Electricity is a general term for disciplines or engineering fields such as the production, transmission, distribution, use of electrical energy, and electrical equipment manufacturing. It is a science to create, maintain and improve confined space and environment by means of electric energy, electric equipment and electric technology, covering three aspects of electric energy conversion, utilization and research, including basic theory, applied technology, facilities and equipment.
Common electrical basic knowledge
1. Active power-in the process of generating and transmitting AC electric energy, the part of energy used for conversion into electromagnetic form is called active power
2. Reactive power-in the process of generating and transmitting AC electric energy, the part of energy used for the exchange of electromagnetic fields in the circuit is called reactive power
3. Power system-the power system consists of generators, power distribution devices, step-up and step-down substations, power lines and electrical energy users. Neutral point displacement: In a three-phase circuit, when the power supply voltage is symmetrical with the three-phase load, if the three-phase load is also symmetrical, the voltage at the neutral point is zero regardless of whether there is a neutral point. But if the three-phase load is asymmetrical, and there is no neutral line or the neutral line has a large impedance, then a voltage will appear at the neutral point. This phenomenon is called a neutral point displacement phenomenon.
4. Operating overvoltage-transient voltage rise caused by the opening and closing operation of the circuit breaker and short circuit or ground fault is called operating overvoltage.
5. Resonance overvoltage-the circuit breaker operation causes the power grid loop to be divided or the iron core element tends to saturate, causing a loop inductance and capacitive reactance to meet the resonance conditions, which may cause resonance and voltage rise, called resonance Overvoltage.
6. Electrical main wiring-mainly refers to the transmission of electric energy that is designed to meet the predetermined power transmission mode and operation requirements in power plants, substations, and power systems, and indicates the interconnection relationship between high-voltage electrical equipment Circuit.
7. Double busbar connection-it has two sets of busbars: working bus I and spare bus 1. Each circuit is connected to two sets of busbars via a circuit breaker and two sets of isolating switches. The busbars are connected by a bus-connecting circuit breaker (referred to as a bus tie), which is called double-bus connection.
8. One and a half circuit breaker wiring-every two components (outgoing line or power supply) use three circuit breakers to form a series connection to two sets of buses, which is called one and a half circuit breaker wiring, also known as 3/2 wiring.
9. Factory electricity-during the start-up, operation, shutdown, and maintenance of the power plant, there are a large number of mechanical equipment driven by electric motors to ensure the main equipment of the unit and coal transportation, coal crushing, ash removal and dust removal. Normal operation of auxiliary equipment such as water treatment. These motors and the electrical equipment for operation, operation, testing, maintenance, and lighting of the whole plant are all factory loads, and the total power consumption is collectively referred to as factory electricity.
10. Auxiliary power consumption rate-the percentage of auxiliary power consumption to the total power generation of a power plant is called the auxiliary power consumption rate. The plant power consumption rate is one of the main economic indicators of power plant operation.
11. Regular load-motors that must be used continuously every day.
12. Infrequent loads-loads used only during maintenance, accidents or the start and stop of the boiler.
13. Continuous load-a load of more than 2 hours of continuous operation each time;
14. Short-time load-load that only runs for 10-120 minutes each time;
15. Intermittent load-working repeatedly and periodically, each cycle does not exceed 10 minutes of load.
16. Self-starting of the motor-the normal operation of the motor in the factory system, “when the voltage of the power supply bus suddenly disappears or decreases significantly, after a short period of time (usually 0.5-1.5s) at the end of its speed Before stopping, if the factory-used bus voltage returns to normal (such as power failure removal or automatic standby power input), the motor will accelerate by itself and return to normal operation. This process is called the motor’s self-starting.
17. Loss of excitation-the sudden partial or complete loss of excitation of a synchronous generator is called loss of excitation.
18. Excitation control system-the entire system composed of excitation regulator, excitation power unit and generator itself is called excitation control system.
19. Self-shunt excitation static excitation system-using a transformer connected to the generator outlet. (Called excitation transformer) as the excitation power supply, after silicon rectification, it supplies the generator for excitation. Because the excitation transformer is connected in parallel at the generator outlet, this excitation method is called self-shunt excitation. Excitation transformers and rectifiers are all static components, so it is also called a self-shunt static excitation system.
20. Mutual inductor-is a sensor used by secondary equipment such as measuring instruments, relay protection and automatic devices in the power system to obtain electrical primary circuit information. The role of the transformer is to proportionally convert high voltage and large current into low voltage and small current.
21. Sulfur hexafluoride circuit breaker-a circuit breaker using SFe gas with excellent arc extinguishing performance and insulation performance as the arc extinguishing medium is called SF 6 circuit breaker. It has the characteristics of strong breaking capacity and small size, but the structure is more complicated, the metal consumption is large, and the price is more expensive.
22. Vacuum circuit breaker-a circuit breaker that uses the high dielectric strength of vacuum to extinguish arcs, called vacuum circuit breaker. This type of circuit breaker has the characteristics of fast arc extinguishing speed, non-oxidized contact material, long life, and small size.
23. Working grounding is the grounding required to ensure the normal operation of the power system. For example, the neutral point of the transformer in the neutral point directly grounded system is grounded, and its function is to stabilize the potential of the power grid to the ground, thereby reducing the insulation to the ground.
24. Lightning protection grounding-is a grounding set for the needs of lightning protection. For example, the grounding of lightning rods (wires) and lightning arresters is designed to smoothly lead the lightning current into the earth to help reduce lightning overvoltage, so it is also called overvoltage protection grounding.
25. Protective grounding-also known as safety grounding, is a grounding set for personal safety, that is, the shell of electrical equipment (including cable sheath) must be grounded to prevent the shell from being charged and endangering personal safety.
26. Instrument control grounding-the grounding set for the thermal control system, data acquisition system, computer monitoring system, transistor or microprocessor-based relay protection system and telecontrol communication system of the power plant in order to stabilize the potential and prevent interference. Instrument control grounding is also called electronic system grounding.
27. Grounding resistance-refers to the resistance encountered when the current enters the earth through the grounding body and spreads to the surroundings.
28. Voltage-When a unit of positive charge changes from a high electric displacement to a low electric potential, the electric field force is called voltage.
29. Electric current is a physical phenomenon in which a large number of electric charges move regularly and oriented under the action of electric field force.
30. Resistance-When the current passes through the conductor, there will be resistance. This is because the free electrons constantly collide with atoms and molecules in the conductor during the movement, so that the free electrons are subject to certain resistance. The resistance of the conductor to the current is called resistance.
31. The rated current of the motor is the maximum operating current of the motor in normal and continuous operation.
32. The power factor of the motor is the ratio of the rated active power to the rated apparent power
33. The rated voltage of the motor is the line voltage in the rated working mode.
34. The rated power of the motor-refers to the mechanical power that the shaft can output when working under rated conditions.
35. The rated speed of the motor-refers to its speed at rated voltage, rated frequency and rated load.
36. Oscillation of the power system-due to the power plant’s lead wire or line switch failure, tripping, etc., the dynamic stability of the power system is destroyed and the frequency meter is abnormal, and the unstable phenomenon of the load meter and voltmeter swinging greatly is called electric power The system oscillates.
37. Protective grounding-connect the metal shells and frames of electrical equipment to the ground reliably through grounding devices; it is an important measure to protect personal safety in systems where the neutral point of the power supply is not grounded.
38. Protecting the zero connection-in the neutral grounding system, connecting the metal shell, frame, etc. of electrical equipment with the neutral lead neutral line is also an important measure to protect personal safety.
39. Bus bar-The bus bar plays the role of collecting and distributing electric energy, also known as bus bar. In principle, it is an electrical node in the circuit. It determines the number of power distribution equipment and indicates how to connect generators, transformers and lines, and how to connect with the system to complete the transmission and distribution tasks.
40. Short circuit-In a three-phase circuit, there is a small impedance or direct connection between the phase and the phase and the phase and the ground, which causes the current in the circuit to increase sharply. This phenomenon is called a short circuit.
41. Line voltage-In a three-phase circuit, no matter which kind of connection method has three phase wires lead out, the voltage between the phase wires is called the line voltage.
42. Automatic reclosing-when the circuit breaks down and the circuit breaker trips, the device can automatically reclose without manual operation.
43. Breakdown voltage-When an insulating medium breaks down, the voltage applied to both ends of the medium is called breakdown voltage.
Essential electrical basic knowledge for electricians
1. Left zero right fire
2. The colors of the three-phase five-wire system are yellow, green, red, and light blue to indicate the dual colors of U, V, W, N protective grounding wire (PE)
3. When the transformer is in operation, the current of each phase of the transformer should not exceed the rated current; the maximum unbalanced current should not exceed 25% of the rated current. The transformer should be checked and repaired regularly after it is put into operation.
4. In a system powered by the same transformer, it is not advisable to mix protective grounding and protective grounding.
5. The rated voltage of the secondary coil of the voltage transformer is generally 100V.
6. The secondary side of the voltage transformer must not be short-circuited during operation. Because a large short-circuit current will be generated during a short circuit, the transformer may be burned out. For this reason, the primary and secondary sides of the voltage transformer are equipped with fuses for protection.
7. One end of the secondary side of the voltage transformer must be grounded. This is to prevent the primary and secondary coil insulation breakdown, the primary high voltage from entering the secondary side, endangering the safety of people and equipment.
8. The secondary side of the current transformer is close to a short circuit condition when it is working. The rated current of the secondary coil is generally 5A
9. The secondary side of the current transformer is never allowed to be open during work.
10. One end of the secondary side of the current transformer must be grounded to prevent high voltage from the primary side from entering the secondary side when the insulation breakdown of the primary and secondary coils occurs.
11. When connecting current transformers, pay attention to the polarity of the primary and secondary coils. Our country’s transformers use the marking method of reduced polarity.
12. During installation, the wiring must be correct and reliable, and no fuse or switch is allowed on the secondary side. Even when the instrument or other devices on the secondary side are to be removed for some reason, the secondary side must be short-circuited first and then removed.
13. Low-voltage switches refer to isolating switches, circuit breakers, fuses, etc. below 1KV
14. The load controlled by the low-voltage power distribution device must be divided clearly, and it is strictly forbidden to have multiple controls with one gate and confusion.
15. The interlocking device of low-voltage power distribution device and self-provided generator equipment should operate reliably. It is strictly forbidden to operate self-provided power generation equipment in parallel with the power grid.
16. Insulating pads should be laid on the passages for front, rear, left, and right operation and maintenance of low-voltage power distribution devices, and it is strictly forbidden to stack other items on the passages.
17. When connecting equipment: connect the equipment first, then 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 wire first, then the live wire.
20. When disconnecting the line: first disconnect the live wire and then the neutral wire.
21. Low-voltage fuses cannot be used as overload protection for motors.
22. The rated voltage of the fuse must be greater than or equal to the working voltage of the distribution line.
23. The rated current of the fuse must be greater than or equal to the rated current of the melt.
24. The breaking capacity of the fuse must be greater than the maximum short-circuit current that may occur in the distribution line.
25. The selection of melt rated current must meet the normal working current of the line and the starting current of the motor.
26. For short-circuit protection of loads such as electric furnaces and lighting, the rated current of the melt is equal to or slightly greater than the rated current of the load.
27. For a single motor, the melt rated current ≥ (1.5-2.5) the motor rated current
28. In the distribution system of the melt rated current, the upper and lower levels should coordinate and cooperate to achieve the purpose of selective protection. The next level should be smaller than the previous level.
29. Porcelain plug-in fuses should be installed vertically, and qualified fuses must be used. Other copper wires must not be used instead of fuses.
30. The power inlet of the screw fuse should be connected to the center terminal of the base, and the outlet of the load should be connected to the terminal of the screw shell.
31. When replacing the melt, the electrical equipment must be disconnected first to prevent arcing
32. The fuse should be installed on each phase wire. It is strictly forbidden to install a fuse on the neutral line of the two-phase three-wire or three-phase four-wire circuit
33. The fuse is mainly used for short-circuit protection
34. When the fuse is used for isolation purposes, the fuse must be installed at the head of the line.
35. The function of the fuse is short-circuit protection. Isolate the power supply for safe maintenance.
36. The function of the knife switch is to isolate the power supply for safe maintenance.
37. Knife switches with plastic cover and porcelain bottom are generally used as control switches for electric lighting circuits and electric heating circuits, and can also be used as power distribution switches for branch circuits
38. The three-pole rubber cover knife switch can be used to start and operate the motor control switch infrequently when the capacity is appropriately reduced.
39. The incoming line of the three-pole rubber cover switch power supply should be pressed on the incoming socket of the static contact end, and the electrical equipment should be connected to the outgoing socket of the fuse below.
40. When the knife switch is in the cut-off state, the handle should be downward, and in the on-state, the handle should be upward. It cannot be upside-down or flat-mounted.
41. The function of the three-pole rubber cover knife switch is short-circuit protection. Isolate the power supply for safe maintenance.
42. The shell of the low-voltage load switch should be grounded reliably.
43. When the automatic air switch is selected as the main switch, there must be an obvious disconnection point on the inlet side of these switches. The obvious disconnection point can be an isolating switch, a knife switch or a fuse.
44. The main function of the fuse is overload or short circuit protection.
45. Capacitor parallel compensation is to connect the capacitor directly with the compensated equipment to 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 should be 1.3 meters from the ground and 0.3 meters from the wall socket
48. The pull switch should be 2-3 meters away from the ground
49. The watt-hour meter should be 1.4-1.8 meters above the ground
50. The entrance line should be 2.7 meters from the ground
51. Roads, primary and secondary roads, tramways, major rivers, weak current lines, special cableways, etc., should not have joints.
52. The plastic sheathed line is mainly used for indoor laying in the open, not directly buried in the plastering layer for hidden laying.
53. Generally, the total cross-sectional area of the wire in the pipe (including the insulation layer) is not more than 40% of the cross-sectional area of the inner diameter of the wire.
54. The wires in the pipe must not have joints, and the joints should be in the junction box; different power circuits, different voltage circuits, alternate circuits, working lighting and emergency lighting lines must not be installed in the same tube.
55. When the pipe is a steel pipe (iron pipe), the wires of the same AC circuit must be worn in the same pipe, and one wire is not allowed to pass through a steel pipe.
56. There should be no more than 8 wires in a tube.
57. When the pipe is a steel pipe (iron pipe), the pipe must be reliably grounded.
58. When the pipe is a steel pipe (iron pipe), plastic protective sleeves must be added to both ends of the pipe.
59. A junction box should be installed in the middle of the wire to pass through the tube over 30 meters (semi-rigid tube).
60. A junction box should be installed in the middle of the wire to pass through the pipe longer than 40 meters (iron pipe).
61. The wire passes through the tube, and the length of a curved tube is not more than 20 meters. A junction box should be installed in the middle.
62. The wire passes through the tube, and the length of two curved tubes does not exceed 15 meters. A junction box should be installed in the middle.
63. The wire passes through the tube, and the length of three curved tubes is not more than 8 meters. A junction box should be installed in the middle.
64. When multi-phase power supply is used, the color of the wire insulation layer of the same building should be the same, that is, the protective wire (PE) should be a green/yellow double-color wire, the neutral wire (N) wire should be light blue; the phase wire should be 65. L1-yellow, L2-green, L3-red. The single-phase power supply switch line is red, and it is generally white or yellow after switching.
65. The joint position of the wire should not be at the fixed position of the insulator, and the joint position should be more than 0.5 meters away from the fixed position of the wire, so as not to hinder the wire binding and breakage.
