Definition of Metal oxide varistors

Metal oxide varistors is a voltage limiting protection devices. Utilizing nonlinear characteristics Metal oxide varistors, when an overvoltage occurs between the two poles of the metal oxide varistors application, the metal oxide varistors application voltage can be clamped to a relatively fixed voltage value, in order to achieve protection of the post-stage circuit. The main parameters of Metal Oxide Varistors (MOV)s are: Metal Oxide Varistors (MOV) voltage, flow capacity, junction capacitance and response time.Metal Oxide Varistors (MOV) response time is ns level, faster than the air discharge, slightly slower than the TVS tube, generally used in electronic circuit overvoltage protection response speed to meet the requirements. When the junction capacitance Metal Oxide Varistors (MOV) is generally on the order of hundreds to thousands of Pf range, and in many cases should not be applied directly to the protection of high-frequency signal lines, the application of the AC circuit protection, as it will greatly increase the drain junction capacitance current protection circuit is designed to take full account. Metal Oxide Varistors (MOV) flow capacity is large, but smaller than the gas discharge tube.
mov metal oxide varistor referred VSR, it is a kind of non-linear voltage-sensitive semiconductor overvoltage protection device. It is used in the circuit text symbol "RV" or "R" represents, the picture is the circuit graphic symbols.
"mov metal oxide varistor" is a noun in mainland China, meaning "within a certain range of the resistance value of the current and voltage with the voltage change," or that "the resistance value of the voltage-sensitive" resistor. mov metal oxide varistor resistive material is a semiconductor, so it is a variety of semiconductor resistor. Now extensive use of "zinc oxide" varistor, its main material of divalent element and hexavalent elemental oxygen posed. So from a material point of view, the zinc oxide varistor is a kind of "Ⅱ-Ⅵ family-oxide semiconductor."
In China Taiwan, varistors are named according to their use, known as the "surge absorber." Varistor according to their use is sometimes also referred to as "electric shocks (surge) suppressor (absorber)."

Metal Oxide Varistors (MOV)

an Metal Oxide Varistors (MOV) is designed to conduct significant power for very short durations (about 8 to 20 microseconds), such as caused by lightning strikes, it typically does not have the capacity to conduct sustained energy. Under normal utility voltage conditions, this is not a problem. However, certain types of faults on the utility power grid can result in sustained over-voltage conditions. Examples include a loss of a neutral conductor or shorted lines on the high voltage system. Application of sustained over-voltage to a mov metal oxide varistor can cause high dissipation, potentially resulting in the MOV device catching fire. The National Fire Protection Association (NFPA) has documented many cases of catastrophic fires that have been caused by MOV devices in surge suppressors, and has issued bulletins on the issue.

Metal Oxide Varistors (MOV)

While an Metal Oxide Varistors (MOV) is designed to conduct significant power for very short durations (about 8 to 20 microseconds), such as caused by lightning strikes, it typically does not have the capacity to conduct sustained energy. Under normal utility voltage conditions, this is not a problem. However, certain types of faults on the utility power grid can result in sustained over-voltage conditions. Examples include a loss of a neutral conductor or shorted lines on the high voltage system. Application of sustained over-voltage to a mov metal oxide varistor can cause high dissipation, potentially resulting in the MOV device catching fire. The National Fire Protection Association (NFPA) has documented many cases of catastrophic fires that have been caused by MOV devices in surge suppressors, and has issued bulletins on the issue.

A 130 volt, 150 J MOV that has undergone catastrophic failure, apparently as a result of a lightning strike, showing evidence of heat and smoke. The 3 amp fast-blow fuse immediately in front of the varistor blew during the same event.
A series connected thermal fuse is one solution to catastrophic MOV failure. Varistors with internal thermal protection are also available.
There are several issues to be noted regarding behavior of transient voltage surge suppressors (TVSS) incorporating MOVs under over-voltage conditions. Depending on the level of conducted current, dissipated heat may be insufficient to cause failure, but may degrade the MOV device and reduce its life expectancy. If excessive current is conducted by a MOV, it may fail catastrophically, keeping the load connected, but now without any surge protection. A user may have no indication when the surge suppressor has failed. Under the right conditions of over-voltage and line impedance, it may be possible to cause the MOV to burst into flames,[5] the root cause of many fires[6] and the main reason for NFPA’s concern resulting in UL1449 in 1986 and subsequent revisions in 1998 and 2009. Properly designed TVSS devices must not fail catastrophically, resulting in the opening of a thermal fuse or something equivalent that only disconnects MOV devices.

Varistor is a voltage

Varistor is a voltage limiting protection devices. Nonlinear characteristic use varistors, when an overvoltage occurs between two poles varistor varistor voltage can be clamped to a relatively fixed voltage value, metal oxide arrester in order to achieve protection of the post-stage circuit. The main parameters of mov metal oxide varistor are: varistor voltage, current capacity, junction capacitance and response time.