ETO ETO Exam papers 📅 Mar 2024

Exam Question

(a) Which of the following three motors has the poorest speed regulation: shunt motor, series motor or cumulative compound motor? Explain.

(b) An 18.65-kW, 4-pole, 50-Hz, 3-phase induction motor has friction and windage losses of 2.5 percent of the output. The full-load slip is 4%. Compute for full load

(i) the rotor Cu loss the rotor input

(ii) the shaft torque

(iii) the gross electromagnetic torque.

Reference Answer

(a) Series motor has the poorest speed regulation among the three motors.
Speed regulation refers to the change in motor speed from no load to full load, expressed as a percentage of the full-load speed:
$$\%\:Speed\:regulation=\frac{No\:load\:speed\:-\:Full\:load\:speed}{Full\:load\:speed}\:\times100$$
Shunt Motor: The field windings are connected in parallel (shunt) with the armature. Shunt motors have a nearly constant speed regardless of load changes, offering excellent speed regulation. This is because the field current remains relatively stable, keeping the magnetic flux constant.

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