Created by: Glen Zhu | Updated Date: Apr 06, 2023
In the most common type of surge protector, a small electronic component called a metal oxide varistor (MOV) plays an important role in diverting excess voltage.
This article provides a general select guide of Metal Oxide Varistors (MOVs) for Surge Protection Devices (SPDs).
Metal oxide varistors, also known as MOVs are one of the most common types of varistors designed to protect electronic devices and electrical circuits against voltage surges and spikes by changing their resistance.
A metal oxide varistor (MOV) consists of a central piece of metal oxide material coupled by two semiconductors to the power and grounding lines.
MOVs are extremely effective at absorbing transient voltage changes due to the usage of metallic oxide during their production.
Components for low-voltage surge protection – Part 331: Performance requirements and test methods for metal oxide varistors (MOV).
This part of IEC 61643 is a test specification for metal oxide varistors (MOV), which are used for applications up to 1 000 V AC or 1 500 V DC in power lines, or telecommunication, or signaling circuits. They are designed to protect apparatus or personnel, or both, from high transient voltages.
The MOV has a number of advantages, including the following:
Like a typical varistor, a metal oxide varistor, or MOV, found in a surge protector directs any excess voltage to ensure that electronics receive a steady power level.
The metal oxide varistor (MOV) is a variable resistor, its resistance will change automatically depending on its voltage. The resistance of the varistor decreases as the voltage across it rises, and thus has a bidirectional current.
This property is very useful for the circuits to protect from high voltage spikes.
While MOVs are generally long-lasting devices designed to conduct substantial power for very brief periods of time, such as caused by lightning strikes, it typically does not have the capacity to conduct sustained energy and occasionally fails.
Due to the frequent abnormal voltage, MOV will have to operate frequently to suppress overvoltage and absorb/release surge energy. It may eventually degrade the MOV.
MOVs used in surge protection systems can fail in one of three ways:
Solution: Using current-limiting fuses is what we recommend, to keep current below the point where damage to the MOV package is possible.
A metal oxide varistor, along with a fuse, is commonly used in various circuits. These two are linked to the protected circuit in parallel.
MOVs can only be used to protect against surges during short circuits; they cannot withstand persistent surges. MOVs’ performance may suffer if they are repeatedly subjected to surges.
MOV which acts as a surge protection device must be installed very close to the fuse as in the below illustration.
When the voltage is within the rated limits the resistance of the MOV will be very high and hence all the current flows through the circuit and no current flows through the MOV.
When a voltage spike occurs within the main voltage, it is visible straight across the MOV due to it is connected in parallel with the AC mains.
This high voltage reduces the resistance of the MOV to an extremely low level. As a result, the MOV is forced to undergo a significant current flow, blowing the fuse and cutting off the circuit from the main power supply and avoid possible catastrophic failures.
Consider the core components MOV of the surge protector you are installing when selecting surge protection device for your critical devices.
Typically, the MOV data sheet will state the Imax (Maximum Current).
For example, a diameter 20 mm metal oxide varistor (MOV) is rated about In: 5kA – Imax: 10 kA. a diameter 25 mm metal oxide varistor (MOV) is rated about In: 10kA – Imax: 20 kA.
Firstly, determine the operating voltage and the application’s maximum peak voltage.
An item of equipment rated for 120 Vac (170 Vpeak) and given that the average transient or swell voltage may go as high as 20% (144 Vac), then a minimum of a 150 Vac or 220 Vdc rated MOV would be adequate in these conditions.
The material thickness and MOV voltage are inversely correlated: the thicker the MOV, the higher the voltage rating.
If a diameter 34 mm metal oxide varistor (MOV) has a rated Imax @ 40 kA, the MOV probably has a rated In @ 20 kA.
Here we’ll guide you to choose the specific Metal Oxide Varistor MOV for Surge Protection Device SPD.
Metal Oxide Varistor MOV for Type 2 AC Surge Protection Device SPD SLP40-275 series (Un = 230Vac, UC = 275Vac, In = 20kA, Imax = 40kA)
Download the PDF of MOV technical parameters (LKD 34SxxxK Specification), search the column of ‘Maximum Allowable Voltage (ACrms)’ and find the data 275V, the equivalent MOV model is found to be 34S431K.
Metal Oxide Varistor MOV for Type 1+2 AC Surge Protection Device SPD FLP7-275 series (Un = 230Vac, UC = 275Vac, In = 20kA, Imax = 50kA, Iimp: 7kA)
Download the PDF of MOV technical parameters (LKD 34SxxxK-1 Specification), search the column of ‘Maximum Allowable Voltage (ACrms)’ and find the data 275V, the equivalent MOV model is found to be 34S431K-1.
Metal Oxide Varistor MOV for Type 1+2 AC Surge Protection Device SPD FLP12,5-275 series (Un = 230Vac, UC = 275Vac, In = 20kA, Imax = 50kA, Iimp: 12,5kA)
Download the PDF of MOV technical parameters (LKD 54SxxxK-1 Specification), search the column of ‘Maximum Allowable Voltage (ACrms)’ and find the data 275V, the equivalent MOV model is found to be 54S431K-1.
Metal Oxide Varistor MOV for Type 2 DC Surge Protection Device SPD SLP-PV600 (UCPV = 600Vdc, In = 20kA, Imax = 40kA)
Let’s take U-configuration for example:
Download the PDF of MOV technical parameters (LKD 34SxxxK Specification), search the column of ‘Maximum Allowable Voltage (DC)’ and find the data 670V, the equivalent MOV model is found to be 34S821K.
Metal Oxide Varistor MOV for Type 2 DC Surge Protection Device SPD SLP-PV1000 (UCPV = 1000Vdc, In = 20kA, Imax = 40kA)
Let’s take Y-configuration for example:
Download the PDF of MOV technical parameters (LKD 34SxxxK Specification), search the column of ‘Maximum Allowable Voltage (DC)’ and find the data 585V, the equivalent MOV model is found to be 34S711K.
Download the PDF to read the complete example.
Metal Oxide Varistor MOV for Type 1+2 DC Surge Protection Device SPD FLP-PV1000 (UCPV = 1000Vdc, In = 20kA, Imax = 40kA, Iimp = 6,25kA)
Download the PDF of MOV technical parameters (LKD 54SxxxK-1 Specification), search the column of ‘Maximum continuous operating voltage (UC)’ and find the data 675V, the equivalent MOV model is found to be 54S751K-1.
Metal Oxide Varistor MOV for Type 1+2 DC Surge Protection Device SPD FLP-PV1000G (UCPV = 1000Vdc, In = 20kA, Imax = 40kA, Iimp = 6,25kA, Itotal = 12,5kA)
Download the PDF of MOV technical parameters (LKD 48SxxxK-1 Specification), search the column of ‘Maximum continuous operating voltage (UC)’ and find the data 745V, the equivalent MOV model is found to be 48S911K-1.
MOV has a wide range of applications since it is primarily used to safeguard power supply interfaces against surges.
The applications of MOV include:
Without a doubt, the quality of the varistors plays a significant effect on the overall quality of inner SPDs, and using high-quality MOV is becoming more crucial.
For more specific recommendations, get in touch with us at https://lsp.global/contact-us/
LSP’s reliable surge protection devices (SPDs) are designed to meet the protection needs of installations against lightning and surges. Contact our Experts!
Copyright © 2010-2024 Wenzhou Arrester Electric Co., Ltd. All Rights Reserved. Privacy Policy
