Difference Between 50 Hz and 60 Hz Frequency System

Electrical Technology

What is the Difference Between 50-Hz and 60-Hz Frequency System?

The electricity that we use in our homes is produced and supplied by huge generators inside the power generation stations. The generator produces electricity whose ratings depend on various parameters and the frequency (such as 50 Hz or 60 Hz) is one of them.

In earlier days, the frequency of the power system was not fixed and was somewhat between 87Hz and 133Hz. Due to harmonics in the power system generated by that range of frequency, later, the frequency was lowered to 50 Hz since there was a strobe effect in lamps at 40 Hz. UK and Europe adopted the 50Hz while the Canadian and Americans adopted the 60Hz power systems. Other countries throughout the world adopted either American or European standards.

Both of these power systems work effortlessly. Machines or appliances are designed for specific frequencies to have the desired performance. However, if you run the same machine on a different frequency system, you will observe several differences in its performance.

Before going into the differences between 50Hz and 60Hz power systems, let’s know about the frequency first.

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What is Frequency?

Frequency is the number of cycles or revolutions in a second. Its unit is Hertz Hz, named after the German physicist Heinrich Rudolf Hertz.

As we know AC voltage swings between its positive and negative values forming a cycle. So the frequency of the power system represents the number of voltage or current cycles per second.

Good to Know:

In early stages, engineers found the best value of frequency lies between 50Hz and 67Hz instead of other low and high frequencies.

Different terms were used before the standard word of Frequency was standardized in the early era.

Most railways in the US used low frequencies such as 25Hz and 16.7Hz in Europe. Also, 133 Hz were used for less noticeable flickering effects in the lighting applications.

Due to the smaller transformers and lighter weight generators, aircrafts operate at up to 400Hz of frequency.

A DC supply has 0 frequency and if the war of AC and DC played today in the era of semiconductor technology, DC would have a winner in that case. That is because the advantages of lower frequency (such as losses in the machines, efficiency of transmission lines etc.) apply to DC in case of AC versus DC.

50 Hz Power System

The 50 Hz power system has 230 V across its two terminals whereas the voltage completes 50 cycles in a second or the current changes direction 50 times in a second. It was standardized by European countries and was later adopted by other countries as well.

A German company AEG standardized the frequency of 50 Hz for 220 to 230V. The rest of the European companies opt out for 50Hz instead of 60Hz because it was easy to fit and use with the metric system.

60 Hz Power System

The 60 Hz power system has 110/120 or 240 volts across its two terminals adopted by the Americans. The voltage completes 60 cycles in a second or the current changes directions 60 times in a second.

Westinghouse Electric by George Westinghouse is responsible for the standardizing the 60Hz frequency for AC voltage levels in the US because he think that 60Hz arc lighting equipment in the US perform better with less flickering on 60Hz instead of 50Hz (standard frequency in UK, EU, AUS and other countries).

Difference Between 50 Hz and 60 Hz Power System

There are several differences between 50 Hz and 60 Hz power systems.

The obvious difference is the difference in frequency. The 60 Hz is 20 % greater than the 50 Hz frequency. This 20% difference plays a huge difference for an appliance.

Speed

For power generation, the generator turbine needs to be rotated at a certain speed to generate the desired frequency. The frequency of a generator is given by

f = PN ÷ 120

Where ‘P’ is the number of poles and ‘N’ is the speed in RPM.

For a 2-pole alternator, the speed must be 3000 RPM to have 50 Hz output as compared to 3600 RPM for 60 Hz output. While for a 4-pole alternator, 1500 RPM is required for 50 Hz output whereas 1800 RPM is required for 60 Hz output. We can say the generator must be rotated at a 20% higher speed for 60Hz as compared to 50Hz.

Similarly, in motors, the speed or RPM (revolution per minute) mainly depends on the frequency and it is directly proportional to it. The speed of the motor will increase with an increase in the frequency given by the formula.

N = 120f ÷ P

A motor will have a 20 % higher speed on a 60 Hz power supply as compared to a 50 Hz power supply.

Cooling

The cooling of a machine depends on its speed. It is directly proportional. Whereas the speed varies directly with the frequency. Therefore we can say that the cooling of a machine is better at 50 Hz than at 60 Hz.

Torque

The torque of a machine mainly depends on the current. Since the current depends on the applied voltage and the 50 Hz system has 220 Volts whereas the 60 Hz system has 110 volts. Therefore, the torque at 50 Hz is larger as compared to the 60 Hz.

Bearing Lifetime

The bearing lifetime depends on the speed of the motor. It is inversely proportional to the speed. Since the speed is directly proportional to the frequency, the bearing lifetime decreases with an increase in the frequency. Therefore, we can say that the lifetime of bearings is lower at 60 Hz as compared to 50 Hz.

Size of Machine

The size of the machine is greatly reduced with an increase in frequency. Therefore the machine at 50 Hz must be larger as compared to the machines at 60 Hz.

Power Factor

The power factor depends on the apparent power and reactive power. Since power depends on the impedance and impedance vary greatly with a change in frequency. Therefore increasing the frequency can reduce the power factor.

The reactance of the coil varies with the frequency. Therefore 50 Hz power system has a slightly higher power factor than 60 Hz for the same machine.

Power Losses

The power losses also vary with the change in frequency. Power losses can be constant and variable power losses.

Constant Power Losses

The constant power losses are Eddy current loss and hysteresis loss. They are both directly proportional to the frequency.

Eddy’s current loss is directly proportional to the square of the frequency. While the hysteresis loss is directly proportional to the frequency as given by the equation below.

P_Eddy= k_e B² f ²t²V

P_Hys = ηB_max^1.6 f V

Hence reducing the frequency of the power system reduces the constant power losses and improves the energy consumption of the machine.

Variable Power Losses

The variable power losses include copper losses or I²Z losses. It depends on the current as well as the impedance. Whereas the impedance depends on the frequency. The inductive reactance of the coil is directly proportional to the frequency. Therefore, the total impedance is directly proportional to the frequency.

Hence, the variable power loss reduces with a decrease in the frequency.

Noise

The frequency noise increases with the frequency. Therefore the humming noise is larger at 60 Hz than at 50 Hz.

Conductor Size

The size of the conductor mainly depends on the amount of current and frequency. The alternating current tends to stay on the surface of the conductor known as the skin effect. Whereas the skin depth is the distance below the surface from where the current density becomes zero.

The skin depth is inversely proportional to the frequency. As the frequency increases, the effective area of the conductor decreases and the overall impedance of the conductor decreases. Therefore the conductor size must be increased to reduce the impedance.

On the other hand, the 60 Hz (higher frequency) power system has a lower voltage of 110/120 volts which increases the current supplied to the load. Therefore, to handle a large current, the size of the conductor must be increased.

Corona Losses

Corona losses occur due to the ionization of air surrounding a high-voltage power line. It produces a hissing sound with a violet glow generating ozone. The energy is dissipated due to the corona effect.

The corona losses are directly proportional to the frequency. Therefore 50 Hz power system has lower corona losses as compared to a 60 Hz power system.

Insulation Cost

The insulation required for the conductor increases with the increase in frequency. Therefore the insulation cost increases with the increase in the frequency.

Efficiency

The efficiency of a machine depends on the amount of power losses in the system. The most efficient system has minimum power losses with low energy consumption. However, we know that the power losses are directly proportional to the frequency.

Therefore we can say that the efficiency of a machine decreases with an increase in frequency.

Comparison Between 50Hz and 60Hz Frequency Systems

The following table shows the comparison between 60Hz and 50Hz frequency in power systems.

Characteristic	50 Hz Power System	60 Hz Power System
Speed	Machines have a lower speed at 50 Hz as compared to 60 Hz.	Machines have a higher speed at 60 Hz.
Torque	Torque is increased to due higher voltages at 50 Hz i.e. 220 volts.	Torque is reduced due to lower voltage at 60 Hz i.e. 110 volts.
Bearing Lifetime	The bearing lifetime increases at 50 Hz.	The bearing lifetime reduces at 60 Hz as compared to 50 Hz.
Size of Machine	The size of the machine is increased as compared to 60 Hz.	The size of the machine is reduced as compared to 50 Hz.
Power Factor	It has a higher power factor as compared to 60 Hz.	It has a lower power factor as compared to 50 Hz.
Power losses	Machines at 50 Hz have lower power losses as compared to 60 Hz.	Power losses increase with frequency, thus they are higher at 60 Hz.
Corona losses	It has lower corona losses.	It has higher corona losses as compared to 50 Hz.
Cooling	It has lower cooling are 50 Hz.	It has relatively better cooling at 60 Hz.
Noise	There is a very lower frequency noise.	The frequency noise is higher at 60 Hz.
Conductor Size	The size of the conductor is smaller as compared to 60 Hz.	The size of the conductor required is larger as compared to 50 Hz
Insulation Cost	It has a lower insulation cost as compared to 60 Hz.	It has a comparatively higher insulation cost.
Efficiency	It has higher efficiency as compared to 60 Hz.	It has lower efficiency as compared to a 50 Hz power system.

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