Why don t China s power grid use three phase, six phase and eight phase?

China's power grid power supply is a three-phase power supply system, not only in China and the world. Because to solve the energy conversion of generators and motors, as well as the control and transmission of electric energy, three-phase electricity is the most reasonable structure, the lowest cost, and the best reliability. Six-phase and eight-phase are not impossible, but the structure is too complex and the investment is not cost-effective.

1: The use of three-phase for high-power electricity consumption is conducive to the balance of power grid load.

2: Three-phase electrical appliances due to the load evenly distributed in the three live wires, the zero line current is small (basically no current), the use of the same wire line loss will be reduced to about one-sixth of the single-phase electrical appliances, which is conducive to users to get good power supply quality.

3: The high-power load is mainly the load of the motor, the single-phase motor does not have high-power (except for the high-voltage motor), and the efficiency is much lower than the three-phase motor of the same power, such as the efficiency of the single-phase motor is the best is 45%, and the efficiency of the three-phase motor is at least 80%.

4: The performance of the three-phase motor is much better than that of the single-phase motor, the starting torque is more than doubled, and the volume and procurement ** are also about twice as low.

To sum up, it is necessary for high-power electrical appliances to use three-phase power supply, and the power of the general civil single-phase motor of China's formal design does not exceed kilowatts, so even if the power of the civil air conditioner is slightly larger, it has to be powered by three-phase power, but even if the cost of purchasing a line and meter is considered by the user, it is still cost-effective, one is that the three-phase power consumption should be at least one-third or more (more power is saved when the wire is farther away), and the second is that the voltage is lower and can be used.

This is because the conditions are not ripe.

Because the generator is three-phase.

What is the difference between three-phase four-wire and three-phase three-wire?

Generally, the practical application is only three-phase four-wire system (not counting the ground wire, counting the ground wire is called the three-phase five-wire system), and the three-phase three-wire system will not be used.

In addition to the three live wires of the three-phase four-wire system, the fourth is called the middle line (note: there is a zero line for single phase, and there is no zero line for three-phase), and the middle line plays a role in ensuring that the voltage of the load phase is unchanged.

If the load connected to each of the three-phase circuits is the same, and the sum of the currents flowing through the center line at each moment is zero, it is possible to remove the center line and use the three-phase three-wire system for power supply. However, this is an ideal situation, and in practice it is impossible for a three-phase load to be perfectly symmetrical in a three-phase circuit with multiple single-phase loads connected to a three-phase circuit. In this case, the midline is particularly important and not optional.

If there is no center line in the case of asymmetrical load, the three-phase three-wire power supply of asymmetrical load is formed. Due to the asymmetry of the load impedance, the phase current is also asymmetrical, and the load phase voltage is naturally not symmetrical. Some phase voltages may exceed the rated voltage of the load, and the load may be damaged (the bulb of the phase is too bright and burned); Some phase voltages may be lower and the load may not work properly (the bulb is dim).

With the light on, the light off and other reasons cause the change of the load impedance of each phase. The phase current and phase voltage all change accordingly, the lights flicker and flicker, and other electrical appliances cannot work properly, or even be damaged. So there must be a center line, that is, a three-phase four-wire system.

3 phase is the minimum number of phases that can produce a stable rotating magnetic field without the use of auxiliary equipment, if you can use it, 360 divisible natural numbers can be, of course, the more the better, but one more phase will have more wires, transformers will have more cores, substations will have more than one set of circuit breakers, and dispatching will have more than one set of monitoring, expensive! Since the 3-phase can generate a rotating and stable magnetic field, and it has also been popularized, and the efficiency is still high and cheap! Then use them all.

Single-phase electricity, any phase from the three-phase electricity is single-phase electricity, three-phase electricity is a single-phase electricity with three phases that are not the same (120 degrees of mutual difference).

phase, prepare phase. In a generator with a pair of magnetic poles, a winding is distributed every 120 degrees in space 360 degrees, and when the magnet rotates, the three windings emit three-phase electricity that is 120 degrees different from each other.

The electricity price has little to do with the three-phase single-phase, the load is large or there is a three-phase motor to use the three-phase, and the load is small and the single-phase is generally used. Electricity price, peak price, peak price, trough price.

less than 1 kV).

Yuan kilowatt-hour (1-10 kV) extended information: ladder electricity price can have a variety of modes, the first mode is that the monthly electricity bill of all residential users is calculated according to the level of electricity consumption multiplied by the level of electricity price, using this model The first tiered subsidized electricity price is enjoyed by all users, and the amount of subsidized electricity and electricity charges is larger. The second mode is the monthly electricity fee of each household for residential electricity, and the first stage of electricity is only used by users whose electricity consumption is less than the first tier, and all users who exceed the electricity consumption of the first tier will be calculated according to the second tier electricity price standard.

If the population of low-income users is 20 million, about 6.7 million households per household and 3 households"Due to the low income of these users, the household electricity consumption is controlled within the first tier. The third model is the implementation of a tiered time-of-use tariff. The main consideration is that some provinces and cities have implemented time-of-use electricity prices in residential electricity consumption before the implementation of the Zhaohu tiered electricity price, and the time-of-use electricity price is conducive to the transfer of peak loads"The cushion family air barricade high evening trough load.

Therefore, when implementing the tiered electricity price, it is best to combine the two electricity prices. That is, it is divided into several tiers according to electricity consumption, and each tier implements a different electricity price; At the same time, the time-of-use price is implemented for each tiered electricity price; In addition, it can also be combined with the implementation of seasonal electricity prices. References:

Electricity price encyclopedia.

Depending on the power billing and the charging with power metering, the main thing is that you don't need to confuse money with electricity fuzzy.

Three-phase alternating current is a form of transmission of electrical energy, referred to as three-phase electricity. Three-phase AC power supply is a power supply composed of three alternating currents with the same frequency, equal amplitude, and 120° difference in phase. Three-phase alternating current has many uses, and most of the alternating current electrical equipment in the industry, such as motors, use three-phase alternating current, which is often referred to as the three-phase four-wire system.

In daily life, single-phase power supply, also known as lighting electricity, is mostly used. When lighting electricity is used, one of the three phases is used to supply power to the consumer, such as household appliances, and the other wire is the fourth wire in the three-phase four-wire, that is, the neutral line, which leads from the neutral point of the three-phase electricity.

Four-phase electricity and five-phase electricity are not currently available, but theoretically it can be realized, and it is enough to increase the phase of the generator. Four-phase electricity, five-phase electricity can be done.

But now the generators are all three-phase electricity.

Because three phases are enough for the generator rotor to rotate continuously, there is no need to engage in four phases or five phases. That would only make the wiring more complicated.

Three-phase electricity has 4-wire and 5-wire connection.

Alternating current (alternating

current), abbreviated as AC. Alternating current is also known as "alternating current", abbreviated as "alternating current". Generally refers to a voltage or current whose magnitude and direction change periodically over time.

Its most basic form is a sinusoidal current. When electromagnetic induction was discovered, the method of generating alternating current was known. Early finished products were developed by Nikola Tesla, Michael Faraday, and Pollit Picksy, among others

alternating

current, abbreviated as AC) refers to an electric current that changes periodically in both magnitude and direction, because the average operating value of the periodic current in a cycle is zero, which is called alternating current or alternating current for short. Unlike direct current, which does not change direction over time.

At present, China's production and distribution are three-phase alternating current. Three-phase alternating current has many advantages, such as the use of three-phase alternating current motors, generators that are energy-saving and material-saving, and easy to maintain, ......Answer: Three-phase is to transmit power and save investment in power equipment.

Because to generate a rotating magnetic field without the use of auxiliary equipment, a minimum three-phase power supply is required...It can produce a more stable rotating magnetic field, but that will increase the cost of substation equipment and power.

It's good to know that you have a weak IQ.

1. Three-phase electricity can not be understood so simply, three-phase electricity is determined by the relative position of the three induction coils of the generator through the same magnetic field when the time (time domain space) is 120 ° in turn, and the three phases together constitute a complete circular layout (360 °), and the three coils of the generator take turns to reciprocate in turn when the generator is working to produce three-phase electricity. There are no four coils to produce four-phase electricity, according to the theory should be possible, but whether it is called four-phase electricity, is unknown.

2. Regarding the usual use (general civil electricity), in addition to the phase wire of three-phase electricity, there is also a concept of zero line (ABC phase wire N zero line), which is generally used as a phase wire and a neutral line to form a general electricity circuit, that is, 220VAC power supply (through step-by-step voltage drop), and when the motor is designed (three-phase motor), in order to achieve higher energy conversion efficiency, it is generally designed as a group of three stator coils with a difference of 120 °, and the three are used for the same thing, without zero line; Of course, the exception is single-phase motors, which are similar to other electrical products.

The three wires of three-phase electricity are live wires, the transmission of electric energy is more efficient, and it is also related to the efficiency of the generator, the voltage of the live wire is not constant, the voltage we measure is calculated according to the conservation of energy, if the voltage is constant, it is direct current, to change the alternating current into constant direct current to use diodes and capacitors.

When we say AC voltage, we mean that the average straight AC electromotive force is constantly changing.

People ask why, what are you. I don't know who is mentally retarded...

Superiority of three-phase alternating current.

1. There are three symmetrical power supplies, which can be connected to the load separately without affecting each other.

3. The three are at an angle of 120, which can generate a rotating magnetic field, which greatly simplifies the structure of the motor and reduces the production cost and maintenance cost.

Look for this circuit book, I'm lazy and don't want to type a lot of words.

Three-phase four-wire, namely: A, B, C three-way live wire plus a loop zero line.

Three-phase five-wire is: A, B, C three live wires plus a loop zero line, and the other is a grounding wire.

The power supply mode of ordinary residents in China is basically single-phase electricity, and some large household appliances (three-phase air conditioners) also use three-phase power supply.