Reduction of Harmonics

There are many ways to reduce harmonics, ranging from variable frequency drive

designs to the addition of auxiliary equipment. The primary methods used today to reduce harmonics are,

1. Power System Design: Harmonics can be reduced by limiting the non-linear load to 30% of the maximum transformer’s capacity. However, with power factor correction capacitors installed, resonating conditions can occur that could potentially limit the percentage of non-linear loads to 15% of the transformer’s capacity.

By default most of the capacitor banks in the low voltage system will have the series inductance.It is small inductance which is added in series? so that it reduces the inrush current of the capacitor as well as it acts as harmonic filter.so in LV capacitor bank the series inductance is inbuilt we need to ask what's the value is, while ordering the APFC we need to be careful what series inductance value which? we need.

2. 12-pulse converter front end:

In this con?guration, the front end of the bridge recti?er circuit uses twelve diodes instead of six. The advantages are the elimination of the 5th and 7th harmonics to a higher order where the 11th and 13th become the predominate harmonics. This will minimize the magnitude of harmonics, but will not eliminate them. The disadvantages are cost and construction.

3. Delta-Delta and Delta-Wye Transformers:

This con?guration uses two separate utility feed transformers with equal non linear loads. This shifts the phase relationship to various six-pulse converters through cancellation techniques, similar to the twelve-pulse con?guration.

4. Harmonic Single tuned Filters:

Used in applications with a high non-linear ratio to system to eliminate harmonic currents. Filters are tuned to a speci?c harmonic such as the 5th, 7th, 11th, etc. In addition, harmonic trap ?lters provide true distortion power factor correction. Filters can be designed for several non-linear loads or for an individual load.

POWER PROJECTS Kishore T Kavitha Paramanandan Suriya kumar S Jegeesh VJ

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