Message Board Thread - "Power loss computation"

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Power loss computation ricky 4/22/2008
In our workplace, most 138/69 KV transmission lines anomalies recorded is on a 3 bolt parallel groove clamp connectors, strain, suspension clamps. While in substation's primary high voltage equipments anomalies spotted is on its plate terminals, dropping connectors and disconnecting switch hinges/contacts. With all the recorded temperatures derived from a ThermaCam and the indices readings from the sending/receiving substation. Anybody here in the forum can shed light on how to determine the power loss of said anomaly? preferably a manual computation, meaning not a software based computation. Thank you very much..
 
Re:Power loss computation neatster77 5/2/2008
ricky wrote:
workplace, most 138/69 KV transmission lines anomalies recorded is on a 3 bolt parallel groove clamp connectors, strain, suspension clamps. While in substation's primary high voltage equipments anomalies spotted is on its plate terminals, dropping connectors and disconnecting switch hinges/contacts. With all the recorded temperatures derived from a ThermaCam and the indices readings from the sending/receiving substation. Anybody here in the forum can shed light on how to determine the power loss of said anomaly? preferably a manual computation, meaning not a software based computation. Thank you very much..
I tried doing this a couple of years ago for hot spots in our 115 and 230 kV switchyards. The end result was disappointing. You end up using the old current squared times resistance formula to calculate watt loss on the conductor. You’ll need the resistance of the conductor material without the anomaly. Then you’ll need to calculate the increase in resistance due to the hot spot. Here’s a reference for the calculation. There’s lots of similar info online for material coefficients and such.

http://spiff.rit.edu/classes/phys273/manual/temp_coeff.html

The increased resistance will of course increase the watt loss. So I^2 * R(with anomaly) minus I^2 * R(without anomaly) gives you the increased watt losses due to the bad connection.

Trying to justify your infrared program? You’re probably better off spending your time trying to calculate dollars lost due to failed equipment. But how do you put that into numbers? I don’t know. We haven’t had any failed disconnects or connections to use as a reference. I think the Level III course at ITC is supposed to address this topic but I haven’t taken it yet. I’d appreciate any guidance you come across.
 
Re:Power loss computation ricky 5/4/2008
Hello Neatster77 ;

For transmission line losses computation, what i did is obtain manufacturer's temperature coefficient of resistivity of the conductor used, then its GPS line length where anomaly is located and the maximum recorded temperature of the anomaly. From this data, resistance with anomaly is already known, then using feeder amperage reading from sending substation power loss will be computed and so on...What i am trying to search is the power loss computation that occurred in substation switchyard. I want all anomalies power loss be accounted for the ROI of the infraCam... Thanks for your informative reply
 
Re:Power loss computation Doctir bob 5/5/2008
I wrote a program for watt loss calculation using Microsoft Excel. Primary use is to calculate the resistance of a bad connection in an oil filled circuit breaker. The I^2*R heating is dissipated primarily by the tank side and top surfaces via convection and radiation. Sometimes things are not so simple and this is one of them. I have made the work as easy as possible as all the math is in the software and the user need only enter the proper values of electric current, temperatures, dimensions and emissivity. Our Level I students receive a copy of this on our ITC Resource CD as well as other good stuff. This calculation is probably not optimal for hot connections as it does not account for heat dissipated down the line via conduction. I mention it as I am familiar with the math and it is not simple.

Also, for connection problems, the power loss is usually not be significant compared to outage and safety costs. We create ‘artificial’ hot spots in our ITC student laboratory using 25 watt soldering iron tips. On connections, this can generate several hundred degree F temperature rise. As another responder said, your real savings are found in avoiding unscheduled outages, improving safety and maintaining reliability.

You can estimate outage costs if you know what it costs when the line is out of service. Or, what you make when it’s up and running. Generation pays good money to get their power shipped to the users. Often, revenue numbers are not shared outside the financial gurus’ circle. But, you could work with management to agree on an avoided downtime savings, if not a direct dollar savings. I know of at least one large automotive company that does this. “We saved 8 minutes of downtime on assembly line A.” is good enough for them. And that’s a lot of money when you’re making cars, and probably a lot if you’re shipping electricity in the South in August at 2:00PM.
 


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