Before selecting a generator for our work we want to know the ratings of the generator and its specifications. Why we do this? the only reason for this is the efficiency. We want generator with good efficiency and should meet our requirements.
So we have to know about the emf that is generated by the generator. Here i will tell you how to find emf equation of dc generator. Before that lets know about the parameters used in the equation.
Let ϕ = flux/pole in weber
Z= total number of armature conductors
= No.of slots×No.of conductors/slot
P = No.of generator poles
A = No.of parallel paths in armature
N = armature rotation in revolutions per minute (r.p.m)
E = e.m.f induced in any parallel path in armature
Average e.m.f generated/conductor = dϕ/dt volts (n=1)
Flux cut/conductor in one revolution dϕ = ϕP weber
No.of revolutions/second = N/60
time for one revolution, dt = 60/N second
according to Faraday's Laws of electromagnetic induction, EMF generated/conductor = dϕ/dt
= ϕPN/60 volts
So we have to know about the emf that is generated by the generator. Here i will tell you how to find emf equation of dc generator. Before that lets know about the parameters used in the equation.
Let ϕ = flux/pole in weber
Z= total number of armature conductors
= No.of slots×No.of conductors/slot
P = No.of generator poles
A = No.of parallel paths in armature
N = armature rotation in revolutions per minute (r.p.m)
E = e.m.f induced in any parallel path in armature
Average e.m.f generated/conductor = dϕ/dt volts (n=1)
Flux cut/conductor in one revolution dϕ = ϕP weber
No.of revolutions/second = N/60
time for one revolution, dt = 60/N second
according to Faraday's Laws of electromagnetic induction, EMF generated/conductor = dϕ/dt
= ϕPN/60 volts
For simplex wave wound generator:
No.of parallel paths = 2
No.of conductors in one path = Z/2
E.M.F generated/path = ϕPN/60 ×Z/2 = ϕZNP/120 volt
For simplex lap wound generator:
No.of parallel paths = P
No.of conductors in one path = Z/P
E.M.F generated/path = ϕPN/60 ×Z/P = ϕZN/60 volt
General E.M.F generator emf , Eg = ϕPN/60 ×P/A volts
where A = 2 for simplex wave winding
= P for simplex lap winding
Also Eg = 1/2𝜫 (2𝜫 N/60)ϕZ(P/A) = ωϕZ/2𝜫×(P/A)
Thus Eg = KaϕN volts
where N in rps
Ka = ZP/A = constant
This is the equation to find the generated emf in the generator and this can be used to calculate the voltage at the amature terminals.
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