Explain how harmonics are eliminated in the electrical distribution system.

Question

Explain how harmonics are eliminated in the electrical distribution system.

Answer 1

Harmonics can not be totally eliminated.

For a distribution system that is owned by a public utility and serves several or many individual customers, the utility must place limits on the harmonic current content allowed in the individual customer load current. That is, they must compel the customers to limit their own harmonics.

If a customer has a few large items of individual equipment that have load currents with harmonic content, they have several alternative ways of limiting the harmonic current. They can purchase equipment that includes design features that limit harminic current. They can install inductors in series with the supply conductors to increase the source impedance. They can install harmonic filters (sometimes called "traps"). If a customer has many small items of equipment that have harmonic content in the load current, they may need to install harmonic filters to reduce the total harmonic content in the facility as a whole.

Harmonic filters are like power factor correction capacitors except that they contain inductors as well as capacitors so that they can be tuned to supply the harmonic current drawn by the loads thus preventing the harmonics from being drawn from the distribution system. Utilities can install harmonic filters, but they are more likely to force large users to do it just as they force large users to install power factor correction. In Europe, there are regulations that put harmonic limits on connected equipment. In the USA, electrical codes don't restrict harmonic loads, but utilities can do that. At some point US codes may force manufacturers to limit harmonic currents drawn by products.