The following details are given on a 225 kW (≈ 300 hp), 250 V, 1200 r/min dc motor (see Figs. 4 and 5):

armature coils    243
turns per coil 1
type of winding lap
armature slots    81
commutator segments 243
field poles                                              6
diameter of armature 559 mm
axial length of armature    235 mm

Calculate

a. The rated armature current
b. The number of conductors per slot
c. The flux per pole

Question

The following details are given on a 225 kW (≈ 300 hp), 250 V, 1200 r/min dc motor (see Figs. 4 and 5):

armature coils    243
turns per coil 1
type of winding lap
armature slots    81
commutator segments 243
field poles 6
diameter of armature 559 mm
axial length of armature    235 mm

Calculate

a. The rated armature current
b. The number of conductors per slot
c. The flux per pole

Accepted Answer

a. We can assume that the induced voltage [latex]E_{ o }[/latex] is nearly equal to the applied voltage (250 V).
The rated armature current is

[latex]\begin{aligned}I &=P / E_{ o }=225000 / 250 \&=900 A\end{aligned}[/latex]

b. Each coil is made up of 2 conductors, so altogether there are 243 × 2 = 486 conductors on the armature.

Conductors per slot = 486/81 = 6

Coil sides per slot = 6

c. The motor torque is

[latex]\begin{aligned}T &=9.55 P / n \&=9.55 imes 225000 / 1200 \&=1791 N \cdot m\end{aligned}[/latex]

The flux per pole is

[latex]\begin{aligned}\Phi &=6.28 T / Z P \&=(6.28 imes 1790) /(486 imes 900) \&=25.7 mWb\end{aligned}[/latex]

Question 5.2: The following details are given on a 225 kW (≈ 300 hp), 250 ...

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