Remove 3rd harmonics on load-side of delta-star transformer.
Remove 3rd harmonics on load-side of delta-star transformer.
(OP)
I am looking for a solution to third-harmonic induced problems. The industrial facility in question is fed with a three-phase 400V arrangement, with no neutral, from a 10 kV/400V delta-star transformer (with an earth taken from the star-point secondary).This distribution configuration feeds many large three-phase loads. Single-phase 230V loads are then accomodated by the provision of multiple 50 kVA 400V/230V delta-star transformers distributed throughout the plant, with the secondary star-point providing the neutral. The problem arises due to the fact that the majority of the transformers are designated as lighting transformers, and feed high-frequency fluorescent lighting loads, which produce high levels of harmonic currents (especially third)in the circuits.The transformers being generally approx. 90% loaded are starting to overheat, but more importantly there are very high rates of failure with the fluorescent tubes and electronic ballasts. My questions are
(a) has anyone heard of harmonic producing electronic loads, producing harmonics, being themselves subject to failure from the effects of harmonics especially as in the situation above where the harmonics may be "locked" into the secondary circuit, and
(b)are there any prooven solutions which are not "tuned" to specific fixed load conditions ? The solution must address the lamp failures as much as, if not more than, the transformer overheating.
(a) has anyone heard of harmonic producing electronic loads, producing harmonics, being themselves subject to failure from the effects of harmonics especially as in the situation above where the harmonics may be "locked" into the secondary circuit, and
(b)are there any prooven solutions which are not "tuned" to specific fixed load conditions ? The solution must address the lamp failures as much as, if not more than, the transformer overheating.






RE: Remove 3rd harmonics on load-side of delta-star transformer.
The failure of both ballasts and lamps makes me wonder if the ballast are being incorrectly applied. There is a wide variety of voltage levels available in ballasts. Also, the lamps used must match the ballasts.
Just curious - have you taken power quality measurements at the 230V level? If so, what levels of harmonic voltages and currents are you seeing?
Transformer and neutral overloading in fluorescent lighting circuits has been an issue for some time. Oversizing neutral conductors and specifying transformers with appropriate K-factor ratings will reduce problems. But this is probably not an attractive option for the existing transformers. But filtering will not be inexpensive, either.
This probably didn't help much, but maybe others have better advice.
RE: Remove 3rd harmonics on load-side of delta-star transformer.
I can also confirm that the ballast manufacturers have released HUGE lots of defective ballasts. If you're experiencing high ballast failure rates, I'd check there first.
RE: Remove 3rd harmonics on load-side of delta-star transformer.
It might be worthwhile determining if the ballasts meet advertised and standards-based harmonic-current limits. The cost of a device like a Fluke 41 may be quickly offset.
RE: Remove 3rd harmonics on load-side of delta-star transformer.
Do the ballasts meet IEC 1000-3 harmonic limits?
RE: Remove 3rd harmonics on load-side of delta-star transformer.
Supply the correct voltage to the ballasts:
For a three-phase system the nominal voltage is the phase to phase voltage. If you connect the ballasts between phase and neutral of 400V/230V three-phase transformer you are supplying the ballasts with 127 V.
Check this, connect the ballasts phase to phase and you will not suffer from third harmonics problems and defectve ballasts any longer.
RE: Remove 3rd harmonics on load-side of delta-star transformer.
To BUSBAR: The ballasts tried are CE rated and meet international standards such as IEC 1000-3
To ELECTRICUWE: The connected voltage is correct, the tubes and ballasts are 230V-rated and the phase-to-neutral voltage on the star-wound secondary is 230 V (Yes its 400V phase-to-phase)
I'm beginning to think that harmonics are the indirect cause of the problem with the fluorescent tubes & ballasts, rather than the direct cause. I have just as a result of some of your bove comments analysed some measurements taken with a Dranetz PP4000 - the 230v voltage waceform out of the transformer shows +350V transients, and sags with the three phase-voltage waveforms becoming co-incidental (one waveform superimposed on the other instead of 120 degrees apart). Is it possible that I have winding-to-winding partial faults/flashovers in the transformers (which are clearly overheating due to current imbalances and 3rd harmonics)and these in turn cause damaging voltage spikes and sags? How can I measure winding to winding inductive reactance to check for short-circuits on the 50 kVA dry-wound transformers ?
RE: Remove 3rd harmonics on load-side of delta-star transformer.
Are the transformer secondaries solidly grounded?
Have you tried returning the failed ballast to the manufacturer to get an explanation of the failure mode?
Is this a standard lighting application, or some special application such as UV disinfection or "grow lamps"? How many ballasts do you have on a single circuit?
Not sure what you are seeing on the Dranetz, but a 230V system has peak voltage of 325 volts and peak-to-peak of 650 volts.
RE: Remove 3rd harmonics on load-side of delta-star transformer.
A complete open on one phase would give you 230 volts to ground on one secondary phase and two phases at 115 volts to ground, each at the same phase angle, 180 degrees from the 230 volt phase.
RE: Remove 3rd harmonics on load-side of delta-star transformer.
RE: Remove 3rd harmonics on load-side of delta-star transformer.
Depending upon the age of the system and current/near-term damage costs, it may be time well spent benching a few of the existing ballasts with your test gear, and maybe compare existing to some currently produced by the same manufacturer, and possibly another brand with similar published ratings. At that point, if the numbers don’t mesh, start asking questions.
With “The transformers being generally approx. 90% loaded are starting to overheat, but more importantly there are very high rates of failure with the fluorescent tubes and electronic ballasts”—again, depending on age and degree of out-of-pocket costs, it may be time to make some phone calls.
You question the situation of “harmonic producing electronic loads, producing harmonics, being themselves subject to failure from the effects of harmonics”—that does not seem ethical of any electrical-component manufacturer or conducive of increased or even continued sales volume of their products. I would be equally concerned in a similar situation for the failing ballasts themselves, possible/likely plant-fire inception and consequent damage to the serving 50kVA drytypes.
It may be wise to secure a copy of IEC 1000 and conducting your own tests—making certain that you equipment is in calibration, and comparing field measurements to those promised by the ballast manufacturer. Your plant would not be first to receive a wholesale changeout of poorly engineered ballast, with every penny paid by the ballast manufacturer. Electronic ballasts are routinely priced at a premium for premium performance, and that goal seems to have been not met.
Repeated “tube pinking” sounds like a clear ballast-design defect, and if so, probably won’t cause the ballast manufacturer to be any easier to work with.
RE: Remove 3rd harmonics on load-side of delta-star transformer.
At your service if you need more ,
Avishai Rash BScEE&PE
a_rash@bigfoot.com
A.Rash BScEE & PE
a_rash@bigfoot.com