Anyone here work in the Electric Utility field?

[atlbraves49]

I am a recent graduate (EE) and have a new job for a utility company. I have some questions regarding various devices, and would find it especially helpful if there was some type of website/forum dedicated to the electric utility world.

It would seem, that with so many different companies in existence, most of them non-competing, there would be a collection of ideas/forum to communicate. Are there any such forums/websites?

 

[Greg Bernhardt]

Or you could ask your questions here :)

 

[psparky]

I would agree such a place exists!

Right here!

Ask away, young jedi.

 

[atlbraves49]

Or you could ask your questions here :)

Wasn't sure if there was a better option, more focused on utility. Didn't want to clutter up this forum if I didn't have to lol.

Anyways, my initial questions pertain to distribution arresters. My company has a lot of lightning activity, and thus, arresters are important. What is the best method of choosing the right arresters? We have transformers damaged (seemingly) by overvoltage, which, in theory shouldn't happen too often if arresters are doing their job. Trying to determine if they're not spec'd correctly, or if there's something else to consider.

 

[Bobbywhy]

Not only do you need to choose the "right" arresters, you need to place them in the optimal locations. Then, you need to monitor them for deteriorating performance. This is not guesswork; one should rely on competent engineers with accredited credentials to advise you. Here are three sites that may assist you to get started:

Exacter Introduces A Lightning Arrester Verification Program to Prepare Electric Utilities for Spring & Summer Storm Season
For electric utilities, this is the season of more frequent lightning-induced power outages. Lightning arresters are the first line of defense against surge-related problems, however, alarming field metrics from Exacter, Inc. are showing that a high percentage (up to 40% in the southeast) of lightning arresters have either failed or deteriorated in performance, and most of these show no visual or heat signature indication of damage.
http://www.prnewswire.com/news-rele...or-spring--summer-storm-season-210859661.html

A long list of technical articles regarding lightning arresters for utilities:
http://www.hubbellpowersystems.com/literature/arresters/

How one company dealt with the problem:
http://tdworld.com/archive/northern-utilities-optimize-lightning-arrester-placement

 

[atlbraves49]

Thank you Bobby, those materials are very helpful.

I am being expected to become knowledgeable about arresters, with very little assistance from anyone else here. Basically the previous engineer that handled them, left, and I'm replacing that role. There are systems in place, and we have been using certain types of arresters, probably for decades. I'm trying to determine if there are any improvements that can be made, or if what we use is acceptable.

From what I've learned so far, the orientation/placement of the arresters are correct. I have these additional questions:

1) We have both 12kV (actually 12.47kV) and 35kV (34.5kV) distribution lines. We use 10kV (duty cycle) and 27kV arresters, respectively. We use "heavy duty" class arresters. Is there any additional considerations in terms of arresters best suited for handling lightning, or is this pretty much it?

2) Your first article mentions checking arresters for deterioration or failures. To my knowledge, due to the size of our region and number of lines/transformers/arresters, "checking" arresters is practically impossible. The only way we know if an arrester fails is if a lineman physically observes a failure, or if the device (transformer, etc) fails, they go out to replace it, and observe an additional arrester failure. This seems like a problem, but I can't see a cost-feasible way of changing this.

3) When an arrester successfully diverts a lightning strike to ground, once the strike is over, the arrester goes back into its high resistance state, and the circuit remains functional? I've read that some arresters have disconnects where they blow a charge out the bottom and thus no longer function. Am I right to assume that this occurs when the arrester becomes completely overloaded? Or when does this occur?

And when that does occur, the device is no longer arrester-protected, correct?

 

[Windadct]

It is also important to note the configuration of the Line - if it is fed by Grounded Wye (Y), High Impedance (resistance grounded)Wye or Delta Fed... and then there is the Basic Impulse Level (BIL) of the transformer being protected.
So as you mention 10KV arrestors - these must be applied to a Grounded Wye - this ensure the voltage across the arrestor ( Line to Ground) does not exceed 10KV - in an operating condition. Example - if the area where the arrestor is applied does not have a good ground connection back to the upstream - feeding transformer, and one of the Lines faults to ground - then the "local gorund voltage" is raised to the line voltage... now the Arrrestors on the other lines see L-L voltage ( 12,5kV) across them... see the issue) -- So transformers at the end of long distribution lines - may need higher BIL rating as well as higher LA ratings. ( similar issues occur with the High Impedance grounded and Delta feeds)

The overvoltage and surge protection is Coordinated (a conscious engineering effort) considering these and other factors - Knowledge and Experience needed to become effective in this role.