The operation of OLTC does

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Not improve voltage stability

Explanation: An On-Load Tap Changer (OLTC) adjusts the transformer turns ratio to regulate output voltage under load. While it maintains a target voltage setpoint, it does not improve voltage stability in the sense of power system steady-state stability or voltage collapse prevention; in fact, aggressive OLTC operation can sometimes exacerbate voltage instability by increasing reactive power demand at the load.

Working Principle: The OLTC changes the effective number of turns in the transformer winding ($N_p/N_s$) to compensate for voltage drops ($V = E - IZ$). By adjusting the tap position, the secondary voltage is kept constant regardless of load variation. However, in a stressed system, raising the voltage via OLTC increases the current drawn by constant power loads, which leads to higher line losses and further voltage drop, potentially leading to voltage collapse.

Key Formulas: $V_{s} \approx V_{p} 	imes \frac{N_{s}}{N_{p}}$ — Relation between turns ratio and voltage; $\Delta Q = \frac{\partial Q}{\partial V} \Delta V$ — Sensitivity of reactive power to voltage changes

Key Points: OLTC is used primarily for voltage regulation (maintaining nominal voltage at load terminals).; Voltage stability is a function of reactive power support ($Q$) and network strength, not just tap position.; OLTC operation can induce 'Voltage Instability' during heavy load conditions due to the restorative action on constant power loads.

Advantages: Maintains constant consumer voltage; Compensates for load-induced voltage drops

Disadvantages: Does not increase the reactive power margin of the system; Can lead to hunting or oscillation if multiple OLTCs are uncoordinated

Applications: Distribution transformers; Substation power transformers

Additional Info: Voltage stability is defined by the ability of a power system to maintain steady voltages at all buses after being subjected to a disturbance.. OLTC is a 'local' controller, whereas voltage stability is a 'system-wide' phenomenon.

Answer: B is correct — OLTC performs voltage regulation by adjusting the turns ratio to maintain a target voltage, but it does not improve the inherent voltage stability of the power grid.

Exam Tip: Always distinguish between 'Voltage Regulation' (local magnitude control) and 'Voltage Stability' (system-wide capability to prevent collapse).

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