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Which of the following is a nonlinear diverter?
Expulsion type arresters
Valve type arresters
Electrolytic type arresters
Road gap type arresters
Valve type arresters
Valve type arresters are classified as nonlinear diverters because they utilize nonlinear resistor elements (usually silicon carbide or zinc oxide blocks) whose resistance drops drastically as the voltage increases. This property allows them to provide a high-resistance path during normal operation and a low-resistance path to discharge surge currents during transient overvoltages.
Valve type arresters are classified as nonlinear diverters because they utilize nonlinear resistor elements (usually silicon carbide or zinc oxide blocks) whose resistance drops drastically as the voltage increases. This property allows them to provide a high-resistance path during normal operation and a low-resistance path to discharge surge currents during transient overvoltages.
I=KV╬▒ тАФ where ╬▒ is the coefficient of nonlinearity (typically 3 to 7 for SiC, higher for ZnO)
R=IVтАЛ=KV╬▒тИТ11тАЛ тАФ resistance decrease with voltage increase
The arrester consists of a spark gap in series with nonlinear resistor elements. When a surge occurs, the spark gap breaks down, and the nonlinear resistor's resistance decreases according to the relation I=KV╬▒ (where ╬▒>1), allowing the surge energy to be diverted to the ground. Once the surge subsides, the resistance increases, helping to extinguish the power-frequency follow current.
Valve type arresters prevent power frequency current follow by increasing resistance after the surge.
The nonlinear resistor is often made of Silicon Carbide (SiC) or Zinc Oxide (ZnO).
They act as a 'valve' that opens for high-voltage transients and closes for normal operating voltages.
Excellent protection for high-voltage equipment.
Capable of handling high energy discharges.
Automatic recovery after the surge is diverted.
More complex and expensive than simple spark gap arresters.
Requires periodic maintenance of spark gaps (for SiC based).
High-voltage transmission substations.
Transformer protection in power grids.
| Feature | Expulsion Type | Valve Type |
|---|---|---|
Current Follow | Significant | Controlled/Minimal |
Zinc Oxide (ZnO) arresters are modern valve-type arresters that do not require series spark gaps because of their superior nonlinearity.
Option D (Rod gap) is a primitive protective device with high time lag and no current-limiting capability.
B is correct тАФ Valve type arresters use nonlinear resistors that provide a low-impedance path to ground during surge conditions and high-impedance during normal system voltage.
Always remember that 'nonlinear' in power system protection refers specifically to voltage-dependent resistance that limits current during surges without significantly increasing system current under normal conditions.