Features : Surge Absorbers

What is surge?

The surges here refer to high-energy surges such as induced lightening surges,open/close surges, and load dumps.

① Lightning surge

  • Lightning as natural phenomenon contains a very large amount of energy.
    A lightning surge can be grouped into direct lightning surges and induced lightning surges.
    Protection against a direct lightning surge is difficult, but protection against induced lightning is possible.
    Induced lightning is a high voltage surge induced by a relatively long wire such as power line or communication cable that is nearby a lightning strike.
    It is presumed that the generation mechanism is an electric charge induced in a cable that is in proximity of an electric field discharged by a lightning strike, or a magnetic field generated by a lightning strike current generates an inductive electromotive force in the cable.
    As shown in the previous diagram, an induced lightning surge has a large amount of energy that can easily destroy electric or electronic components even though it is not as destructive as a direct lightning surge, thus requiring prevention measures.

② Open/close surge

  • Open/close surge is a transient high voltage surge induced in a switch or relay during its on and off operation, particularly when turning off, which causes rapid current change and inductance of the circuit or wiring.
    Voltage generated by an open/close surge is very high, and in some cases, it generates spark, heat or radiates an electromagnetic wave caused by a large damping oscillation current generated by floating static capacitance of inductance and contact.
    This high voltage surge may cause a malfunction of an electronic circuit, and in some cases, lead to the destruction of a component.
    And the emission of an electromagnetic wave through damping oscillation causes EMI, thus requiring suppression measures for an open/close surge.

③  Load dump

  • Load dump is a surge generated by cutting the battery connection off on an automobile.
    The most severe instance occurs when the battery connection is lost while the automotive engine is in operation and the alternator (battery charging generator) is charging the battery.
    The magnitude of surge voltage is determined by the alternator rotation speed and magnetic field excitation strength at the moment of cut off.
    Surge voltage exceeds 100 V in some cases for a duration of several hundred milliseconds.
    Because this surge has such a large amount of energy, it can easily destroy an electronic component.
    Permissible load dump is specified by auto-makers and automotive equipment makers in the form of maximum voltage, line impedance, and duration time.
    For load dump testing, JASO A-1 (Japan) and ISO-7637-2 Pulse 5 (U.S.) is applied.

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Panasonic's“ZNR®”surge absorbers"

Panasonic offers a wide variety of surge absorbers with the product name "ZNR®" surge absorbers for use to handle these surges, ranging from models used in power generation plants to common electronic devices.
Please note that the "ZNR®" surge absorbers are ceramic varistors for surge absorption, and ZNR stands for zinc-oxide non-linear resistor.

ZNRRサージアブソーバ graph
基本構造 graph
Panasonic was the first manufacturer in the world that commercialized ceramic varistors with a superior ceramic material design and process technology backed by many achievements in device design and production engineering. “ZNR®” surge absorbers are produced mainly from the material zinc oxide (ZnO) and several additives, as well as the ceramic element created using the sintering technique. This product provides excellent voltage non-linearity characteristics in parallel with those of zener diodes along with large current resistance characteristics not found in other products. This product can be used for a wide variety of applications such as voltage stabilization, pulse voltage suppression, open/close surge voltage absorption, and protection from a lightning surge.

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Principle of surge suppression

varistors have a high electrical resistance when the terminal voltage is low, but the resistance suddenly becomes low when the voltage gets higher.
By using this tendency, the component prevents a surge from entering the circuit by bypassing the current when a high voltage surge occurs in an electric circuit.

バリスタ電流電圧特性
The diagram to the right illustrates how to protect a power supply circuit from induced lightning surge by using a varistor. By connecting a varistor in parallel with the power input side line, an induced lightning surge, as high as several-thousand volts, is restricted by the varistor to a level that won’t cause component destruction or deterioration of the power supply circuit.
バリスタ使用事例

Examples of surge suppression effects

● Results of surge tests using D type φ14, 470 V products

Surge voltage original waveform:15000V (2Ω)
サージ電圧原波形:15000V (2Ω)
右横矢印
Clamping voltage waveform
(Waveform applied to equipment)
制限電圧(機器に印加される)波形
Surge current waveform
flowing through ZNR
ZNRに流れるサージ電流波形
The application of a surge voltage causes a surge current to flow through the ZNR surge absorber, thereby limiting the surge voltage.

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