Fuse Disconnects Effective against Lightning Surges 4

[CuriousElectron]

Hi guys,

Is it a good practice to install surge/lightning arrestors on distribution poles ahead of service taps to guard against lightning strikes or surges? I don't think overhead fuse disconnects by themselves are an adequate protection against this..

I think the answer to this is based on local Utility practice...

Thanks,
EE

 

[VEBill]

Our local pole-mounted transformer was destroyed by a lightning strike years ago. The replacement transformer is equipped with a lightning diverter device (between the high voltage side to ground).

Fuses are presumably too slow, considering that the arc would establish itself and continue until the end of the strike. Speculation alert, standby for others to confirm this.

 

[crshears]

At the moment I'm on shift with a senior manager [former lines superintendent] who reports that my employer's corporate standard is to include a surge arrestor, most commonly of the metal oxide varistor type, at not only every pole-mounted transformer we own, but also on every other piece of pole-mounted equipment such as in-line regulators, power factor corrective mid-feeder capacitor banks, and at the primary overhead "dip" onto buried cable. Like VEBill said, the operating time of fuses is far too slow to clear the steep-front wave / "spike" typical of lightning strikes on feeders, and this approach is far cheaper than constantly replacing blown trafos. I'm told that historically MOVs were not installed in portions of the lower mainland in British Columbia [ read: Vancouver ] that were not statistically subject to severe electrical storms...yet every few years such a storm would pass through the area, following which "all hands on deck" was declared and every available and qualified crew was set to replacing blown trafos, although there were times they ran out of them, leading to extended delays in restoring all customers.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[davidbeach]

An arrestor that conducts for a half cycle does the trick, a blown fuse requires a callout. An arrestor that does its thing prevents (limits) damage while there has to be damage to get the current necessary to blow a fuse.

 

[dpc]

Common practice is to install a surge arrester on the primary of every transformer. I can't remember not seeing this done - in the US at least.

 

[CuriousElectron]

Are we talking about pole mounted transformers? How about a scenario where a transformer receives its feed from overhead line, should we still include surge arrestors on the line to prevent the surge traveling down the service conductors and hitting the xmfr?

Thanks,
EE

 

[dpc]

Arrestor should be as close the transformer primary bushing as possible. Always.

 

[jraef]

And just to clear this part up, a fuse is there to operate based on CURRENT flow, it is not going to protect anything from lightning strikes until AFTER the lightning causes the kind of damage that makes current flow.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[stevenal]

Curious,

Are you speaking of a pad-mounted transformer? Use an elbow arrestor to prevent overvoltage at the transformer, close like dpc said. Also use a riser pole arrestor, since surges bounce around and double up at every characteristic impedance change. Like the transformer insulation, the UG cable insulation will not recover if over-stressed.