Two phase electricity. Two-phase electrical network

Two-phase electrical networks were used at the beginning of the 20th century in electrical distribution networks alternating current. They used two circuits, the voltages in which were shifted in phase relative to each other by 90 degrees. Usually 4 lines were used in the circuits - two for each phase. Less commonly, one common wire was used, which had a larger diameter than the other two wires. Some of the earliest two-phase generators had two full rotors with windings physically rotated 90 degrees.

Story

For the first time, the ideas of using a two-phase current to create a torque were expressed by Dominic Arago in 1827. Practical use was described by Nikola Tesla in his patents from 1888, around the same time he developed the design of the corresponding electric motor. Further, these patents were sold to the Westinghouse company, which began to develop two-phase networks from the USA. Later, these networks were replaced by three-phase ones, the theory of which was developed by the Russian engineer Mikhail Osipovich Dolivo-Dobrovolsky, who worked in Germany at AEG. However, due to the fact that Tesla's patents contained general ideas for the use of polyphase circuits, the Westinghouse company was able to restrain their development through patent litigation for some time.

Advantages

The advantage of two-phase networks was that they allowed a simple, soft start of electric motors. In the early days of electrical engineering, these networks with two separate phases were easier to analyze and design. At that time, the method of symmetrical components had not yet been created (it was invented in 1918), which subsequently gave engineers a convenient mathematical toolkit for analyzing asymmetric load modes of multi-phase electrical systems.

The rotating magnetic field created in two-phase systems allowed electric motors to create torque from zero motor speed, which was not possible in single-phase asynchronous electric motors (without special starting tools). Asynchronous motors, designed for two-phase systems, have the same winding configuration as single phase motors with start capacitor.

A three-phase electrical network requires lines with a lower mass of conductive materials (usually metals) at the same voltage and higher transmitted power, compared to a two-phase four-wire system. Two-phase lines have been superseded by three-phase lines in electrical distribution networks, but they are still used in some control systems.

The transmitted instantaneous active power in three-phase and two-phase electrical networks is constant at symmetrical load. However, in single-phase networks the instantaneous active power oscillates at a frequency twice that of the line voltage. These power ripples lead to increased noise and mechanical vibrations in electrical equipment with magnetizable materials due to the magnetostrictive effect, as well as to rotational vibrations of the motor shafts.

Two-phase circuits usually use two separate pairs of current-carrying conductors. Three conductors can also be used, however, the vector sum of the phase currents flows through the common wire, and therefore the common wire must have a larger diameter. In contrast to this, in three-phase networks with a symmetrical load, the vector sum of the phase currents is zero, and therefore it is possible to use three lines of the same diameter in these networks. For electrical distribution networks, the requirement of three conductive lines is better than the requirement of four, as this provides significant savings in the cost of conductive lines and in their installation costs.

Two-phase voltage can be obtained from a three-phase source by connecting single-phase transformers in the so-called Scott circuit. A symmetrical load in such a three-phase system is exactly equivalent to a symmetrical three-phase load.

You can often hear how electrical networks are called three-phase, two-phase, less often - single-phase, but sometimes these concepts are not the same. In order not to get confused, let's figure out how these networks differ and what they mean when they say, for example, about differences between three-phase and single-phase current .

Single-phase networks

Two-phase networks

Three-phase networks

The passage of current is possible with a closed circuit. Therefore, the current must first be brought to the load, and then returned back.

With alternating current, the wire carrying the current is a phase. Its circuit designation is L1 (A).

The second is called zero. Designation - N.

This means that two wires must be used to transmit single-phase current. They are called phase and zero, respectively.

The voltage between these wires is 220 V.

There is a transfer of two alternating currents. The voltage of these currents is shifted in phase by 90 degrees.

Currents are transmitted by two wires: two phase and two zero.

It is expensive. Therefore, now it is not generated at power plants and is not transmitted through power lines (power lines).

Three alternating currents are transmitted. In phase, their voltages are shifted by 120 degrees.

It would seem that six wires had to be used to transfer current, but, using the connection of sources according to the “star” scheme, they manage with three (the type of circuit is similar to the Latin letter Y).

Three wires are phase, one is zero.

Economical. Current is easily transmitted over long distances.

Any pair of phase wires has a voltage of 380 V.

A pair of phase wire and zero - voltage 220 V.

Thus, the power supply of our houses and apartments can be single-phase or three-phase.

Single phase power supply

Single-phase current is connected in two ways: 2-wire and 3-wire.

The first (two-wire) uses two wires. One by one flows phase current, the other is for the neutral wire. In a similar way, almost all old houses built in the former USSR are supplied with electricity.
At the second - add another wire. It is called grounding (PE). Its purpose is to save human life, and devices from breakage.

Three-phase power supply

The distribution of three-phase power throughout the house is carried out in two ways: 4-wire and 5-wire.

A four-wire connection is made with three phase and one neutral wire. After the electrical panel, two wires are used to power sockets and switches - one of the phases and zero. The voltage between these wires is 220V.
Five-wire connection - a protective, grounding wire (PE) is added.

In a three-phase network, the phases should be loaded as evenly as possible. Otherwise, a phase imbalance will occur. The result of this phenomenon is very deplorable and unpredictable for human life and technology.

It depends on what electrical wiring in the house and what electrical equipment can be included in it.

For example, grounding, and hence sockets with a grounding contact, are required when the following are connected to the network:

appliances with high power - refrigerators, stoves, heaters,
electronic household appliances - computers, televisions (it is necessary to remove static electricity),
devices connected with water - jacuzzi, shower cabins (water current conductor).

And for the power supply of motors (relevant for a private house), a three-phase current is needed.

How much does it cost to connect single-phase and three-phase electricity?

Costs for expendable materials and installation of equipment are also planned based on the most preferred connection. And if it is difficult to predict the cost of sockets, switches, lamps (it all depends on your whims and design imagination), then installation costs are about the same. On average this is:

assembly of a switchboard, in which circuit breakers are installed (12 groups) and a meter costs from $ 80
installation of switches and sockets 2-6$
installation spotlights 1.5-5$ per unit.

Personally, I also thought about solar panels - I studied a little on http://220volt.com.ua, now I'm trying to structure my thoughts, how and what to do with their connection ...

Two-phase electrical networks were used in the early 20th century in AC electrical distribution networks. They used two circuits, the voltages in which were shifted in phase relative to each other by 90 degrees. Usually 4 lines were used in the circuits - two for each phase. Less commonly, one common wire was used, which had a larger diameter than the other two wires. Some of the earliest two-phase generators had two full rotors with windings physically rotated 90 degrees.

For the first time, the ideas of using a two-phase current to create a torque were expressed by Dominic Arago in 1827. The practical application was described by Nikola Tesla in his patents of 1888, around the same time he developed the design of the corresponding electric motor. Further, these patents were sold to the Westinghouse company, which began to develop two-phase networks from the USA. Later, these networks were replaced by three-phase ones, the theory of which was developed by Russian engineer Mikhail Osipovich Dolivo-Dobrovolsky, who worked in Germany at AEG. However, due to the fact that Tesla's patents contained general ideas for the use of polyphase circuits, the Westinghouse company managed to restrain their development for some time through patent litigation.

Two-phase circuits usually use two separate pairs of current-carrying conductors. Three conductors can also be used, however, the vector sum of the phase currents flows through the common wire, and therefore the common wire must have a larger diameter. In contrast, in three-phase networks with a symmetrical load, the vector sum of the phase currents is zero, and therefore it is possible to use three lines of the same diameter in these networks. For electrical distribution networks, the requirement of three conductive lines is better than the requirement of four, as this provides significant savings in the cost of conductive lines and in their installation costs.