In addition, the complex thermal processes that occur as a result of placing multiple varistors in one case, increase leakage current and also reduce the life of spd. 3. Level of protection level of protection 1 is very important for the spd parameter characterizing the degree of its impact on the isolation of the protected equipment. Today time is often electrical equipment category I for resistance of insulation (1,5 kV) 2 is set immediately after the main switchboard, which naturally determines the requirements for highly lower value of the level of protection spd. In this case, is not only the maximum level of protection, but its value during the entire period of application of pulsed voltage, since, as experience shows, the isolation electrical equipment is often damaged during the long decay time of the pulse.
Maximum level of protection for both devices is approximately the same and amounts to about 1000, but at the SPD-based varistors, this value preserved for all time application of the pulse, while a combined spd on the basis of a spark gap and varistor is very fast (few microseconds) is reduced to a value close to nominal. Naturally, the combined spd provides for the isolation of the equipment you are much more favorable conditions. And in this case, as shown by comparison, the level of protection combined spd is much lower than the varistor (including the maximum value, 1140 vs. 1300). 4. Conclusion The comparison circuit design and test results showed that the spd Class I + ii, based on a combination of the spark gap and varistor have greater reliability and better performance than similar devices based varistors. Because of the differences of the current – voltage characteristics of varistors connected in parallel one of them always is more loaded than others, which leads to premature failure, especially when powerful lightning impulse.
At the same time, the combined spd these powerful impulses safely discharged spark gap. With regard to response time, thanks to technologies of active energy management in combined schemes, it is identical in both schemes spd. In terms of impact on the insulation protected equipment, the combined unit also has all the advantages in comparison with the device in varistor: its level of protection is much lower as the momenta of 10/350 ms, and 8 / 20 microseconds, and both on maximum value, and as long as the application of the pulse. Thus, the combined device surge protection class I + ii on the basis of a spark gap – the universal high secure modern solution for the effective protection of electrical equipment from lightning and switching surges. Literature: 1.GOST P 51992-2002 (IEC 61643-1-98). Devices for surge protection in low-voltage power distribution systems. Part 1. Health requirements and test methods. 2.GOST P 50571.19-2000 (IEC 60364-4-443-95). Electrical installations of buildings. Part 4. Security requirements. Chapter 44. Surge protection. Section 443. Privacy electrical installations from lightning and switching surges. 3.IEC 61312-1: Protection against lightning electromagnetic pulse. Part 1. Basic principles. 4.J. , H. Heckler, K. Scheibe, M. Wetter. Discharge capability and residual voltage of class I and class ii SPDs. 28th International Conference on Lightning Protection. 5.IEC 60060-1: Technology of High-voltage test. Part 1. General definitions and test requirements.