Transcript Slide 1
SEE 3433 ELECTRICAL MACHINES DC Generators - Shunt (self excited) Shunt (self excited) dc generator - no load It = 0 Ia Rfc Vt = Ea - IaRa + Vt Ea Ra Rfw Vt = IfRf Vt If , Rf = Rfc+Rfw + Ea Ea Field excitation comes from armature circuit Assume armature driven at certain speed Residual magnetism must exist If Shunt (self excited) dc generator - no load Ia Rfc EaVt It SW + Ra Vt If Rfw + Ea Ear1 Ear SW open, rotor rotates, residual magnetism Ear If1 If2 SW close, Ear will cause If1 to low in field hence increases Ea to Ear1 Voltage builds up until crossing point is reached If Shunt (self excited) dc generator - no load EaVt If Shunt (self excited) dc generator - no load EaVt Critical field circuit resistance Changing of Rfc results in different slopes If Rf must be set less than critical value Field winding must be connected such that it helps the flux build up Shunt (self excited) dc generator - with load It Ia Rfc + Ra Vt If Rfw + Ea Ia = It + If Vt = Ea - IaRa Ea - Vt = IaRa Ea = ka a function of If Rload Shunt (self excited) dc generator - with load – without AR Ea Vt Ia1Ra Vt Vt If Ia1 Ia,max Ia Shunt (self excited) dc generator - with load – with AR Ea Equivalent If(AR) IaRa Vt without AR VtA with AR If