This paper presents a new circuit topology of dc bus line side active resonant snubber assisted voltage source high frequency link soft switching PWM half-bridge inverter type dc-dc power converter for arc welder. The proposed power converter is composed of a typical voltage source-fed half-bridge high frequency PWM inverter with a high frequency transformer link in addition to two dc bus line side power semiconductor switching devices for PWM control scheme and two capacitive lossless snubbers. All the active power switches in the half-bridge arm and dc bus lines can achieve ZCS turn-on and ZVS turn-off transition commutation and consequently the total switching power losses can be effectively reduced. As a result， a high switching frequency of using IGBTs can be actually selected more than about 22 kHz. The effectiveness of this new dc-dc power converter topology is proved to be more suitable for low voltage and large current dc-dc power supplies such as arc welder fro皿apractical point of view.
Safe earthing design has a objective to assure that a person in the vicinity of earthed facilities is not exposed to the danger of critical electric shock which is caused by touch voltage or step voltage of human body. The current through the body and touch/step voltage depend on the contact resistance between the earth and the feet. In the substation，high resistivity material such as gravel is spread on the earth’s surface above the earthing grid to increase the contact resistance. This paper investigates the resistivity measurement method of silicon coated gravel，and proposes reduction measure of touch/step voltage by using the silicon coated gravel which is high resistivity material.