There are two types of power supplies; AC & DC. Both the supplies have common terms voltage and current. Yet, one term creates a difference between the two. That term is “frequency“.
In general, Frequency means something happening continuously & symmetrically. In Electrical, Frequency of power supply defines how many cycles are occurring per second.
DC stands for Direct current. As name suggests, DC remains direct or constant at its magnitude with respect to time.
GIF below shows the waveform of Direct current. It moves with respect to time at a fixed magnitude. It does not change its direction.
AC stands for Alternating current. While moving, AC changes its direction continuously at fixed intervals. Alternating current is visualized through a GIF below:
GIF of alternating current below. It represents a sinusoidal waveform moving with respect to time. It also changes its direction at fixed intervals. Actually, It has two halves, One is positive While another one is negative. Both the halves in complete represents ‘one cycle’.
FREQUENCY
The sinusoidal AC waveform continuously changes its direction. This change is continuous & happening at fixed intervals. One positive half & One negative half constitute a ‘cycle’.
Frequency of power supply defines how many cycles are occurring per second.
This means AC power has the term frequency, while DC does not. In India, Power frequency standard is 50 Hz While in USA power frequency standard is 60 Hz.
A attached image below shows the AC sinusoidal waveform with having a frequency of 3 Hz.
APPLICATIONS OF FREQUENCY IN ELECTRICAL SYSTEM
Alternating current exist due to the term frequency. Alternating current has multiple applications. Alternating current is everywhere. It is working from a small walkie-talkie to Large power transformer.
Next, Some of applications of frequency in AC been discussed !
Poly-phase System
Poly-phase means multiple phases; more than 1 phase; Such that 3 phase system. It is the frequency which make a poly-phase system; a possibility. Poly-phase system is more reliable & more useful than single phase system that why used widely.
Power transmission, Distribution & even consumption’s are happening at poly-phase level.
Induction Motor
Induction motors are working on the principle of Faraday law of Electromagnetic Induction. Which states that When a changing magnetic field links with a current carrying conductor; A torque get produced.
The key point of the principle that is Changing magnetic field; is all due to the term frequency. Which is the reason behind the changing magnetic field.
Electrical Transformers
“When a changing magnetic field links with the conductor, An EMF get generated”. That is the phenomenon behind the working of transformer. Again changing magnetic field which is happening due to frequency.
Transformer is a powerful static Electrical machine which transfer electrical power from one circuit to another. It is the most efficient machine which makes it; the first choice for voltage variation.
Induction heaters & Furnaces
Induction stoves and furnaces operate on the principle of induction. This principle is based on a changing magnetic field. A wide range of machines, from household appliances to industrial equipment, use this technology.
In a metallic object near to magnetic field, eddy current & hysteresis losses get generated. At normal working frequency, these losses are very minimal. However, increasing the frequency significantly above the normal rated frequency causes these losses to rise multiple times.
This results in high temperatures being generated in the metallic element. At certain point of temperature these metallic element starts burning & melting. This phenomenon is used in induction heaters & furnaces.
Speed Control of Induction Motor
In Induction motor, Its rotating rotor tries to catch the rotating magnetic field of stator. The speed at which stator’s magnetic field rotates is known as Synchronous Speed.
Synchronous Speed is equal to; [(120*F)/P] Where; F = frequency of power supply & P = Number of poles of motor winding
- If frequency is 50 Hz & No. of poles are 2 than Synchronous speed becomes; 3000 rpm.
- If frequency is 50 Hz& No. of poles are 4 than Synchronous speed becomes; 1500 rpm.
- If frequency is 60 Hz & No. of poles are 2 than synchronous speed becomes; 3600 rpm.
Since number of poles of the winding are fixed Which can not be changed easily. It is the frequency which can be used to vary the speed. For proper speed controlling; Variable frequency drives are used.
A Variable frequency drives, or VFD, is a type of electronic device. It takes power supply at standard rating. It produces the output with changing voltage and frequency according to set parameters.
SUMMARY
- DC stands for Direct current. As name suggests, DC remains direct or constant at its magnitude with respect to time. AC stands for Alternating current. While moving, AC changes its direction continuously at fixed intervals.
- Frequency of power supply defines how many cycles are occurring per second.
- The sinusoidal AC waveform continuously changes its direction. This change makes cycles continuous. This means AC power has the term frequency, while DC does not.
- In India, Power frequency standard is 50 Hz While in USA power frequency standard is 60 Hz.
- It is the frequency which make a poly-phase system; a possibility. Power transmission, Distribution & even consumption’s are happening at poly-phase level.
- Induction motors are working on the principle of faraday law of Electromagnetic Induction. Which states that When a changing magnetic field links with a current carrying conductor; A torque get produced. The key point of the principle that is Changing magnetic field; is all due to the term frequency.
- “When a changing magnetic field links with the conductor, An EMF get generated”. That is the phenomenon behind the working of transformer. Again changing magnetic field which is happening due to frequency.
- Induction stove to induction furnaces. From houses to large industries. All these important machines work on the principle of Induction. They rely on a changing magnetic field.
- For speed controlling of Induction motor; Variable frequency drives are used. VFD’s produces power supply with change in frequency & voltage.