Why Supply Frequency is 50 Hz or 60 Hz?
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.
- When people think about large power generation system, they puzzled with the standard that to be adopted by them. Finally it reveals about single standard for all. They came to conclusion regarding to their issue, from the analysis and performance evaluation conducted on different standards of power system by them.
- Then they felt single standard is essential! because production of electric devices were limited by realm of power system boundary i.e., suppose a country consist of 10 different standards then 10 different manufacturing measures and processes are required for same device. This factor puts hurdles in batch production of device. It leads electric devices much more costly.
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
Technical Reasons for not using Higher Frequencies
- It increases series impedance in electrical transmission system. This reduces power transfer capability so we cannot access full fruit of transmission system.
- Constant losses are directly proportional to frequency and its square, so they may increase system losses.
- Harmonics with higher frequency can carry more power and it introduces excess heat losses.
- 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.
- 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.
- 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.