Well, if you were to average all of the voltage values at each point across the cycle, the result would be approximately V so that must not be the answer. Why then is the value, as measured by a VOM, V?
It has to do with something we call "effective voltage". If you were to measure the heat produced by a DC current flowing through a resistance, you would find that it is greater than that produced by an equivalent AC current. This is due to the fact that AC does not maintain a constant value throughout its cycle.
If you did this in the laboratory, under controlled conditions, and found that a particular DC current generated a heat rise of deg, its AC equivalent would produce a Therefore the effective value of AC is It also turns out that the effective value of an AC voltage is equal to the square root of the sum of the squares of the voltage across the first half of the curve. If the peak voltage is 1 and you were to measure each of the individual voltages from 0 deg to deg, the effective voltage would be 0.
This effective voltage is also known as the root mean square or RMS voltage. It follows that the peak voltage will always be 1. We will see the effects of peak voltage a little later. Well, I have probably gone on about this longer than necessary but, I wanted you to gain an understanding of effective voltage so that you will understand the illustration below. In addition to varying frequency, a frequency converter must also vary voltage even though voltage has nothing to do with the speed at which an AC motor operates.
The illustration shows two V AC sine waves. The red one is a 60hz curve while the blue one is 50hz. Both have a peak voltage of V but, the 50hz is much broader. You can easily see that the area under the first half 0 — 10 ms of the 50hz curve is greater than that of the first half 0 — 8. And, since the area under the curve is proportional to effective voltage, its effective voltage is higher. This increase in effective voltage becomes even more dramatic as frequency decreases. If a V motor were allowed to operate at these higher voltages, its life could be decreased substantially.
Therefore, the frequency converter must constantly vary "peak" voltage, with respect to frequency, in order to maintain a constant effective voltage. The lower the operating frequency, the lower the peak voltage and vice versa. It is for this reason that 50hz motors, used in Europe and parts of Canada, are rated for V.
See, I told you that AC can be a bit complex! You should now have a pretty good understanding of the workings of a frequency converter and how it controls the speed of a motor. Most frequency converters offer the user the ability to set motor speed manually via a multi-position switch or keypad, or use sensors pressure, flow, temperature, level etc to automate the process. Excellent article and very good explanation of how frequency convertors control AC induction motor speed.
Can we use the same inverter for cycle and cycle a. This can be essential for applications that require advanced controlling abilities, multiple stops and starts, and applications looking for the energy savings only a VFD can provide. Move Items to Quote. Skip to Content Have questions? Call us at Compare Products. Variable Frequency Drives. Electric Motors.
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US Motors - Nidec. What is a Variable Frequency Drive? VFD Buying Guide. VFD Panel. How to Read a Motor Nameplate. VFD How to Videos. This not only increases efficiency, but also intelligently supports your applications. To serve as a link for integration, various bus systems, such as Profi Net, are available.
The robust and compact design of our converters guarantees high temperature and vibration resistance while still allowing adaptation to your specific requirements.
Once you let the smoke out of the equipment, you cannot put it back in. Larger and 3 phase equipment cannot operate on the wrong frequency. This can cause damage or premature wear on the equipment. If you force the equipment to operate outside its design criteria, there will be trouble. Most likely, the equipment will be damaged immediately remember the smoke? If not immediately, it will fail over time from fatigue and overheating. With our ever growing global economy, equipment from other parts of the world are being used more frequently in countries that they were not manufactured in.
This usually results in the need of a Frequency Converter also called a frequency changer. As a result, it will be compatible with the power requirements of the equipment you are trying to operate also called the load. Specific industries have unique frequency requirements and this is based on how they supply power to their equipment. Aviation and Weapons systems require Hz , therefore equipment used on the ground operating at Hz require ground power support for the electrical system.
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