1. I. Introduction

With the Surge Protection Device (SPD) are increasingly popular applications, manufacturers around the production of SPD mushroomed first emerged.Pressure limiting type SPD basically have to use tiles ZnO varistor (MOV), and the use of MOV valve geometry is usually large, 8/20μS Flow demanding, for example, in line with IEC standards: Nominal Flow 20kA, the largest 40kA, 34 × 34mm for valves are most commonly used. Φ20 the following ordinary general-purpose Varistor contrast, because of their large geometric dimensions, in the small current parameters measured during the election has its own peculiarities, the author frequently encountered at work, a lot of SPD manufacturers, knows very little, simple in use Φ20 the following general-purpose Varistor three-parameter measurement method of the valve should be screened for the performance of the MOV request unreasonable prejudice to the right of the MOV valve selection, great need to author a number of awareness of this issue in light of actual work, in this to make some introductory remarks.

2. Varistor voltage U1mA, leakage current IL, non-linear coefficient α

A typical ZnO varistor voltage-current characteristic curves shown in Figure 1. This is to emphasize the following general-purpose Φ20 varistor, the varistor voltage U1mA inflection point can be approximated as non-linear voltage U1mA/cm2, also known as the breakdown voltage or breakdown voltage, that is, when the valve on the role of the voltage is below the inflection point voltage, the voltage and current near-linear relationship, at this time non-linear coefficient α low; the valve once the role of the on-chip voltage exceeds inflection point voltage, a small increase in voltage will result in a sharp increase in current, voltage, with the ammeter emerged in a strong non-linear relationship, there is a high non-linear coefficient α; When the current is increased to more than a certain level, enter the high electric field area, non-linear will be gradually reduced to disappear into the low resistance state, At this point the body resistance of ZnO grains play a dominant role. Therefore, a typical non-linear coefficient α and the current density curve shown in Figure 2, below the inflection point voltage, nonlinear coefficient α is relatively low. Lightning on the 34 × 34mm valves, since the Φ20 followed the following general-purpose Varistor three-parameter measurement method, with the measured U1mA voltage corresponding to the current density of about 1mA/3.4 × 3.4cm2, the basic with Φ20 the following general-purpose Varistor U0.1mA equivalent to the difference with the non-linear inflection point voltage U1mA/cm2 large, is still a low electric field area can be seen from the foregoing, thereby U1mA, U0.1mA calculated non-linear coefficient α is not high, nor to judge the pros and cons of valve non-linear criterion. In our view, 34 × 34mm Lightning valves for U10mA/U1mA by measuring the pressure ratio to calculate the non-linear coefficient α obtained a better characterization of the pros and cons of non-linear valves.  Table 1. Lists produced by Guizhou Fei Ge, 34 × 34mm mine-valve films U10mA/U1mA and U1mA/U0.1mA control.

Table 1. 34 × 34mm film U1mA/U0.1mA lightning valve control and U10mA/U1mA

● Test Equipment, Xi'an Jiaotong University for the manufacture of power electronics by ICG-Ⅱ Impulse Current Generator.

Can be seen from Table 2, with the second process (fast cooling speed) processing valves leakage current, U1mA/U0.1mA α-factor high, but far less impact resistance capacity of the first process. Of course, the internal structure of its roots is different, but can be interpreted as a rapid cooling so that the image of Figure 1 in the non-linear curve of the left drift occurred, thus valve Flow capacity decrease. Therefore, in valve timing measurements and not the pursuit of high α coefficient and the leakage current is too small.

3. Conclusion

3.1. For a large mine geometry valves, measuring U10mA, U1mA calculated pressure ratio to a better characterization of non-linear coefficient α pros and cons of non-linear valves. Φ20 below follow the general pressure-sensitive resistance measurement method of the three parameters measured only as a reference, can not serve as non-linear valves to determine strengths and weaknesses of the criteria.

3.2. Is easy to use, we recommend based on experience measuring 34 × 34mm lightning valve U1mA/U0.1mA the α coefficient, its value should be between 20 to 35, if more than 40 valves Flow capacity of poor increased possibility; to note that α in the 20 to 35 do not necessarily like Flow capacity; 75% U1mA under the leakage current IL should be 4 ~ 12μA between the poor is too small. Measuring geometry selected valves larger (multi-chip parallel), then the U1mA/U0.1mA of α should be lower, IL may be appropriate to enlarge, but not with proportional to the area.

3.3. Only the rapid cooling before they can receive a small IL and high non-linear coefficient α, but the rapid cooling will result in greater stress affect its stability, larger size of the square of the geometric valve (thermal expansion and contraction when the of the inequality), in particular, 8/20μS Flow capacity will be reduced and with the release of internal stress of the performance will be apparent sudden change for the limit flow capacity to pass the test are more prone to burst.Therefore, in valve selection, people should not pursue a high α-factor and the leakage current is too small. 

4. Other

Guizhou Flyboat Electronics Co., Ltd. comes from the restructuring of scientific research units specializing in SPD by high-performance ZnO Varistor the production of research and development, product performance, continuously improve, supported by the National High-tech SMEs technology innovation fund and high-tech industry of Guizhou Province The free assistance special fund. The current produced by high-performance ZnO film by the multi-valve testing, the overall performance of basic and similar products of large international companies roughly equivalent to fully meet the IEC61643 standards. The 8/20μS Flow capacity, after the impact of lightning current rate of change of leakage current, leakage current on temperature stability, the exchange of power frequency over-voltage tolerance, etc. ranks leading domestic level. Currently in use in mine valves main production equipment includes four tunnel kiln; a Taiwan 50kg / h evaporation of the spray granulation machines; 45 tons of floating press, 50 tons of two-way press, 63 tons of floating press the a platform; a bi-directional automatic printing silver production line; specially designed large valves dip soldering equipment, a set of electrodes, automatic epoxy resin powder coating machines, testing equipment worth millions of dollars a number of other production equipment. We are good at producing research and development, is willing to provide our clients with OEM services; China will do its best to mine the popularity of products, lightning protection technology, to improve and make due contributions. Warm welcome to visit or call or visit.