Not every layman understands what electrical circuits are. In apartments, they are 99% single-phase, where the current flows to the consumer through one wire, and returns through another (zero). A three-phase network is a system for transmitting electric current, which flows through three wires with return one at a time. Here, the return wire is not overloaded due to the phase shift of the current. Electricity is generated by a generator driven by an external drive.
An increase in the load in the circuit leads to an increase in the current passing through the generator windings. As a result, the magnetic field is more resistant to rotation of the drive shaft. The number of revolutions starts to decrease, and the speed controller gives a command to increase the drive power, for example by supplying more fuel to the internal combustion engine. The speed is restored and more electricity is generated.
The three-phase system consists of 3 circuits with an EMF of the same frequency and a phase shift of 120 Β°.
Features of connecting power to a private house
Many people believe that a three-phase network in a house increases power consumption. In fact, the limit is set by the power supply organization and is determined by factors:
- supplier capabilities;
- number of consumers;
- condition of the line and equipment.
To prevent voltage surges and phase imbalance, they should be loaded evenly. The calculation of a three-phase system is approximate, since it is impossible to determine exactly which devices are currently connected. The presence of pulsed devices currently leads to increased power consumption when they are started.
The three-phase switchgear is taken in larger sizes than with single-phase power. Options are possible with the installation of a small introductory shield, and the rest are made of plastic for each phase and on outbuildings.
Connection to the highway is realized by the underground method and by air line. They prefer the latter due to the small amount of work, low cost of connection and ease of repair.
Now itβs convenient to make an air connection using a self-supporting insulated wire (SIP). The minimum cross section of an aluminum core is 16 mm 2 , which, with a large margin, is enough for a private house.
SIP is mounted on supports and the wall of the house using anchor brackets with clamps. Connection with the main air line and the cable input to the electrical panel of the house is made by branching piercing clamps. The cable is taken with non-combustible insulation (VVGNG) and passed through a metal pipe inserted into the wall.
Air connection of three-phase power supply at home
At a distance of more than 15 m from the nearest support, installation of one more column is necessary. This is necessary to reduce the load resulting in sagging or wire breakage.
The height of the connection point is 2.75 m and above.
Power distribution cabinet
Connection to a three-phase network is made according to the project, where inside the house consumers are divided into groups:
- lighting;
- sockets;
- separate powerful appliances.
Some loads can be disconnected for repair while others are working.
The power of consumers is calculated for each group where a wire of the required cross section is selected: 1.5 mm 2 for lighting, 2.5 mm 2 for outlets and up to 4 mm 2 for powerful devices.
Wiring is protected against short circuit and overload by circuit breakers.
Electric meter
With any connection scheme, a meter for electricity consumption is required . The 3-phase meter can be connected directly to the network (direct connection) or through a voltage transformer (semi-indirect), where the meter readings are multiplied by a coefficient.
It is important to follow the connection procedure, where odd numbers are power, and even numbers are load. The color of the wires is indicated in the description, and the circuit is located on the back cover of the device. The input and corresponding output of the 3-phase counter are indicated in one color. The most common connection order is when the phases go first and the last wire is zero.
A 3-phase direct-current meter for a home is usually designed for power up to 60 kW.
Before choosing a multi-tariff model, you should agree on the issue with the energy supply company. Modern devices with tariffing instruments make it possible to calculate the electricity charge depending on the time of day, to register and record power values ββin time.
Temperature indicators of devices are selected as wide as possible. On average, they range from -20 to +50 Β° C. The service life of devices reaches 40 years with an intertesting interval of 5-10 years.
The meter is connected after the opening three- or four-pole circuit breaker.
Three phase load
Consumers include electric boilers, induction motors and other electrical appliances. The advantage of their use is the uniform distribution of the load on each phase. If a three-phase network contains unevenly connected single-phase high-power loads, this can lead to phase imbalance. At the same time, electronic devices begin to malfunction, and the lighting lamps dimly glow.
Scheme of connecting a three-phase motor to a three-phase network
The operation of three-phase electric motors is characterized by high performance and efficiency. It does not require the presence of additional starting devices. For normal operation, it is important to properly connect the device and follow all recommendations.
The scheme for connecting a three-phase motor to a three-phase network creates a rotating magnetic field with three windings connected by a star or a triangle.
Each method has its own advantages and disadvantages. The star scheme allows you to smoothly start the engine, but its power is reduced to 30%. This loss is absent in the triangle circuit, but at startup the current load is much larger.
Motors have a connection box where the windings are located. If there are three of them, then the circuit is connected only by a star. With six leads, the motor can be connected in any way.
Power consumption
For the owner of the house, it is important to know how much energy is consumed. This is easy to calculate for all electrical appliances. Adding all the powers and dividing the result by 1000, we get the total consumption, for example 10 kW. For household appliances, one phase is sufficient. However, current consumption increases significantly in a private house, where there is a powerful technique. One device can account for 4-5 kW.
It is important to plan the power consumption of a three-phase network at the design stage to ensure symmetry in voltage and current.
A four-wire wire in three phases and a neutral enters the house. The voltage of the electric network is 380/220 V. Between the phases and the neutral wire, 220 V electrical appliances are connected . In addition, there may be another three-phase load.
The calculation of the power of a three-phase network is made in parts. First, it is advisable to calculate purely three-phase loads, for example an electric boiler of 15 kW and an asynchronous electric motor of 3 kW. The total power will be P = 15 + 3 = 18 kW. In this case, a current I = Px1000 / (β3xUxcosΟ) flows in the phase conductor. For household power networks cosΟ = 0.95. Substituting the numerical values ββin the formula, we obtain the current value I = 28.79 A.
Now you should determine the single-phase loads. Let for the phases they amount to P A = 1.9 kW, P B = 1.8 kW, P C = 2.2 kW. The mixed load is determined by the summation and is 23.9 kW. The maximum current will be I = 10.53 A (phase C). Adding it to the current from the three-phase load, we get I C = 39.32 A. The currents in the remaining phases will be I B = 37.4 kW, I A = 37.88 A.
In calculations of the power of a three-phase network, it is convenient to use power tables taking into account the type of connection.
It is convenient to select circuit breakers from them and determine the wiring cross-sections.
Conclusion
With the right design and maintenance, a three-phase network is ideal for a private home. It allows you to evenly distribute the load in phases and connect additional power consumers, if the cross-section of the wiring allows.