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An electric motor draws a current of 10 amp with a voltage
Chapter 2, Problem 2.62(choose chapter or problem)
An electric motor draws a current of 10 amp with a voltage of 110 V, as shown in Fig. P2.62. The output shaft develops a torque of \(9.7 \mathrm{~N} \cdot \mathrm{m}\) and a rotational speed of 1000 RPM. For operation at steady state, determine for the motor
(a) the electric power required, in kW.
(b) the power developed by the output shaft, in kW.
(c) the average surface temperature, \(T_{s} \text {, in }{ }^{\circ} \mathrm{C}\), if heat transfer occurs by convection to the surroundings at \(T_{\mathrm{f}}=21^{\circ} \mathrm{C}\).
Questions & Answers
QUESTION:
An electric motor draws a current of 10 amp with a voltage of 110 V, as shown in Fig. P2.62. The output shaft develops a torque of \(9.7 \mathrm{~N} \cdot \mathrm{m}\) and a rotational speed of 1000 RPM. For operation at steady state, determine for the motor
(a) the electric power required, in kW.
(b) the power developed by the output shaft, in kW.
(c) the average surface temperature, \(T_{s} \text {, in }{ }^{\circ} \mathrm{C}\), if heat transfer occurs by convection to the surroundings at \(T_{\mathrm{f}}=21^{\circ} \mathrm{C}\).
Step 1 of 3
a)
Calculate the required electric power by using the following formula:
\(\mathop W\limits^. = - VI\)
Here, V is the voltage, and I is the current.
Substitute 110 V for V and 10 amp for I in the above formula, and we get,
\(\mathop W\limits^. = - 110\left( {10} \right)\)
\(\mathop W\limits^. = - 1100\)
\(\mathop W\limits^. = - 1.1\;{\rm{kW}}\)
Therefore, the electric power required is determined as -1.1 kW.
Step 2 of 3
b)
Calculate the power developed by the output shaft.
\(\mathop {{W_{shaft}}}\limits^. = T\omega \)
Here, T is the torque, and \(\omega \) is the angular velocity.