Article Source: Wenzhou Reaper Electrical Technology Co., Ltd. combined with welding accident, why install leakage protection mechanism of electric shock will happen explore secondary electric shock protector of principle, the operator should strengthen inspection and secondary electric shock protection, thus ensuring the electric resistance welded can be normal.
AC arc welder (referred to as the Welding Wire China machine) is one of the commonly used equipment in the construction site, but it also is a high risk of electrical equipment, its operator belonging to special operations personnel must undergo professional training, the current leakage protection range used for the control of welding machine electric shock played a certain role, but the contact in the secondary side of the welding machine accidents still occur.
1. Accidents stories
A construction company employees in July 2007 Lee construction site welding pipe, due to the wet ground (leakage) hand touched homemade welding the exposed part of the secondary voltage circuit formed by Lee's body, causing Lee died of electric shock.
2. Incidents mechanism
Install leakage protection welding machine why would an electric shock fatalities, Is leakage protection does not work, inspection and leakage protection leakage characteristics are considered qualified. To understand the cause of the accident must analyze the entire Welding Material machine system.
Electric welding works, welding machine is essentially an electromagnetic induction transformer to achieve the purpose of welding, arc welding is based on the high temperature of the arc to melt the metal, which must first arc ignition, the initial stages due to the arc welding wire and The pieces of the air gap is not hot enough, the high arc voltage (70v-90v), to promote air ionization, but this arc voltage requirements to reach the safe voltage (36v), when the operator touches result in electrocution death when the pilot arc occurs, the air became conductor, acting on the arc voltage of over 20 volts below the safe voltage requirements, generally safe, we can see the danger in the secondary side of the welding machine is no load welding line high voltage, and can thus be seen that the leakage protection simply will not work. The leakage protection is used for detecting the remaining current action, that is, when the outflow leakage protection current and flow back into the leakage protection current equal leakage protection that the circuit is not leakage occurs actions. Primary coil and the wire itself to form a closed loop, leakage protection can protect this part of the circuit. The secondary side is another relatively independent closed circuit, the secondary coil by electromagnetic induction generates an electromotive force, equivalent to the power of this portion of the circuit. Relatively independent part of the circuit is no protection, so that when the secondary leakage will cause electric shock fatalities. The secondary side is an incomplete loop, part of the current abnormal flow, while the primary side of the circuit and current is still intact, and therefore leakage protector does not work.
3 secondary principle of protection against electric shock
Of secondary electric shock protection (about the secondary protector) protection on the secondary side of the welding machine to achieve through the buck.
Signal circuit portion does not work when the secondary side (open), the secondary protective device detects the disconnection signal, the control circuit so that the the buck circuit portion starting, and the input the welder side of the voltage reduction. Welding machine no-load voltage ratio is certain, the secondary voltage decreases when the primary voltage is decreased, after the installation of the secondary protector secondary no-load voltage is below 36v safe voltage requirements, are generally 24v , if necessary, the welder work, operating the same is not installed on the protection device, the contact of the welding wire and member, resulting in a short circuit, to enlarge the signal transmitted to the control circuit for controlling the buck circuit to stop working through electromagnetic induction, primary side of the welder voltage and the secondary voltage rise rapidly, so that the secondary voltage of the arc voltage requirements, this short-circuit signal is generated by the secondary side resistance is less than 500?, this boost process time ≤ 0.05s, does not substantially affect the normal job. When the pilot arc is successful, the secondary voltage and quickly reduce to 24v, when to stop welding or operator error caused when the arc is extinguished, the welding machine to restore the empty state, the secondary voltage increased rapidly to ensure that welding work continuity , the same time to ensure safety, the secondary voltage of the secondary protective allows a delay period, generally 1s click within this time, the secondary side voltage (70V-90V), 1S secondary protective device after the no-load voltage drops to a safe voltage, visible secondary electric shock protector after the entire work process of the welding machine is installed, the time of the the dangerous secondary side voltage is very short (process) exist only in the arc and interrupter and arc ignition hazardous voltage secondary side short, strict control of hazardous voltage from production conditions and there is a time to produce the possibility of electric shock is greatly reduced, which greatly improve the security in the secondary side of the welding machine. Because the degree of risk of electric shock is the current intensity, the greater the role of the longer, the greater the risk even in the event the electric shock, the breaking resistance is much smaller than the body resistance, the allocation of the current in the human body is also very small, and because the arc start time short, acting on the body current time is also very short, the risk of electric shock is also greatly reduced.Early secondary electric shock protection by taking the secondary side signal to control the work. More cumbersome installation of line has basically stopped production, most of the products currently produced, has adopted a method to control the work of the side signal wiring is very simple, some leakage protection and secondary protection against electric shock function together, production side leakage protection and the secondary electric shock secondary protection against electric shock protector.
It needs to be pointed out that the initial use secondary protection against electric shock may feel arc is more difficult, because the arc voltage has a step-up process (generally in the 0.03s) below. This process as much as possible to keep the welding and weldment stability should not always quick click of the weldment arc voltage is not increased so click or not arc, the purpose of the circuit and open circuit, voltage drop, can not reach the arc . After a period of time, the operator can adapt to the arc delay the.
4 Conclusion
Secondary protection against electric shock does have to prevent welding machine secondary electric shock casualties occurred, but can not relax our vigilance. Welding equipment must strictly enforce the relevant safety requirements, the operator must operate in safety procedures, and secondary protection against electric shock should strengthen inspection, to ensure that it is working properly, and to ensure that when on the one hand the failure, on the other hand can be timely play a role.
Performed in strict accordance with the Ministry of Construction JGJ46-2005 construction site temporary electrical safety technology standards to ensure the safety of people's lives and property.