# Why is the frequency of AC in India 50 Hz while in US 60Hz?

Last Updated on November 7, 2022 by Electricalvolt

In this article, we will discuss the important reasons for using a 50 Hz AC power system in India over a 60 Hz AC power system in the US.

But before that, it is important to understand the frequency and why it is so important in AC power systems.

Frequency is defined as the number of cycles of a repeating signal per unit of time, i.e.

The number of cycles of AC signal measured per second is called Hertz (Hz). Thus, the unit of frequency measurement is Hertz (Hz).

The duration of one cycle in a repeating signal is called the time period of the signal. Thus, the time period is the reciprocal of the frequency of the signal, i.e.

For example, if a sinusoidal signal in the AC system completes 50 cycles per second, then the frequency of the signal is 50 Hz and the time period is 20 milliseconds.

## What is a 50 Hz AC System?

A power supply system is said to be a 50 Hz AC system when the waveform of the current or voltage completes 50 cycles in a second. This means that the waveform of the current or voltage changes its direction alternatively 50 times in a second. The 50 Hz AC system is very popular in India. In India, AC power having a sine waveform is generated and transmitted at 50 Hz.

## What is a 60 Hz AC System?

A power supply system is said to be a 60 Hz AC system when the waveform of the current or voltage completes 60 cycles per second. In this system, the waveform of the current or voltage changes its direction alternatively 60 times in a second. The 60 Hz AC system is extensively used in the US. In the US, AC power having a sine waveform is generated and transmitted at 60 Hz.

## Reason of use of 50 Hz supply in India & 60 Hz in the US

Now, let us discuss all the possible reasons why a 50 Hz supply power system is used in India and a 60 Hz supply power system in the US.

In India, when the British were ruling in India, they chose a 50 Hz AC power system and implemented it at a large scale. On the other hand, the US implemented its power system and developed appliance to operate at 60 Hz. After a long period of time, when they examine their power systems, it became quite difficult to change in the operating frequency due to the large scaling of the system and devices. It is the most fundamental reason behind the use of a 50 Hz supply system in India and 60 Hz in the US.

## Advantage of a 50 Hz Power system over a 60 Hz power system

### 1. Reduction in Constant Power Losses:

In any AC electrical machine, the power loss due to hysteresis and eddy current is considered the constant loss. Both hysteresis loss and eddy current loss are frequency-dependent losses. The eddy current loss is directly proportional to the supply frequency, and the hysteresis loss is directly proportional to the square of the supply frequency. Thus, the constant losses decrease with a decrease in the supply frequency. Therefore, the machine efficiency increases with a decrease in the supply frequency.

### 2. Reduction in Impedance & Losses of the Transmission Line:

A practical transmission line has three important parameters namely line resistance, line inductance, and line capacitance. The line inductance and capacitance cause the line reactance which is a function of the frequency of the power transmitting through the line. Therefore, the line reactance decrease with a decrease in the supply frequency.

The power loss in the transmission line is given by,

If we consider only inductive effect, then

Hence, from the above equation, it is clear that the reduction in the supply frequency reduces the impedance in the path of current through the transmission line. Thus, it reduces the variable power loss(I2Z).

The increase in the supply Voltage at the utility side decreases the current. The decrease in the current cause lower power loss in transmission and distribution. The power loss is proportional to the square of the current. Thus, if we increase the voltage from 110 V to 220 V, the current will decrease to half, and the power loss becomes 1/4th with 220 volts system. Thus, the line loss reduces with an increase in voltage.

### 3. The Reduced Frequency Increases the Power Generation Capacity:

The reduction in the frequency of the system reduces the auxiliary power consumption. As we know the decrease in the supply frequency, decreases the losses of the plant, and hence reducing the auxiliary power consumption in the system. Consequently, the power generation capacity is increased due to a reduction in the frequency of the system.

### 4.Reduction in Conductor Size:

The reduction in the frequency of the system decreases the impedance of the transmission line. Thus, the current carrying capacity of the line is increased, and hence we need a smaller-sized conductor for power transmission. Therefore, the reduction in supply frequency reduces the size of the conductor in the transmission line.

### 5. Reduced Insulation Cost:

When the frequency of power generated by an alternator is increased, it also increases the output voltage. Thus, it requires more insulation and high insulation cost. As we know, for an alternator,

Also,

### 6.Reduced Vibrations in Machines:

The machines operating at lower frequencies give fewer vibrations. In an electrical machine, the main cause of vibrations is harmonics and alternation in the power supply.

### 7.Reduced Corona Loss:

The electric corona loss depends upon the frequency of the system. The corona loss can be calculated using the following mathematical formula.

Therefore,

Therefore, the reduction in supply frequency reduces the corona loss in the line. Thus, a 50 Hz system has less corona loss as compared to a 60 Hz system.

### 8. Increase in the Speed of the Machine

The speed of the induction motor and synchronous machines is proportional to the supply frequency. The speed of the machine is;

Hence, the machine parts need to design for a higher speed if we use a 60 Hz power supply system.

## Disadvantages of 50 Hz Supply System

As discussed above, a 50 Hz supply system has several advantages, but there are some disadvantages as well, which are.

• The reduced supply frequency increases the size of the electrical machines. Which in turn increases the cost and area required for installation.
• The standard voltage rating of the 50 Hz system is 230 V per phase and, the standard voltage of the 60 Hz system is 110 V. Thus, the higher voltage has more electric safety issues against electric shocks.