A DC generator can be considered as

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Examoogle · Accepted Answer

Rotating amplifier

Explanation: A DC generator is classified as a rotating amplifier because a small change in the field excitation current results in a large change in the armature output voltage. By controlling the input signal (field excitation), one can linearly control the output power, mirroring the behavior of a static electronic amplifier.

Working Principle: In a DC generator, the output voltage is given by $E_g = \frac{P\Phi ZN}{60A}$. Since the armature resistance $R_a$ is constant, the relationship between field current $I_f$ and output power is nearly linear in the unsaturated region. This allows the machine to function as a power amplifier, where the field winding acts as the control circuit and the armature winding acts as the load circuit.

Key Formulas: $E_g = k_g I_f$ — Where $k_g$ represents the machine constant, showing the amplification factor.; $P_{out} = V_a I_a$ — The output power controlled by the field excitation.

Key Points: The input control circuit is the field winding.; The output circuit is the armature winding.; Amplification is possible due to the interaction between magnetic flux and rotational speed.; Often used in systems like Ward-Leonard speed control.

Advantages: High power gain capability.; Capability to control very large loads with small signals.

Disadvantages: Slow response time compared to electronic amplifiers due to magnetic inertia (inductance).; Requires mechanical rotation (prime mover).

Applications: Ward-Leonard control systems.; Old servo mechanisms.; Voltage regulators for high-power DC machines.

Additional Info: A rectifier converts AC to DC, whereas a generator performs energy conversion (mechanical to electrical).. A prime mover (like a diesel engine) provides mechanical energy, it does not act as an amplifier.

Answer: C is correct — The DC generator acts as a rotating amplifier because the output armature voltage is controlled by the input field current through electromagnetic induction.

Exam Tip: Always remember: DC generators are 'rotating' amplifiers, whereas transistors or Op-Amps are 'static' amplifiers.

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