One, 50 electrical control knowledge 1. Classified by purpose, low-voltage electrical appliances are divided into control appliances, main electrical appliances, protective electrical appliances, electrical distribution electrical appliances and electrical appliances. 2. According to the classification of executive functions, low-voltage electrical appliances are divided into contact electrical appliances and non-contact electrical appliances. 3. Classified according to the working principle, low-voltage electrical appliances are divided into electromagnetic appliances and non-electricity control appliances. 4. The electromagnetic mechanism consists of several parts such as an attracting coil, a core, and an armature. 5. Electromagnetic appliances are divided into two major categories, DC and AC, which are all made using the principle of electromagnets. 6. When the knife switch is connected, the power incoming line should be connected to the incoming end of the static socket, and the electrical equipment should be connected to the outlet of the movable cutter. 7. When using the iron shell switch, the outer casing should be grounded reliably to prevent electric shock caused by leakage. 8. The contactor is mainly composed of an electromagnetic system, a contact system, and an arc extinguishing device. 9. The DC contactor does not generate eddy currents and hysteresis losses, so it does not generate heat. 10. A relay is an automatic switching device that controls the on/off of a circuit based on an external input signal. 11. The relay and the contactor are used to switch the control circuit and the protection circuit of the small current, so the relay has no arc extinguishing device, and there is no distinction between the main and auxiliary contacts. 12. The speed relay is mainly used for the reverse brake control of the cage asynchronous motor. 13. The proximity switch is also called a contactless travel switch. 14. The fuse consists mainly of a melt and a melt tube that mounts the melt. 15. The circuit breaker is mainly composed of a contact, an arc extinguishing system and a trip unit. 16. Commonly used short circuit protection appliances are fuses and automatic air circuit breakers. 17. A commonly used overload protection device is a thermal relay. 18. The hardware of the PLC is composed of a host, an I/O expansion module, and various external devices. 19. The software system of the PLC consists of a system program and a user program. 20. The process of executing a program by PLC is divided into three stages: input sampling or input processing, program execution, and output refresh or output processing. twenty one. Usually a PLC instruction consists of three parts: step number, mnemonic and component number. twenty two. The relays in the PLC equivalent circuit are not actual relays. In order to distinguish them from actual relays, they are often referred to as "soft relays". twenty three. In the state transition diagram, each state provides three functions: driving load, specifying conversion conditions, and setting new state. 24, low-voltage electrical appliances refers to a variety of electrical appliances operating at 1500 VDC or 1200 VAC. 25. The contactor can be divided into DC_contactor and AC_contactor according to the type of current passing through its main contact. 26. The relay contactor control circuit is composed of various _buttons, travel switches, relays, contactors, fuses and other components to realize the control of the starting, speed regulation, braking and reverse of the electric drive system. Protection to meet the requirements of the production process for power drag control. 27. The thermal relay is a protection device that works by the principle of the thermal effect of the current. It is mainly used as the _ overload protection of the three-phase asynchronous motor in the circuit. 28. The speed relay is mainly used as the reverse brake control. 29. The time relay refers to the electric appliance used to realize the control of the contact delay on or the delay off. 30. The electrical control system of the machine tool is made up of a number of electrical components connected according to certain requirements to realize automatic electrical control of the machine tool. In order to facilitate the design, analysis, installation, commissioning, use and maintenance of the control system, it is necessary to connect the electrical components and their interconnections with the texts, symbols and figures specified by the state. This figure is a diagram of the electrical control system. The electrical control system diagram includes: electrical schematic diagram, electrical component wiring diagram, electrical component layout diagram. 31. In the electronic control of the machine tool, short circuit protection _ fuse _; overload protection thermal relay _; over current protection _ over current relay _. 32. Each scanning process of PLC is divided into three phases, which are: input sampling phase, program execution phase and output refresh three phases. 33. The electrical control diagram is generally divided into two parts: the main circuit and the control circuit. 34. The structural form of the contact has a bridge contact and a finger contact. 35. The contactor is an automatic switching device for frequently turning on or off the AC/DC main circuit and the large-capacity control circuit at a long distance. 36. The rated on-off capability of the contactor refers to the current value at which the main contact is reliably turned on and off under specified conditions. 37. A relay is a kind of change in various physical quantities, which converts a change in electric quantity or non-electric quantity into an electromagnetic force or a step change in an output state, thereby causing a contact or a sudden change in the same circuit or another circuit. A control element for the operation of other devices or devices. 38. The adjusting device of the relay is used to change the operating parameters of the relay. 39. Low-voltage electrical appliances are divided according to their use: low-voltage distribution electrical appliances, low-voltage control electrical appliances, etc. 40. The electromagnetic relay reflects the electrical signal. When the coil reflects the voltage signal, it is a voltage relay; when the coil reflects the current signal, it is a current relay. 41. The electromagnetic voltage relay coil is connected to the circuit voltage to reflect the circuit voltage. 42. The electromagnetic current relay coil is serially connected in the circuit to reflect the magnitude of the circuit current. 43. Three-phase squirrel-cage asynchronous motor Y-△ step-down starting current is 1/3 times of direct starting current. This method can only be used for motors with Δ connection in stator winding. 44. Starting mode of CMC-MX soft starter: current limiting start, voltage ramp start; parking mode: free stop, soft stop. 45. Xichi integrated high-pressure solid-state soft starter combines the switchgear and the starter cabinet into one. 46. ​​When selecting the contactor, it should start from its working condition. The AC contactor should be used to control the AC load; the DC contactor should be used to control the DC load. 47. When the contactor is selected, the rated working voltage of the main contact should be greater than or equal to the voltage of the load circuit. The rated working current of the main contact should be greater than or equal to the current of the load circuit. The rated voltage of the attracting coil should be the control loop. The voltages match. 48. The role of the intermediate relay is to turn an input signal into multiple output signals or to amplify the signals. 49. Commonly used braking methods for cage asynchronous motors are: electric braking and mechanical braking. 50. According to the national standard, the “stop†button must be red, and the “start†button must be green. Second, electrical practical speed algorithm 1. The current on the low-voltage side of the transformer is 1.5 times the capacity (1.44 times when accurate) 2. The three-phase short-circuit current of the transformer low-voltage outlet is 150 times the capacity divided by the transformer short-circuit impedance percentage (144 times when it is accurate) 3. The rated current of the 10kV side of the transformer is 6% of capacity (5.8% when accurate); the rated current of 6kV side is 10% of capacity (9.6% when accurate) 4. The rated current of 0.4kV three-phase compensation capacitor is 1.5 times of capacity (1.44 times when accurate) 5, 380V three-phase motor rated current is capacity and 2 times 6. Under normal circumstances, the low-voltage side power factor is compensated to 0.95, and the capacitor capacity is about 1/3 to 2/5 of the transformer capacity. Generally used in places where special occasions such as electric resistance furnaces or gas discharge lamps have large capacity 7. Copper discharge flow estimation table Copper row cross section S (mm2), allowable current carrying capacity I (A), copper row cross section S (mm2), allowable current carrying capacity (IA) S≤100 I=3.5S; 200<S≤600 I=2.5S 100<S≤200 I=3S ; S>600 I=2S Note: The smaller the thickness of the copper bar, the larger the current per mm2. 8. Calculation of rated and starting current protection of three-phase 380V cage motor The rated current amperage is twice the capacity of kilowatts, and its starting current is about 12 to 14 times the capacity. For the direct-start motor, the short-circuit of the short-circuit molded case switch is 17 to 24 times its capacity; for light load For motors that do not start frequently, the fuse current is 2.5 to 3 times the rated current of the motor; for heavy-duty starting motors, the fuse current is 4 to 5 times its rated current. 9. How to choose the capacity of low-voltage compensation capacitors? How to choose the protection fuses? In general, the total compensation is 1000 volts and 30% to 40% of the transformer capacity, and the single-capacity amperage is 1.5 times the capacity of the capacitor. The fuse current of the fuse is not less than the rated current of the capacitor. 1.5 times. Estimated example: A 1250kVA transformer, short circuit impedance is 6%, low voltage 0.4kV rated current Ie=1.5*1250=1875A; low voltage short circuit current Ik=1250*150/6=31250=31.25kA; high voltage 10kV side current I, I=1250* 6% = 75A; The low-voltage capacitor compensation capacity is about Q=1250*1/3=420kVar. Therefore, the high voltage current transformer is selected 75/5; Low-voltage current transformer 2000/5,2500/5; The circuit breaker can select the flow breaking capacity to be no less than 35kA; Two compensation capacitor cabinets, one 200kVar, one 220kVar. Note: If the high-voltage current transformer is not stable, the ratio can be increased or the current transformer can be selected. Metals Customization Products.Connector, hardware accessories, connection terminals, shrapnel, metal stamping parts, round hole machined pin. Metals Customization Products ShenZhen Antenk Electronics Co,Ltd , https://www.antenkelec.com