Summary of electrical basic knowledge 89 cases! Part one

- Sep 08, 2017 -

Summary of electrical basic knowledge 89 cases

Part one

1. What is protective grounding?

A: is usually not charged electrical equipment, metal shell through the grounding body and the earth close connection.

2. What is repeating grounding?

A: The transformer on the low side of the neutral point of the power distribution system, the zero line on one or more through the grounding of the power distribution system, the zero line of one or more through the grounding device and the earth tightly connected The

3. What is the grounding short circuit?

A: The operation of the electrical equipment and power lines, if the insulation damage caused by the live part of the metal parts touch or ground directly connected with the earth when the ground short circuit.

4. Which electrical equipment must be grounded or protected?

A) 1) generator transformer, high and low voltage electrical appliances; 2) power equipment transmission; 3) transformer secondary coil; 4) switchboard and control panel

5. What is the short-circuit current?

A: When a short circuit occurs, the short-circuit current flows into the ground through the access point.

6. What is the ground voltage?

A: electrical equipment occurs when a phase ground, the ground part of the large potential is equal to zero potential difference

7. What is the use of the inverted switch?

A: mainly used to control the small-capacity motor to do positive and negative full-pressure start

8. What is the effect of repeated earthing?

A: 1) reduce the ground voltage of the leakage device enclosure; 2) reduce the risk of zero line disconnection

9. What is overload protection?

A: When the line or equipment load exceeds the allowable range can delay the power off a protection

10. What are the conditions for overheating electrical equipment?

A: The main heat generated by the current, including the following:

(1) short circuit; (2) overload; (3) poor contact; (4) iron core heat; (5) poor heat dissipation.

11. Electrical equipment high pressure, low pressure of the points

A: high pressure: equipment to ground voltage above 250V. Low voltage: equipment to ground voltage below 250V.

12. What is the load rate? How to increase the load rate?

A: The load rate is the percentage of the average active load and the maximum active load in a certain period of time to measure the difference between the average load and the maximum load. To increase the load rate, the load is mainly reduced and the average load is increased.

13. What is the abnormal sound of the motor running?

A: electrical aspects: (1) winding ground or phase short circuit: (2) winding short-circuit; (3) winding or part of the polarity of the coil wrong; (4) phase loss operation. Mechanical aspects: (1) fan blade touch end cover; (2) bearing wear or ball damage; (3) bearing inner ring and shaft contact is not strong; (4) sweep chamber.

14. After the three-phase asynchronous motor can not start how to do?

(3) check the motor fuse; (4) check the motor terminal board connector; (5) check the motor is open circuit; (2) check the motor switch is good; (2) check the motor switch is good; (6) check the stator and rotor winding with or without short circuit fault.

15. How can the motor start with a direct start?

A: (1) star a triangle starter; (2) since the lotus transformer starter; (3) resistance, reactance buck starting.

16. What is the utilization of the transformer?

A: The ratio of the actual output power of the transformer to its rated output power.

17. How to determine the four basic state of electrical equipment?

A: 1) "running" status, circuit breakers and disconnectors are closed, power and equipment connected. "Hot standby" state, the circuit breaker has been disconnected, the power is interrupted, the equipment is out of service, but the disconnector on both sides of the circuit breaker is still connected. 3) "cold standby" status, device breaker and disconnector are disconnected. 4) "overhaul" status, equipment circuit breaker and disconnector disconnect, and has been hanging sign, no shelter, while grounding.

18. How to improve the power factor?

(3) triangular wiring motor to star wiring, manual adjustment, the installation of the capacitor is the most Economy, the most effective way.

19. How to choose the connection method of the capacitor bank?

A: should be based on the voltage of the capacitor, protection and capacity to choose. When the rated voltage of the capacitor and the network rated voltage consistent with the use of triangular wiring; when the capacitor rated voltage is lower than the network rated voltage, the use of star wiring

20. What is overcurrent protection?

A: When the short circuit on the line, its important feature is the rapid increase in current in the line, when the current exceeds a certain value, the reaction of the current switch and the action of the protection device.

21. What are the parts of the secondary circuit?

(2) AC voltage circuit, by the voltage transformer secondary side and three-phase five-column voltage, the transformer opening triangle (2) AC voltage circuit, by the voltage transformer secondary side and three-phase five-column voltage, the transformer opening triangle (3) DC circuit, all the circuit of the DC system; 2) According to the circuit to use points: (1) measuring circuit (2) relay protection circuit

22. What is a capacitor?

A: Capacitor, also known as capacitive, is a static electrical equipment that can hold the charge, when the charge is released when the formation of current is a kind of energy storage device

23. What is power, current, voltage, resistance, circuit, electric power?

A: The amount of electricity charged by the object is called the amount of electricity, the unit is Coulomb. Current --- charge in the conductor to move the formation of the current, the unit called amps, referred to as security. In 1 second through the conductor cross-sectional area of electricity is 1 Coulomb, the current intensity is 1 amp. Voltage - the voltage difference between a two points in the circuit called the voltage, the unit is volts. Resistance - the resistance of the current in the conductor is called resistance. The unit is ohm. Circuit --- current through the path called circuit. The circuit consists of four basic parts of voltage, electrical appliances, switches and connecting wires. Power supply is the device to generate electricity; electrical light bulbs, electric fans, etc .; connecting wires connected with power, electrical appliances and switches, and must be connected into a circular path. Electric power --- that the unit time to do the number of power, referred to as power, in watts. 1 hour consumption of 1 kilowatt of electricity called "1 kWh"

24. What is the motor?

A: The motor is the electrical equipment that converts electrical energy into mechanical energy and outputs mechanical energy. Commonly used is a three-phase AC asynchronous motor. All kinds of cotton spinning machinery are widely used to drive the motor.

25. What is a contactor? What is the role of the contactor?

A: The contactor is an automatic electromagnetic switch that closes and disconnects the contact by the action of an electromagnetic force, causing the current to turn on and off. Not only that, the contactor also has a low-pressure release function, suitable for frequent operation and running distance control.

26. What is a fuse?

A: Fuse, also known as fuse or fuse, it is an effective electrical protection device, to avoid short circuit damage

27. What is a thermal relay?

A: The thermal relay makes use of current effects, made of overload protection of electrical appliances

28. What is FireWire?

A: The generator or transformer three-phase coil connected to each other into a star, from the beginning of the coil leads to three lines called phase line, three phase line also called FireWire.

29. What is zero line?

A: The three-phase coil of the common point, called the neutral point, derived from the neutral point of the wire and the earth equipotential, because the earth is zero potential, so the neutral point called zero. Neutral line is called zero line

30. What is the ground wire?

A: In order to prevent electrical insulation damage and was electrocuted, commonly used wire and the earth connected together, this wire is called protection ground.

31. What is the measure of safe electricity?

A: Fire line must be into the switch, so that the switch is in a broken state, electrical appliances are not charged.

32. What is a low voltage electric shock protector?

A: It is an effective protection against low voltage electric shock. If an electric shock occurs in a low voltage network or insulation is damaged, it will immediately send an alarm signal or command to cut off the power supply, or the device is protected.

33. What is gas spacing?

A: In order to prevent the body close to the charged body or to prevent the collision of objects such as vehicles too close to the charged body, to prevent electrical short-circuit accidents and therefore cause a fire, between the charged body and the ground, charged body and charged body, equipment must be maintained between a certain Of the safe distance.

34. What is safe voltage?

A: The human body and electrical contact, the body of the organization will not cause any damage to the voltage for the safety voltage.

35. Three-phase electricity imbalance hazards?

A: As the three-phase voltage imbalance in the induction motor stator will produce a reverse rotation of the magnetic field, then the induction motor is running under the action of two negative magnetic field, because the positive sequence to the magnetic field than the reverse magnetic field, so the motor The rotation direction is rotated in the positive order direction, but the rotor reverse sequence resistance is very small, so the reverse sequence current is large, because there is reverse sequence current and the existence of the magnetic field to produce a large braking force, will reduce the power.

36. What is the three electricity?

A: Three power refers to plans to use electricity, saving electricity, safe electricity.

37. Star-Triangle (Y- △) Buck Start?

A: For the rated voltage of 380V when running for the triangular connection of the motor at the start, you can first stator winding into a star, to be combined and then connected into a triangle, this method is called star-shaped triangular step-down start.

38. What is the earth?

A: When the electrical equipment ground fault occurs, the ground current through the ground wire and grounding into the ground, and to the local hemispherical evacuation. In the vicinity of the grounding body, the hemispherical surface is small, the resistance is large, the ground current through the voltage drop here is also large, the potential is high; in the distance from the grounding body, hemisphere larger, small resistance, voltage drop Also small, its potential is also low To the grounding body as the center, the spherical radius of about 20m, the potential actually approaches zero, commonly known as the earth or ground.

39. What is the grounding body?

A: The metal conductor or metal conductor group in direct contact with the earth's soil is called a grounding or grounding group.

40. What is the grounding wire and grounding device?

A: Connect the electrical equipment to the ground part of the metal conductor with the grounding body, called the ground wire. The grounding body and the grounding line are called the grounding device.

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