What determines the response time of surge protector?

- Sep 28, 2019-

The response time of the surge protector refers to the time when the surge protector on the line is operated when the line is transient overvoltage caused by lightning strikes or starting or stopping of electrical equipment. The shorter the response time of the surge protector, the better the protection. However, what is the corresponding time of the surge protector?

First, the components of the surge protector

The components of the surge protector generally include varistor, gas discharge gap, semiconductor components, voltage-stabilized semiconductor devices, isolation transformers, and optocoupler isolators. According to the definition of the surge protector in the Building Lightning Protection Technical Specification, the surge protector only needs a nonlinear component. The nonlinear component mainly has four kinds of discharge gaps, a ceramic gas discharge tube, a glass discharge tube, and a metal oxide varistor. Depending on the protection target of the surge protector, the level of protection, and the design of the surge protector from various manufacturers, the nonlinear components used are different, so the performance of the surge protector is different (including quality).

Second, the performance of nonlinear components determines the response time of the surge protector

The nonlinear components that make up the surge protector have different materials and their response times are different, which determines the response time of the surge protector, as follows:

1. Discharge gap

The metal discharge gap is a simple lightning protection device consisting of two metal electrodes. Wherein, one electrode is fixed on the insulator, and is connected to the charged wire, and the other electrode is connected to the grounding device through the auxiliary gap, and a predetermined gap distance is maintained between the two electrodes. The reaction time is long, up to about 100ns, which is not conducive to circuit protection. A surge protector consisting of a discharge gap has a longer response time.

2. Ceramic gas discharge tube

Ceramic gas discharge tubes are the most widely used switching devices in surge protectors, which use metallized ceramic tubes to seal one or more discharge gaps with two or more electrodes. The ceramic tube is filled with an inert gas. When the voltage across the gas discharge tube reaches its DC discharge voltage, the internal gas is broken down and discharged. The utility model has the advantages of small volume, low cost, stable performance and long service life, but the discharge delay is large, and the response time is slow, generally about 80 ns. A surge protector consisting of a ceramic discharge tube also has a longer response time.

3. Glass discharge tube

The glass discharge tube consists of two electrodes that are spaced apart by a distance in a glass tube filled with an inert gas. When the voltage at both ends is lower than the discharge voltage, the gas discharge tube is an insulator. When the voltage at both ends rises above the discharge voltage, it can change the high impedance between the two stages at a speed of two stages of 10-9s. Low impedance, arc discharge, very short response time, mainly used in surge protectors for communication equipment such as high frequency circuits.

4. Metal oxide varistor

Metal oxide varistor is a compound semiconductor component made by ceramic process. Its conductance increases rapidly with increasing voltage within a certain temperature range and a certain voltage range. It is a widely used and economical component. Divided into silicon carbide varistor and zinc oxide varistor. The response time of the zinc oxide varistor is about 25 ns, generally not more than 50 ns, which is shorter than that of the silicon carbide varistor or the gas gap discharge tube.