Is 49.9 Hz frequency is permissible instead of 50 Hz in Electrical System

Electricity has played very important role in life of every human being, everybody wants to uninterrupted, smooth and clean electricity in our society but no one can be supported to electrical utility companies for this work. Now a days as you have seen that everyone suffer from the fluctuations in supply system, these disturbance depends on the various factors such environmental conditions, consumer and industrial load, efficiency of electrical system but voltage and frequency of system has a two important factor for any electrical system.

What is Frequency

According to a definition, Frequency defines as numbers of cycles completed by rotating or oscillating devices (i.e. alternator) at a constant number of poles. So frequency, F = N*P/120, Where N = no of rotations in rpm; P = No. of poles.

Now comes to question, why we used 50 hz electrical frequency in India

  1. According to the definition, frequency is directly proportional to the speed, so higher the frequency will increase the speed of alternator, so it will also increase the rate of change of magnetic flux generate the more voltage. (Faraday’s laws of electromagnetic induction – Induced E.M.F E=Ndø/dtE=Ndø/dt). 
  2. To maintain the voltage level under acceptable limits we need to decrease the number of poles in the alternator and in the other hand if frequency is low we need to increase the number of poles in alternator to maintain the voltage level constant.
  3. Indian electrical system has 50Hz/240V and USA Supply System has 60Hz/110V.
  4. Low-frequency system shows more flicker than higher frequency system. Lower Frequency also reduces the Humming sound in audio devices.
  5. Inductive line losses are less in lower frequency system.
  6. For same power ratings, lightly configured transformer are used in higher frequency system.
  7. In Lower frequency operation, an alternator is more costly than higher frequency operation.
  8. Line losses also depend on frequency, because line has reactance XL= 2∏f L, so when we increase the frequency, it will increase the losses in the transmission line vice-versa.


The regulators in household fans are based on frequency modulators. When you turn the knob to LOW, a low frequency is given to the fan, then less amount of current is delivered to the fan for the same voltage, so the fan rotated slowly. Now if we apply a higher frequency, it will burn the internal circuitry for the amount of current flow at the same voltage.

List of Countries as per Voltage and Frequency

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