For improving power factor, capacitor bank always connected in ________

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Examoogle · Accepted Answer

Delta

Explanation: Capacitor banks used for power factor improvement are connected in a delta configuration because it provides a lower capacitance requirement to achieve the same reactive power compensation compared to a star connection. In a three-phase system, connecting capacitors in delta subjects them to full line voltage, whereas star connection would only subject them to phase voltage.

Working Principle: The principle relies on injecting leading reactive power (VARs) into the system to counteract the lagging reactive power consumed by inductive loads. Since reactive power $Q = V^2 \omega C$ for a single capacitor, the delta connection ensures that each phase of the capacitor bank experiences the line voltage ($V_L$), resulting in three times the reactive power compared to a star connection with the same capacitance value ($Q_{\Delta} = 3 Q_Y$). This allows for smaller, more economical capacitors to achieve the desired correction.

Key Formulas: $Q = 3 \cdot V_L^2 \cdot \omega \cdot C_{\Delta}$ — Reactive power in Delta configuration; $PF_{new} = \cos(	an^{-1}(	an(\phi_{old}) - \frac{Q_c}{P}))$ — Power factor improvement calculation

Key Points: Delta connection allows capacitors to operate at full line voltage.; Higher voltage rating of capacitors is required in delta connection.; Lower capacitance value per phase is required for the same total KVAR rating.; Delta connection prevents the flow of triple-frequency harmonic currents in the supply neutral if present.

Advantages: Requires less total capacitance for the same KVAR rating.; Compact installation size.; Better utilization of capacitor dielectric strength.

Disadvantages: Capacitors must be rated for full line voltage (higher insulation stress).; Switching surges can be more pronounced.

Applications: Industrial power factor correction panels.; Automatic Power Factor Correction (APFC) units.; Grid voltage regulation support.

Additional Info: Most LV (Low Voltage) capacitor banks are configured in delta to minimize physical footprint.. Option A (Star) is rarely used for PF correction as it requires higher capacitance values and is more susceptible to voltage fluctuations in the neutral path.

Answer: B is correct — Capacitor banks are connected in delta to maximize the reactive power output per phase by utilizing the line voltage across each capacitor.

Exam Tip: Always remember: $Q \propto V^2$. Delta connection exploits higher voltage availability to achieve required kVAR using smaller capacitance, making it standard for industrial APFC panels.

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