You don't know the basics of these electricians, you are probably a fake electrician!

Basic Knowledge of Electricians

1. Left zero right fire.

2. In a three-phase five-wire system, the colors are yellow, green, red, and light blue respectively for U, V, W, and N. The protective grounding wire is double-color (PE).

3. When a transformer is in operation, the current of each phase should not exceed its rated current. The maximum unbalanced current must not exceed 25% of the rated current. After being put into operation, the transformer should be inspected regularly.

4. In a system powered by the same transformer, it's not advisable to use both grounding protection and zero protection together.

5. The rated voltage of the secondary coil of a voltage transformer is generally 100V.

6. During operation, the secondary side of a voltage transformer must not be short-circuited, as this can cause large currents that may damage the transformer. To prevent this, fuses are installed on both the primary and secondary sides for protection.

7. One end of the secondary side of a voltage transformer must be grounded. This prevents the high voltage from the primary side from leaking into the secondary side due to insulation failure, which could endanger people and equipment.

8. The secondary side of a current transformer operates close to a short circuit condition. The rated current of the secondary coil is typically 5A.

9. The secondary side of a current transformer must never be open during operation.

10. One end of the secondary side of a current transformer must be grounded to prevent high voltage from the primary side from entering the secondary side if the insulation fails.

11. When connecting a current transformer, pay attention to the polarity of the primary and secondary coils. In China, the reducing polarity labeling method is used.

12. When installing, ensure that the wiring is correct and reliable. The secondary side must not have fuses or switches. Even if an instrument or device on the secondary side needs to be removed, the secondary side must be short-circuited before removal.

13. Low-voltage switches include isolation switches below 1kV, circuit breakers, fuses, etc.

14. The loads controlled by low-voltage power distribution devices must be clearly separated and strictly prohibited from being mixed.

15. The interlocking device between low-voltage power distribution equipment and self-supplied generator equipment must be reliable. It is forbidden to run the generator in parallel with the grid.

16. Insulation mats should be laid in the channels for operation and maintenance of low-voltage power distribution equipment, and no items should be stacked on the passage.

17. When connecting a device, connect the device first, then the power supply.

18. When disassembling equipment, disconnect the power supply first, then remove the device.

19. When connecting a line, connect the neutral (zero) line first, then the live (fire) line.

20. When dismantling a line, remove the live line first, then the neutral line.

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 operating voltage of the distribution line.

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

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

25. The selection of the rated current of the fuse element must meet the normal working current of the line and the starting current of the motor.

26. For loads such as electric furnaces and lighting, the rated current of the fuse is equal to or slightly larger than the rated current of the load.

27. For a single motor, the rated current of the fuse is ≥ (1.5-2.5) times the rated current of the motor.

28. In the power distribution system, the rated current of the fuse at upper and lower levels should coordinate to achieve selective protection. The next level should be smaller than the previous one.

29. Porcelain plug-in fuses should be installed vertically, using qualified fuses, and never replace them with copper wires.

30. The power supply line of the screw-type fuse should be connected to the center terminal of the base, and the load output line should be connected to the threaded case terminal block.

31. When replacing the fuse element, the electrical equipment must be disconnected first to prevent arcing.

32. 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. Fuses are 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 the fuse is short-circuit protection, isolated power supply, and safe maintenance.

36. The function of the knife switch is to isolate the power supply and safely repair it.

37. The rubber-covered porcelain-bottom knife switch is commonly used as a control switch for electric lighting lines and electric heating circuits, and can also be used as a distribution switch for branch circuits.

38. The three-pole rubber-covered knife switch can be used to infrequently start motor control switches when the capacity is properly reduced.

39. The input line of the three-pole rubber-covered knife switch power supply should be placed on the static contact end, and the electrical equipment should be connected to the outlet of the fuse below.

40. When turning off the knife switch, the handle should be down. When turning on, the handle should be up, not flipped or flat.

41. The function of the three-pole rubber-covered knife switch is short-circuit protection, isolated power supply, and safe maintenance.

42. The outer casing of the low-voltage load switch should be reliably grounded.

43. When using an automatic air switch as the main switch, there must be clear disconnection points on the incoming line side of these switches. The disconnection point can be an isolation switch, knife switch, or fuse.

44. The main role of the fuse is overload or short-circuit protection.

45. Capacitor shunt compensation involves connecting the capacitor directly to the same circuit as the compensated device to improve the power factor.

46. There are several methods to improve the power factor, and the most convenient is to parallel compensate the capacitor.

47. Wall switches should be 1.3 meters from the ground, and wall sockets should be 0.3 meters.

48. Pull switches should be 2-3 meters from the ground.

49. Electricity meters should be 1.4-1.8 meters from the ground.

50. Entrance lines should be 2.7 meters from the ground.

51. Roads, roads, electric lanes, major rivers, weak lines, special ropeways, etc., should not have joints.

52. Plastic-sheathed wire is mainly used for indoor installation and laying, and should not be directly buried in the plastering layer for concealed installation.

53. When wiring through pipes, the total cross-sectional area of the wires (including insulation) should not exceed 40% of the inner diameter of the pipe.

54. There should be no joints in the pipe, and the joints should be in the junction box. Different power circuits, different voltage circuits, alternating circuits, and work lighting and emergency lighting lines should not be installed in the same pipe.

55. When the pipe is steel (iron), the wires of the same AC circuit must be in the same pipe, and one wire must not pass through a steel pipe.

56. The number of wires installed in one pipe should not exceed 8.

57. When the pipe is steel (iron), the pipe must be reliably grounded.

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

59. If the length of the wire through the pipe is more than 30 meters (semi-hard pipe), a junction box should be installed in the middle.

60. If the length of the wire through the pipe is more than 40 meters (iron pipe), a junction box should be installed in the middle.

61. The length of the curved pipe should not exceed 20 meters; a junction box should be installed in the middle.

62. If the pipe has two bends and the length is no more than 15 meters, a junction box should be installed in the middle.

63. If the pipe has three bends and the length is no more than 8 meters, a junction box should be installed in the middle.

64. When using multi-phase power supply, the color of the wire insulation in the same building should be consistent. The protective wire (PE) should be green/yellow, the neutral line (N) should be light blue, and the phase lines should be L1-yellow, L2-green, L3-red. The single-phase power supply switch line is red, and the switch is usually white or yellow.

65. The joint position of the wire should not be fixed at the insulator. The joint should be more than 0.5 meters away from the wire so as not to interfere with tying and breaking.

2

Circuit Symbols for Electricians

Character Circuit Diagram Symbols:

AAT - Power Automatic Input Device

AC - Alternating Current

DC - Direct Current

FU - Fuse

G - Generator

M - Motor

HG - Green Light

HR - Red Light

HW - White Light

HP - Light Plate

K - Relay

KA(NZ) - Current Relay (Negative Sequence Zero Sequence)

KD - Differential Relay

KF - Flash Relay

KH - Thermal Relay

KM - Intermediate Relay

KOF - Outlet Intermediate Relay

KS - Signal Relay

KT - Time Relay

KV (NZ) - Voltage Relay (Negative Sequence Zero Sequence)

KP - Polarization Relay

KR - Reed Relay

KI - Impedance Relay

KW (NZ) - Power Direction Relay (Negative Sequence Zero Sequence)

KM - Contactor

KA - Transient Relay; Instantaneous with or without Relay; AC Relay

KV - Voltage Relay

L - Line

QF - Circuit Breaker

QS - Isolation Switch

T - Transformer

TA - Current Transformer

TV - Voltage Transformer

W - DC Bus

YC - Closing Coil

YT - Trip Coil

PQS - Active Reactive Power

EUI - Electromotive Voltage and Current

SE - Experiment Button

SR - Reset Button

f - Frequency

Q - Circuit Switching Device

FU - Fuse

FR - Thermal Relay

KM - Contactor

KA - 1. Instantaneous Contact Relay 2. Instantaneous with or without Relay 3. AC Relay

KT - Delayed with or without Relay

SB - Push Button Switch

SA - Transfer Switch

Ammeter PA

Voltmeter PV

Active Energy Meter PJ

Reactive Energy Meter PJR

Frequency Table PF

Phase Meter PPA

Maximum Demand Meter (Load Monitor) PM

Power Factor Table PPF

Active Power Meter PW

Reactive Power Meter PR

Reactive Current Meter PAR

Acoustic Signal HA

Optical Signal HS

Indicator Light HL

Red Light HR

Green Light HG

Yellow Light HY

Blue Light HB

White Light HW

Connecting Piece XB

Plug XP

Socket XS

Terminal Board XT

Wire and Cable Bus W

DC Bus WB

Plug-in (Feed) Busbar WIB

Power Branch Line WP

Lighting Branch Line WL

Emergency Lighting Branch Line WE

Power Main Line WPM

Lighting Trunk WLM

Emergency Lighting Trunk WEM

Slide Line WT

Closing Small Busbar WCL

Control Small Busbar WC

Signal Small Bus WS

Flash Small Bus WF

Accident Sound Small Bus WFS

Predictive Sound Small Bus WPS

Voltage Small Busbar WV

Accident Lighting Small Busbar WELM

Arrester F

Fuse FU

Fast Fuse FTF

Drop Fuse FF

Voltage Limiting Protection Device FV

Capacitor C

Power Capacitor CE

Forward Button SBF

Reverse Button SBR

Stop Button SBS

Emergency Button SBE

Test Button SBT

Reset Button SR

Limit Switch SQ

Proximity Switch SQP

Manual Control Switch SH

Time Control Switch SK

Level Control Switch SL

Humidity Control Switch SM

Pressure Control Switch SP

Speed Control Switch SS

Temperature Control Switch Auxiliary Switch ST

Voltmeter Switch SV

Ammeter Switch SA

Rectifier U

Thyristor UR

Control Circuit with Power Supply Rectifier VC

Inverter UF

Converter UC

Inverter UI

Motor M

Asynchronous Motor MA

Synchronous Motor MS

DC Motor MD

Wound Rotor Induction Motor MW

Squirrel Cage Motor MC

Electric Valve YM

Solenoid Valve YV

Fire Damper YF

Smoke Exhaust Valve YS

Electromagnetic Lock YL

Tripping Coil YT

Closing Coil YC

Pneumatic Actuator YPAYA

Electric Actuator YE

Heating Device (Electric Heating) FH

Lighting (Lighting Device) EL

Air Conditioner EV

Electric Heater Heating Element EE

Induction Coil Reactor L

Excitation Coil LF

Arc Suppression Coil LA

Filter Capacitor LL

Resistor Varistor R

Potentiometer RP

Thermistor RT

Photoresistor RL

Varistor RPS

Grounding Resistance RG

Discharge Resistance RD

Start Varistor RS

Frequency Sensitive Varistor RF

Current Limiting Resistor RC

Photoelectric Cell Thermoelectric Sensor B

Pressure Transducer BP

Temperature Converter BT

Speed Converter BV

Time Measuring Sensor BT1BK

Level Measurement Sensor BL

Temperature Measuring Sensor BHBM

3

Selection of Blade Switches

1. Selection of Structural Form

The structural form is determined based on its function in the line and its installation position in the power distribution unit. If it is only used to isolate the power supply, a product without an arc-extinguishing cover is sufficient. If it is used to break the load, a product with an arc-extinguishing cover and operated by a lever should be used. For example, the central handle type blade switch cannot cut off the load current. Other forms can cut off a certain load current, but a blade switch with an arc chute must be selected. Additionally, the operation direction (front or side), whether it is direct operation or lever transmission, and whether it is front panel wiring or rear panel wiring should be considered when selecting the structural form.

HD11 and HS11 are used in magnetic stations, where the circuit with load is not cut off, and only used for isolation current.

HD12 and HS12 are used in the front side of the switchgear for front-end operation. The blade switch with an arc extinguishing device can cut off the load circuit below the rated current.

HD13 and HS13 are used in the switchgear for front-end operation and maintenance. The blade switch with an arc extinguishing device can cut off the load circuit below the rated current.

HD14 is used in a power distribution box, where a blade switch with an arc extinguishing device can be operated with a load.

2. Selection of Rated Current

The rated current of the blade switch should generally be no less than the sum of the rated current of each load in the circuit being shut down. If the load is an electric motor, it must be considered whether the maximum short-circuit peak current that may occur in the circuit is below the electric stability peak current corresponding to the rated current level (when a short-circuit accident occurs, if the blade switch can pass a certain maximum short-circuit current, the deformation or damage caused by the huge electric power generated by it or the phenomenon that the blade is automatically ejected, the short-circuit peak current is the peak current of the electric stability of the blade switch). If there is more than one, a blade switch with a higher rated current should be used.

4

Common Methods for Inverter Maintenance Testing

In daily maintenance of frequency converters, various problems are often encountered, such as peripheral line problems, poor parameter settings, or mechanical failures. If the inverter is faulty, how to determine which part of the problem is involved is briefly introduced here.

1. Static Test

Test Rectifier Circuit

Find the P and N terminals of the internal DC power supply of the inverter. Adjust the multimeter to the resistance X10 range. Connect the red probe to P and the black probe to R, S, T respectively. The resistance should be about tens of ohms and basically balanced. Reverse the probes, connect the black probe to P, and the red probe to R, S, T sequentially. The resistance should be close to infinity. Connect the red probe to the N terminal and repeat the above steps. The same result should be obtained. If the following results are found, it can be determined that the circuit has an abnormality. A. The three-phase resistance is unbalanced, which can explain the rectifier bridge failure. B. When the red probe is connected to the P terminal, the resistance is infinite, which indicates that the rectifier bridge is faulty or the starting resistor is faulty.

b. Test the Inverter Circuit

Connect the red probe to the P terminal, and the black probe to U, V, W respectively. There should be a resistance of several tens of ohms, and the resistance values of the phases should be basically the same, and the inversion should be infinite. Connect the black probe to the N terminal. Repeat the above steps to get the same result. Otherwise, the inverter module fault can be determined.

2. Dynamic Testing

After the static test result is normal, dynamic testing can be performed, i.e., the power test machine is powered on. The following points must be noted before and after power-on:

a. Before powering on, confirm whether the input voltage is wrong. If 380V power supply is connected to a 220V inverter, it will cause a bomb (fried capacitor, varistor, module, etc.).

b. Check if the connection ports of the inverter are properly connected. If the connection is loose, it may cause abnormal connections, which may lead to inverter malfunctions. In severe cases, a bomb may occur.

c. After powering on, detect the fault display content and preliminarily determine the fault and its cause.

d. If no fault is displayed, first check if the parameters are abnormal. After resetting the parameters, start the inverter under no-load (no motor), and test the U, V, W three-phase output voltage value. If there is a phase loss or a three-phase imbalance, the module or the drive board is faulty.

e. Perform a load test when the output voltage is normal (no phase loss, three-phase balance). When testing, the full load test is the best option.

3. Fault Judgment

a. Rectifier Module is Damaged

Usually caused by grid voltage or internal short circuit. Replace the rectifier bridge with the internal short circuit removed. When dealing with faults on site, it is important to check the user's power grid conditions, such as grid voltage, and whether there are equipment such as welding machines that are polluting the power grid.

b. Inverter Module is Damaged

Generally caused by motor or cable damage and drive circuit failure. After repairing the drive circuit, replace the drive waveform and the module. After replacing the engine board in the field service, you must also check the motor and connecting cables. Run the frequency converter without any faults.

c. No Display after Power On

Generally, the switching power supply is damaged or the soft charging circuit is damaged, resulting in the DC circuit not receiving DC power. If the starting resistor is damaged, the panel may be damaged.

d. Display Over Voltage or Under Voltage after Power On

Generally due to input phase loss, the circuit is aging, and the board is exposed to moisture. Find out its voltage detection circuit and detection points and replace the damaged device.

e. Overcurrent or Ground Short Circuit after Power On

This is generally due to damage to the current sensing circuit, such as Hall components, op amps, etc.

f. Start Display Over Current

Usually caused by damage to the drive circuit or inverter module.

g. No-load Output Voltage is Normal, Showing Overload or Over Current after Loading

This kind of situation is generally caused by improper parameter setting or aging of the drive circuit and module damage.

5

Refrigerator Evacuation and Refrigerant Solution

For the maintenance of refrigeration equipment, evacuation is the second step of general failure. The first is to suppress (not including changing the compressor or changing the tube). In the case of determining that the pipeline is not leaking, the next step is to evacuate. There are two common methods:

1. Pump down with a vacuum pump. It is also possible to use a compressor instead of a vacuum pump, but the pumping time is longer than using a vacuum pump because the compressor (two) is relatively smaller than the vacuum pump. Connect a working valve with a pressure gauge to the process pipe on the refrigerator, one end is welded to the compressor, the other end is connected to the vacuum pump with a liquid adding pipe, the method (valve) door of the watch is opened, and the vacuum pump or external compression is activated. The machine starts to evacuate. When there is no gas exhausted from the exhaust port on the vacuum pump, the pumping is completed.

2. Use your own compressor to evacuate yourself. This method is very suitable for outdoor repairs without the need for a vacuum pump. The method is: if the filter on the original machine is double-tailed, open the working port (originally welded), start the compressor, there will be a lot of air discharged from this port, when the mouth has no gas to drain, block by hand This port, unplug the power. (Be sure to pay attention to safety) Open the filling method door and fill the system with refrigerating liquid. When the working port of the filter has gas discharge, clamp the port with pliers, and then seal the port with gas welding.

Add refrigerant liquid: After the refrigerant liquid filling pipe valve is connected, open the liquid adding door, open (unscrew) one end of the liquid feeding pipe, and tighten the flange when the refrigerant liquid is discharged at the pipe head. Open the watch valve on the compressor, and then turn the refrigerant liquid cylinder upside down to add liquid. When the gauge pressure shows a pressure of 4 kg, close the dosing valve. Powering the refrigerator, the pressure on the watch drops as the machine works. Look at the pressure when the hands are stable. Normally between 0:00 and 0:00, it is normal pressure. The static plus 4 kg is based on the fact that the low pressure of the refrigerator is at least 4 times the pressure at rest. As the working time of the refrigerator increases, the temperature inside the box keeps falling. When the normal charging amount is used, the back pipe should be connected to the dew after running for a period of time. The temperature of the filter is similar to the ambient temperature or the hand is hot. . If the frost on the return pipe indicates that the refrigerant liquid is increased, open the dosing valve to release some, slow down, and observe the return pipe while laying, and close the valve when you see the frost. If the temperature on the return pipe is still not cool or dewed for a long time, open the dosing valve and add some refrigerant.

6

Selection and Maintenance of Low Voltage Motor Fuses

Practice has proved that fuses are simple and effective protection devices for phase-to-phase short circuit, single-phase short-circuit fault, and overload of low-voltage motors. However, if the type and parameters of the fuse are not properly selected or the maintenance is unfavorable, the expected protection is not achieved.

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