In the modern world, every person has been exposed to electricity since childhood. The first mention of this natural phenomenon dates back to the time of the philosophers Aristotle and Thales, who were intrigued by the amazing and mysterious properties of electric current. But it was only in the 17th century that great scientific minds began a series of discoveries regarding electrical energy that continues to this day.
The discovery of electric current and the creation by Michael Faraday in 1831 of the world's first generator radically changed human life. We are used to the fact that our lives are made easier by devices that use electrical energy, but until now most people do not have an understanding of this important phenomenon. To begin with, to understand the basic principles of electricity, it is necessary to study two basic definitions: electric current and voltage.
Content
What is electric current and voltage
Electricity is the ordered motion of charged particles (carriers of electric charge). The carriers of electric current are electrons (in metals and gases), cations and anions (in electrolytes), holes at electron-hole conductivity. This phenomenon is manifested by the creation of a magnetic field, a change in the chemical composition or heating of the conductors. The main characteristics of the current are:
- current strength, determined by Ohm's law and measured in Amperes (BUT), in the formulas is denoted by the letter I;
- power, according to the Joule-Lenz law, measured in watts (Tue), denoted by the letter P;
- frequency, measured in hertz (Hz).
Electric current, as an energy carrier, is used to obtain mechanical energy using electric motors, to obtain thermal energy in heating appliances, electric welding and heaters, to excite electromagnetic waves of various frequencies, to create a magnetic field in electromagnets and to obtain light energy in lighting fixtures and various kinds of lamps. .
Voltage is the work done by the electric field to move a charge of 1 pendant (Cl) from one point of the conductor to another. Based on this definition, it is still difficult to understand what stress is.
In order for charged particles to move from one pole to another, it is necessary to create a potential difference between these poles (That is what is called tension.). The unit of voltage is the volt (AT).
To finally understand the definition of electric current and voltage, an interesting analogy can be given: imagine that the electric charge is water, then the pressure of the water in the column is the voltage, and the speed of the flow of water in the pipe is the strength of the electric current. The higher the voltage, the greater the electric current.
What is alternating current
If you change the polarity of the potentials, then the direction of the flow of electric current changes. It is this current that is called variable. The number of direction changes over a certain period of time is called frequency and is measured, as mentioned above, in hertz (Hz). For example, in a standard electrical network in our country, the frequency is 50 Hz, that is, the direction of current movement changes 50 times per second.
What is direct current
When the ordered movement of charged particles always has only one direction, then such a current is called constant. Direct current occurs in a constant voltage network when the polarity of the charges on one side and the other is constant over time. It is very often used in various electronic devices and technology, when energy transmission over a long distance is not required.
Sources of electric current
Source of electric current usually called a device or device with which an electric current can be created in a circuit. Such devices can create both alternating current and direct current. According to the method of creating an electric current, they are divided into mechanical, light, thermal and chemical.
Mechanical Electric current sources convert mechanical energy into electrical energy.These equipments are of various kinds. generators, which, due to the rotation of an electromagnet around the coil of asynchronous motors, produce an alternating electric current.
light sources convert photon energy (light energy) into electricity. They use the property of semiconductors to produce voltage when exposed to a light flux. Solar panels are one such device.
Thermal - convert heat energy into electricity due to the temperature difference between two pairs of contacting semiconductors - thermocouples. The magnitude of the current in such devices is directly related to the temperature difference: the greater the difference, the greater the current. Such sources are used, for example, in geothermal power plants.
Chemical a current source produces electricity as a result of chemical reactions. For example, such devices include various kinds of galvanic batteries and accumulators. Current sources based on galvanic cells are usually used in stand-alone devices, cars, technology and are direct current sources.
AC to DC conversion
Electrical devices in the world use direct and alternating current. Therefore, there is a need to convert one current into another or vice versa.
From alternating current, direct current can be obtained using a diode bridge or, as it is also called, a “rectifier”. The main part of the rectifier is a semiconductor diode, which conducts electricity in only one direction. After this diode, the current does not change its direction, but ripples appear, which are eliminated with the help of capacitors and other filters. Rectifiers are available in mechanical, electrovacuum or semiconductor versions.
Depending on the quality of manufacture of such a device, the current ripple at the output will have a different value, as a rule, the more expensive and better the device is made, the less ripple and the cleaner the current. An example of such devices are Power supplies various devices and chargers, rectifiers of electric power plants in various modes of transport, DC welding machines and others.
Inverters are used to convert direct current to alternating current. Such devices generate an alternating voltage with a sinusoid. There are several types of such devices: inverters with electric motors, relay and electronic. All of them differ from each other in the quality of the output alternating current, cost and size. An example of such a device is uninterruptible power supplies, inverters in cars or, for example, in solar power plants.
Where is it used and what are the advantages of alternating and direct current
Various tasks may require the use of both AC and DC. Each type of current has its own advantages and disadvantages.
Alternating current most often used when there is a need to transmit current over long distances. It is more expedient to transmit such a current from the point of view of possible losses and the cost of equipment. That is why most electrical appliances and mechanisms use only this type of current.
Residential houses and enterprises, infrastructure and transport facilities are located at a distance from power plants, so all electrical networks are AC. Such networks feed all household appliances, industrial equipment, train locomotives. There are an incredible number of devices operating on alternating current and it is much easier to describe those devices that use direct current.
D.C used in autonomous systems, such as on-board systems of cars, aircraft, ships or electric trains. It is widely used in the power supply of microcircuits of various electronics, in communications and other equipment, where it is required to minimize the amount of interference and ripple or eliminate them completely. In some cases, such a current is used in electric welding with the help of inverters. There are even railway locomotives that run on DC systems. In medicine, such a current is used to introduce drugs into the body using electrophoresis, and for scientific purposes to separate various substances (protein electrophoresis, etc.).
Designations on electrical appliances and diagrams
Often there is a need to determine at what current the device operates. After all, connecting a device operating on direct current to an alternating current electrical network will inevitably lead to unpleasant consequences: damage to the device, fire, electric shock. For this, there are generally accepted conventions for such systems and even color coding of wires.
Conventionally, on electrical appliances operating on direct current, one line, two solid lines or a solid line together with a dotted line, located one below the other, are indicated. Also, such a current is marked with a designation in Latin letters DC. The electrical insulation of wires in DC systems for the positive wire is colored red, the negative wire blue or black.
On electrical apparatus and machines, alternating current is indicated by the English abbreviation AC or wavy line. On the diagrams and in the description of devices, it is also indicated by two lines: solid and wavy, located one under the other. Conductors in most cases are designated as follows: phase is brown or black, zero is blue, and ground is yellow-green.
Why is alternating current used more often
Above, we have already talked about why alternating current is currently used more often than direct current. And yet, let's look at this issue in more detail.
The debate about which current to use is better has been going on since the discoveries in the field of electricity. There is even such a thing as a "war of currents" - the confrontation between Thomas Edison and Nikola Tesla for the use of one of the types of current. The struggle between the followers of these great scientists lasted until 2007, when the city of New York was switched to alternating current from direct current.
The biggest reason why AC is used more often is because the ability to transmit it over long distances with minimal losses. The greater the distance between the current source and the end consumer, the greater the resistance wires and heat losses for their heating.
In order to get maximum power, it is necessary to increase either the thickness of the wires (and thereby reduce the resistance), or increase the voltage.
In AC systems, you can increase the voltage with a minimum thickness of wires, thereby reducing the cost of electrical lines. For systems with direct current, there are no affordable and effective ways to increase the voltage, and therefore for such networks it is necessary either to increase the thickness of the conductors, or to build a large number of small power plants. Both of these methods are expensive and significantly increase the cost of electricity compared to AC networks.
With the help of electrical transformers, the alternating current voltage is effective (with efficiency up to 99%) can be changed in any direction from minimum to maximum values, which is also one of the important advantages of AC networks. The use of a three-phase AC system further increases efficiency, and machines such as motors that run on AC power are much smaller, cheaper and easier to maintain than DC motors.
Based on the foregoing, we can conclude that the use of alternating current is beneficial in large networks and when transmitting electrical energy over long distances, and for accurate and efficient operation of electronic devices and for autonomous devices, it is advisable to use direct current.
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