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Switching over voltages may be caused by
Sustained earth fault on phase conductor
Energisation or reclosure of long lines
Load rejection at the receiving lines
Fault initiation
1 and 2
2 and 3
1, 2 and 3
1, 2, 3 and 4
1, 2, 3 and 4
Switching overvoltages, also known as switching surges, are transient voltages that occur in power systems during circuit breaker operations or sudden changes in system conditions. These transients result from the sudden redistribution of energy stored in the electromagnetic fields of inductors and capacitors when the circuit path is abruptly altered.
Switching overvoltages, also known as switching surges, are transient voltages that occur in power systems during circuit breaker operations or sudden changes in system conditions. These transients result from the sudden redistribution of energy stored in the electromagnetic fields of inductors and capacitors when the circuit path is abruptly altered.
v(t)=LdtdiтАЛ тАФ Voltage across an inductor during transient
VpeakтАЛ=VsourceтАЛ├Ч(1+eтИТ2LRтАЛt) тАФ Approximation for switching surge magnitude
When a circuit is energized, reclosed, or subjected to faults, the sudden change in current i through inductances (L) creates a voltage spike defined by v=LdtdiтАЛ. Because dt is extremely small during switching operations, the induced voltage v becomes very large. Similarly, load rejection causes a sudden drop in current, forcing the magnetic energy stored in line inductances to discharge, leading to voltage oscillations across system capacitances.
Switching surges are characterized by short duration, typically ranging from a few hundred microseconds to a few milliseconds.
The magnitude of switching overvoltages is usually expressed in per-unit (p.u.) of the maximum phase-to-neutral system voltage.
Long transmission lines are more prone to higher switching overvoltages due to the charging of line capacitance and wave reflection phenomena.
System damping (resistance) helps in reducing the peak amplitude and decay time of these oscillations.
Design of insulation coordination in EHV and UHV systems
Selection of Surge Arresters (MOA)
Circuit breaker insulation design
Switching surges are the primary factor determining insulation levels for transmission lines above 300 kV.
Option 4 is correct because fault initiation essentially acts as a sudden change in network topology, forcing the system to re-equilibrate, which triggers transient surges.
D is correct тАФ All listed conditions represent sudden changes in network state that trigger electromagnetic energy exchange between system inductances and capacitances, resulting in transient overvoltages.
In power systems, always relate transient magnitude to the system's surge impedance (ZcтАЛ=L/CтАЛ); higher inductance and lower capacitance generally favor higher peak overvoltages.