Now let's graphically compare an alternating current wave, and a direct current wave.
The AC sine wave varies constantly in direction (polarity) and magnitude. Usually, the DC wave is considered to be a steady, non-varying, uni-directional wave. The direction (polarity) of an AC wave generally reverses on a cyclical basis, that is, the wave takes on both positive and negative values, alternately.AC Voltage-Single-Phase and Three-Phase
AC can be Single-Phase or Three-Phase. Single-phase is used for small electrical demands such as in the home. Single-phase is what we have been discussing. Three-phase is used where large blocks of power are required in commercial and industrial facilities. Three-phase is a continuous series of three overlapping AC cycles. Each wave represents a phase, and is offset by 120 degrees.
AC can be Single-Phase or Three-Phase. Single-phase is used for small electrical demands such as in the home. Single-phase is what we have been discussing. Three-phase is used where large blocks of power are required in commercial and industrial facilities. Three-phase is a continuous series of three overlapping AC cycles. Each wave represents a phase, and is offset by 120 degrees.
Sine Wave ValuesYou learned earlier in this module that the sine wave represents the rise and fall of voltage and current in an AC circuit over time. There are several values that can be determined from the sine wave.
Peak Value: The peak value of a sine wave occurs twice each cycle, once at the positive maximum value and once at the negative maximum value.
Peak-to-Peak Value: The peak-to-peak value is the value of voltage or current between the positive and negative peaks.
Instantaneous Value: The instantaneous value is the value at any one particular time from zero to the peak value.
Effective Value: As would be expected, there are a number of different values of voltage with alternating current constantly changing. The effective value was developed as a way to translate the varying values into a constant equivalent value for AC. This is known as the RMS Value (root-mean-square).
Effective Value: As would be expected, there are a number of different values of voltage with alternating current constantly changing. The effective value was developed as a way to translate the varying values into a constant equivalent value for AC. This is known as the RMS Value (root-mean-square).
The average home uses 120 volts, which is the RMS value. The effective value works out to be about 0.707 times the peak value. The formula is as follows:RMS = 0.707 x peak
Insulation is designed, for example, to deal with the peak value as well as the effective value. Calculate the peak value by multiplying the effective value by 1.41. In the average home example just given, the peak value would calculate out to be approximately 169 volts.
This formula is arrived by the following means:
Or peak = RMS x 1.414So peak is 120 x 1.414 or 169V Labels: Electrical Power
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