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Tervline
03-20-2008, 12:54 PM
Looked through the archives and didn't find this topic. New to the forum, but a long time reader with 27 years in distribution. There are a lot of small co-generation sites showing up on our grid here in Connecticut. Some are solar,wind or water and are designed for an individual house. They come in as less than 6 KW with a bi-directional meter and we are wondering what is being done elsewhere to mark the dedicated transformers, etc.? Has anyone had a negative experience with one of these set-ups? Thanks in advance for your ideas.

mainline
03-20-2008, 07:48 PM
I don't have an answer, but I do have another question. What happens when there is a large outage and a bidirectional meter is backfeeding because the cogen is still producing? Is there a safety to stop that? I have been wondering this for a while.

BigClive
03-20-2008, 09:26 PM
They apparently do have safety systems to stop them backfeeding onto a dead line, but would you trust them?

Imagine you're working comfortably on cable that you've tested and know is dead and the wind gets up to the point some defective device suddenly decides to smack some power out. The answer will ultimately be to ground bond everything regardless, but how many will take their chances on a small street. I mean, what are the chances......

theweber
03-20-2008, 11:42 PM
The system is called a grid tie inverter , be it wind , water or solar. The GTI matches the frequency and voltage. When the CPU detects a service interruption it opens its main contacts. There should be a main disconnect below the meter before the two way meter is installed. If the power company is on its game opening ,locking and tagging then disconnect will be a step of switching for clearance.

australiantroubleman
03-21-2008, 12:32 AM
We have a few installed here in Sydney Australia , they are solar panels fitted on the roof feeding a battery ,some kind of inverter and a bi directional meter.
Im not sure of the rating but it wouldn't be anywhere near 6kw.

We have special warning labels affixed to the distributor fuses associated with the house at the pole transformer or pad mount sub if its underground.
The locations are noted on our maps and we have to isolate each premises prior to any work commencing .

I ALWAYS ground any backfeed and treat any house as a potential source of supply because of the widespread use of generators and who knows what these days.

Im told they will not backfeed into a interrupted supply but as Clive said I wouldn't trust any electronic device so we pull the house service fuse and danger tag it.

mainline
03-21-2008, 08:14 AM
That could make it an absolute nightmare for crews during a storm situation. Having to find and isolate every side tap that could potentially have cogen. The fact that it should be marked on circuit maps. I don't know about everyone elses utilities but our mapping systems is never completely current. I also would never trust a computer system to provide a means of disconnection. We all know how reliable computer systems are. Still it is really interesting.

Ski_Digger
03-21-2008, 03:17 PM
We have a couple of them and they are marked in our maps and we have pics in our shop of were they are, what lines feed them. All of them have lock-out-tag-out, switches for us to use. They are not rated for the back feed if the souce side of the meter is off because they could not handle the large load. They are only rated to handle the house or some of and the exra comming back on our side.
Work safe, test, ground and get the people back on.
Ski:)

thrasher
03-21-2008, 03:39 PM
In Virginia any house that mounts a renewable energy generator is supposed to register with the utility and the generator converter has to meet Underwriter's Laboratory (UL) standard 1741. I'm not worried about the permanently installed gensets the problems we have had is with protable gasoline generators that the idiots make a double male plug cord and plug in to the dryer plug. This has already happened here three times. Before you ask no has been hurt because the crews TESTED before grounding and found the line hot. Twice we found the genset and pulled the meter the third time the crew treated the line as hot and did all repairs with gloves and sleeves. Then they threw in the OCR and let it cook. Never did find out what happened to genset but I hope it was spectacular.

Tervline
03-23-2008, 07:32 PM
I have a meeting tomorrow 3-24-2008 with the safety dept. and I will see what they have to say. I know that our maps aren't current, that is what started the issue. I will push for the labeling on the transformers, and I like the idea that each OH pot should be fused. The company does a "witness test" when one of these co-gens goes online to show that the safety shutoff works if our regular feed goes out. I don't believe that there is a follow up check and will ask that question also. Thanks for the input.

Ski_Digger
03-25-2008, 11:30 PM
Tervline-
Did not catch how many of these you have know on the system. Maybe in your AM. meeting when all the guys are together your mapping person should hand out a copy of that map page so everyone could update the truck maps? Or maybe when the two dirrection meter is set take some pics of the meter setup and disconnects for it so everyone can see.
Just a thought trying to be a help work safe.
Ski:D

Tervline
03-28-2008, 09:47 AM
I believe the figure is 630 units operating or in the process of going on-line. These are the <10KW units. More than I thought on the system(large company) and there will be follow-up meetings. Way behind the curve...