QUESTION:
Why is the voltage of electric power always given in multiples of 11 such as
110V, 220V, 440V & 11 KV?
ANSWER:
The electric power in use
today, is of A.C. (Alternating Current) in nature. But, before the advent of AC
power generating electrical machines, the sources of electricity were primary
cells whose power is D.C. (Direct Current) in nature.
So, when machines were developed
to produce AC electricity, their capacity was to be compared with the already
available DC electricity. Thus a value called the RMS (Root Mean Square) value
for the AC electricity was coined. This RMS value equated the power of the AC
electricity with the DC electricity. This RMS value is the effective or virtual
value of the AC electricity. It is of prime importance practically, because all
general-purpose electrical indicating instruments record only the RMS value of
their respective parameters.RMS value of AC electricity could be calculated
either by the mid-ordinate method or by the analytical method and is equal to
0.707 x Max. value of measuring quantity. But, it is easier to calculate the
average value or the arithmetic mean value of the AC electricity than to
calculate the RMS value and the average value is equal to 0.637 x max. value of
measuring quantityA factor could be calculated to relate the RMS value and the
Average value. That is the Form Factor, which is equal to:
Form Factor = RMS Value/ Average
value = 0.707 x Max Value/ 0.637 x Max. Value = 1.11
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