Voltage collapse typically occurs in the power system due to

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Examoogle · Accepted Answer

All of above

Explanation: Voltage collapse is a system-wide phenomenon characterized by a progressive and uncontrollable decline in voltage, typically occurring when the reactive power demand exceeds the reactive power transfer capability of the transmission network. It is a manifestation of the system's inability to maintain the stability of the voltage magnitude at critical load buses.

Working Principle: Voltage instability is intrinsically linked to the maximum power transfer capability of the transmission system. As load increases, the reactive power losses ($I^2X$) in the transmission lines grow quadratically, leading to voltage drop. If the system cannot supply enough reactive power to compensate for these losses due to line constraints, faulted conditions, or exhausted reserves, the operating point moves towards the 'nose' of the P-V curve, eventually leading to collapse.

Key Formulas: $Q_{loss} = I^2 X$ — Reactive power loss in a line with reactance $X$ and current $I$; $V = \sqrt{\frac{P^2 + Q^2}{S^2}} \cdot V_{bus}$ — General voltage dependency on power flow

Key Points: Voltage collapse occurs when the system cannot meet the demand for reactive power.; Heavily loaded lines increase $I^2X$ losses, consuming reactive power reserves.; Faults reduce the effective transmission impedance or disconnect reactive sources.; The 'Nose' of the P-V curve represents the point of maximum power transfer and instability.

Applications: Power System Stability Analysis; Voltage Control and Compensation Planning

Additional Info: Voltage collapse is a dynamic process that can lead to large-scale blackouts.. Option B (Faulted line) is correct because a fault increases the severity of reactive power absorption in the system due to high fault currents.. Option C is the most fundamental cause, as the shortage of reactive power is the physical mechanism behind the collapse.

Answer: D is correct — Voltage collapse is a multi-causal phenomenon stemming from the inability of the power system to support reactive power requirements, which is exacerbated by heavy loading, faults, and insufficient reactive reserves.

Exam Tip: Always remember that voltage instability is a local phenomenon that can escalate into a global system collapse; it is primarily reactive-power dependent, whereas rotor angle stability is primarily active-power dependent.

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