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Peak values can be calculated from RMS values from the above formula, which implies V P = V RMS × √ 2, assuming the source is a pure sine wave. Thus the peak value of the mains voltage in the USA is about 120 × √ 2 , or about 170 volts.
When the RMS voltage exceeds the nominal voltage by 10 to 80% for 0.5 cycle to 1 minute, the event is called a "swell". A "dip" (in British English) or a "sag" (in American English the two terms are equivalent) is the opposite situation: the RMS voltage is below the nominal voltage by 10 to 90% for 0.5 cycle to 1 minute.
A voltage sag happens when the RMS voltage decreases between 10 and 90 percent of nominal voltage for one-half cycle to one minute. [2] [4] Some references define the duration of a sag for a period of 0.5 cycle to a few seconds, [5] [6] and a longer duration of low voltage would be called a sustained sag. [5]
Various properties of ripple voltage may be important depending on application: the equation of the ripple for Fourier analysis to determine the constituent harmonics; the peak (usually peak-to-peak) value of the voltage; the root mean square (RMS) value of the voltage which is a component of power transmitted; the ripple factor γ, the ratio ...
where V k is the RMS voltage of the kth harmonic, I k is the RMS current of the kth harmonic, and k = 1 is the order of the fundamental component. It is usually the case that we neglect higher voltage harmonics; however, if we do not neglect them, real power transferred to the load is affected by harmonics.
The SCR shuts off when the current falls to zero and the supply voltage drops at the end of the half cycle, ready for the circuit to start work on the next half cycle. This circuit is called a leading-edge dimmer or forward phase dimming. Waveform of the output voltage of a thyristor dimmer set for 60 volts RMS output, with 120 V input.
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A sine wave, over one cycle (360°). The dashed line represents the root mean square (RMS) value at (about 0.707). Below an AC waveform (with no DC component) is assumed. The RMS voltage is the square root of the mean over one cycle of the square of the instantaneous voltage.