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The reflection of surges at open ends leads to voltage build up, which may eventually damage the high voltage equipment
True
False
Can not say anything
True
When an incoming surge (traveling wave) reaches an open end of a transmission line, it encounters an infinite impedance. The reflected wave has the same polarity and magnitude as the incident wave, resulting in a total voltage at the terminal equal to twice the incident voltage, which can lead to insulation failure.
When an incoming surge (traveling wave) reaches an open end of a transmission line, it encounters an infinite impedance. The reflected wave has the same polarity and magnitude as the incident wave, resulting in a total voltage at the terminal equal to twice the incident voltage, which can lead to insulation failure.
VreflectedтАЛ=╬▓VincidentтАЛ тАФ voltage reflection relationship
VtotalтАЛ=VincidentтАЛ(1+Z2тАЛ+Z1тАЛZ2тАЛтИТZ1тАЛтАЛ) тАФ general voltage reflection at a junction
The reflection coefficient (╬▓) at the end of a transmission line is defined as ╬▓=Z2тАЛ+Z1тАЛZ2тАЛтИТZ1тАЛтАЛ. For an open end, the terminating impedance Z2тАЛ=тИЮ. Substituting this into the reflection formula yields ╬▓=1. Consequently, the total voltage VtтАЛ at the open end is VtтАЛ=VincidentтАЛ+VreflectedтАЛ=VincidentтАЛ(1+╬▓)=2VincidentтАЛ. This voltage doubling phenomenon is a significant hazard for high voltage switchgear and transformers.
At an open circuit, the reflected voltage wave is identical in phase and magnitude to the incident wave.
Voltage doubling occurs almost instantaneously at the open terminal, creating a stress point for insulation.
Surge arresters are placed at equipment terminals to clamp this voltage below the Basic Insulation Level (BIL).
Concept helps in designing insulation coordination strategies.
Explains the necessity of surge protection devices near equipment.
Open-ended lines are highly susceptible to transient overvoltages.
Reflected waves can create standing waves that stress cable dielectric strength.
Transmission line protection
Transformer insulation design
Switchgear sizing
The phenomenon is known as the 'doubling effect' in traveling wave theory.
Option B is false because the incident and reflected waves add constructively at an open-ended terminal.
A is correct тАФ The reflection of surges at an open end results in the doubling of the incident voltage wave, which creates high electrical stress on insulation.
Always remember that for a short circuit, the reflection coefficient ╬▓=тИТ1, causing the voltage at the point to collapse to zero.