Source: Power Jianghu
In our daily life, electricity can be described as normal, until a sudden power outage one day, only to realize the importance of electric energy, only to care about our power people [snickering], many people only understand electricity, and do not know how electric energy is transmitted and distributed to thousands of households, today Xiaobian will take you to understand the five major links of electricity!
generate electricity
The first step in the generation of electrical energy
transmit electricity
A link that transmits electrical energy to a distant place
Substation
The link to increase or decrease the electrical energy voltage level
power distribution
The link that distributes electrical energy to users
Electricity
The link that consumes electricity
Overview of power generation
Power generation refers to the production process of converting hydropower, fossil fuels (coal, oil, natural gas) into electricity, nuclear energy, solar energy, wind energy, geothermal energy, marine energy, etc. It is used to supply the needs of various sectors of the national economy and people's lives.
Type of power generation
According to the type of energy, power generation power units are divided into thermal power plants, hydropower power devices, nuclear power plants and other energy power generation power devices.
Thermal
The use of coal, oil and natural gas and other fossil fuels contained in the energy to generate electricity is collectively referred to as thermal power generation: according to the power generation mode, thermal power generation is divided into coal-fired steam turbine power generation, oil-fired steam turbine power generation, gas-steam combined cycle power generation and internal combustion engine power generation. Thermal power generation is now the main force of power development, in the current proposed harmonious society, circular economy environment, we should focus on improving the direction of thermal power technology to consider the impact of electricity on the environment, the impact of non-renewable energy, although there are now some nuclear power units in China, but thermal power still occupies most of the power market;
hydropower
Hydropower is a comprehensive engineering facility that converts water energy into electric energy: it generally includes the water diversion system of reservoirs and hydropower stations formed by water retaining and draining buildings, power generation plants, mechanical and electrical equipment, etc.: the high water level water of the reservoir flows into the plant through the water diversion system to drive the hydro-generator set to generate electric energy, and then enters the power grid through step-up transformers, switching stations and transmission lines.
By 2007, China's total installed hydropower capacity had reached 145 million kilowatts, and the development and utilization rate of hydropower energy had increased from less than 10% before the reform and opening up to 25%. The rapid development of hydropower has made important contributions to the national economic and social development, and has also led to the prosperity of China's power equipment manufacturing industry.
Wind power
Wind power is the use of wind power to drive the windmill blades to rotate, and then increase the speed of rotation through the speed increaser to promote the generator to generate electricity. With current windmill technology, a breeze speed of about three kilometers per second (the degree of the breeze) is enough to start generating electricity.
Wind power generation is one of the most mature and large-scale power generation methods in the field of new energy, and the development of wind power is of great significance for ensuring energy security, adjusting the energy structure, reducing environmental pollution, and achieving sustainable development.
nuclear power
Nuclear power plant is a new type of power station that uses the energy contained in the atomic nucleus to generate electricityNuclear power plants can be roughly divided into two parts: one is a nuclear island that uses nuclear energy to produce steam, including a reactor device and a primary circuit system, and the other part is a conventional island that uses steam to generate electricity, including a steam turbine generator system.
The mainland's nuclear industry has a history of more than 40 years of development, has established a fairly complete nuclear fuel cycle system from geological exploration, mining, component processing, reprocessing, etc., has built various types of nuclear reactors and has many years of experience in safety management and operation, and has a professional and skilled team. The construction and operation of nuclear power plants is a complex technology: "The mainland is now able to design, build and operate its own nuclear power plants.
Other energy sources for power generation
In addition to the above-mentioned types of power generation, there are other types of energy generation:
Biomass power generation: a power generation method in which human beings use organisms that can generate strong bioelectricity, and collect and convert the bioelectricity generated by them.
Tidal power generation: Electricity is generated using the potential energy of water formed by the ebb and flow of seawater.
Solar thermal power generation: the use of sunlight or heat, converted into European electricity generation mode.
Overview of Transmission
Transmission is the transmission of electrical energy. It and substation, distribution, electricity together, constitute the overall function of the power system: through transmission, the distant (up to thousands of kilometers) power plants and load centers are linked, so that the development and utilization of electric energy beyond the geographical limit, and other energy transmission (such as coal transportation, oil transportation, etc.) compared with the transmission of electricity, transmission loss is small, high efficiency, flexible and convenient, easy to regulate, and environmental pollution is less: transmission can also connect power plants in different locations to implement peak and valley regulation. Transmission is an important embodiment of the superiority of electric energy utilization, and it is an important energy artery in a modern society.
Transmission line composition
Compared with substation equipment, the transmission line is relatively simple, and the composition is relatively simple; According to the equipment state maintenance, the transmission line is mainly divided into 7 units and 1 environments, and the 7 units are towers, ground wires, insulators, fittings, tower foundations, grounding devices, and ancillary facilities, and an environment refers to the channel environment.
Type of transmission
According to the nature of the transmitted current, power transmission is divided into AC transmission and DC transmission; In the 80s of the 19th century, direct current transmission was first successfully realized. However, due to the difficulty of continuing to increase the voltage of DC transmission under the technical conditions at that time, the transmission capacity and efficiency were limited. At the end of the 19th century, direct current transmission was gradually replaced by alternating current transmission. The success of AC and Transmission ushered in a new era of electrified society in the 20th century. At present, three-phase AC transmission is widely used, with a frequency of 50 Hz (or 60 Hz). Since the 60s of the 20th century, there has been a new development of DC transmission, which is combined with AC transmission to form an AC and DC hybrid power system.
Transmission voltage level
The level of transmission voltage is the main indicator of the development level of transmission technology, and the main voltage levels of transmission lines in mainland China are:
Generally speaking, the larger the transmission capacity, the higher the voltage level used in the line. The use of ultra-high voltage transmission can effectively reduce the line loss, reduce the unit cost of the line, occupy less cultivated land, make full use of the line corridor, reduce the power loss on the transmission line and the cause of the line impedance voltage drop: P=U*I
According to the above formula, under the premise of constant power, increasing the voltage can reduce the current, thereby reducing the heat loss of the transmission line.
Overview of substations
Substation is the power system. Through the process of changing the voltage from low grade to high grade (step-up) or from high-grade to low-grade (step-down) through certain equipment, the rated voltage of the generator in the power system is generally below (15~20) kV. The commonly used transmission voltage levels are 765 kV, 500 kV, 220-110 kV, 35-60 kV, etc.: the distribution voltage level is 35-60 kV, 3-10 kV, etc.; The electrical appliances of the power department have high-voltage electrical devices with a rated voltage of 3~15 thousand volts and low-voltage electrical equipment such as 110 volts, 220 volts, and 380 volts.
Substation classification
There are two types of voltage transformer: step-up and step-down:
1. Boost
In the power system, the power plant converts natural primary energy into electric energy and transmits power to distant power users, and in order to reduce the power loss on the transmission line and the line impedance voltage drop, the voltage needs to be increased.
2. Buck pressure
In order to meet the safety requirements of power users, the voltage should be lowered and distributed to each user.
Principle of transformer device
The main component of the transformer is the transformer, its main principle is the principle of electromagnetic induction, when the transformer applies AC voltage UI at one time, the current flowing through the primary winding is I1, then the current will produce alternating magnetic flux in the iron core, so that the primary winding and the secondary winding have electromagnetic contact, according to the principle of electromagnetic induction, the alternating magnet through these two windings will induce electromotive force, its size is proportional to the number of winding turns and the maximum value of the main pass, the voltage on the side with more winding turns is high, and the voltage on the side with fewer winding turns is low, When the secondary side of the transformer is open, that is, when the transformer is no-load, the secondary terminal voltage is proportional to the number of turns of the primary and secondary windings, and the transformer plays the purpose of transforming the voltage.
Substation - substation
The substation is the place where the voltage and current of electric energy are transformed, concentrated and distributed in the power system, and it is the intermediate link between the power plant and the power user, and the power grid of each voltage level is linked through the substation; In order to ensure the quality of power and the safety of equipment, voltage regulation, power flow (flow direction and distribution of voltage, current and power in each node and branch of the power system) control and protection of transmission and distribution lines and main electrical equipment are also required in the substation.
Overview of power distribution
Distribution refers to the network that plays the role of power distribution in the power grid. It usually refers to the network of direct or step-down power supply to users on the low-voltage side of the secondary step-down transformer in the power system, which is the link in the power system that is directly connected to the user and distributes electric energy to the user.
Distribution network composition
The distribution system is composed of a distribution substation (usually the transmission voltage of the power grid is reduced to a distribution voltage), a high-voltage distribution line (that is, a voltage of more than 1,000 volts), a distribution transformer, a low-voltage distribution line (a voltage below 1,000 volts) and corresponding control and protection equipment.
Distribution network classification
Distribution is generally divided into high-voltage distribution, medium-voltage distribution and low-voltage distribution according to voltage:
High-voltage distribution voltage: 35KV, 63KV, also known as local power grid;
Medium voltage distribution voltage: 10kV:
Low-voltage distribution voltage: 380/220V
Power distribution is divided into urban distribution network, rural distribution network, and factory distribution network according to the power supply area:
Urban distribution network: provide urban currency residents to work and live, and the load is relatively concentrated
Rural distribution network: provide electricity for agricultural production and normal rural life. Large power supply radius
Factory distribution network: provide the electrical energy required for the production of industrial bases, and the load is large
Power distribution is divided into AC power supply mode and DC power supply mode according to the power supply mode:
AC power supply mode:
Three-phase three-wire system: divided into triangle wiring (for high-voltage distribution, three-phase 220-volt motors and lighting) and star wiring (for high-voltage distribution, three-phase 380-volt motors)
Three-phase four-wire system: used for 380/220 volt low-voltage power and lighting hybrid power distribution.
Three-phase, two-line, one-place system: mostly used for rural power distribution.
Three-phase single-wire system: often used for traction power supply for electric railways.
Single-phase two-wire system: mainly for residential electricity.
DC power supply mode:
Two-wire system: used for power supply of urban trolleybuses, subway locomotives, mine traction locomotives, etc.;
Three-wire system: supply power plants, substations, distribution stations for their own power and secondary equipment, electrolysis and electroplating.
The main indicators of the distribution network
There are four main indicators of the distribution network:
Power supply reliability: Power supply reliability refers to the reliability of continuous power supply for users.
Grid loss rate: The network loss rate can be defined as the ratio of the power loss of the power grid to the total power supply, which is usually expressed as a percentage.
Voltage fluctuation and voltage flicker: Voltage fluctuation refers to rapid changes in grid voltage or periodic changes in voltage envelope. Voltage flicker refers to the main perception of the human eye on the flash of the lamp, which causes the flicker fluctuation voltage of the lamp, which is called the flicker voltage.
Voltage qualification rate: The voltage qualification rate refers to the percentage of the voltage qualification time in the total time of the voltage at a certain point of the power system in the statistical time.
Development of distribution networks
The high and medium voltage distribution network frame is developing into a grid shape
Closed-loop operation
Major changes in the relay protection configuration
AC scheme and light DC scheme of the grid
Superconductivity of AC grids
Power flow controllers are widely used
Power distribution role
The main functions of the distribution network are the following two points:
1. The main function of the distribution network is to receive electric energy from the transmission network, and distribute it step by step or consume it locally, that is, to reduce the high-voltage electric energy to various voltages that are suitable for operation and user needs, and form a multi-level distribution network to supply power to various users.
2. The distribution line of 10kV and below provides power supply to users and is responsible for the task of transmitting and distributing electric energy.
Overview of electricity consumption
Electricity is the process of consuming electrical energy through electrical appliances, which is the last node of the electricity link, and there are electricity links everywhere in daily life: fluorescent lamps, computers, air conditioners, washing machines, industrial machines.
Classification of electricity consumption
Electricity consumption is divided into four main categories according to load:
Urban electricity consumption: household appliances for urban residents, which has a trend of annual growth, as well as obvious seasonal passive characteristics.
Rural electricity consumption: electricity consumption for rural residents and electricity consumption for clothing production.
Commercial electricity consumption: The lighting, air conditioning, power and other electricity consumption of the commercial sector covers a large area, and the growth of electricity consumption is stable, and the commercial load also has the characteristics of seasonal fluctuations.
Industrial electricity consumption: the proportion of electricity used in industrial production and general industrial electricity is in the first place in the composition of electricity consumption.
Electrical feedback
Through the electricity consumption, it can also guide the construction of the four links of power generation, transmission, transformation and distribution in the power system, so it can also be said that electricity is the first link of "generation, transmission, transformation and distribution" of electric energy.