**EMF Equation of an Alternator / AC Generator**

An alternator or AC generator (dynamo) is a device which convert mechanical energy to electrical energy. When we supply the magnetizing current by DC shunt generator through two slip rings (in recent alternators, they use electronic starting system instead of slip rings and commutators) because the field magnets are rotating. keep in mind that most alternators use a rotating magnetic field with a stationary armature.

When the rotor rotates, the stator conductors which are static in case of alternator cut by magnetic flux , they have induced EMF produced in them (according to **Faraday’s law of electromagnetic induction** which states that if a conductor or coil links with any changing flux, there must be an induced emf in it.

Note: We will discuss the construction, Working & Operation. Types of Alternators in details in our next posts.

This induced EMF can be found by the **EMF equation of the alternator** which as follow:

Lets,

**P** = No. of poles

**Z** = No. of Conductors or Coil sides in series/phase i.e. **Z = 2T**…Where T is the number of coils or turns per phase (Note that one turn or coil has two ends or sides)

* f* = frequency of induced EMF in Hz

**Φ** = Flux per pole (Weber)

**N** = rotor speed (RPM)

Where Distribution factor = **K _{d }**=

**K _{c }**or

**K**=

_{P}**Cos α/2**

If induced EMF is assumed sinusoidal then,

**K_{f }= Form factor = 1.11**

In one revolution of the rotor i.e. in **60/N** seconds, each conductor is cut by a flux of **ΦP** Webers.

*d***Φ **= **Φ P** and also

**= 60/N seconds**

*d*Φthen induced e.m.f per conductor ( average) = ….. *(i)*

But we know that:

** f = PN / 120** or

**N= 120**

*f*/ PPutting the value of **N** in **Equation (i)**, we get,

** Average value of EMF per conductor = ∴ (N= 120f/P)**

If there are **Z** conductors in series per phase,

then average e.m.f per phase = **2 f Φ Z** Volts

**= 4**

*f***Φ**

**T**….. (Z=2T)

*Volts*Also we know that;

** Form Factor= RMS Value / Average Value**

= RMS value= Form factor x Average Value,

**= 1.11 x 4 fΦT = 4.44fΦT Volts. **

(Note that is exactly the same equation as the EMF equation of the transformer)

And the actual available voltage per phase

**= 4 K _{c} K_{d }f ΦT = 4 K_{f }K_{c} K_{d }f ΦT Volts.**

Note: If alternator or AC generator is star connected as usually the case, then the Line Voltage is √3 times the phase voltage as derived from the the above formula.

You may also read:

**JLCPCB - Prototype 10 PCBs for $2 + 2 days Lead Time**

China's Largest PCB Prototype Enterprise, 300,000+ Customers & 10,000+ Online Orders Per Day

Get quote online easily

Excellent Post About Emergency MELTDOWN Generators Shutdown and <a href="http://www.adpower.ae/" rel="nofollow">Ac generator parts</a>.<br />

Its very usefull……thanxxx

Nice but little lendi

Generator kV to hp Calculation explain …