# A DC shunt motor is running at 1200 RPM when excited with 220 V dc. Neglecting the losses and voltage dropped of the motor when connected to a 175 V supply is:

A DC shunt motor is running at 1200 RPM when excited with 220 V dc. Neglecting the losses and voltage dropped of the motor when connected to a 175 V supply is:

### Right Answer is: 1200 RPM

#### SOLUTION

Extracting the data from the given problem: Speed of DC shunt motor is 1200 rpm, the excitation voltage is 220V. The new excitation voltage is given as 175 V DC. In a DC shunt motor, the field current is given as

The speed equation of DC motor

$N \propto \dfrac{{{E_b}}}{\Phi } \propto \frac{{V – IaRa}}{\Phi }$

The flux of DC motor is φ = K’V.
Where K is the  constant based on armature design
Now the losses and voltage drop is neglected therefore
Voltage is also equal to back emf

V = Eb = KφN

N = V/Kφ = V/KK’V = 1/KK’

Now, it is observed that speed is constant and independent of voltage. Therefore, the value of voltage is 1200 rpm.

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