Leakage current and hazard of electromechanical equipment

Leakage fault: generally refers to the insulation damage, rupture or personal electric shock of one or two phases of the power grid. (When the symmetry of the insulation of the power grid to the ground decreases, although the power grid is still symmetrical and operates normally, in fact, the power grid has been in a sub-healthy state. Especially for the underground power grid in coal mines, it will increase the personal electric shock current and single-phase grounding current, which is extremely detrimental to the power supply safety. Therefore, this symmetry of the insulation of the power grid is also considered as a leakage fault, and it is called a symmetrical leakage fault.)
In the figure, Ua, Ub and Uc are three-phase power supply voltages, ZL is load impedance, Ca, Cb, Cc and ra, rb and rc are phase-a, b and c-phase conductor ground capacitance and insulation resistance respectively (see Figure 2-1, b), ZN is transformer neutral grounding element (if the neutral point is not grounded, ZN=∞, if the neutral point is grounded through reactance, ZN is the impedance of grounding reactance), Rr is leakage fault resistance (if the single-phase is directly grounded, Rr=0).
Large leakage current may cause the following hazards:
(1) Increase the possibility of electric shock.
(2) Ignition or explosion of gas and coal dust.
(3) Burn electrical equipment.
(4) Cause the early explosion of electric detonator.
The main factors causing electric shock hazard to human body include:
The size of electric shock current passing through the human body. The greater the current, the more dangerous it is.
Duration of personal electric shock. The longer the time, the more dangerous.
Impact of electric shock current through human body:
1. Perceived current refers to that when a person holds a live conductor with his hand, he can sense the slight heat in the palm of his hand under DC conditions; In the case of communication, the nerves are stimulated to feel slight stabbing. The average value is 1.1 mA.
2. Reaction current refers to that it can cause unexpected and involuntary reactions and may cause accidents.
3. Get rid of current refers to the maximum current that the human body can tolerate. Under the action of this current, the stimulated muscles of the human body can get rid of the charged body. Repeated exposure will not have adverse consequences for human body; Get out of danger without the help of others. It is the absolutely safe limit current for a person to get an electric shock. Normal male is 9mA.
4. Ventricular fibrillation current. In addition to the current size, the electric shock time also has a great influence on ventricular fibrillation.