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Why Supply Frequency is 50 Hz or 60 Hz?

Published on 24/2/2012 and last updated on Thursday 17th of May 2018 at 03:36:55 PM
In olden days people do not have integrated power system as we have now. They had their own standard and load items which are suitable for their power system. That time they had operating frequency range between 16.75 Hz to 133.33 Hz.

There is no strong technical reason behind 50 Hz or 60 Hz. This is not like that these values give best performance among all other available standard values of supply frequencies. But these two frequencies give good optimized performance among others. Since superior performance has been found finally these values 50 Hz and 60 Hz were picked by most of the electrical power systems.

Technical Reasons for not using Higher Frequencies

  1. It increases series impedance in electrical transmission system. This reduces power transfer capability so we cannot access full fruit of transmission system.
  2. Constant losses are directly proportional to frequency and its square, so they may increase system losses.
  3. Harmonics with higher frequency can carry more power and it introduces excess heat losses.
  4. As the frequency directly proportional to the rotating speed of alternator and it is not practical to construct very high speed gigantic alternators. Hence it is practically difficult to achieve high frequency electrical power during generation.

Problems with Lower Frequencies

Olden days they observed some issues with frequencies which are less than 40 Hz.
  1. Perceptible flickering in filament lamp, starting problem in arc lamp and arcing devices so they need additional devices for starting purpose and for maintaining better operation.
  2. Frequency is directly proportional to power hence size of lower frequency devices are quite larger than higher frequency so material involved, cost involved in manufacturing and transporting are also quite larger than that of higher frequency devices.
These are the reasons for using higher frequencies in aircraft, in ships and in similar type isolated load.

From these relations we can conclude without confusion, larger frequency reduces area of core in transformer and magnetic circuits. Devices which have bigger magnetic circuit weight more. It is needless to say weight of net system is in great concern in ship and aircraft. So there we have higher frequency devices.

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Why Supply Frequency is 50 Hz or 60 Hz?
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