installations where the transmitter is mounted in an enclosure at grade. Some are more likely than others to sustain some type of repeated surge damage- often it's a matter of lack of grounding and bonding etc at the enclosure. That's when I started to wonder whether the power company can tell whether or not their arrestors are damaged/functional, whether they only check them when there's a failure that takes out a phase etc.

 

[cranky108]

The sad truth is they only check them when they drive by. If it is a remote site, they won't drive by very much.

However, if you have a street light you rent from them, they will typically drive by it monthly. So for an extra $15 to $25 a month you can get the utility to check the arrester.

I don't know if they have remote meter reading, or have a live person read the meter, but the meter readers don't usually know what to look for, so don't depend on that.

We do serve a few remote sites, and sometimes we have issues, but I don't hear that many.