Defective CT

[brian john]

I received a call this afternoon customer that says they have primary at metering of the line side of a at 36KV delta transformer (information he supplied I have no idea if this is correct), they lost a CT on C phase and the utility wants to recover back revenue, based on the loss of the CT. MY question is is this as simple as the KW is 1/3 less with the loss of a single CT, or is it more involved that this?

My thought was look at average revenues and for the same periods of time and arrive at a settlement with the utility, his bosses want to know try and base the pay on close to actual usage.

 

[hmspe]

My first questions would be:

When did the CT fail? How do they know the failure date?

Was the CT reading high before it failed? Or low? Or did it just open circuit? How do they know?


I would agree that historic usage data would be a more reasonable approach than assuming that they should just add 50%, especially if they are guessing as to when and how the CT failed. On the other hand, if the CT was utility equipment and it was the utility's responsibility to maintain the equipment then the honorable thing for the utility to do is eat the loss.

 

[mivey]

If #1) the CT were failed for the ENTIRE metered period, AND #2) the load was approximately balanced, then the metered load is approximately 1/3 less than actual.

This is I say this because a primary meter usually has 3 CTs so it would be true for that case. This will not be the case for some other meter configurations.

As for the possible errors:

If the meter records interval data, then they should be able to tell about when the CT failed and that would take care of #1.

If the load is not balanced, but is a very stable load, the you can estimate your way around #2 using current load balance data.

 

[mivey]

I would agree that historic usage data would be a more reasonable approach than assuming that they should just add 50%,

Depends on the stability and seasonality of the load.

then the honorable thing for the utility to do is eat the loss.

The other customers would ultimately eat the loss. However, when estimates are necessary, we try to err in the consumer's favor but not to an unreasonable stretch. Most customers would agree that the honorable thing would be for the consumer to pay for what they used and most policies outline a method to make a reasonable estimate when needed.

 

[brian john]

My first questions would be:

When did the CT fail? How do they know the failure date?

Was the CT reading high before it failed? Or low? Or did it just open circuit? How do they know?

I am not sure of this as this was a call out of the blue an facility manager on the eastern shore of Maryland was told I might have the answer. And due to the brains here I may very well have the answer.

[QUOTE}
I would agree that historic usage data would be a more reasonable approach than assuming that they should just add 50%, especially if they are guessing as to when and how the CT failed. On the other hand, if the CT was utility equipment and it was the utility's responsibility to maintain the equipment then the honorable thing for the utility to do is eat the loss.[/QUOTE]


My understanding is this is a large food processing facility and1/3 is a sizable sum. I have been involved in similar issues in the past and in my experience the two sides come up with a number and then negotiate to a middle ground.

 

[G._S._Ohm]

You may be able to come up with presumed actual usage +/- some tolerance band. This may easier than getting both sides to accept it.

If you can post B4 and after data using simple Excel statements and lookup tables I can give you the two numbers above to some level of confidence, but not even engineering companies like doing this.
They don't understand it.
And they don't want to, either, unless it gives them numbers that they like.

 

[mivey]

If you can post B4 and after data using simple Excel statements and lookup tables I can give you the two numbers above to some level of confidence, but not even engineering companies like doing this.
They don't understand it.

Like engineering companies don't get statistics.:roll: Everything doesn't require a statistical analysis, especially when an experience level tells you you are close enough. Also, the level of confidence will depend on the assumptions and that can make a big difference.

Besides, we often see that feel-good decisions rule the day and the data gets thrown out along with consistency, accuracy, etc.

 

[brian john]

I called the customer regarding this and was told his bosses asked to "stand down" as the firms lawyers will handle this.

 

[hillbilly1]

I had a customer that I put in a new 800 amp delta service for, and the POCO metering department marked the meter with the wrong multiplier. After about a year they sent the customer a bill for $60,000. They told them they didn't have to pay it all at once since it was an error on their part!

 

[brad9m]

Often times there is additional metering on the lines that isn't qualified as "revenue" metering. I would ask if there are any other meters or relays with metering enabled on the line. That would get you much closer to actual.

 

[brian john]

Often times there is additional metering on the lines that isn't qualified as "revenue" metering. I would ask if there are any other meters or relays with metering enabled on the line. That would get you much closer to actual.

Having been involved in quite a few projects where the lawyers get involved, I generally take my exit here. Logic, common sense and actual facts often are cast aside in the discussion and my frustration levels rise.