Why is 50 Hz or 60 Hz frequency adopted around the world?

It depends upon your grid and transmission. If you are using for farther areas, you would surely need more voltage and in order to overcome this you would need frequency of50 Hz. while for those areas, where you are using for comparatively nearer, you might need110-120v so your frequency has to increase to60. basically frequency frequency is number of on-off cycles. As distance increases, no of cycles automatically decreases.

Those two frequencies are supposed to grant optimum functionality of electric equipments and transformers

Much easier to go with a popular old standards than to come with a new non popular with insignificant use.

Hi,

There is a long history to how we have arrived in this situation.  The two frequency were chosen by2 major power engineering players in1891, namely Westinghouse at Pittsburg (60Hz) and AEG in Berlin (50 Hz).  You read up on the history here.  So basically, with the Gensets producing such frequencies, appliance makers must follow, otherwise their product is "not compatible".

Now, as there are already numerous appliances in use, new genset makers end up need to follow the frequencies too.  Otherwise the gensets is "not suitable".  However, for experimental/special purpose, it is always possible.

If you wonder why not just1 frequency, I answered a similar question here.

Cheers.

Hey its just an standard. You may proceed with30 Hz instead of50 Hz, then you have to design all your appliances according to30 Hz. All around the world its50 or60 Hz, so that people can use and design appliance as an international standard.