Analysis of Harmonics due to nonlinear core at no load | Electrical Machines | GATE Preparation | EE

by / Monday, 26 June 2017 / Published in Blog

Real Life Application
The application of magnetizing curve of non-linear core in transformers is very important in the design of the transformer connection, wherever a transformer is to be installed. The induced emf, the load current, the source current, the magnetic flux waveforms depend on the type of connection in the transformer. For example: 1 phase transformer or Star- Star isolated or Star(grounded)-Delta etc. are some of the possible connections of a transformer. Now, harmonic content of a waveform will depend on the shape of the waveform. Thus, understanding the relationship of connection (transformer) and the waveform of these quantities is important.

Explanation
The relation between the magnetic field intensity, H and the magnetic flux density, B can also be expressed as the magnetic permeability μ=B/H and the relative permeability: μr =μ/μo. The relative permeability of vacuum, air, diamagnetic substance and paramagnetic substance is constant. Thus the relationship between B and H is linear. The relative permeability of ferromagnetic materials is not constant, but depends on H. In ferromagnetic materials, the relative permeability increases with H to a maximum, then it saturates.

When AC supply is given to the ferromagnetic core, Hysteresis Loop (B-H curve) is formed. Here, the B and H have non-linear relationship. (Magnetic flux waveform will be similar to magnetic flux density waveform and magnetizing current waveform will be similar to that of magnetic field intensity). Then, either the magnetic flux waveform or the magnetizing current waveform will be sinusoidal, as they have non-linear relationship. Now, whether the magnetizing current will be sinusoidal or not, will depend on, whether the path for third harmonics is present in the connection of the transformer or not. Third harmonics has similar property to that of zero sequence current. Basically, both need a closed path to exist. If the flux waveform is sinusoidal then, the magnetizing current will be of peaky shape. If the magnetizing current is sinusoidal then, the flux waveform will be of flat-topped shape or also called camel-hump shape.

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