January 25, 1999What are harmonics and what cause harmonics?
Harmonics are currents or voltages with frequencies that are integer multiples of the fundamental power frequency being 50 or 60Hz (50Hz for European power and 60Hz for American power). For example, if the fundamental power frequency is 60 Hz, then the 2nd harmonic is 120 Hz, the 3rd is 180 Hz, etc. In modern test equipment today harmonics can be measured up to the 63rd harmonic. When harmonic frequencies are prevalent, electrical power panels and transformers become mechanically resonant to the magnetic fields generated by higher frequency harmonics. When this happens, the power panel or transformer vibrates and emits a buzzing sound for the different harmonic frequencies. Harmonic frequencies from the 3rd to the 25th are the most common range of frequencies measured in electrical distribution systems.
Additionally, harmonics are caused by and are the by-product of modern electronic equipment such as personal or notebook computers, laser printers, fax machines, telephone systems, stereos, radios, TVs, adjustable speed drives and variable frequency drives, battery chargers, UPS, and any other equipment powered by switched-mode power supply (SMPS) equipment. The above-mentioned electronic SMPS equipment is also referred to as non-linear loads. This type of non-linear loads or SMPS equipment generates the very harmonics theyre sensitive to and that originate right within your building or facility. SMPS equipment typically forms a large portion of the electrical non-linear load in most electrical distribution systems. There are basically two types of non-linear loads: single-phase and three-phase. Single-phase non-linear loads are prevalent in modern office buildings while three-phase non-linear loads are widespread in factories and industrial plants.
In todays environment, all computer systems use SMPS that convert utility AC voltage to regulated low voltage DC for internal electronics. These non-linear power supplies draw current in high amplitude short pulses. These current pulses create significant distortion in the electrical current and voltage wave shape. This is referred to as a harmonic distortion and is measured in Total Harmonic Distortion (THD). The distortion travels back into the power source and can effect other equipment connected to the same source.
To give an understanding of this, consider a water piping system. Have you ever taken a shower when someone turns on the cold water at the sink? You experience the effect of a pressure drop to the cold water, reducing the flow of cold water. The end result is you get burned! Now imagine that someone at a sink alternately turns on and off the cold and hot water. You would effectively be hit with alternating cold and hot water! Therefore, the performance and function of the shower is reduced by other systems. This illustration is similar to an electrical distribution system with non-linear loads generating harmonics. Any SMPS equipment will create continuous distortion of the power source that stresses the facilitys electrical distribution system and power equipment.
Harmonics are generally not an issue if you do not have any electronic SMPS equipment or non-linear loads in your building or facility. However, for the remainder of this discussion, we are assuming that you do.
In an electrical distribution system harmonics create:
Above we identified the problems directly affecting your electrical distribution system. In turn, these problems affect your entire site or facility in a number of different ways:
First, one must understand that the electrical distribution system of most sites or facilities was never designed to deal with an abundance of non-linear loads. Its a problem that has only recently begun to be recognized in the building industry. Within the last decade, the widespread use of computers and SMPS equipment is turning modern office buildings, factories, and industrial plants into high-tech computer environments. Even older buildings that are renovated are not retrofitted with modern harmonic treatment or cancellation. The end result is a building or facility unable to fully support todays technology and the high-tech problems that it brings along with it. Obviously, given the problems harmonics can cause, it is imperative that todays electrical distribution systems be designed for non-linear electronic loads, not just linear electrical loads. Unfortunately standard building codes and engineering designs do not meet the requirements of todays technology. With the advent of newer SMPS equipment the harmonic problem will continue to get worse along with inadequate facility grounding. Grounding which is another subject is mentioned here because it too is seldom addressed or considered a problem area (See grounding paper under "Library" heading).
These are recommended ways to wire for the harmful effects that harmonics cause. However, these recommendations only keep the electrical distribution systems safe. These wiring recommendations do not eliminate or cancel high levels of harmonics.
In order to ensure the highest "Power Quality" for your building or facility, it is necessary to treat harmonics. Harmonic treatment can be performed by two methods: filtering or cancellation. A harmonic filter consists of a capacitor bank and an induction coil. The filter is designed or tuned to the predetermined non-linear load and to filter a predetermined harmonic frequency range. Usually this frequency range only accounts for one harmonic frequency. This application is mostly used when specified for a UPS or variable frequency drive motor in a manufacturing plant.
Harmonic cancellation is performed with harmonic canceling transformers also known as phase-shifting transformers. A harmonic canceling transformer is a relatively new power quality product for mitigating harmonic problems in electrical distribution systems. This type of transformer has patented built-in electromagnetics technology designed to remove high neutral current and the most harmful harmonics from the 3rd through 21st. The technique used in these transformers is call "low zero phase sequencing and phase shifting". These transformers can be used to treat existing harmonics in buildings or facilities. This same application can be designed into new construction to prevent future harmonics problems.
Listed below are four patents that are used in the design of these transformers.
In closing, it is important to consult with a power quality expert before applying any of the recommendations or methods as discussed throughout this paper. A power quality consultant will be able to analyze the severity of the harmonics problem and design a plan tailored to your specific harmonics situation. If you know or think that your building or facility has a harmonic problem, please go to our "Power Problems" web page and register for your free 15 minutes of consulting.
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