In this article we will discuss about the sources of over-voltage and its protection. Sources of Over-Voltage: Transients are disturbances that occur for a very short duration (less than a cycle) and the electrical circuit is quickly restored to original operation provided no damage has occurred due to the transient. An electrical transient is a cause-and-effect phenomenon. For transients to [...]
The following points highlight the five main devices used for protection from over-voltage. The devices are: 1. Surge Arresters and Transient Voltage Surge Suppressors 2. Isolation Transformers 3. Low-Pass Filters 4. Low Impedance Power Conditioners 5. Utility Surge Arresters. Device # 1. Surge Arresters and Transient Voltage Surge Suppressors: Arresters and TVSS devices protect equipment from transient over-voltages by limiting [...]
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 following points highlight the three main techniques used for measuring flicker in voltage during electricity supply. The techniques are: 1. RMS Strip Charts 2. Fast Fourier Transform 3. Flicker Meters. Technique # 1. RMS Strip Charts: Historically, flicker has been measured using rms meters, load duty cycle, and a flicker curve. If sudden rms voltage deviations occurred with specified [...]
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 [...]
Harmonic currents produced by nonlinear loads can interact adversely with the utility supply system. The interaction often gives rise to voltage and current harmonic distortion observed in many places in the system. Therefore, to limit both voltage and current harmonic distortion, IEEE Standard 519-19922 proposes to limit harmonic current injection from end users so that harmonic voltage levels on 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 [...]