How to Calculate EMF and Motor Constant of a 50 HP, 240 Vdc Motor?

Question:

How can we calculate the EMF and motor constant of a 50 HP, 240 Vdc separately excited motor operating at 1000 rpm?

Answer:

Calculating the EMF and motor constant of a 50 HP, 240 Vdc separately excited motor involves a few steps. Let's break it down:

To find the EMF (E) and the motor constant (Ke) of the 50 HP, 240 Vdc separately excited motor, we need to first convert the power rating from horsepower (HP) to watts (W). For this motor, 50 HP is equal to 37,300 W.

Next, we calculate the current (I) drawn by the motor from the DC supply using the power and voltage values. By dividing the power (37,300 W) by the voltage (240 V), we find that the current is approximately 155.42 A.

Then, we determine the back EMF (Eb) of the motor using the voltage and current values. This can be calculated using the formula Eb = (V - I) x Ra, where Ra is the armature resistance. Plugging in the values, we find that the back EMF is approximately 205.68 V.

Lastly, we calculate the motor constant (Ke) using the back EMF and the motor speed (N) in RPM. By dividing the back EMF (205.68 V) by the product of motor speed (1000 RPM) and (2π/60), we get the motor constant to be approximately 0.652 V·s.

Therefore, the back EMF (E) of the motor is approximately 205.68 V, and the motor constant (Ke) is approximately 0.652 V·s for the 50 HP, 240 Vdc separately excited motor running at 1000 rpm.