Why AC voltage?
The thing is that direct current, when transmitted over long distances, loses its energy by heating the wires. The Joule-Lenz law is to blame here
It is not difficult to guess that the more current flows through the wires, and the longer the wires are, the more they will heat up, since the resistance of the wire is expressed by the formula:
An alternating voltage generator does not have such disadvantages. Its operating principle is shown below
Such generators are called three-phase, since they have three phases: A, B, C. In English literature you can see the designation R, S, T or L1, L2, L3. The point where the end of all windings is connected is designated by the letter N (zero).
That is, in fact, 4 wires come out of the generator: phases A, B, C and 0, also known as neutral N, which connects one end of each of the three windings.
When the rotor-magnet rotates, an electric current is created in each winding. If you use an oscilloscope to display oscillograms of three windings at once, you can see something like this:
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It's not conductivity that matters. If it is a metal pin, but reliably isolated from the ground, then it is no more dangerous than a plastic pin. It’s worse if it’s a wooden but wet handle of a shovel stuck into damp soil. The main thing is that one hand does not touch the phase, and the other does not touch grounded conductive objects, or worse, zero. The resistance in this case is the minimum possible and the current will flow through the chest. Well, if your feet are on good “ground” without insulation, then that will also be the end. Very dangerous. Z.Y. And look, everything is clearly explained below.
Transmission of electric current over long distances
So, we have received an electric current. Now we need to somehow transmit it over long distances, not forgetting about the Joule-Lenz law: Q=I 2 Rt. That is, we need to somehow miraculously reduce the current that will flow through the wires, since it is mainly responsible for large losses.
Transfer of electricity from the generator to the final consumer
With hydroelectric power plants, the voltage is increased to several kilovolts, most often to 110 kV. All this is achieved using a three-phase high-voltage step- up transformer (2).
Next, the high-voltage voltage travels along the high-voltage line (3) and reaches a city or regional center.
Each regional center or city has its own substation, which already has its own high-voltage step-down transformer (4), which converts a voltage of 110 kV into 10 kV, or 6 kV (5).
Then, from the substation, the voltage is distributed to transformer “booths”, which can already be seen in every area.
What kind of lighting do you prefer?
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You've probably often seen in the news headlines that in one country or another, a person died from electric shock while talking on a cell phone in the bathroom. The phone was naturally connected to the charger in the nearest outlet.
In general, with the advent of fully waterproof smartphones, such cases have only become more frequent.
If previously a person was stopped by the fear of ruining his gadget by dropping it in the water, now they are not afraid of this either.
For many who are ignorant of electrical engineering, a logical question arises: “How is this even possible?” It is well known that USB charging produces a voltage of only 5 volts.
At the same time, according to safety regulations, wiring up to 42V is allowed even in high-risk areas! How can regular exercise harm a person?
The thing is that the USB charger does not always produce this same 5V. And under certain circumstances, the charging voltage may jump. To understand the reason why a charging smartphone can kill a person in a bath, you will have to remember the school physics course, namely Ohm’s law.
This formula is almost fundamental for all electrics. According to it, the current in the circuit directly depends on the applied voltage and is inversely proportional to the resistance. That is, the higher the voltage and the lower the resistance, the greater the current.
By analogy with our case, this formula can be translated into the following visual relationship:
Let's start with the cause of death first - current. Yes, yes, it is the current that kills, not the voltage. At a certain amount of current, cardiac fibrillation and paralysis occur.
What current should this be? Here is a table widely known to all electricians:
Guaranteed to kill a current of 100mA. But this is under normal conditions. For a person lying in a bath, in a certain situation, a value of more than 30 mA is quite enough.
Voltage 220 Volts – Practical Electronics
So, the generator at our power plant converts mechanical energy into electrical energy. What's next? In what form and how exactly to transfer energy to the consumer? How to avoid colossal transmission losses?
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10,000 volts through a person. Survival story with photos | Columnist For this purpose, he purposefully pierced his fingertips with the sharp probes of a multimeter and received a fatal blow, just from a 9-volt battery. Ask, I'm in touch!
Comments
It's not conductivity that matters. If it is a metal pin, but reliably isolated from the ground, then it is no more dangerous than a plastic pin. It’s worse if it’s a wooden but wet handle of a shovel stuck into damp soil. The main thing is that one hand does not touch the phase, and the other does not touch grounded conductive objects, or worse, zero. The resistance in this case is the minimum possible and the current will flow through the chest. Well, if your feet are on good “ground” without insulation, then that will also be the end. Very dangerous. Z.Y. And look, everything is clearly explained below.
Edited at 2014-02-11 09:37 am (UTC)
We were lucky - we didn’t short-circuit the current through ourselves. And since they didn’t know that they were under tension, they themselves didn’t tense up, which means they acted confidently and calmly, i.e. made no mistakes, increasing the likelihood of a safe completion.
If they knew, they would start to get nervous, fear constrains and makes them twitch - numb hands are poorly controlled, and the twitching is chaotic and therefore far from the optimal trajectory of movements, the likelihood of getting into the wrong place increases.
Only if you had shortened the wiring not with yourself, but with a knife, you would not have been electrocuted, but you would have observed a short-term fireworks display with a crash, a spark, and quite possibly a splash of hot metal. The screwdrivers then leave jagged edges.
Edited at 2014-02-10 07:21 pm (UTC)
Can TV kill? | Free communication
In general, I probably won’t describe in detail my war for life (which ended in St. Petersburg at the Institute of Emergency Medicine), I’ll just briefly list the facts from the treatment:
— Amputation of a leg at the level of the upper third of the thigh (immediately near the knee, my knee was burned with a wire
— Sepsis happened, and then drug-induced hepatitis also happened (the liver stopped coping with
— For treatment, my father went into debt, took out an urgent loan from the enterprise where he worked, the boss went to him
to the meeting. As a result, almost $30,000 was spent (I later returned it through the court)
— I physically (not psychologically) became a drug addict dependent on painkillers. As a result,
The doctors had a very difficult dilemma: If you continue to numb the pain, your heart will die and it won’t be able to withstand such dependence...
and the liver too. They then tried innovative spinal anesthesia on me (an injection in the spinal
brain so that pain signals from the nerves of the limbs do not enter the brain) It ended sadly
— During the entire time I had sepsis (blood poisoning), I lost a lot of weight. I weighed 36 kilograms.
My mother then carried me to wash in her arms. I saw myself how my heart was beating - the skin between the ribs
— They spent about a liter of staphylococcal bacteriophage on me. (VERY
an expensive drug with a base that seems to be based on human blood or some kind of bacteria. )
— In order to stand on the remaining leg, I had to remove the ankle from contracture about
35% (when the foot is forward [pull the foot forward with your fingers and imagine
that this is your only position of the foot...]and it’s as if the joint has become candied in
in such a state...) During training, I specially stretched everyone
ligaments - terrible pain - it was very difficult after the condition occurred
when you no longer have to endure, force yourself to endure again.
— That the patient’s condition does not pose a threat to the lives of my parents
They were able to say only after 2.5 months. For a month and a half, no one in this is so much
I didn’t believe it, but everyone knew that I wouldn’t survive (I mean the doctors).
— They let my mother into the intensive care unit (I was already in St. Petersburg), as we later understood
— Was treated and recovered for a total of 5 years (difficulties with the second
- Now I have resistance to strong painkillers... they
After all this I survived. It's been 8 years already. And now you can understand this on the street only by my limp and the scars on my arms (the rest are not visible). Those who don’t know about amputation simply don’t believe in it.
Now I appeal to those people who have lost hope for the future and for their lives:
Guys, don’t give up, fight for life. Neither a glass nor a needle nor a joint will save you from your thoughts. You can’t walk around heartbroken and be the most miserable person in the world. Take my example. I graduated, I work, I do what I want, I live and am happy. You can never give up!
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Fatal injury by direct low-voltage electric current If the victim breathes poorly and spasmodically or does not breathe at all, immediately begin mouth-to-mouth artificial respiration. Ask, I'm in touch!
Dangerous current values
Electrical damage varies and is influenced by three factors:
- What is the frequency: constant or variable;
- Force;
- In what direction does it move as it passes through the body?
The effect of electric current on a person
Electric current is also divided depending on how it affects human health:
- Noticeable - only irritates the skin. Safe value – no more than 0.6 milliamps;
- Non-releasing - variable with periodic impulses, due to which a person “sticks” to the source of electricity. Happens if the current exceeds 0.025 amperes;
- Fibrillation – it causes fibrillation of internal organs, primarily the heart. If the electrical strength exceeds 0.1 ampere, the organ may stop.
Need to know! The human body resists electricity. The force of the blow depends on many factors: the health of the victim at the time of the blow, mental state and even the quality of the shoes. Based on the electrical resistance values, current voltage readings that are dangerous to humans are derived.
Based on safety precautions, the following voltage indicators are dangerous:
- 65 volts – residential premises and public buildings that are heated and have internal humidity up to 60%;
- 36 volts – rooms with high humidity levels (up to 75%). These are basements, kitchens, and so on;
- 12 volts – very wet spaces (100%): swimming pool, bathhouse, laundry room, boiler room, and so on.
Note! The frequency of the electric current also plays a role. A value from 50 to 60 hertz is considered dangerous for humans.
What's next
Depending on the situation, you can either call for help or leave the scene of the confrontation. Another option would be to apply a Taser to the criminal and hold him down. Threatening repeated use to force him to lie face down with his hands behind his back. After this, you can call the police and wait for their arrival.
The discharger should not be used in the head or neck area; it should be used with caution against elderly people. When using it in rainy weather, you should aim at exposed skin, as the arc can pass through a layer of water on clothing and not cause harm to the target.
Press the stun gun tightly against the attacker to reduce the amount of air in the folds of clothing; it can act as a dielectric, preventing the arc from passing to the desired location.
How many volts are in a stun gun, what are its permitted parameters in Russia, and some rules for its use
The socket is a source of voltage and the current will depend on the load. In addition, we must not forget that it is not 220 volts, but 308, since 308 is the amplitude value.
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Viktor Pavlovich Strebizh, lighting and electrical expert
Any questions ask me, I will help!
The power sources for low-voltage electrical networks are step-down transformers operating from ordinary household electrical networks with a voltage of 220 V, as well as 12 or 24 volt batteries. If there is something you don’t understand, write to me!
