Junior high school maintenance electrician test questions - Solutions - Huaqiang Electronic Network

GW MB10F 0.8A 1000V rectifier bridge

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

SMD aluminum electrolytic capacitor

Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

1. Fill in the blank 1. The rotor of the DC motor is composed of armature core, winding commutator, rotating shaft and fan blade, which is an important part of energy conversion.
2. The excitation mode of DC motor can be divided into other excitation, shunt excitation, series excitation and compound excitation.
3. When the DC motor is running under rated load, its # grade should not exceed 1.5.
4. The rated capacity of the three-phase transformer is the maximum apparent power that can be output to ensure that the temperature rise of the primary unit does not exceed the rated value when the rated voltage is applied to the primary winding. It is equal to √ 3 times the product of the rated voltage of the secondary winding and the rated current.
5. When the transformer is in operation, the loss caused by the thermal effect of the current in the winding is usually called copper loss; the loss caused by the alternating magnetic field in the core can be divided into hysteresis loss and eddy current loss, collectively referred to as iron loss.
6. Because the current is large when the transformer is short-circuited, and the applied voltage is very low, it is generally pressurized on the high-voltage side to short-circuit the low-voltage side.
7. The part of the AC motor winding unit embedded in the slot is called the effective part, and the part of the outer part of the slot is called the part.
8. The steering of the rotating magnetic field of the three-phase asynchronous motor is determined by the phase sequence of the power supply. If the steering of the rotating magnetic field changes during operation, the steering of the rotor changes.
9. The insulation class of Y series AC motors is Class B.
10. The rotor of synchronous motor has two kinds of salient pole and hidden pole. The rotor of general diesel generator and synchronous motor for factory is convex.
11. The speed of the three-phase asynchronous motor depends on the magnetic field pole pair P, the slip ratio S and the power supply frequency f.
12, winding drying often uses the following three methods of drying room drying method, bulb drying method, current drying method.
13. The arc is generated because the gas in the contact gap is released, and a large amount of electrons and ions are generated, so that the insulated gas becomes a conductor. The electrical energy consumed by the current passing through this free zone is converted into thermal energy and light energy, thus emitting light and heat effects.
14, RL1 series spiral fuse, the inside of the melt is filled with quartz sand. When the current is cut off, the quartz sand can quickly extinguish the arc.
15. The contactor contact opening distance is the shortest distance between the static and dynamic contacts when the contact point is completely separated.
16. The main contact of the DC contactor is in the analysis of the arc generated by the DC circuit than the AC arc? It is difficult to extinguish, so the arc extinguishing device is usually used.
17. The purpose of the zero-position protection of the bridge crane is to prevent the motor from starting and causing an accident when the controller is not at the zero position and the power is turned off after the power is cut off.
18, the fixed part of the magnetic and electronic instrument mainly has ?? and ??, the rotor part is mainly composed of ??
19. When the RLC series circuit is equal, the current in the circuit reaches the maximum value. This phenomenon is called.
20, the principle of three-phase load connected to the three-phase power supply line is: If the rated voltage of the load is equal to the power line voltage, the load should be Δ-coupled; if the rated voltage of the load is equal to the power-phase voltage, the load should be Y-coupled.
21, the most basic logical operation refers to the three operations of AND, OR, and NOT.
22, the cooling method of the transformer is oil immersed from cold, oil immersed air, strong oil and air cooling.
23, when the input of the no-load transformer, the magnetizing inrush current will occur, and its value can reach 6~8 times of the rated current.
24, the parallel operation of the transformer should meet the three conditions of equal ratio, the same connection group, and the same short-circuit voltage. 25, When measuring the insulation resistance, the factors that affect the accuracy are temperature, humidity and the degree of contamination of the insulation surface.
26, the absorption of the insulating medium is the ratio of the insulation resistance at 60 seconds to the insulation resistance at 15 seconds.
27. The circuit that supplies power from the DC system in the substation has a main closing circuit, a control protection circuit, an accident lighting circuit, and a signal circuit.
28, the amount of electricity stored in the cadmium nickel battery is judged according to the terminal voltage of the battery, not based on the specific gravity.
29, the operating current of the overcurrent protection is set to avoid the maximum load current.
30. Gas protection is set according to the characteristics that will generate and decompose gas when the internal fault of the transformer.
31. When the operating voltage exceeds 1.1 times the rated voltage of the capacitor, the running capacitor should be taken out of operation, and the rated voltage of the capacitor of the factory is.
32. In the work of electrical equipment, the organization measures to ensure safety include work ticket system, operation ticket system, inventory site and comprehensive payment system, work permit system, work supervision system, work interruption and work transfer system, and work termination and power transmission system.
33. There are three types of defects in substation operation equipment, namely general defects, serious defects and critical defects.
34. When a ground fault occurs in a high-voltage equipment, all indoor personnel should be more than 4 meters away from the fault point, and outdoor personnel should be more than 8 meters away from the fault point.
2. Judgment Question 1. The rated power of the transformer refers to the maximum power allowed by the secondary side when the temperature rise does not exceed the allowable temperature rise when the primary side is applied with the rated voltage. (×)
2. When the transformer is used, the iron core will gradually oxidize and rust, so the vacuum load current will gradually decrease accordingly. (×)
3. The speed of the three-phase asynchronous motor depends on the power frequency and the number of pole pairs, and has nothing to do with the slip rate. (×)
4. The lower the rotational speed of the three-phase asynchronous motor rotor, the larger the slip of the motor and the higher the rotor electromotive frequency. (√)
5. When applying the short-circuit tester to check whether the three-phase asynchronous motor winding is short-circuited by one phase, for the windings of multiple parallel or parallel branches, each branch must be disassembled first. (√)
6, no matter what kind of load the transformer, as long as the load current continues to increase, its output voltage will inevitably decrease. (×)
7. Any contactor with an arc-extinguishing hood must be energized to start the motor after the arc-extinguishing hood is installed. (×)
For the convenience of observation, when the no-load and light-load test are carried out, the motor can be started without the arc-extinguishing cover.
8. In series magnetic blowout mode, the direction of magnetic blow force is independent of current direction. (√) Parallel magnetic blowout mode, the direction of the magnetic blow force is independent of the current direction. (×)
9. The short circuit ring on the core of the AC contactor will not release the moving iron core. (×)
10. When the parameter point in the circuit changes, the voltage between two points will also change. (×)
11. The magnitude of the self-induced electromotive force is proportional to the rate of change of the current in the coil, independent of the magnitude of the current in the coil. (√)
12. For an inductive circuit, if the power supply voltage is kept constant and the power supply frequency is increased, the total current in the circuit is reduced. (√)
13. The tube voltmeter can correctly measure DC, AC, sine and non-sinusoidal signals. (×)
14. The electronic oscilloscope can only display the waveform of the signal under test, but it cannot be used to measure the size of the signal under test. (×)
15. The power factor of a purely resistive circuit must be equal to 1. If the power factor of a circuit is 1, the circuit must be a circuit containing only resistors. ( × )
16. From no-load to full load, as the load current increases, the copper loss and temperature of the transformer increase, and the combined magnetic flux of the primary and secondary windings in the core also increases. (×)
17. When the transformer is in no-load, the active component of the current is small, and the reactive component is large. Therefore, the transformer with no-load operation has a low power factor. (√)
18. For a three-phase asynchronous motor with rated load torque, if the power supply voltage is lower than the rated voltage, its current will be lower than the rated current. (×) 19. If the film on the explosion-proof pipe of the oil-immersed transformer is cracked due to damage by external force, the transformer must be powered off and repaired. (×)
20. The volume of a single-phase asynchronous motor is larger than that of a three-phase asynchronous motor of the same capacity, but the power factor, efficiency, and overload capability are lower than those of a three-phase asynchronous motor of the same capacity. (√)
21, the power distribution device includes measuring electrical appliances, so portable voltmeters and ammeters belong to the power distribution device. ( × )
22, "jumping" of the high-voltage circuit breaker refers to the phenomenon that the circuit breaker is closed and then jumped off, jumped and closed. (√)
23, large-capacity high-voltage isolating switch is equipped with two blades on each pole, the purpose is to increase the conductive cross-sectional area, thereby increasing the capacity. (×)
24. When the low-voltage air circuit breaker is equipped with a shunt release and a voltage loss release, it is called a double trip device. (×)
25, the purpose of installing reactors is to increase the short circuit impedance, limit the short circuit current, reduce voltage fluctuations. (√)
26, electromagnetic AC contactor and DC contactor are equipped with a short circuit ring to eliminate the vibration and noise of the core. (×)
27, when working in a flammable or explosive place, as long as you pay attention to safety and prevent electric shock, there is generally no danger. (×)
28, the butter coated by the explosion-proof electrical equipment is to prevent rust, should not be erased when used. (×)
29 Generally speaking, the better the quality of the relay, the simpler the wiring, and the fewer the number of contacts included, the more reliable the protection device is. (√)
30. The gas (gas) relay can respond to all faults of the transformer and act accordingly. (×)
Third, the question and answer questions 1, in the single-phase bridge rectifier circuit, if there is a diode short circuit, open circuit or reverse connection, what will happen?
Answer: In a single-phase bridge rectifier circuit, if one diode is short-circuited, it will become half-wave rectified, and the other half-wave power supply will be short-circuited. If there is a diode open circuit, half-wave rectification will be formed. If there is a diode reverse connection, The circuit does not rectify and no current flows through the load.
2. What is the main role of the transformer in the power system?
A: The main function is to replace the voltage to facilitate the transmission of power. After the voltage is boosted by the step-up transformer, the line loss can be reduced, the power transmission economy can be improved, and the long-distance power transmission can be achieved, and the voltage drop can meet the needs of users who use voltage at all levels.
3. What are the main parameters of the transformer?
Answer: (1) rated voltage; (2) rated current; (3) rated capacity; (4) no-load current; (5) no-load loss; (6) short-circuit loss; (7) impedance voltage; Connection diagram, phasor diagram, and connection group label.
4. Why is the temperature rise of the transformer winding specified as 65 °C?
Answer: The transformer will generate iron loss and copper loss during operation. Both of these losses will be converted into heat, which will insulate the core and winding. It affects the service life of the transformer. Therefore, the national standard stipulates that the insulation of the transformer winding adopts Class A insulation and the temperature rise of the winding is 65 °C.
5. What is the hazard to the operation when the circuit breaker's split and closing speed is too high or too low?
Answer: If the speed of opening and closing is too high, the running mechanism or related components will exceed the mechanical stress that can be withstood, resulting in component damage or shortened service life.
The opening speed is too low, especially when the initial speed of the opening is low, the fault cannot be quickly removed. If the closing speed is too low, when the circuit breaker is short-circuited, the action of the contact closing electric power cannot be overcome. If the head vibrates or is stagnant, the contacts will burn out.
6. What should I pay attention to in the voltage transformer?
Answer: There are (1) YY- wiring; (2) YY wiring; (3) VV wiring.
7. What should I pay attention to when I disable the voltage transformer?
A: The following points should be noted:
(1) First of all, the protection and automatic device of the voltage transformer should be considered, and the relevant protection and automatic device can be deactivated to prevent misoperation; (2) If the voltage transformer is equipped with an automatic switch device or a manual switching device The protection and automatic device it carries may not be deactivated; (3) When the voltage transformer is deactivated, the secondary fuse should be removed to prevent reverse charging.
8. What role does the DC system play in the substation? A: The DC system provides a reliable DC power supply for control signals, relay protection, automatic devices and accident lighting in the substation, and also provides reliable operating power for operation. The reliability of the DC system plays a vital role in the safe operation of the substation and is the guarantee for the safe operation of the substation.
9. What are the requirements for installing a contactor?
Answer: (1) Check whether the voltage of the contactor coil meets the actual use requirements before and after the contactor is installed, and then wipe off the anti-rust oil on the pole surface of the electromagnetic core. And manually separate the movable part of the contactor, check whether the contact of each contact is good, whether the pressure is consistent, and whether there is jamming; (2) when the contactor is installed, the inclination of the bottom surface and the ground should be less than 5 degrees; 3) The contacts of the contactor are not allowed to be oiled.
10. What is the reverse brake?
Answer: When the motor drives the production machinery, in order to stop or reverse quickly, the power can be reversed (any two relative adjustments), then the motor's rotating magnetic field changes direction immediately, thus changing the direction of the torque. Since the direction of rotation is opposite to the direction in which the rotor is rotated by inertia, it acts as a brake. This kind of braking method is quick to persuade, but the power consumption is large. When the braking speed drops to zero, the power supply should be cut off quickly, otherwise reverse power generation will occur.
11. What kinds of situations should I consider when choosing a power system?
Answer: (1) The rated voltage of the cable should be equal to or greater than the rated voltage of the power grid; (2) When selecting the cable according to the long-term allowable load, consider the laying method, soil temperature, number of cables and the surrounding environment; 3) Cable laying method: armored cable should be selected for direct burial, and armored cable for cable trenching can be selected; (4) Consider the cable laying environment.
12, what is lightning protection grounding? What parts of the lightning protection grounding device are included?
Answer: In order to quickly introduce lightning current into the earth, the grounding for preventing multi-purpose lightning is called lightning protection grounding. The lightning protection grounding device comprises the following parts: (1) lightning receiving device; (2) grounding lead-up line; (3) grounding device.
13. What is the safety voltage and what is the safety voltage value?
A: The voltage that the human body touches does not cause any damage to the tissues and organs of the human body is called a safe voltage. According to China's regulations, the safe voltage values ​​are as follows:
65V in buildings without high electrical energy hazards; 36V in buildings with high risk of electric shock; 12V in buildings with special electric shock hazard.
14. Why do the AC contactors sometimes cause a lot of noise during operation and how to deal with them?
A: The main reason for the noise is: the armature is not good. The reason for the poor suction and the treatment method are: (1) The end face of the iron core is dusty, greased or rusted. The treatment method is: wiping, removing the rust with a fine abrasive cloth; (2) the short-circuit ring is damaged or broken. Treatment method: repair the welding short circuit ring or replace the coil with a DC silent running device; (3) the voltage is too low, the electromagnetic suction is insufficient. Treatment method: adjust the voltage; (4) the spring is too hard, and the active part is jammed. Treatment: Replace the spring and repair the jamming part.
15. How to choose a lighting circuit fuse?
Answer: (1) The trunk line insurance should be equal to or slightly larger than the sum of the fuse capacities of the branch lines; (2) the capacity of each branch fuse should be equal to or slightly larger than the sum of the working currents of the lamps.
16. How to choose the thermal relay of the motor? What are the two access methods?
Answer: The selection of the thermal relay is based on the rated current of the motor. Generally, the current range of the thermal element is selected at 1.2 times the rated current. Then select the model and component current rating of the thermal relay.
General thermal relay installation can be divided into direct access and indirect access. Direct access: The thermal relay and AC contactor are assembled together and the thermal components pass directly through the load current. Indirect access: The thermal relay and the current mutual inductance device are used together, and the thermal element passes through the secondary current of the current transformer. This thermal relay current range is selected based on the secondary current through the current transformer.
17. What are the requirements for wire threading?
Answer: (1) The total area of ​​the wires (including the insulating layer) worn in the pipe should not be greater than 40% of the internal cross section; (2) the wires in the pipe are not allowed to have joints and twisting; (3) the wires of the same phase, No matter how many roots should be penetrated into one tube, and different circuit and different voltage line conductors are not allowed to pass through one tube. AC and DC line conductors must not be worn in one tube, and one phase line is not allowed to penetrate separately. Steel Pipe. 18. What is the definition and classification of secondary circuits?
Answer: The secondary circuit is used to monitor the measuring instrument, control the operating signal, all the low-voltage circuits of the relay and the automatic device are called the secondary circuit, and the secondary circuit can be divided into the following circuits according to the power supply and use: (1) current circuit; (2) voltage loop; (3) operating loop; (4) signal loop.
19. What is the role of working grounding?
Answer: (1) reduce the contact voltage of the human body; (2) quickly cut off the faulty equipment; (3) reduce the design insulation level of electrical equipment and power lines.
20, the asynchronous motor's no-load current is the rated current is appropriate?
Answer: The no-load current of large and medium-sized motors accounts for 20%~35% of the rated current, and the no-load current of small motors accounts for 35%~50% of the rated current.
21. What causes the asynchronous motor's no-load current to be too large?
Answer: The reasons are: (1) the power supply voltage is too high; (2) the air gap is too large; (3) the stator winding turns are insufficient; (4) the triangle and Y wiring are wrong; (5) the motor insulation aging.