Voltage level is a potential characteristic of quality of electric power supply to consumers. Devices are operated for a long time if they operate within the permissible power range of the mains. A distinction is made between phase voltage and line voltage in three-phase circuits to determine the function and connection parameters. At the output from the manufacturer, the voltage is changed for transport, and after the reverse conversion steps, it acquires the value applied by consumers.
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What is phase?
Phase is the value of a trigonometric function, such as defining a species or describing a wave or oscillatory motion. The value is identical to the angle or argument of a periodic function. The dependence of integer phase on coordinates and time is not always linear and harmonic. The end of the conductor through which current enters the circuit, or clamp, represents the beginning of the phase. The change in voltage of a circuit through time is the projection of the ray vector on the coordinate axis.
Circuits are the standard elements - power generator, transmission circuit, and receiver. The concept of what is phase, line voltage, and their interaction requires phase definition. The phase position applies only to AC mains. The concept is defined in the form of a vector rotation sector equation with one end fixed in the origin coordinates.
Electrical lines differ in the number of phases: one-, two-, three-, and multi-phase.
In Russia, three-phase network is popular for powering consumers, which are represented by domestic buildings or industrial facilities. The connection is characterized by advantages compared to the electrical supply of a single-phase circuit:
- economy due to the advantageous use of materials;
- possibility of transporting a large amount of electricity;
- inclusion of electric generators and motors of high power in the operating circuit;
- creation of different voltage values depending on the variant of inclusion of the consuming load in the electric line.
Operation in a three-phase circuit depends on the mutual relation of its components. The voltage reading depends on the phase (the angle of the vector beam to the coordinate plane of the axis). The voltage is determined by the ground potential, which is zero. Because of this, a cable with voltage present is referred to as a phase cable, and the grounding wire is referred to as a zero cable. The phase angle of the unit vector is of no particular importance, because in a line it makes a complete 360° turn in 1/50th of a second. The inter-phase angle of relativity of the 2 vectors is taken into account.
In a network with reactive parts, the angle is taken between the vector values of the electric current and the voltages, it is called the phase shift. If the values of the connected loads do not change over time, the value of the shift will always be constant. The invariability of the index is used in the calculation of the electric line and the analysis of work.
When multiple turns of wire are wound on the coil, the nominal voltage increases in proportion to the number of turns. The phenomenon led to the development of generators that provide electricity to consumers. Multiple coils are sometimes installed for the effect of the magnetic field. The stator magnetic field per rotation of the rotor crosses 3 coils at the same time, which leads to an increase in generator power. This allows 3 users to be powered at once.
What is phase voltage?
On the three-phase mains in most states, the voltage size is 220 volts. Phase volts are measured in the gap between the phases at the beginning and end of the wire. Practically, it is the value in the middle of the neutral conductor and stressed cable. In a star connection, the values of line currents and phase electricity do not differ.
The phase voltage - is the voltage between the neutral conductor and one of the phase conductors (220 V).
The symmetrical system eliminates the presence of the neutral conductor, in the asymmetrical method, the neutral cable maintains commensuration with the source. The second method often includes lights in the circuit and requires independent operation of the 3 working cables, then the terminals of the receiver are united in a delta type.
Inter-phase voltage is used in the apartment sector with stores or offices on the first floors. In this way it is possible to power retail outlets power cables in order to provide 380 volts. In high-rise buildings, the connection provides elevators, escalators, industrial refrigerators. The wiring is relatively simple, given that there is a zero and a load core in the dwelling, and three working cables and a neutral core are tapped for the public premises.
The difference between three-phase current and single-phase current is that the network value is the linear power, and the parameters relevant to the load are the phase voltages. A line is drawn from the station to the consumer, including the working conductors and the neutral conductor. Inverters are placed at the beginning and end of the circuit to reduce leakage as it passes through, but the picture does not change from this. The neutral wire captures and transports to the user the stated potential received at the output. The power in the wire under load is created based on the value in the neutral.
The magnitude of the phase voltage is detected and occurs relative to the center of the winding connection, the neutral wire. In a three-phase circuit that is symmetrical with respect to the loads, a current with minimum values is transmitted through the zero. At the output of such a line, the wires under load are colored in the common standard colors:
- wire L1 - brown
- wire L2 - black;;
- cable L3 - gray;
- neutral braid N - blue;
- yellow or green - provided for grounding.
Such powerful lines are conducted to large consumers - entire neighborhoods, factories. For small receivers, a single-phase line is installed, which includes a loaded wire and an additional zero. When the power distribution in the single-phase branches is even, there is a balance in the three-phase design. For the routing of the component branches, the phase voltage of one conductor relative to the neutral is assumed.
What is the line voltage?
In a three-phase trunk line an additional voltage can be isolated by connecting a jumper between 2 loaded cables. Its value is higher because it is the projection on the coordinate plane of the 2 vectors that make an angle of 120° between them. The addition to the phase voltage value is 73% or calculated as √3-1. The generally accepted line voltage on an electric line is always 380 volts.
The line voltage - is the voltage between the two phase conductors (380 V).
The voltage is calculated between the phases or between the phase leads. When installing the circuit, difficulties arise in the inaccuracy of the conductor calculation, which sometimes causes a crash. Wiring diagrams differ in the way the loaded conductors and the source of electricity are combined. The advantages of a single-phase network are:
- Safe operation of equipment, since the danger in terms of shock comes from 1 cable;
- The scheme is used for efficient wiring, selection of operating principles, calculation of parameters and measurements.
The calculations in the system are simple and based on standard physical formulas. A multimeter is used to measure the values of the circuit. Characteristics of the connection to the phase are determined by using special voltmeters, current sensors.
Linear voltage occurs when electrical current flows in the submarine when the power source and receiver are combined. The phase voltages also change as the power goes down in the area between the generator output and the consumer. Knowing the line parameters, it is not difficult to calculate the value of the phase voltage.
Network features:
- no professional devices are required when wiring, a screwdriver with a built-in indicator is sufficient;
- Zero is not used when connecting wires - because of the neutral conductor there is no danger of electric shock;
- the scheme is applicable to DC networks and lines with alternating current;
- the single-phase connection is made in a three-phase line, but not vice versa.
Use of line and phase voltages
Electrical circuits come in DC and AC. More often, three-phase AC circuits are used to connect a source of electricity to a consumer. This type of current has several advantages:
- lower energy transmission costs;
- It is possible to create electromotive force for the operation of asynchronous equipment (elevators, elevators);
- Linear and phase voltages can be used simultaneously.
To connect generators in the mains use the delta or star principle. In the first version, the windings are connected in series, the beginning of the phase and the end of the other phase are connected. The scheme allows to increase the voltage by several times. In the second case, the initial sections of the windings are combined into a common point, there is no increase in power.
Classification of power grid according to the composition of working elements:
- active;
- passive;
- linear;
- non-linear.
By using 4 cables in a trunk, it is possible to use both line and phase currents simultaneously by varying the connections, which extends the range of application. Three-phase trunks are considered universal because a large load, such as a 10 volt mains, is connected. If an appropriate receiver, such as a three-phase electric motor, is connected to the line, its mechanical power will reach values 3 times higher than those of a single-phase unit.
In the multi-family sector, the main receivers are household appliances and appliances powered by 220V. Uniform separation between the wires with the load is required, so the apartments are connected in a staggered scheme. In private households, the concept of dispersing the load to each cable from all household appliances and equipment is adopted. The conductor currents transmitted during the switching on of the maximum number of devices are taken into account.
By plugging the same electric motors into the network with 1 or 3 phases, you can get a difference in the power of its operation. If you additionally choose an efficient way of connection, the output values will triple. Considering the relationship between the phase and line currents, the windings should be calculated for increased values. The relative value of the charge difference between the loaded wires is always greater than the similar value between phase and zero. The main difference between the linear voltage and phase power characteristics is in the parameters of the resulting voltages.
A classic example of the application of both voltages is the connection when installing a three-phase generator. Secondary windings and primary windings connected by one of the schemes are used. The relationship of line voltage and phase value in delta connection helps to equalize the current and both powers become almost equal. Similarly, motors, inverters, and transformers.
The star version involves connecting the contacts of all windings to a single circuit using jumpers. The conductors carry current with the indicators of this network, and the voltage is transferred to the active terminals and contacts.
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