Topics: Why are harmonics produced in a transformer?
on Power Supply
Why are harmonics produced in a transformer?
how and why are harmonics produced in a transformer? how can we get rid of them...please explain
09-17-2013 12:21 PM
The harmonics are created by the loads that the transformer supplies power to. If your loads include a high percentage of electronic loads like IT equipment, electronic ballast lighting, electronic motor controls, etc., there can be a very high amount of harmonics that circulate back to the transformer. The harmonics create an increase in the neutral currents. Most standard transformers are not designed to handle the higher harmonics and corresponding high temperature. Type K rated transformers are designed o withstand the higher harmonics, without derating the transformer or limiting its maximum load. There are harmonics filters on the market as well as the use of isolation transformers.
09-17-2013 02:22 PM
The question is: "how and why are harmonics produced in a transformer"
Strictly speaking they don't. They don't produce anything. So before going off on a tangent, perhaps more detail is needed.
09-17-2013 05:15 PM
Mr. Nageen, Usage of Convertor transformers would serve your purpose.
09-17-2013 07:30 PM
B/H curve of the magnetic material forming the transformer core is not linear, so if a sinusoidal voltage is being applied for a sinusoidal current (and hence sinusoidal flux & a sinusoidal secondary voltage), the magnetizing current is not sinusoidal. Thus the magnetizing current of a transformer having an applied sinusoidal voltage will comprise a fundamental component and various harmonics. The magnitude and composition of these harmonics will depend on the magnetizing characteristic of the core material and the value of the peak flux density.
09-17-2013 10:03 PM
First and in general, I agreed with Mr. George that Harmonics are generated by Electronic Load that called now " Non-Linear Loads ", and these Harmonics circulate to the source.
By the way, I want to mention to the following points :
- The standard Transformer " Non-saturated " generate Harmonics only in transient case when the power is supplied, and after this too small time it doesn't generate any kind of Harmonics
- The Transformer generates Harmonics if it's saturated
- We should take care when selecting the Transformer's Power if there are a lot of installed Non-linear Loads, so for this case, we can select the power after define the correction factor by using the special curve done by " IEC ", or calculating this factor by using a special Formula done by " UTE - France "
09-18-2013 12:49 AM
i totally agree with mr Follow Spir Georgesith
09-18-2013 02:50 AM
thanks Robert...for giving such a good elaboration...
09-18-2013 04:59 AM
Dear Follow Spir Georgesith
Can you brief about this "IEC" and "UTE-France" curve, what exactly it will help us in case of design of transformer for higher harmonics..
09-18-2013 07:19 AM
In addition to the explanation given by Asif, I would like to add that the amount of harmonic generated during charging is also depends on the point of switching in a particular cycle. The exact amount of harmonic generated can be determined by modelling the transformer in time domain analysis, I.e. PSCAD or EMTP. However is is a short time phenomenon and will die down when transformer is charged.
09-18-2013 09:32 AM
hello Spir Georges,
When the transformer is saturated , what kind/order of harmonics do you forsee. Have you personally experienced it .
09-18-2013 12:00 PM
The Fundamental answer also comes from Mathematics !!. All AC signals are sinusoidal and periodic. These periodic signals can be resolved into a kind of trigonometric series - fourier series which is a summation of a fundamantal and multiples of fundamantal frequency.
The moment there is slight distortion from sinusoidal nature , it leads to harmonics in addition to the fundamental signal.. One way is to use DC signals... no harmonics.
As long as the AC signal is perfect sinusoidal , load & source is linear, there will be no harmonics. The way to get rid of harmonics is to have perfect source and perfect loads.
The non linearity introduced due to energy storing magnetic circuits, switching circuits, energy converting & inverting circuits distort the waveform to non sinusoidal. Therefore leads to harmonics. .
The way, there are antibiotic medicines for diseases. One need to install the filter devices, which produce counter currents to suppress the effects of harmonics. The filters contain capacitors , inductors & power electronic components which are switched in anti-phase to harmonics producing elements. Thereby absorb harmonics.
09-18-2013 02:06 PM
Harmonics, in general, are not "produced" in a transformer. In fact, they are produced in all power electronic, non-linear loads and percolate into the transformer. But, in some rare cases, over-excited transformers too can become sources of harmonics.
To get rid of harmonics either you should stop using loads that generate harmonics or do a power quality study of the installation & install suitable harmonic filters.
09-18-2013 04:48 PM
Bhupendra, nice to see on chat line and your answer, you are right and covered all aspects of what creates harmonics and how to manage them going in to fundamentals . This is right technical answer.
09-18-2013 07:41 PM
@ Pradeep Modi. The dominant harmonics generated by the iron core transformer in saturation transformer are always odd harmonics since it has waveform symmetry but from these odd harmonics the most dominant are 3rd and 5th harmonics. I had analysed these harmonics using power quality analyzer.