When arranging a new apartment or house, renovating or renovating housing, one has to deal with elements designed for the flow of electric current. It is important to know what an electrical circuit is, what it consists of, why a circuit is needed, and what calculations need to be performed.
What are electrical circuits
An electrical circuit is a complex of different elements interconnected. It is designed for the flow of electric current, where transients occur. The movement of electrons is provided by the presence of a potential difference and can be described using terms such as voltage and current.
The internal circuit is provided by connecting the voltage as a power source. The rest of the elements form an external network. For the movement of charges in the power source of the field, an external force will be required. It can be a winding of a generator, a transformer or a galvanic source.
For such a system to function correctly, its circuit must be closed, otherwise the current will not flow. This is a prerequisite for the coordinated operation of all devices. Not every circuit can be an electrical circuit. For example, grounding or protection lines are not such because no current flows through them normally. They can be called electrical by the principle of action. In an emergency, current passes through them, and the circuit closes, going into the ground.
Depending on the power source, the voltage in the circuit can be constant or variable. The battery of cells provides constant voltage, and the windings of generators or transformers provide alternating voltage.
Main components
All components in a circuit participate in one electromagnetic process. They are conventionally divided into three groups.
- Primary sources of electrical energy and signals can convert non-electromagnetic energy into electrical energy. For example, a galvanic cell, battery, electromechanical generator.
- The secondary type, both at the input and at the output, has electrical energy. Only its parameters change - voltage and current, their shape, magnitude and frequency. An example would be rectifiers, inverters, transformers.
- Active energy consumers convert electric current into lighting or heat. These are electrothermal devices, lamps, resistors, electric motors.
- Ancillary components include switching devices, measuring devices, connecting elements and a wire.
The simplest line circuit includes a galvanic cell. With the help of wires, an incandescent lamp is connected to it through a switch. To measure the current and voltage, a voltmeter and an ammeter are included in it.
Circuit classification
Electric circuits are classified according to the type of complexity: simple (unbranched) and complex (branched). There is a division into DC and AC circuits, as well as sinusoidal and non-sinusoidal.Based on the nature of the elements, they are linear and non-linear. AC lines can be single-phase and three-phase.
Branched and unbranched
The same current flows in all elements of an unbranched circuit. The simplest branched line includes three branches and two nodes. Each branch has its own current. A branch is defined as a section of a chain that is formed by series-connected elements enclosed between two nodes. A node is the point at which three branches converge.
If a point is put on the diagram at the intersection of two straight lines, there is an electrical connection of the two lines at this place. If the node is not marked, the chain is not branched.
Linear and non-linear
An electrical circuit in which consumers do not depend on the voltage value and the direction of currents, and all components are linear, is called linear. The elements of such a circuit include dependent and independent sources of currents and voltages. In linear, the resistance of an element does not depend on the current, for example, an electric furnace.
In nonlinear, passive elements depend on the values of the direction of currents and voltages, have at least one nonlinear element. For example, the resistance of an incandescent lamp is affected by voltage surges and current surges.
Designations of elements in the diagram
Additional documents are attached to the drawing. Their list can be indicated in alphabetical order with digital sorting on the drawing itself, or on a separate sheet. Ten types of circuits are classified; in electrical engineering, three main circuits are usually used.
- Functional has minimal detail. The main functions of the nodes are represented by a rectangle with letter designations.
- The schematic diagram shows in detail the design of the elements used, as well as their connections and contacts. The required parameters can be displayed directly on the diagram or in a separate document. If only part of the installation is indicated, this is a one-line diagram, when all elements are indicated - complete.
- In the wiring diagram, the reference designations of the elements, their location, installation method and sequence are used.
To read electrical circuits, you need to know the conventional graphic symbols. The wires that connect the elements are shown with lines. The solid line is a general designation for the wiring. Above it can be indicated data on the method of laying, material, voltage, current. For a single line diagram, a group of conductors is shown with a dashed line. At the beginning and at the end, indicate the marking of the wire and the place of its connection.
Vertical notches on the wire line indicate the number of wires. If there are more than three of them, digital designation is performed. The dashed line denotes control circuits, a network of security, evacuation, emergency lighting.
The switch in the diagram looks like a circle with a line tilted to the right. By the type and number of dashes, the parameters of the device are determined.
In addition to the main drawings, there are equivalent circuits.
Three-phase electrical circuits
Among electrical circuits, both single-phase and multi-phase systems are common. Each part of a polyphase circuit is characterized by the same current value and is called a phase. Electrical engineering distinguishes between two concepts of this term. The first is a direct component of a three-phase system. The second is a value that changes sinusoidally.
A three-phase circuit is one of the multiphase AC systems, where sinusoidal EMF (electromotive force) of the same frequency acts, which are shifted in time relative to each other by a certain phase angle. It is formed by windings of a three-phase generator, three power receivers and connecting wires.
Such circuits serve to ensure the generation of electrical energy, for its transmission, distribution, and has the following advantages:
- cost-effectiveness of generating and transporting electricity in comparison with a single-phase system;
- simple generation of a magnetic field, which is necessary for the operation of a three-phase asynchronous electric motor;
- the same generator set produces two operating voltages - line and phase.
The three-phase system is beneficial when transmitting electricity over long distances. In addition, the consumption of materials is much lower than that of single-phase ones. The main consumers are transformers, asynchronous electric motors, converters, induction furnaces, powerful heating and power plants. Among single-phase low-power devices, one can note power tools, incandescent lamps, household appliances, power supplies.
The three-phase circuit is distinguished by a significant balance of the system. The methods for connecting the phases received the structure "star" and "triangle". Usually, the phases of generating electric machines are connected by a "star", and the phases of consumers are connected by a "star" and a "triangle".
The laws in force in electrical circuits
- Ohm's law for a straight section of a circuit, which determines the relationship between the electromotive force, the voltage of the source with the current flowing in the conductor and the resistance of the conductor itself.
- To find all currents and voltages, Kirchhoff rules are used, which operate between currents and voltages of any part of the electrical circuit.
- The Joule – Lenz law quantifies the thermal effect of an electric current.
In direct current circuits, the direction of action of the electromotive force is indicated from negative to positive potential. The direction is taken as the movement of positive charges. In this case, the arrow is directed from a higher potential to a lower one. The voltage is always directed in the same direction as the current.
In sinusoidal EMF circuits, voltage and current are indicated using a half-cycle of the current, while it does not change its direction. To emphasize the difference in potentials, they are indicated by the signs "+" and "-".
How are electrical circuits calculated
- a method based on Ohm's law and Kirchhoff's rules;
- method for determining loop currents;
- reception of equivalent transformations;
- method for measuring the resistance of protective conductors;
- calculation of nodal potentials;
- identical generator method, and others.
The basis for calculating a simple electrical circuit according to Ohm's law is the determination of the current strength in a separate section with a known resistance of the conductors and a given voltage.
According to the condition of the problem, the resistances of the resistors R1, R2, R3, R4, R5, R6 connected to the circuit are known (without taking into account the resistance of the ammeter). It is necessary to calculate the strength of the currents J1, J2… J6.
There are three consecutive sections on the diagram. Moreover, the second and third have ramifications. The resistances of these sections will be denoted as R1, R ', R ". Then the total resistance is equal to the sum of the resistances:
R = R1 + R '+ R "where
R ' - total resistance of parallel connected resistors R2, R3, R4.
R " - total resistance of resistors R5 and R6.
Using the law of parallel connection, we calculate the resistance R 'and R ".
1 / R '= 1 / R2 + 1 / R3 + 1 / R4
1 / R "= 1 / R5 + 1 / R6
To determine the current strength in an unbranched circuit, knowing the total resistance at a given voltage, you can use the following formula:
I = U / R, then I = I1
To calculate the current strength in individual branches, you need to determine the voltage on the sections of serial circuits according to Ohm's law:
U1 = IR1; U2 = IR '; U3 = IR ";
Knowing the voltage of specific sections, you can calculate the current strength on individual branches:
I2 = U2 / R2; I3 = U2 / R3; I4 = U2 / R4; I5 = U3 / R5; I6 = U3 / R6
Sometimes it is necessary to find out the resistance of sections by the known parameters of voltage, current strength, resistance of other sections, or to make a voltage calculation using the available resistance data and current strength.
The main part of the methods is aimed at simplifying the calculations. This is achieved by adapting the systems of equations, or the circuit itself. The calculation of electrical circuits is carried out in various ways, depending on the class of their complexity.
