By looking at which part of the motor, it can be easily confirmed that a particular motor is DC motor?
A
Frame
B
Shaft
C
Commutator
D
Stator

Question

By looking at which part of the motor, it can be easily confirmed that a particular motor is DC motor?

Examoogle · Accepted Answer

Commutator

Explanation: The presence of a commutator is the defining visual characteristic of a DC machine, as it acts as a mechanical rectifier. It performs the crucial function of converting the AC induced in the armature conductors into unidirectional (DC) current at the output terminals.

Working Principle: In a DC motor, the armature coils rotate within a magnetic field, inducing an alternating emf. The commutator, consisting of copper segments insulated by mica, works in conjunction with carbon brushes to reverse the connection of the armature coils to the external circuit precisely when the current direction reverses, thereby ensuring unidirectional flow.

Key Formulas: $E_g = \frac{P \phi Z N}{60 A}$ — Generated EMF in a DC Machine; $T_a = 0.159 \phi Z \frac{I_a P}{A}$ — Armature Torque Equation

Key Points: The commutator is mounted on the shaft and rotates with the armature.; Commutator segments are typically made of hard-drawn copper.; Without a commutator, the machine would act as an AC machine (synchronous or induction machine).; Brushes remain stationary while the commutator segments move against them.

Advantages: Enables unidirectional current collection.; Allows for speed control over a wide range.

Disadvantages: High maintenance due to brush sparking.; Mechanical complexity and friction wear.

Applications: Electric traction and locomotives.; Industrial variable speed drives.

Additional Info: Frame: Acts as a yoke and magnetic path, not exclusive to DC motors.. Shaft: Used in all rotating electrical machines.. Stator: Present in both DC and AC machines; in DC machines, it houses the field poles.

Answer: C is correct — The commutator is the specific component that performs mechanical rectification, identifying the machine as a DC type.

Exam Tip: Always look for the 'Commutator' in visual inspection questions regarding DC machines; in AC machines, look for 'Slip Rings' or 'Squirrel Cage' rotors.

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