In a two-value capacitor motor, the capacitor used for running purposes is ________________ & _______________

Question

In a two-value capacitor motor, the capacitor used for running purposes is ________________ & _______________ duty.

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Option D: Paper spaced oil-filled type, continuous

Explanation & Concepts:
In a two-value capacitor motor (also known as a capacitor-start capacitor-run motor), two capacitors are used to optimize starting torque and running efficiency. The running capacitor remains continuously connected in series with the auxiliary winding, requiring a paper-spaced oil-filled continuous-duty capacitor to prevent overheating.

Working Principle: During starting, a high-value electrolytic capacitor (short-duty) is connected in parallel with the run capacitor via a centrifugal switch to provide high starting torque. Once the motor reaches approximately 75% of full speed, the centrifugal switch disconnects the starting capacitor. The paper-spaced oil-filled capacitor remains in the circuit continuously during operation to improve the running power factor, efficiency, and torque capability while minimizing phase angle imbalance.

Key Formulas: $C_{start} \gg C_{run}$ — capacitance relationship between start and run units; $\phi = 	heta_{aux} - 	heta_{main} \approx 90^\circ$ — phase displacement for maximum torque

Key Points: Run capacitor rating: Continuous duty, paper-spaced oil-filled type.; Start capacitor rating: Short duty / intermittent duty, electrolytic type.; The continuous-duty capacitor stays in circuit during both starting and running conditions.

Advantages: High starting torque combined with high running efficiency and power factor.; Quieter and smoother operation compared to single-capacitor induction motors.

Disadvantages: Higher initial cost due to two separate capacitors and a centrifugal switch.; Larger physical size compared to standard single-phase induction motors.

Applications: Refrigeration compressors and air conditioners; High-load machinery like lathes, conveyors, and heavy-duty pumps

Additional Info: Option A & B: Electrolytic and Ceramic capacitors are non-continuous/intermittent rated and would overheat if connected continuously in AC supply.. Option C: Air capacitors have very low capacitance per unit volume and are impractical for power application duty.

Answer: D is correct — The running capacitor in a two-value capacitor motor must withstand continuous dielectric stress, making a paper-spaced oil-filled continuous-duty capacitor necessary.

Exam Tip: Remember for competitive exams: Start capacitors are high-value short-duty electrolytic types, whereas Run capacitors are low-value continuous-duty paper/oil/polypropylene types.

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Option A: Electrolytic Capacitor, Intermediate duty

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Option B: Ceramic type, Intermediate duty

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Option C: Air capacitor, continuous

Feature	Starting Capacitor ($C_{start}$)	Running Capacitor ($C_{run}$)
Capacitor Type	Electrolytic Type	Paper Spaced Oil-Filled Type
Duty Cycle	Short / Intermediate Duty	Continuous Duty
Capacitance Value	High ( $100 - 400\ \mu\text{F}$ )	Low ( $10^{-50}\ \mu\text{F}$ )

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