Basic knowledge of electric power

Basic knowledge of electricity. In daily life, electricity is almost everywhere. Electricity is inseparable from our life, so many people want to master the basic knowledge of electricity as a practical skill. Let's look at the basics of electricity first.

Basic knowledge of electric power 1 1. Basic concepts of electric power system

1, basic concept

Electric energy is a very important secondary energy, which can be easily and economically converted from primary energy (coal, oil, natural gas, solar energy, hydropower, wind energy, etc.). ) is contained in nature and can be converted into other energy for people to use.

Electric energy is generated by power plants. Large-capacity power plants are often built in places rich in fuel and hydraulic resources, and users are often far away from power plants. It is necessary to build long transmission lines for power transmission, build step-up and step-down substations for power transformation, and supply power to various users through distribution lines.

Power system-a unified whole consisting of power generation, transmission, transformation, distribution and electricity consumption. It is one of the most important and complicated systems engineering in modern society.

Power grid-the part composed of transmission, transformation and distribution. Including step-up and step-down transformers and transmission lines of various voltages. Its task is to transmit the electric energy produced by distant power plants to the load center, and at the same time, it is also connected to the regional power grid. The northeast, north, central, east, northwest and southern power grids in China all belong to this type.

Power network-a system that includes the power parts of power plants (such as boilers, steam turbines and reservoirs in hydropower plants, turbines and reactors in nuclear power plants, etc.). ) on the basis of the power system.

2. Composition of power system

The system composed of generators, step-up and step-down substation equipment, power grid and power users (electrical equipment) of power plants is collectively called power system.

(1) power plant: producing electric energy.

(2) Power network: divided into transmission network and distribution network.

Transmission network: the transmission network connecting power plants, substations or substations with high voltage or even ultra-high voltage, so it is also called the main network in the power network.

Distribution network: a network that directly delivers electric energy to users. Its function is to distribute electric energy to different users, transform voltage and transmit electric energy.

Power networks are classified by voltage level:

Low voltage network: the voltage level is below 1kV;

Medium voltage network:1~ 35kv;

High voltage network: higher than 35kV and lower than 330kV；;

EHV network: below 750kV; ;

UHV power grid: 1000kV and above.

(3) Electrical equipment: Power consumption.

Second, the advantages of high-power system:

1 to improve the reliability of power supply; 2. Reduce the spare capacity of the system; 3. Reduce the peak load of the system; 4. Improve the quality of power supply; 5. It is convenient to use high-power resources.

Three, the characteristics of power production:

1, at the same time, electric energy cannot be stored in large quantities, and the unified whole composed of all links is inseparable, and the transition process is very fast. The power generated instantly must be equal to the power taken instantly, so every link of power production, transmission and distribution to users is very important;

2, centralization, power production is highly centralized and unified, no matter how many power plants, power supply companies and power grids must be unified in dispatching, unified in management standards and unified in management methods; There are strict requirements for safety in production, organizational discipline and professional ethics;

3. Applicability: The service objects of power companies are all-round, involving all people in the whole society. Power quality and electricity price level are closely related to the interests of the majority of power users.

To promote the national economy, we must first develop electric power.

Four, the requirements of the power system:

1 to ensure the reliability of power supply; 2. Ensure power quality; 3. Improve the economy of power system operation; 4. Environmental protection issues

Basic knowledge of electric power 2 1. What are power systems, power systems and power grids?

Answer: The unified whole of power facilities, equipment, power generation, transmission, substation, distribution, electrical equipment and corresponding auxiliary systems of general power generation enterprises is called power system; The unified whole of electric energy production, transmission, distribution and use, which consists of power generation, transmission, substation, distribution, electrical equipment and corresponding auxiliary systems, is called power system; The unified whole of transmission, substation, distribution equipment and corresponding auxiliary systems is called power grid.

2. What are the characteristics of modern power grid?

A: 1) The main power grid is composed of a strong EHV system.

2) The power grids are closely connected, and the voltage level is relatively simplified.

3) It has sufficient capacity of peak regulation, frequency regulation and voltage regulation, can realize automatic power generation control and has high power supply reliability.

4) It has corresponding safety and stability control system, highly automated monitoring system and highly modern communication system.

(5) Having a technical support system suitable for the operation of the power market, which is conducive to the rational utilization of energy.

3. What is the significance and function of regional power grid interconnection?

A: 1) It can make rational use of energy and strengthen environmental protection, which is conducive to the sustainable development of the power industry.

2) Large-capacity and high-efficiency thermal power units, hydropower units and nuclear power units can be installed, which is conducive to reducing costs, saving energy and accelerating power construction.

3) Use time difference and temperature difference to stagger the peak of electricity consumption, and use the different time of electricity consumption in different regions to adjust the load, so as to reduce the spare capacity and installed capacity.

4) It can supply power to each other, exchange needed goods and be standby for each other, which can reduce the standby capacity of accidents, enhance the anti-accident ability and improve the safety level of power grid and the reliability of power supply.

5) It can bear large impact load, which is beneficial to improve power quality.

6) Hydropower can be regulated across river basins, and economic dispatching of hydropower and thermal power can be carried out in a wider range, thus achieving greater economic benefits.

4. What is the principle of reactive power compensation in power grid?

Answer: The principle of reactive power compensation in power grid is that reactive power compensation in power grid is basically considered in accordance with the principle of layered partition and local balance, and adjusted with load or voltage, so as to ensure that the voltage of each hub point of the system can meet the specified requirements in normal and accident situations and avoid transmitting reactive power through long-distance lines or multi-stage transformers.

5. What is the difference between voltage characteristics and frequency characteristics of power system?

Answer: The frequency characteristics of power system depend on the frequency characteristics of load and generator. The characteristics of generator output changing with frequency are called generator frequency characteristics, which are determined by the active load balance of the system and have little to do with the network structure (network impedance). In the absence of oscillation, the steady-state frequency of the same power system is the same. Therefore, the system frequency can be adjusted and controlled centrally.

Basic knowledge of electric power 3 1, left zero right fire.

2. The yellow, green, red and light blue used in the three-phase five-wire system respectively represent the two colors (PE) of U, V, W and N protective grounding wires.

3, transformer in operation, the transformer phase current should not exceed the rated current; The maximum unbalanced current shall not exceed 25% of the rated current. After the transformer is put into operation, it should be overhauled regularly.

4. In the power supply system of the same transformer, protective grounding and protective zero connection should not be mixed.

5. The rated voltage of the secondary coil of the voltage transformer is generally100V. ..

6. The secondary side of voltage transformer should not be short-circuited at work. Because of short circuit, a large short circuit current will be generated, which may burn out the transformer. Therefore, both the primary side and the secondary side of the voltage transformer are equipped with fuses for protection.

7. One end of the secondary side of voltage transformer must be grounded. This is to prevent the primary high voltage from entering the secondary side when the insulation of the primary and secondary coils is broken down, endangering personal and equipment safety.

8. When the current transformer is working, the secondary side is close to short circuit. The rated current of the secondary coil is generally 5A.

9. The secondary side of current transformer shall not be open at work.

10, one end of the secondary side of the current transformer must be grounded to prevent the high voltage on the primary side from entering the secondary side when the primary and secondary coils are insulated and broken down.

1 1. When connecting the current transformer, pay attention to the polarities of its primary and secondary coils. In China, transformers are labeled with decreasing polarity.

12, when installing, be sure to pay attention to the correct and reliable wiring, and the secondary side is not allowed to be connected with fuses or switches. Even if the instrument or other equipment on the secondary side is to be dismantled for some reason, the secondary side must be short-circuited first, and then dismantled.

13, low-voltage switches refer to disconnectors, circuit breakers, fuses, etc. below 1KV.

14, the load controlled by low-voltage power distribution equipment must be clearly divided, and it is forbidden to control more than one brake and use it confusedly.

15. Interlocking devices of low-voltage power distribution devices and self-provided generator equipment shall be reliable. It is forbidden to run self-provided power generation equipment in parallel with the power grid privately.

16. Insulating mats should be laid on the passages for operation and maintenance of low-voltage distribution equipment, and other articles are strictly prohibited to be piled on the passages.

17. When connecting equipment: connect the equipment first, and then connect the power supply.

18. When disassembling the equipment: disassemble the power supply first, and then disassemble the equipment.

19. When connecting the line: connect the neutral line first, then the live line.

20. When disconnecting the line: disconnect the live line first, and then disconnect the zero line.

2 1, low-voltage fuse cannot be used as overload protection of motor.

22. The rated voltage of fuse must be greater than or equal to the working voltage of distribution line.

23. The rated current of fuse must be greater than or equal to the rated current of melt.

24. The breaking capacity of the fuse must be greater than the possible maximum short-circuit current of the distribution line.

The selection of rated melt current must meet the normal working current of the line and the starting current of the motor.

26. For short-circuit protection of electric furnace and lighting load, the rated current of the melt is equal to or slightly greater than the rated current of the load.

27. For a single motor, rated melt current ≥( 1.5-2.5) rated motor current.

28. When the rated current is melted in the power distribution system, the upper and lower levels should be coordinated to achieve the purpose of selective protection. The next level should be less than the previous level.

29, porcelain plug-in fuse should be installed vertically, must use qualified fuse, shall not use other copper wire instead of fuse.

30. The power inlet of the spiral fuse should be connected to the central terminal of the base, and the outlet of the load should be connected to the terminal of the threaded shell.

3 1. When changing the melt, you must first disconnect the electrical equipment to prevent arcing.

Fuses should be installed on each phase line. It is forbidden to install fuses on the neutral line of two-phase three-wire or three-phase four-wire circuits.

33, fuse is mainly used for short circuit protection.

34. When the fuse is used for isolation purposes, it must be installed at the head end of the line.

35, the function of fuse is short circuit protection. Isolate the power supply and maintain safety.

36. The role of the knife switch is to isolate the power supply and maintain safety.

37. The knife switch with plastic cover and porcelain bottom is generally used as the control switch of electric lighting circuit and electric heating circuit, and can also be used as the distribution switch of branch circuit.

38. When the capacity is appropriately reduced, the three-pole rubber cover knife switch can be used to occasionally operate the motor control switch.

39. The incoming power supply of the three-pole rubber knife switch should be on the incoming seat of the static contact end, and the electrical equipment should be connected to the outgoing seat of the fuse below.

40. When the knife switch is closed, the handle should be downward, and when it is opened, the handle should be upward, and it cannot be inverted or paperback.

4 1, three-pole rubber breaker is used for short circuit protection. Isolate the power supply and maintain safety.

42, low voltage load switch shell should be reliable grounding.

43. When the automatic air switch is selected as the main switch, the incoming side of these switches must have obvious disconnection points. The obvious disconnection point can be an isolating switch, a knife switch or a fuse.

44, the main function of fuse is overload or short circuit protection.

45. Capacitor parallel compensation is to connect the capacitor directly with the compensated equipment in parallel on the same circuit to improve the power factor.

46. There are many measures to improve the power factor, among which the most convenient method is to connect compensation capacitors in parallel.

47. The wall switch is off the ground 1.3m, and the wall socket is 0.3m. ..

48, stay switch should be 2-3 meters from the ground.

49. The electric energy meter shall be 1.4- 1.8 meters from the ground.

50, into the door line should be 2.7 meters from the ground.

5 1, roads, primary and secondary trunk roads, tramways, major rivers, weak current lines, special ropeways, etc. , there should be no joint.

52, plastic sheath line is mainly used for indoor Ming with laying, shall not be directly buried in the plaster layer with laying.

53. Generally speaking, it is required that the total cross-sectional area (including insulation layer) of the conductor in the pipe is not more than 40% of the cross-sectional area of the inner diameter of the pipe.

54, tube wire can not have joint, joint should be in the junction box; Different power supply circuits, different voltage circuits, mutually standby circuits, working lighting and emergency lighting circuits should not be installed in the same tube.

55. When the pipeline is steel pipe (iron pipe), the wires of the same AC circuit must be worn in the same pipe, and it is not allowed to wear a steel pipe for a wire.

56, a tube containing some wires shall not exceed 8.

57, pipe for steel pipe (iron pipe), pipe must be reliable grounding.

58. When the pipeline is steel pipe (iron pipe), plastic protective covers must be added at both ends of the pipeline outlet.

59, wire tube length more than 30 meters (semi-rigid tube) which should be installed junction box.

60, wire tube length more than 40 meters (including iron pipe) should be installed junction box.

6 1, the conductor passes through the pipe, and the length of a bent pipe is less than 20m. A junction box should be installed in the middle.

62. When the conductor passes through the pipe, the length of two curved conduits shall not exceed 15m. A junction box should be installed in the middle.

63. The conductor passes through the pipe, and the length of three bent pipes shall not exceed 8m. A junction box should be installed in the middle.

64. When using multiphase power supply, the color selection of conductor insulation layer in the same building should be consistent, that is, the protective conductor (PE) should be green/yellow double-color line, and the neutral conductor (N) should be light blue; The phase lines are 65, L 1- yellow, L2- green and L3- red. The switch wire of single-phase power supply is red, and white or yellow is generally used after the switch.

66, wire joint position should not be in the insulator fixed place, joint position should be more than 0.5 meters away from the wire fixed place, so as not to interfere with the wire and broken.