ALTERNATOR – ‘Generating Alternating Current’

ALTERNATOR

Alternator is a type of machinery which converts mechanical power into an Electrical power. A mechanical power means such as Diesel Engine, Petrol Engine, Turbine, Bio Fuel Engine; is connected as an input to alternator.
Alternator converts mechanical power into an electrical power. The Electrical power generated by the alternator; is a type of Alternating current, That’s Why known as ‘ALTERNATOR’.

WORKING PRINCIPLE OF ALTERNATOR

An Alternator works on the principle of faraday law of Electromagnetic Induction Which states that; A changing magnetic field linking with the conductor; creates an EMF !

GIF shows Working of Alternator
GIF shows Working of Alternator

 

” A GIF above clearly explains the working of Alternator. At Starting, Rotor is standstill. There is no emf in between Rotor & Stator. When rotor starts rotating; It get excited through some sort of means Which results Rotor’s winding becomes electromagnet. Rotor’s magnetic field continuously changing with respect to the stator. That changing magnetic field continuously linking to Stator’s winding Which results an EMF get generated in Stator’s winding. “

Alternator is all about the changing magnetic field linking with the conductor. Field winding can be at stationary side or can be at rotating side. But due to heavy ratings & cost perspective, Armature winding from where heavy load current flows; is generally being kept on stationary side of the alternator. While a field winding where a very minor current flow is placed on above the rotor.

 

PARTS OF ALTERNATOR

As explained; Alternator has mainly 2 parts; ‘STATOR’ & ‘ROTOR’.

ROTOR

Rotor as name suggests; It is a rotating element Which rotates in center of the stator. Rotor contains some sort of means which produces magnetic field. There are two means to produces a magnetic field in Rotor that is; permanent magnet and field winding.
1. Permanent magnet, Rotor’s upper layer is made up from permanent magnet which produces magnetic field continuously even in standstill condition. When Rotor starts rotating; Magnet’s magnetic field started linking to stator’s winding & EMF get generated in stator’s winding.

2. Field winding, As shown in a GIF above, Rotor’s stamping carries the field winding whose terminals been brought either through slip rings or carbons brushes. When rotor starts rotating, external DC supply either through external DC generator been given to the field winding. Then Field winding becomes an Electromagnet whose magnetic field started linking to stator’s winding & EMF get generated in stator’s winding.

“ A Gif attached below shows; how an external DC generator excites the rotor of the main alternator. Main alternator’s stator feeds the power to the stator of DC generator through AVR(Automatic Voltage Regulator). Then Rotor of the generator feed power to the rotor of main alternator through bridge rectifier. “

Gif shows external dc generator excites the rotor of the main alternator
Gif shows external dc generator excites the rotor of the main alternator

STATOR

Stator is the stationary part which generally contains heavy winding placed in slots of silicon steel stamping. Winding of the stator is arranged in particular manner most probably in Star so that neutral get available. Stator’s terminals been brought out from the stator; Through which total load is being connected.

Stator of Induction Motor
Stator of Induction Motor, Similar to the stator of Alternator

 

ALTERNATOR’S IMPORTANT DETAILS 

For Alternator’s important details; Name plate’s of 500 KVA & 125KVA  alternators been discussed below > 

DETAILS OF 125KVA ALTERNATOR

125KVA Alternator's name plate
125KVA Alternator’s name plate | Made by STAMFORD

DETAILS OF 500KVA ALTERNATOR

500KVA Alternator's Name plate
500KVA Alternator’s Name plate | Made by STAMFORD
 
TECHNICAL WINDING DATA 

Technical Winding data of 500KVA alternator by STAMFORD
Technical Winding data of 500KVA alternator by STAMFORD

 

IMPORTANT TERMS RELATING TO ALTERNATOR

Relation between speed & frequency

Alternator’s frequency depend upon number of poles & speed of the alternator.
As synchronous speed formula is :
Ns=120f/P
Where Ns is synchronous speed, f is frequency, P is number of  Poles
 
 

Rating

Alternator’s are designed in Apparent power(KVA) Which is only the product of voltage & Current.
P=√3*V*I
Taking the example of 500KVA alternator & finding the rated current of the alternator.
Where,
P=500*1000
V=415
I=500000/(√3*415)
I=695.6 (Same as shown in name plate)
 
 

SUMMARY

  • Alternator is a type of machinery which converts mechanical power into an Electrical power.
  • Electrical power generated by it; is a type of Alternating Current that why known as ‘ALTERNATOR’.
  • Diesel Engine, Petrol Engine, Turbine, Bio Fuel Engine; Which produces mechanical power; connects Infront of the alternator.
  • An Alternators works on the principle of faraday law of Electromagnetic Induction Which states that; A changing magnetic field linking with the conductor; creates an EMF.
  • Alternator has mainly two parts; ‘STATOR’ & ‘ROTOR’.
  • Rotor as name suggests; Is a rotating element Which rotates in center of the stator. 
  • Rotor contains some sort of means which produces magnetic field. 
  • There are mainly two means to produces a magnetic field in Rotor that is; permanent magnet and field winding. 
  • Stator is the stationary part which generally contains heavy winding placed in slots of silicon steel stamping.
  • Synchronous Speed, Ns=120f/P Where f is frequency & P is pole.
  • Frequency of alternator’s supply depend upon 2 things that is; ‘speed of rotor’ & ‘Number of poles of the stator winding’.
  • Alternators are rated in KVA & KVA is Apparent power in which power factor term is not included.
  • Apparent power is the product of Voltage & Current, 3phase Apparent power is P=√3*V*I Where V is voltage & I is current.
 
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