Which of the following methods is/are used for reactive or voltage compensation

Question

Examoogle · Accepted Answer

All of the above

Explanation: Reactive power compensation is essential to maintain stable voltage profiles across power transmission and distribution networks. By injecting or absorbing reactive power, system operators can regulate voltage levels, improve power factor, and enhance overall power transfer capacity.

Working Principle: Shunt capacitors provide reactive power to support voltage at weak load buses, while series capacitors compensate for the line inductive reactance to increase power transfer capability. Generation excitation control, specifically using Automatic Voltage Regulators (AVR), adjusts the field current of synchronous generators to modify the reactive power output and regulate terminal voltage.

Key Formulas: $Q_c = V^2 \omega C$ — Reactive power supplied by a shunt capacitor; $Q_s = I^2 X_c$ — Reactive power compensation in series capacitor; $V = E_f - I(R + jX_s)$ — Voltage regulation relationship in a synchronous machine

Key Points: Shunt compensation primarily regulates local voltage levels.; Series compensation is used to increase the stability limit ($P_{max} = \frac{V_1 V_2}{X_L - X_C}$).; Excitation control is the primary method for voltage regulation at the source.; Reactive power balance is vital to prevent voltage collapse.

Advantages: Improved voltage profile; Reduced line losses; Increased power transfer capability

Disadvantages: Over-compensation can cause excessive voltage rise; Potential for sub-synchronous resonance (SSR) with series capacitors

Applications: Transmission lines; Distribution feeders; Power generating stations

Additional Info: Shunt capacitors are connected in parallel with the load.. Series capacitors are connected in series with the transmission line.. Excitation control adjusts internal EMF $E_f$ by varying the DC field current.

Answer: D is correct — All listed methods are standard techniques employed in power systems to maintain bus voltages within acceptable operational limits.

Exam Tip: Always remember: Shunt compensation controls voltage at a specific bus, while series compensation acts to reduce the effective impedance of the transmission line to enhance stability.

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