______________ has a relatively wider range of speed control.

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______________  has a relatively wider range of speed control.

Examoogle · Accepted Answer

D.C. shunt motor

Explanation: A D.C. shunt motor allows for a wide and smooth range of speed control by adjusting the field flux or armature voltage. This makes it superior to induction or synchronous motors, which generally operate at fixed speeds governed by supply frequency and pole pairs. Working Principle: The speed of a DC motor is governed by the relation $N \propto \frac{E_b}{\Phi}$. By controlling the shunt field current using a rheostat, the flux $\Phi$ can be varied, resulting in speed variations above the rated value (field control). Alternatively, varying the applied armature voltage $V$ allows for speeds below the rated value (armature control), providing a versatile operational envelope. Key Formulas: $N = K \frac{V - I_a R_a}{\Phi}$ — Fundamental speed equation for a DC motor; $P_{mech} = E_b I_a$ — Mechanical power developed Key Points: Speed control in DC shunt motors is achieved without the need for complex power electronics (though they are now commonly used).; Field control provides constant power drive characteristics.; Armature control provides constant torque drive characteristics.; Synchronous motors run at a constant speed defined by $N_s = \frac{120f}{P}$. Advantages: Wide range of speed control; Smooth and precise speed regulation; Simple control circuit Disadvantages: Requires DC supply or rectifier; Maintenance due to brushes and commutator; Lower efficiency compared to brushless AC motors Applications: Machine tools; Lathes; Conveyor belts; Fans and blowers Additional Info: The Squirrel cage induction motor is primarily a constant speed motor; speed variation requires Variable Frequency Drives (VFDs).. Slip ring induction motors allow speed control via rotor resistance, but it is less efficient due to heat loss in resistors. Answer: B is correct — The D.C. shunt motor provides a relatively wider range of speed control through armature voltage and field flux variation. Exam Tip: Always remember that in DC motors, field weakening ($ \Phi \downarrow $) increases speed, whereas in AC induction motors, changing frequency ($ f $) is the primary method for speed control.

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