Varistor explained

Also known as a voltage-dependent resistor (VDR), it has a nonlinear, non-ohmic current–voltage characteristic that is similar to that of a diode. In contrast to a diode however, it has the same characteristic for both . How a common surge strip works explained by GE Global Research Engineer Bill Morris. The resistance of a varistor is variable and depends on the voltage applied.

A varistor is a voltage dependent resistor (VDR).

The word is composed of parts of the words “variable resistor”. Their resistance decreases when the voltage increases. In case of excessive voltage increases, their resistance drops.

They have the advantage over transient suppressor diodes in as much as they can absorb . This further can be explained as the DC voltage applied across the terminals of the varistor that allows a current of milli Ampere to flow through it. The current flowing through the varistor body is dependent on the material used for the construction of the varistor. At this rated voltage level, the functionality of .

To know more about it, check the link given below. TAKE A LOOK : VARIABLE RESISTORS – WORKING AND APPLICATIONS. Metal-oxide varistors (MOVs) are relatively simple devices, choosing the right one requires some knowledge.

The key to explaining metal-oxide varistor operation lies in understanding the electronic phenomena occurring near the grain boundaries, or junctions between the ZNO grains. While some of the early theory supposed that electronic tunneling occurred through an insulating second phase layer at the grain boundaries, . The above figure shows varistor application in various power systems protection systems. Each varistor application is explained below with varistor circuit.

By doping impurities in the crystal structure, semiconducting ZnO can be made into conductor. Varistor Circuit for Single Phase Line to Line Protection. By using impurity doped ZnO in combination with insulating ceramic matrix, a new type of material is made.

This new type of material is called varistor. Explanation of Part Numbers. The principle of overvoltage protection by varistors is explained in chapter Selection pro- cedure in section 1. Microstructure and conduction mechanism.

Sintering zinc oxide together with other metal oxide additives under specific conditions produces a polycrystalline ceramic whose resistance exhibits a pronounced . The nonlinear phenomenon can be explained by the semiconducting behaviour of the varistor filler.

Starting at around 1°C, the epoxy matrix expands strongly due to the melting of crystalline areas. This leads to a separation of the varistor fillers and causes an increased resistivity. This is known as the electrical–thermal.

The spark gap acts as a switch to prevent conduction in the silicon carbide varistor during normal operation of the mains, as explained in Chapter 8. Silicon carbide secondary arresters are suitable for protecting insulation from damage by transient overvoltages. They should offer adequate protection for motors and . This phenomenon is called the varistor effect. With the VAR-series, TDK offers various ring varistors using a SrTiO(strontium titanate) semiconductor ceramic material.

Features and electrical and physical characteristics of the. The observed overshoot voltage across a varistor is explained by the inductance ofthe connecting leads when a nanosecond rise time transient current is applied through the varistor. When a varistor conducts current, especially if . This dependence is fitted by the dotted curve, which will be explained in Sect. Electrical Transport in Polycrystalline ZnO 2.