IEEE 519 - 1992
IEEE 519 - 1992
(OP)
In reviewing the standard I notice that the Isc used for the calcs appears to be infinite source. For those of you that have done the TDD calcs, do you use the infinite source or use the actual when it is available?
Just wondering what the intent of the standard is in this regard.
Thanks
Just wondering what the intent of the standard is in this regard.
Thanks
Alan






RE: IEEE 519 - 1992
RE: IEEE 519 - 1992
I don't recognize TDD, and expect you mean THD or Total Harmonic Distortion, and I know that calc requires the use of the actual Utility source contribution. A system can tolerate much more distortion if it's a strong source.
John M
RE: IEEE 519 - 1992
Once you have a intervening transformer of known impedance, the variation in THD calcs due to utility side SCC are minimized, but can still be a factor, if the numbers are border line.
Assuming an infinite bus when it is not would give lower THD, than actual and could be misleading.
Rafiq Bulsara
http://www.srengineersct.com
RE: IEEE 519 - 1992
I agree that using infinite source when it is not would make the source seem stiffer than it actually is, hence my question.
The standard is quite misleading, at least to me, in that what they call "actual" source Z is calculated as infinite bus.
Alan
RE: IEEE 519 - 1992
And yest it is a misleading/confusing document, frequently misused at the expense of end users.
Neil
RE: IEEE 519 - 1992
I understand the concept and understand that Isc/Iload will be greatly affected by that choice. Just trying to get a feel for how others are applying it and if anyone knows the actual intent of the committee.
It seems to me that if actual is known it should be used, but then you could have engineers doing it both ways. As rafiq says, using infinite when we know it is not will give you higher margins for TDD.
Hence my question.
Thanks
Alan
RE: IEEE 519 - 1992
Has anyone ever seen a Utility come back on a power user with numbers showing violation of IEEE 519-1992?? I might expect th at an obvious violator that's causing tripounts in the neighborhood might get flagged, but certainly not small to medium sized service customers.
John M
RE: IEEE 519 - 1992
My experience has been that in most cases the customer is causing their own problems with current distortion, but the supply voltage is still well within the THD recommendations of 519. No other customers on the service. We end up telling them that as long as they can live with it, so can we.
Alan
RE: IEEE 519 - 1992
This Isc is the short circuit current at the Point of Common Coupling (PCC) between the utility and the customer, the point accessible to both, usually the service or metering point.
It isn't proper to specify that a piece of equipment meet IEEE-519 based on the load harmonic and fundamental current in that piece of equipment. For one thing, the equipment is probably not the only source of harmonic distortion and the IEEE-519 limits are for the entire plant. You also have to know the Isc at the PCC to determine the limits.
RE: IEEE 519 - 1992
Now that I have gotten a chance to review the document, it does not refenence infinite source as some, not here, have stated.
I agree that it is not proper to spec the equipment that way, but some do!
Thanks for all the input.
Alan
RE: IEEE 519 - 1992
With the high Isc at this bus the current TDD limit would be 12%, not 5%, if the 519 recommendations were applicable to this bus and equipment. As John M, said the client is creating his own problems.
I did calculations per ANSI standards to derate the oversized upstream equipment for harmonic heating effects and determined that the load of 54% of transformer rating is actually equivalent to 56% load for those 20 second periods. No other equipment has been affected.
Together with vendors, we spent over $500K adding notch filters and active equipment on the circuits to cure the non-problem. But, when the drive's feeder breaker opened, the filter capacitors discharged through the drive transformer creating surges that eventually blew up the drive input electronics, just prior to warranty completion, twice. My solution of turning off the filters was not accepted, except as a stop gap measure.
More design changes are in progress to solve problems caused by solutions to a non-problem.
Moral: make sure 519 is properly applied or you will waste $$ and resources with no benefit to the client.
RE: IEEE 519 - 1992
David Castor
www.cvoes.com
RE: IEEE 519 - 1992
Alan