Basic knowledge of electrician

Basic knowledge of electrician

Electricity is a mature and systematic subject, with a complete set of theories, and it is mathematics that supports this complete set of theories. The theoretical knowledge of electricity used by electricians is also inseparable from the foundation of mathematics.

1. In a system powered by the same transformer, it is not advisable to mix protective grounding and protective grounding.

2. 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. After the transformer is put into operation, regular maintenance should be carried out.

3. Left zero and right fire.

4. The three-phase five-wire system uses the colors yellow, green, red, and light blue to represent the dual colors (PE) of the U, V, W, and N protective grounding wires.

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 when a short circuit occurs, 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 during operation. The rated current of the secondary coil is generally 5A

9. The secondary side of the current transformer is never allowed to be open when it is working.

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. my country's transformers use the marking method of reduced polarity.

12. Be sure to pay attention to the correct and reliable wiring during installation, and no fuse or switch is allowed to be connected to the secondary side. Even if 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. When disassembling the equipment: disassemble the power supply first, and then disassemble the equipment. When connecting the line: connect the neutral wire first, then the live wire. When removing the line: first remove the live wire, and then remove the neutral wire.

18. Low-voltage fuses cannot be used as overload protection for motors.

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

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

21. The breaking capacity of the fuse must be greater than the maximum short-circuit current that may occur in the distribution line.

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

23. 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.

24. For a single motor, the melt rated current ≥ (1.5-2.5) × motor rated current.