If the current passing through your body is very weak, for example, when you touch the two electrodes of a dry cell battery with your hand, you will not feel anything unusual in your body because the current is so small (about 1.5 volts).
But by the time you feel a current pass through your body, you've been electrocuted. Electricity is not the slightest bit merciless, no matter who you are, once electrocuted you will feel numbness or pain all over your body to varying degrees, at which point the human body forms part of the circuit. If you put the two leads of the positive and negative poles of a 1.5-volt dry cell battery on your tongue and taste it, you will feel an astringent flavor. This is because the electric current causes the tongue muscles to contract, just as an astringent persimmon causes the tongue muscles to contract with an astringent flavor.
The current generated by a dry cell battery is small, but it can make a person feel astringent. If the current through the body increases to a certain value, it will make the body muscle spasm. Experiments have shown that when 1 milliamp industrial frequency (50 weeks/second) current through the human body, it will make people feel uncomfortable; 10 milliamp industrial frequency current through the human body, it will endanger human life. The danger is greatest if the current passes through the human heart or brain organs. If the current flows from one foot to the other, only about 0.5% of the current passes through the area near the heart. However, if the current flows from head to toe, it is very dangerous. However, if a very weak electric current is made to flow in a certain period of time in the parts near the heart, it can stimulate the malfunctioning heart and make it work normally again. Based on this principle, a medical device called a pacemaker has been made, which has dramatically changed human health and played a major role in prolonging the lives of people with heart conditions.
Electrocution occurs frequently in human beings, such as when they accidentally touch a power switch with warm hands.
As long as there is an electric current passing through the body it can electrocute a person. So, under what circumstances will there be current through the human body? We can think of the human body as a resistor, according to Ohm's law, only when there is a voltage acting on both ends of the resistor, there is current through the resistor. If you touch two power lines at the same time, the human body is equivalent to a load of the power supply, the current flows from one end of the power supply, through the human body and then flow back to the other end of the power supply, the higher the voltage of the power supply, the higher the current flowing through the human body.
In fact, the resistance of the human body varies from person to person, from a few hundred ohms to tens of thousands of ohms. In humid, sweaty conditions, the body's resistance decreases dramatically. Therefore, in a humid environment, even if the voltage is very low, may be electrocuted. In order to protect personal safety, staff need to frequently contact with electrical equipment, such as running lights, machine tool lighting, etc., generally should be used below 36 volts of safe voltage, in a particularly humid place, must be used below 12 volts of voltage.
In the installation and maintenance of electrical equipment, electricians often need to use a test pen. Take 100 volts of the two power lines, one of which can make the test pen bright wire, usually people call it "firewire", the other can not make the test pen bright, called "ground", this is because "ground This is because the "ground wire" in the power transformer has been grounded, this line and the earth between the voltage is not, and is therefore safe.
If someone accidentally touches the "fire wire", then, because he is standing on the ground, so he is equivalent to contact the power supply at the same time the two wires, so it will still be electrocuted; if he touches the "ground", it will not be electrocuted. Another example is the bird in the air, it does not know which wire is "fire", which is "ground", but people often see birds standing on the wire, but not electrocuted. This is because the birds only touch a wire, if there is such a big bird, its feet can touch two power lines, even if it has great ability, will immediately be struck by a strong current and death. Therefore, will be electrocuted, the key lies in the human body is not subjected to the role of voltage. According to this reasoning, imagine someone hanging in the air climbing on a "fire wire", it seems that he will not be electrocuted, in fact, in the case of high voltage, close to a high-voltage transmission line will still be dangerous, so we should never go to do this kind of risky behavior.
Transformer
Transformer, that is, the power system of the voltage and current of the electric energy to transform, centralize and distribute the place. In order to ensure the quality of power and equipment safety, in the substation also need to voltage adjustment, trend (power system nodes and branches in the voltage, current and power flow and distribution) control, and transmission and distribution lines and the protection of major electrical equipment. According to the use can be divided into power substations and traction substations (for electric railroads and trams).