Earthing of transformer neutral through reactance will improve its

Question

Examoogle · Accepted Answer

Option A: Transient stability

Explanation & Concepts:
Earthing the transformer neutral through a reactor (Petersen coil or neutral reactor) limits the ground fault current by introducing inductive reactance. This limitation reduces the severity of the fault, thereby allowing the system to maintain synchronism more effectively during transient disturbances, which improves transient stability.

Working Principle: During a line-to-ground fault, the neutral reactor provides a high-impedance path to ground. This reduces the magnitude of the fault current ($I_f$). By minimizing the energy imbalance between input mechanical power and output electrical power during the fault duration, the swing equation ($M \frac{d^2\delta}{dt^2} = P_m - P_e$) results in less severe rotor angle oscillations, directly enhancing transient stability.

Key Formulas: $P_e = \frac{V_1 V_2}{X_{eq}} \sin \delta$ — Power transfer equation; $M \frac{d^2\delta}{dt^2} = P_m - P_e$ — Swing equation defining stability

Key Points: Neutral reactance limits fault current, reducing electrical shock to mechanical components.; Transient stability is primarily concerned with the system's ability to withstand sudden, large disturbances.; Steady-state stability relates to small, gradual changes in load, which are less affected by neutral grounding impedance.; The use of a reactor is distinct from solid grounding, which would maximize fault current.

Advantages: Reduced mechanical stress on windings during faults; Improved transient stability limits; Lower fault current magnitude

Disadvantages: Potential for overvoltages during arcing ground faults; Requires precise tuning of the reactance

Applications: Transmission systems; Large power transformer neutrals

Additional Info: Steady-state stability depends primarily on the synchronizing power coefficient and the line reactance, not the neutral grounding method. Thus, option (b) is incorrect as grounding method changes have negligible impact on steady-state stability.. Solid grounding is usually preferred for protection schemes, whereas reactance grounding is specifically chosen to mitigate fault severity and transient effects.

Answer: A is correct — Earthing the transformer neutral through a reactor limits the fault current, which reduces the severity of power oscillations during faults and thereby improves transient stability.

Exam Tip: Always remember that neutral grounding techniques (solid, resistance, or reactance) are designed for protection and transient control, while steady-state stability is primarily improved by reducing line impedance (series compensation) or using fast-acting excitation systems.

Examoogle · Answer

Option B: Steady state stability

Examoogle · Answer

Option C: Both (a) and (b)

Examoogle · Answer

Option D: None of above

Correct Answer

Discussion (0)

Correct Answer

Related Questions

Discussion (0)