A complete collection of symbols for electrical circuits

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 brand

K relay

Ka (NZ) current relay (negative sequence zero sequence)

KD differential relay

KF flash relay

KH thermal relay

Km intermediate relay

Intermediate relay at KOF outlet

KS signal relay

KT time relay

KV (NZ) voltage relay (negative sequence zero sequence)

KP polarization relay

KR dry spring relay

Ki impedance relay

KW (NZ) power direction relay (negative sequence zero sequence)

Km contactor

Ka instantaneous relay; instantaneous with or without relay; AC relay

KV voltage relay

L line

QF circuit breaker

QS disconnector

T transformer

TA current transformer

TV voltage transformer

W DC bus

YC closing coil

YT trip coil

PQS active and reactive apparent power

EUI electromotive force voltage and current

Se experiment button

SR reset button

F frequency

Q — switching device of circuit

Fu — fuse

Fr — thermal relay

Km — Contactor

Ka-1, instantaneous contact relay 2, instantaneous with or without relay 3, AC relay

KT — delay with or without relay

Sb — button switch Q — switch device of circuit

Fu — fuse

Km — Contactor

Ka-1, instantaneous contact relay 2, instantaneous with or without relay 3, AC relay

KT — delay with or without relay

Sb button switch

SA transfer switch

Ammeter pa

Voltmeter PV

Active watt hour meter PJ

Reactive energy meter pjr

Frequency meter PF

PPA phase meter

Maximum demand scale (load monitor) PM

Power factor meter PPF

Active power meter PW

Reactive power meter pr

Var ammeter par

Acoustic signal ha

Optical signal HS

Indicator HL

Red light HR

Green light Hg

Yellow light hy

Blue light HB

White light HW

Connector XB

Plug XP

Socket XS

Terminal board XT

Wire and cable bus w

DC bus WB

Plug in (feeder) bus WIB

Power branch line WP

Lighting branch line WL

Emergency lighting branch line we

Power line wpm

Lighting trunk WLM

Emergency lighting trunk line WEM

Sliding contact wire wt

Closing small bus WCL

Control small bus WC

Small signal bus WS

Flash mini bus WF

Small bus WFS for emergency sound

Forecast sound small bus WPS

Voltage small bus WV

Emergency lighting small bus WELM

Arrester f

Fuse Fu

Fast fuse FTF

Drop out 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

SQP proximity switch

Manual control switch sh

Time control switch sk

Liquid 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

SCR ur

Rectifier VC with power supply in control circuit

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

Trip coil YT

Closing coil YC

Pneumatic actuator ypaya

Electric actuator Ye

Heating device (electric heating) FH

Lamp (light emitting device) el

Air conditioner ev

Heating element ee of electric heater

Induction coil reactor L

Excitation coil LF

Arc suppression coil La

Filter capacitor ll

Resistor rheostat R

Potentiometer RP

Thermistor RT

Photoresistor RL

Varistor RPS

Grounding resistance Rg

Discharge resistance Rd

Start rheostat RS

Frequency sensitive rheostat RF

Current limiting resistor RC

Photocell thermoelectric sensor B

Pressure converter BP

Temperature converter BT

Speed converter BV

Time measurement sensor bt1bk

Liquid level measurement sensor bl

Temperature measurement sensor bhbm


Basic knowledge of electrician

1. Zero on the left and fire on the right

2. For three-phase five wire system, yellow, green, red and light blue are respectively used to indicate double colors (PE) of u, V, W and N protective grounding wires

3. During the operation of the transformer, the current of each phase of the transformer shall not exceed the rated current, and the maximum unbalanced current shall not exceed 25% of the rated current. The transformer should be overhauled regularly after it is put into operation.

4. In the power supply system of the same transformer, it is not suitable to mix protective grounding with protective neutral.

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

6. The secondary side of voltage transformer shall not be short circuited during operation. Because the short-circuit will produce a large short-circuit current, it may burn the transformer, so 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 high voltage from channeling into the secondary side when the primary and secondary coil insulation breaks down, endangering the safety of personnel and equipment.

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

9. The secondary side of current transformer must not be open circuit during operation

10. One end of the secondary side of the current transformer must be grounded to prevent the high voltage of the primary side from channeling into the secondary side when the insulation of the primary and secondary coils breaks down.

11. When the current transformer is connected, the polarity of its primary and secondary coils should be paid attention to.

12. During installation, the wiring must be correct and reliable, and the secondary side is not allowed to connect fuses or switches. 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 before removal.

13. Low voltage switch refers to the disconnector, circuit breaker, fuse, etc. below 1KV

14. The load controlled by the low-voltage power distribution device must be separated clearly, and it is strictly forbidden to control multiple switches and mix them up.

15. The interlocking device between low-voltage power distribution device and self provided generator equipment shall operate reliably. It is strictly forbidden to operate the self provided power generation equipment in parallel with the power grid without permission.

16. Insulation pad shall be laid on the left and right operation and maintenance channels of low-voltage distribution device, and other articles shall not be stacked on the channel.

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

18. When dismantling the equipment: remove the power supply first and then the equipment.

19. When connecting the line: connect the zero line first and then the live line.

20. When removing the line: remove the live line first, and then the neutral line.

21. Low voltage fuse can not 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 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 the rated current of the melt 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 melt is equal to or slightly greater than the rated current of load.

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

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

29. The porcelain plug-in fuse shall be installed vertically, and the qualified fuse shall be used, and other copper wires shall not be used to replace the fuse.

30. The power incoming line of spiral fuse shall be connected to the central terminal of base, and the outgoing line of load shall be connected to the terminal of threaded shell.

31. When replacing the melt, the electrical equipment must be disconnected first to prevent electric arc

32. The fuse shall be installed on each phase line. It is forbidden to install fuse on neutral line of two-phase three wire or three-phase four wire circuit

33. Fuse is mainly used for short circuit protection

34. When the fuse is used for isolation purpose, 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 it safely.

36. The function of knife switch is to isolate the power supply for safe maintenance.

37. The rubber covered porcelain bottom knife switch 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 of the three pole rubber cover knife switch is reduced properly, it can be used to operate the motor control switch infrequently

39. The incoming line of three pole rubber cover knife switch power supply shall be on the incoming line base of the static contact end, and the electrical equipment shall be connected to the outgoing line base of the fuse below.

40. When the knife switch is in the cut-off state, the handle should be downward. When the knife switch is in the on state, the handle should be upward. It cannot be upside down or flush mounted

41. The function of triode rubber cover knife switch is short circuit protection. Isolate the power supply and maintain it safely.

42. The shell of low voltage load switch shall be reliably grounded.

43. When the automatic air switch is selected as the main switch, there must be obvious disconnection points on the incoming line side of these switches, and the obvious disconnection points can be isolated switch, knife switch or fuse, etc.

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 to the same circuit, so as to improve the power factor.

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

47. The wall switch should be 1.3m from the ground and the wall socket should be 0.3m

48. The pull switch should be 2-3m above the ground

49. The watt hour meter should be 1.4-1.8m above the ground

50. The entrance line should be 2.7m above the ground

51. There should be no joints for roads, first and second class highways, tramways, main rivers, weak current lines, special cableways, etc.

52. The plastic sheathed wire is mainly used for outdoor laying, and shall not be directly buried in the plastering layer for concealed laying.

53. It is generally required that the total cross-sectional area (including insulation layer) of the conductor in the pipe should not be greater than 40% of the cross-sectional area of the inner diameter of the pipe.

54. There shall be no joint for the wire in the pipe, and the joint shall be in the junction box; different power supply circuits, different voltage circuits, mutual standby circuits, working lighting and emergency lighting circuits shall not be installed in the same pipe.

55. When the pipe is steel pipe (iron pipe), the conductor of the same AC circuit must be in the same pipe, and it is not allowed for one conductor to pass through one steel pipe.

56. No more than 8 wires shall be installed in one pipe.

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

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

59. If the length of the conductor through the pipe exceeds 30 meters (semi-rigid pipe), a junction box shall be installed between them.

60. If the length of the conductor through the pipe exceeds 40m (iron pipe), a junction box shall be installed between them.

61. When the conductor passes through the pipe, there is a bending pipe with a length of no more than 20m. A junction box shall be installed between them.

62. The conductor passes through the pipe with two bends, and the length of the pipe is not more than 15m. A junction box shall be installed between them.

63. The conductor passes through the pipe with three bends, and the length of the pipe is not more than 8m. A junction box shall be installed between them.

64. When using multi-phase power supply, the color selection of conductor insulation layer of the same building should be consistent, that is, the protective conductor (PE) should be green / yellow double color line, the neutral line (n) should be light blue, and the phase line should be 65, L1 – yellow, L2 – green, L3 – red. Single phase power supply switch line is red, and white or yellow is generally used after switching.

66. The joint position of the conductor shall not be at the fixed place of the insulator, and the distance between the joint position and the fixed place of the conductor shall be more than 0.5m, so as not to hinder the wire binding and breaking.


Selection of knife switch for board

1. The choice of structural form

Its structure is determined according to its function in the line and its installation position in the complete set of power distribution equipment. If it is only used to isolate the power supply, it is only necessary to select the product without arc extinguishing cover; if it is used to cut off the load, it is necessary to select the product with arc extinguishing cover, which is operated by lever; if the central handle knife switch cannot cut off the load current, other forms can cut off a certain load current, but the knife switch with arc extinguishing cover must be selected. In addition, the structure should be selected according to the front operation or side operation, direct operation or lever drive, front board wiring or rear board wiring.

HD11 and HS11 are used in magnetic station. They do not cut off the circuit with load, but only for isolating current.

Hd12 and hs12 are used in the switch cabinet for front side operation and maintenance. The knife switch with arc extinguishing device can cut off the load circuit below the rated current.

HD13 and hs13 are used in front operation and back maintenance switch cabinet, in which the knife switch with arc extinguishing device can cut off the load circuit below the rated current.

Hd14 is used in power distribution box, in which the knife switch with arc extinguishing device can be operated with load.

2. Selection of rated current

The rated current of the knife switch shall not be less than the sum of the rated current of each load in the circuit to be turned off. If the load is a motor, it is necessary to consider whether the maximum short-circuit peak current in the circuit may be below the peak current of electric stability corresponding to the rated current level (when a short-circuit accident occurs, if the knife switch can be connected with a certain maximum short-circuit current, it will not deform, damage or automatically pop up due to the huge electric force generated, Then the short-circuit peak current is the peak current of the electric stability of the knife switch. If it exceeds the rated current, the knife switch with a higher rated current should be selected.


Common methods of inverter maintenance and detection

In the process of inverter daily maintenance, we often encounter a variety of problems, such as peripheral circuit problems, poor parameter setting or mechanical failure. If the frequency converter fails, how to judge which part of the problem, here is a brief introduction.

1. Static test

a. Test rectifier circuit

Find the p-terminal and N-terminal of the internal DC power supply of the frequency converter, adjust the multimeter to the resistance X10, connect the red meter bar to P, and connect the black meter bar to R, s, t respectively. The resistance value should be about tens of ohm, and basically balanced. On the contrary, connect the black meter bar to the P end, and connect the red meter bar to R, s and T in turn, with a resistance value close to infinity. Connect the red meter rod to the N-terminal and repeat the above steps to get the same result. If there are the following results, it can be judged that the circuit has been abnormal: a. the three-phase imbalance of resistance value can indicate the fault of rectifier bridge. B. When the red meter bar is connected to the p-terminal, the resistance is infinite, so it can be concluded that the rectifier bridge is faulty or the starting resistance is faulty.

b. Test inverter circuit

Connect the red meter bar to the P end, and connect the black meter bar to u, V and W respectively. The resistance value should be tens of ohm, and the resistance value of each phase is basically the same. The reverse phase should be infinite. Connect the black meter bar to the N-terminal and repeat the above steps to get the same result, otherwise the inverter module fault can be determined.

2. Dynamic test

After the static test results are normal, the dynamic test can be carried out, that is, power on test machine. Pay attention to the following points before and after power on:

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

b. Check whether the interfaces of the frequency converter have been correctly connected and whether the connection is loose. The abnormal connection may sometimes lead to the failure of the frequency converter, and in serious cases, the machine may explode.

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

d. If the fault is not displayed, first check whether the parameters are abnormal, and reset the parameters, start the inverter under no-load (no motor connection), and test the U, V, w three-phase output voltage value. In case of phase loss or three-phase imbalance, the module or drive board is faulty.

e. Under the condition of normal output voltage (no open phase, three-phase balance), test with load. When testing, Zui is good for full load testing.

3. Fault diagnosis

a. The rectifier module is damaged

It is usually caused by grid voltage or internal short circuit. When the internal short circuit is eliminated, replace the rectifier bridge. When dealing with the fault on site, we should focus on checking the user’s power grid, such as the grid voltage, whether there are welding machines and other equipment that pollute the grid.

b. Inverter module damaged

Generally due to motor or cable damage and drive circuit failure. After repairing the drive circuit, replace the module when the drive waveform is good. After replacing the drive board in the field service, the motor and connecting cable must also be inspected. Operate the inverter after confirming that there is no fault.

c. No display when power on

It is usually caused by the damage of switching power supply or soft charging circuit, which makes the DC circuit have no DC power. If the starting resistance is damaged, it may also be the panel damage.

d. Over voltage or under voltage is displayed after power on

Generally due to input phase loss, circuit aging and circuit board caused by moisture. Find out the voltage detection circuit and detection point, and replace the damaged device.

e. Over current or short circuit to ground after power on

Generally, the current detection circuit is damaged. Such as hall element, operational amplifier, etc.

f. Start display over current

It is usually caused by the damage of driving circuit or inverter module.

g. The no-load output voltage is normal, and overload or over-current will be displayed after loading

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

Leave a Reply

Your email address will not be published. Required fields are marked *