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Harmonic Distortion and Understanding it in the Petrochemical Industry

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Harmonic Distortion and Understanding it in the Petrochemical Industry

This paper provides an in depth discussion on harmonic distortion on power systems in the petrochemical industry. The paper begins with a discussion on harmonics caused by saturable magnetic devices such as generators, transformers and motors. Production and control of harmonic voltages and currents produced in these devices will be covered. Then, a discussion on the production and control of harmonic voltages and currents produced by power electronic devices will be discussed. An example of power system harmonics and harmonic suppression techniques will be presented.

Electric power systems throughout the petrochemical industry are designed to normally operate at 50 or 60 Hz. Throughout history, efforts have been made to analyze the distortions on the power system created by the non-linear electromagnetic circuits such as generators, transformers and motors. In short, the non-linear devices may, and many times do, create distortions on the sinusoidal voltage of the ac power system.

Non-linear devices are also referred to as harmonic sources that result in the flow of harmonic currents. These sources can be categorized into:
• Saturable magnetic devices
• Power electronic devices

The distortion on the power system voltages and currents can be analyzed through the study of higher frequencies commonly referred to as power system harmonics. With the fundamental frequency of 50 or 60 Hz being the first harmonic and integer multiples of the fundamental frequency being referred to as higher order harmonics, some lower order harmonics are shown in Table 1.

In an AC power system, even harmonics do not normally exist. Therefore, the common harmonics in a power system include odd harmonics.

A term called distortion factor or harmonic factor is often times used to express the amount of harmonic distortion. It can be used to express the amount of voltage distortion or current distortion in a system.

With proper planning during the design phase of the power system for a petrochemical plant, certain harmonics can be minimized. For example the pitch factor of a generator can be modified to minimize and eliminate certain harmonics. (The pitch of two conductors in a generator is normally thought of as being at 180 electrical degrees apart.

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A Better Understanding of Harmonic Distortion in the Petrochemical Industry