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Application of zinc oxide varistors and precautions

1, zinc oxide varistors application principle
Varistors being protected electrical equipment or components used in parallel. When the circuit appears lightning over voltage or over-voltage transient operating Vs, varistors and the protection of equipment and components withstand Vs, due to the fast response of the varistor, it nanosecond time quickly render Nonlinear excellent electrical properties (see Figure 3 in the breakdown zone), then the voltage drop across the varistor rapidly, far less than the Vs, on such equipment and components to be protected actual withstand voltage is much lower than had voltage Vs, so that the equipment and components from over-voltage shocks.

2, preferences zinc oxide varistor
Under the protected supply voltage selector varistor voltage V1mA current. General selection principle is:
For DC circuit: V1mA≥2.0VDC
For AC circuit: V1mA≥2.2V RMS
If the electrical equipment voltage level Vo is low, and the surge of energy and relatively large, they can choose a low varistor voltage V1mA, slice larger diameter varistors; if Vo is higher, you can select the varistor voltage V1mA Higher varistors, both to protect the electrical equipment, but also to extend the service life of the varistor.

3, zinc oxide varistors of use
Varistor is a non-polar overvoltage protection element, either AC or DC circuits, simply varistors and is to protect electrical equipment or components parallel protection device purposes (see Figure 4 )

When the over-voltage amplitude is higher than the predetermined voltage currents, over-current amplitude is less than Varistor maximum peak current (absence varistor enough to damage equipment components), varistors in the breakdown region may be transient overvoltage limit low in magnitude, this time through the varistor surge current magnitude less (100A / cm2), not enough to produce varistors degradation; when the over-voltage amplitude When the value is high, the varistor overvoltage limit at a low level (less than the device breakdown voltage level), through the varistor surge current is large, so that the performance degradation varistors expiring, At this time a large current through the fuse, the fuse is disconnected, so that can make the electrical equipment, components from over-voltage shocks can be avoided due to the deterioration of varistor breakdown caused by line LN, L-PE's Room shorted (Recommended fuse sizes are shown in Table 1).

Varistor overvoltage protection circuit, if the normal pre-breakdown region in FIG. 3 and the breakdown area, in theory, is not damaged. However, due to long-term bear varistor power supply voltage, the circuit transient over-voltage, over-voltage random super-energy continue to impact and absorption circuit release energy storage element, and therefore, varistors also be damaged and its life Depending on where the circuit is subjected to over-voltage amplitude and energy and different.

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