Southern California Outages - Utility Perspective

[saladhawks]

I work for an utility in Southern California and have been amazed by the number of distribution transformer failures over the previous week or so. The temperatures have been extremely hot and I have started to consider this summer to be similar to a "100 year storm."

I have heard of local utilities with 50 kVA transformers failing with 12 residential homes connected. This is a very aggressive distribution transformer loading policy and I wonder if times have changed and transformers should be sized to handle a "100 year storm."

Any thoughts???????????????

 

[SphincterBoy]

50 KVA transformer capacity per every 12 homes? Where I'm at we typically place 50 KVA per every 5 or 6 homes.

I don't know all the usage logistics of SoCal. but I'd say you need to connect a power logging monitor and perform a system study to see if you are undersizing your distribution transformers.

 

[Zogzog]

There have been soem recent problems with insulating oils in new transformers (After 1999) that causes failures in warm climates. The problem is corrosive sulfurs in the oil. ASTM D1275 has a new alternate method for testing these oils.

 

[stevenal]

Yes I would say times have changed. Many of these policies were based on the costs of losses and labor in place at the time the policy was implemented. I think you'll find the labor to replace has outpaced the costs of the losses. As far as the "100 years", I don't think typical transformer life expectancies have reached that mark yet. I'm not sure you'll need to wait a hundred years for similar temperatures to hit, though.

 

[uhn1]

I have 8 houses on a 50kVA TS. The rated FLA is 208 amps. If each house averages 30 amps, this pot is overloaded. Also since this high loading generally occurs during the hottest part of the day, windings have no break from ambient cooling. Try to stick to 5 or 6 (average sized) houses.

Please note that house energy usage can vary widely.

 

[Robert789]

Typically, we would place up to 5 or 6 houses on a 50 KVA transformer. I'm figuring on around 10 KVA per house during peak times.

When it gets hot enough, I think you have to expect that everyone's air conditioning will be running at the same time. It was in the mid 90's in North Carolina last week. I have two air conditioning units on my house and my digital thermostats indicate that they were running about 14 hours per day.

 

[subtech]

What you are seeing here isn't at all a surprise to me.
As utilities "transition" from being managed primarily by those with practical operational experience to those who make binding decisions based soley on dollar amounts, you'll see folly abound. In effort to save the difference in price between a 50 KVA and 75 KVA transformer, some companies will spend $7,000.00 replacing the 50 KVA unit 3 times in a two year time period. I can't tell you how many times in the past few years I've heard "My calculations indicate" or, "the engineering data supports my theory that...." or "in this application, the temperature rise of this unit will be insignificant".
Really, I think Einstein said it best when he said, "I try not to let my education get in the way of my learning".

Unfortunately, we here in the U.S. will have to run through what I call the "sore butt cycle". That is to say, it will take some time for utilities to learn (again) that instead of worrying about appeasing the stockholders every 90 days and making the quarterly stock report look good, we need to worry a whole bunch more about building things in a substantial and longlasting fashion, and doing everything we can to keep unplanned outages to a bare minumum. Yes, robust construction and installing one size larger transformer IS more expensive when one looks at the initial costs. However, when computing the savings accrued over the next 15 summers when crews are NOT called out to replace the transformer which is still humming along, that initial "extra" expense will seem mighty small.
So, what should we "little folks" do in the mean time while utilitys learn all over again to build heavy duty
and focus on what works?
Well, I do the following.
1. Purchase a generator of adequate size to run the critical loads in your home or business.
2. Start and run said generator at least once per month to check its operation.
3. Keep enough fuel on hand to to run this unit at 1/2 of its output capacity for a minimum of 72 hours. (Remember, if you don't have lights the chances are that the gas station down the road from you won't have power either. No power = No fuel)
4. Lastly, I NEVER give financial investment advice to anyone but, I will say this. I work for a utility in the middle U.S. and I can garantee you I have NOT ONE THIN DIME invested in it. The reason for this is simple.
Learning (or in this case re-learning)is sometimes painful, and almost always expensive.

 

[itsmoked]

Interesting sub.

I subscribed to your policy but had problems with the fuel storage. Gasoline stores sooo badly in sooo many ways. I would find that I had 3-4 year old fuel in what seemed like a year. And trying to turn the stuff over is a major pain in the butt. What with dripping nozzles and nozzles that pop out of the jerry cans in the middle of pouring them into my car. And hauling jerry cans around to gas stations it was becoming a real chore. I stopped.

I think a couple of propane tanks makes more sense.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

Hi itsmoked.
I like your solution. It's easy to say diesel when you are advising someone else, but a little harder when it is your own money. Propane sounds like a good compromise.
Respectfully

 

[itsmoked]

Yeah then you can rotate the tanks thru your barbecue to boot. And in an emergency cook with it directly. Try that with gas or diesel.

There are some nice conversion kits out there too.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[SphincterBoy]

Right on subtech! Couldn't agree with you more. I bought my 5 KVA generator ten years ago for the very reason you stated.

I had an old power professor who told us "the problem with the utility industry is the politicians and bean counters have control, not the technical workers".

Sadly, I don't think any of our comments will make any impact with saladhawks' managers. They'll say "rolling blackouts" are the answer, rather than take the correct and logical actions necessary.

 

[fredpar]

In the utility I work for we have been splitting the load and adding transformers. I bet you are talking about pole mounted transformers in old neighborhoods [30+ years]. In some cases you may have to run a primary span to feed the transformer. In those neihgborhoods we have end it up installing a transformer in almost every pole. I do not recomend installing larger transformers because it means more customers out of service when it fails,
Sincerely

 

[apowerengr]

If we had transformers failing due to overload in hot weather the replacement would be double the size of the existing failed unit. Given that transformer fusing tables typically provide for 200-300% of nameplate load, this strategy tried to provide for these types of overloads given the "real-world" demand measurement indicated by the failed unit. From a planning perspective I've used 6 kVA/house with a design target of not more than 125% load on a transformer during peak conditions. 10 customers on a 50kVA transformer has only failed me once - parade of homes where every light was on, the AC was maxed out and any in-floor heat was turned on as well......
The only trick to the doubling of the existing transformer is fault current withstand of customer's equipment - Grandma's 60 amp service with plug-fuses does not like a new 100kVA transformer 60' away........used current-limiting fuses on that particular service in that instance.