Concept:
Back emf:
- In dc motor also generator action takes place.
- Because of this generator action the rotating conductor's cuts the flux and emf induced in the conductors.
- This induced emf is called back emf. It always opposes the supply voltage.
The back emf induced in the dc motor can be given by,
Eb = (ϕZNP) / (60 A)
Where,
ϕ = flux/pole
Z = total number of conductors
A = number of parallel paths
N = speed in RPM
P = number of poles
Calculation:
\(E = \frac{{\phi ZNp}}{{60A}} = \frac{{0.01 \times 666 \times 4 \times 1000}}{{60 \times 2}} = 222 V\)
Ia = (V - E) / Ra = (230 - 222) / 0.267
Ia = 29.96 A
Internal power ( Pd) \(= \;EI_a = 222\; \times \;29.96 = 6651.685 Watt\)
Shaft Power output,
Pout = Pd - Rotational losses
\(\begin{array}{l} {P_{out}} = 6651.685\;-\;600\; = 6051.685\\ T = \frac{{{P_{out}}}}{\omega } = \frac{{6051.685}}{{2\pi \times \frac{{1000}}{{60}}}} = 57.78\;Nm \end{array}\)