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Which of the following are the important limitations of rod gap surge arrester?
They are not capable of sealing off power frequency follow up current
┬аAfter a discharge, roads are destroyed completely
┬аPerformance is affected by climatic condition
1, 2 and 3 are correct
1 and 2 are correct
2 and 3 are correct
1 and 3 are correct
1 and 3 are correct
A rod gap surge arrester is a simple protective device consisting of two electrodes (rods) separated by an air gap. It fails to self-extinguish power frequency follow-up currents after a discharge and is highly susceptible to variations in environmental conditions like humidity, pressure, and dust.
A rod gap surge arrester is a simple protective device consisting of two electrodes (rods) separated by an air gap. It fails to self-extinguish power frequency follow-up currents after a discharge and is highly susceptible to variations in environmental conditions like humidity, pressure, and dust.
VbтАЛ=KтЛЕSn тАФ where VbтАЛ is spark-over voltage, S is gap length, and K,n are constants
╬┤=273+T0.392тЛЕPтАЛ тАФ air density correction factor, where P is pressure and T is temperature
When an overvoltage exceeds the spark-over value of the gap, a flashover occurs, diverting the surge current to the ground. However, since the air gap does not regain its insulating property immediately while the system voltage is still present, the arc persists as a power-frequency short circuit until the circuit breaker trips. The breakdown voltage VbтАЛ is non-linear and dependent on climatic factors (e.g., air density correction factor ╬┤ and humidity factor k).
Does not possess non-linear resistor characteristics (like SiC or MOV arresters).
Cannot isolate follow-up power current once the arc is established.
Spark-over voltage is highly dependent on ambient air density and humidity.
Used primarily as a secondary or backup protection due to low cost.
Extremely low cost and simple construction
Maintenance-free design (no moving parts)
Unable to quench power-follow current
High sensitivity to climatic changes
High probability of phase-to-ground fault during operation
Backup protection for transformers
Protection of bushing and insulators
The rod gap is considered 'coarse' protection compared to lightning arresters (surge arresters) like valve-type or metal-oxide types.
Statement 2 is incorrect because the rods are usually sacrificial but not necessarily destroyed completely after a single discharge; they sustain pitting and erosion over multiple operations.
D is correct тАФ The rod gap arrester cannot clear the power frequency follow current and its breakdown voltage varies significantly with atmospheric conditions.
In competitive exams, remember that any arrester without a non-linear valve element (like ZnO blocks) will inevitably lead to a short-circuit condition during operation.