An increased load angle will cause electromagnetic torque to increase. This in turn will increase the load angle. This means, as the mechanical power input to the synchronous generator is increased through prime mover, the field poles will be dragged ahead of the stator pole or flux. As discussed earlier in this post, load angle is the angle between the field flux and the resultant air gap flux. Let us first understand the physical significance of this parameter before going into some sort of mathematical formula or expression. In synchronous machine, load angle is a very important parameter. This angle of lag is called load or power angle. In a synchronous generator, the stator mmf lags behind the resultant air gap mmf. Power angle can also be defined in terms of armature or stator mmf and resultant air gap mmf. A simple phasor diagram showing the relation between the E f, V t, Ø f and Ø r. Thus the angle between E f and V t will be equal to the angle between field flux and resultant air gap flux. Thus terminal voltage V t will lag behind the resultant air gap flux Ø r by 90 degree. Terminal voltage is the voltage across the armature terminal which is induced due to the resultant air gap flux. Here emf is induced by the field flux hence it lags the field flux by 90 degree. This emf will be lagging by 90 degree with the field flux.Īlways remember that the generated emf always lags by 90 degree the flux that generates it. How? This is because under no load condition the emf will be induced in the armature or stator winding just because of the field flux or rotor flux Ø f. Note that this definition is having no difference with the previous definition.

Load angle is also defined as the angle between the no load excitation voltage E f and terminal voltage V t.

In Synchronous machine, we are well aware of the term Armature Reaction which affects the field ( field winding is wound on the rotor for synchronous machine) generated flux. Resultant air gap flux is the net flux in the air gap of machine due to combined action of stator as well as rotor flux. There are basically three different types of flux in a rotating electrical machine: Stator flux, Rotor flux and Resultant air gap flux.

Load angle formula