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SEE 3433 ELECTRICAL MACHINES DC Generators - Shunt (self excited)

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Shunt (self excited) dc generator - no load V t = E a - I a R a V t = I f R f, R f = R fc +R fw +Ea+Ea +Vt+Vt RaRa R fc R fw IaIa I t = 0 IfIf Field excitation comes from armature circuit Residual magnetism must exist V t E a EaEa IfIf Assume armature driven at certain speed

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+Ea+Ea +Vt+Vt RaRa R fc R fw IaIa ItIt IfIf SW SW open, rotor rotates, residual magnetism E ar EaVtEaVt IfIf E ar I f1 E ar1 I f2 Voltage builds up until crossing point is reached SW close, E ar will cause I f1 to low in field hence increases E a to E ar1 Shunt (self excited) dc generator - no load

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EaVtEaVt IfIf

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EaVtEaVt IfIf Critical field circuit resistance Shunt (self excited) dc generator - no load Changing of R fc results in different slopes R f must be set less than critical value Field winding must be connected such that it helps the flux build up

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Shunt (self excited) dc generator - with load +Ea+Ea +Vt+Vt RaRa R fc R fw IaIa ItIt IfIf R load I a = I t + I f V t = E a - I a R a E a = k a a function of I f E a - V t = I a R a

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Shunt (self excited) dc generator - with load – without AR EaEa IfIf IaIa VtVt I a,max I a1 VtVt VtVt I a1 R a

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Shunt (self excited) dc generator - with load – with AR EaEa IfIf Equivalent I f(AR) V t without AR V tA with AR IaRaIaRa

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