In this article we will discuss about: 1. Definition of Harmonics 2. Harmonic Number (h) 3. Types 4. Causes. Definition of Harmonics: Harmonics are sinusoidal voltages or currents having frequencies that are integer multiples of the frequency at which the supply system is designed to operate. Harmonics as pure tones making up a composite tone in music. A pure tone [...]
The topic of harmonics is interesting because of the harmful effects they have on power system devices. What makes harmonics so insidious is that very often the effects of harmonics are not known until failure occurs. Insight into how harmonics can interact within a power system and how they can affect power system components is important for preventing failures. In [...]
Many of the loads installed in present-day power systems are harmonic current generators. Combined with the impedance of the electrical system, the loads also produce harmonic voltages. The nonlinear loads may therefore be viewed as both harmonic current generators and harmonic voltage generators. Prior to the 1970s, speed control of AC motors was primarily achieved using belts and pulleys. Now, [...]
The primary limit on individual customers is the amount of harmonic current that they can inject into the utility network. The current limits are based upon the size of the consumer relative to the size of the supply. Larger customers are restricted more than smaller customers. The relative size of the load with respect to the source is defined as [...]
In this article we will discuss about:- 1. Equipment Design for Harmonic Current Mitigation 2. Harmonic Current Cancellation 3. Harmonic Filters. Equipment Design: The use of electronic power devices is steadily increasing. It is estimated that more than 70% of the loading of a facility by year 2010 will be due to nonlinear loads, thus demand is increasing for product [...]
The response of the system magnifies one or more harmonics to a greater degree than can be tolerated. When a problem occurs, the basic options for controlling harmonics are: 1. Reduce the harmonic currents produced by the load. 2. Add filters to either siphon the harmonic currents off the system, block the currents from entering the system, or supply the [...]
The strategies for mitigating harmonic distortion problems differ somewhat by location. The following techniques are ways for controlling harmonic distortion on both the utility distribution feeder and end-user power system. Control Harmonic Distortion on Utility Distribution Feeders: The X/R ratio of a utility distribution feeder is generally low. Therefore, the magnification of harmonics by resonance with feeder banks is usually [...]
Harmonic studies play an important role in characterizing and understanding the extent of harmonic problems. Harmonic studies are often performed when: 1. Finding a solution to an existing harmonic problem 2. Installing large capacitor banks on utility distribution systems or industrial power systems 3. Installing large nonlinear devices or loads 4. Designing a harmonic filter 5. Converting a power factor [...]
There are various organizations on the national and international levels working in concert with engineers, equipment manufacturers, and research organizations to come up with standards governing guidelines, recommended practices, and harmonic limits. The primary objective of the standards is to provide a common ground for all involved parties to work together to ensure compatibility between end-use equipment and the system [...]
The following points highlight the four main methods used for controlling harmonic distortion in power system. The methods are: 1. Constant Frequency Control 2. Constant Tolerance Band Control 3. Variable Tolerance Band Control 4. Discontinuous Current Control. Method # 1. Constant Frequency Control: A usage of frequency controlled drives with AC motors (like asynchronous or synchronous) increased in last few [...]