電工基礎(chǔ)考試試題（Basic examination questions of Electrical Engineering）

1、電工基礎(chǔ)考試試題（Basic examination questions of Electrical Engineering）2007 fall semester electrician foundation final exam paperFill in the blanks (each empty part)1. The circuit is a closed loop consisting of, etc.2. The electricity used in household life is alternating current, and the voltage effective

2、value is volts.3. The safety voltage is volts.4, R1 = 5, R2 = 3, if two resistors are connected in series, the total resistance is omega.5, with multimeter test resistance, every time change rate files, should be re.6 、 constant voltage source is provided, constant current source is provided.7 trans

3、former mainly consists of two parts. The core is laminated.8. The motor consists of two basic parts.9, three-phase alternating current refers to what three-phase?,.Two, multiple-choice questions (each subject points)1, the rated voltage of an electric appliance is 220V, and it should be connected to

4、 the power voltage of 380V.A series capacitor, B series resistor, C shunt resistor, D shunt capacitor2, in general, diodes, transistors, resistors, pins are.A233B332C232D2223. The same battery. The light bulb is powered by two batteries connected in series. The light second is powered by two batteri

5、es in parallel, and the two lamp.A is as bright as B, a light is on, C B is light, D is not sure4, the following components, with filtering function is.A resistor, B inductor, C capacitor, D diode5, electricity can produce magnetism, and when the current is the same, which of the following sets prod

6、uces the greatest magnetic field strength?.A straight wire, B single coil, C coreless solenoid, D with iron core solenoid6, winding parts of the transformer can not be used below what kind of winding system?.A enameled wire B line C D bare copper wire.7, three-phase alternating current, the line vol

7、tage and phase voltage are respectively how many volts?.A220 220B220 380C380 220D380 3808, the closed wire for cutting magnetic induction line movement can produce current, the current size and what factors are irrelevant.A magnetic field strength, B traverse speed, C wire length in magnetic field,

8、D wire movement timeThree, Jane answer (each subject points)1, drawing and explains how to apply the double switch in the two control lamp?2, draw three phase load triangle, star connection, and say about this different connection, plus the voltage on the load each for how much?Four, the calculation

9、 questions (each subject points)1. The resistance of an electric appliance is 5, and the voltage at both ends is 10V. How much is the size of the current through it and how many Ma is it?2, a power use of 2 kilowatts, 3 hours after the normal work, how much electricity?3, a node has four branch conn

10、ections, including I1=2A, I2=3A, I3=1A, in which I1 and I2The inflow node, I3 and I4, flows into the node. How much is the size of the I4?4, transformer primary winding N1 = 500, two winding N2 = 800,If the voltage added to the N1 is 100V, how much is the output voltage at the N2 end V?Electrician c

11、lass three examination questions, 2008, 02, Thursday, 14, 22:28, fill in the blanks1. The rotor of DC motor is composed of armature core, winding commutator, rotating shaft and fan blade. It is an important part of energy conversion.2, the excitation mode of DC motor can be divided into its excitati

12、on, shunt excitation, series excitation and compound excitation.3, DC motor under the rated load operation, the # level should not exceed 1.5 level.4. The rated capacity of three-phase transformer is the maximum apparent power that is allowed to output when the rated voltage of the winding is not hi

13、gher than the rated value. It is equal to two times the product of winding rated voltage and current tick 3 times.5, in the operation of the transformer, the loss caused by the thermal effect of the winding current is usually called the copper loss; loss caused by alternating magnetic field in the c

14、ore can be divided into hysteresis loss and eddy current loss, collectively known as the iron loss.6, because the transformer short-circuit test current is larger, but the voltage is very low, so generally in the high pressure side pressure, so that the low voltage side short circuit.7. The part of

15、the motor winding unit embedded in the slot is called the effective part, and the part outside the slot is called the part.8, three-phase asynchronous motor rotating magnetic field is decided by the power of the phase sequence, in operation, if the rotation of the rotating magnetic field changed, th

16、e rotors steering will change.9, Y series AC motor insulation level is B level.10, synchronous motor rotor with convex pole and hidden pole of two kinds,The rotor of diesel generator and synchronous motor used in general factory is convex type.11, three-phase asynchronous motor speed depends on the

17、magnetic field, the pole number P, slip S and power frequency f.12, winding drying often adopts the following three methods: drying room, drying method, bulb drying method, current drying method.13, arc generation is due to the gap in the gas is free, produce a large number of electrons and ions, so

18、 that the insulating gas into a conductor. The electric energy consumed by the current passing through this free zone is changed into heat and light energy, so the effect of light and heat is emitted.14, RL1 series spiral fuse, the melt is filled with quartz sand. When cutting off an electric curren

19、t, the quartz sand rapidly extinguishes the arc.15. The opening distance of contactor contact is the shortest distance between the static and dynamic contact points when the contact point is completely separated.16 、 the main contact of the DC contactor is difficult to extinguish because of analyzin

20、g the arc generated by the DC circuit than the AC arc, so the arc extinguishing device is usually used.17, the purpose of setting up zero protection for bridge crane is to prevent the accident of motor starting when the controller is not in the zero position and is sent again after the power has bee

21、n cut off.18 、 the fixed parts of magnetic electronic instrument mainly include, and, and the rotor part, mainly by the needle, pointer and composition.19, in the RLC series circuit is equal to, when the current in the circuit reaches the maximum value, this phenomenon is called.20. The principle of

22、 three-phase load connected to three-phase power supply line is that if the rated voltage of the load is equal to the voltage of the power line, the load should be connected by delta;If the rated voltage of the load is equal to the supply phase voltage, the load should be Y connected.21, the most ba

23、sic logical operations refer to and / or, or not, three operations.22, transformer cooling methods are oil immersed, self cooled, oil immersed air-cooled, strong oil air-cooled.23, input no-load transformer will produce inrush current, its value can reach the rated current of 68 times.24. The parall

24、el operation of the transformer shall meet three conditions of equal change ratio, same connection group and short circuit voltage.25, when measuring insulation resistance, the factors affecting accuracy are temperature, humidity and the degree of dirt on the insulation surface.26. The absorption of

25、 insulating medium is the ratio of the insulation resistance in 60 seconds to the insulation resistance in 15 seconds.27 、 the main circuit for the DC system to provide power supply is the main switching circuit, the control and protection circuit, the accident lighting circuit, the signal circuit a

26、nd so on.28, the storage capacity of Ni Cd batteries is determined by the terminal voltage of the battery, not by the repetition.29, over-current protection action current according to avoid maximum load current to adjust.30, gas protection is based on the transformer internal fault will produce and

27、 decompose the gas characteristics of the set.31, when the running voltage exceeds 1.1 times the rated voltage of capacitor, the capacitor shall be run out of operation. The rated voltage of the capacitor is.32 、 work in electrical equipment,To ensure the safety of the organization measures work tic

28、ket system, operation ticket system, inventory site and comprehensive work system, work permit system, work system, work and work continuously monitoring the transfer system and the working end and power transmission system.33, the defects of substation operation equipment are divided into three cat

29、egories, namely, general defects, serious defects and critical defects.34, high voltage equipment grounding fault occurs, indoor personnel should be from the fault point is greater than 4 meters outside, outdoor personnel should be from the fault point is greater than 8 meters.Two 、 judgment questio

30、ns1. The rated power of a transformer is the maximum power output allowed on the two side when the temperature rise is not higher than the allowable temperature rise when the rated voltage is applied to the primary side. (x)2. When the transformer is in use, the core will gradually oxidize and rust.

31、 Therefore, the vacuum carrying current will gradually decrease accordingly. (x)3, three-phase asynchronous motor speed depends on the power frequency and the number of poles, and nothing to do with the slip. (x)4, three-phase asynchronous motor rotor speed is lower, the motor slip ratio is bigger,

32、the rotor electromotive force frequency is higher. (V)5, the use of short circuit tester to check whether the three-phase asynchronous motor winding is one phase short-circuit, for multiple winding or shunt winding, you must first disassemble the branches. (V)6, regardless of the nature of the load

33、transformer, as long as the load current continues to increase, the output voltage will inevitably decrease. (x)7 、 every contactor with arc extinguishing cover must be equipped with arc extinguishing cover, and the motor can be energized before starting. (x)In order to observe the convenience, no-l

34、oad and light load test,Starting motor without arc extinguishing cover allowed.8 、 series magnetic blow out arc method, the direction of magnetic blowing force is independent of current direction. (V) parallel magnetic quenching, independent magnetic blow force direction and current direction. (x)9

35、、 the short circuit ring on the AC contactor core will not release the static and dynamic core when it is broken. (x)10, when the parameter point in the circuit changes, the voltage between two points will change accordingly. (x)11, the magnitude of the self inductance is proportional to the rate of

36、 change in the current in the coil, independent of the magnitude of the current in the coil. (V)12, the inductive circuit, if the supply voltage is kept constant and increase the power frequency, then the total current in the circuit is reduced. (V)13 、 the tube voltmeter can measure the DC, AC, sin

37、e and nonsinusoidal signals accurately. (x)14, electronic oscilloscope can only show the signal waveform, and can not be used to measure the size of the signal being measured. (x)15. The power factor of the pure resistance circuit must be equal to 1. If the power factor of a circuit is 1, then the c

38、ircuit must be a circuit with only resistors. (*)16, from no-load to full load, as the load current increases, the transformer copper consumption and temperature are increased, and the one or two winding in the core of the synthetic magnetic flux also increases. (x)17. When the transformer is in no-

39、load, the active component of its current is smaller, and the reactive component is larger, so the no-load transformer is very low in power factor. (V)18 、 three-phase asynchronous motor with rated load torque, if the supply voltage is lower than the rated voltage, then the current will be lower tha

40、n the rated current.(x)19, oil immersed transformers, explosion-proof tubes on the film if due to external damage and be split, you must make the transformer outage repair. (x)20. Although the size of single-phase asynchronous motor is larger than that of three-phase asynchronous motor of the same c

41、apacity, the power factor, efficiency and overload capacity are lower than that of three-phase asynchronous motor of the same capacity. (V)21. The power distribution unit includes measuring electric appliances, so portable voltmeter and ammeter belong to the power distribution unit. (*)22, high volt

42、age circuit breaker jump refers to the circuit breaker closing and tripping tripping and closing phenomenon. (V)23, each big pole of the large capacity high-voltage isolating switch is provided with two blades, the purpose of which is to increase the sectional area of electric conductivity so as to

43、increase the capacity. (x)24. When the low voltage air circuit breaker is equipped with a shunt release and a pressure release, it is called a double tripping device. (x)25. The purpose of installing reactor is to increase short-circuit impedance, limit short circuit current and reduce voltage fluct

44、uation. (V)26 、 electromagnetic AC contactor and DC contactor are equipped with short circuit ring to eliminate the vibration and noise of the core. (x)27, in flammable and explosive places live line work, as long as the attention to safety and prevent electric shock, generally not dangerous. (x)28,

45、 explosion-proof appliance factory when the butter is to prevent rust, use should not be erased. (x)29. Generally speaking, the better the quality of relay, the simpler the connection, and the less the number of contacts, the more reliable the protection is. (V)30, gas (gas) relay can respond to all

46、 the faults of transformers and make corresponding actions.(x)Four. Questions and answers1, in the single-phase bridge rectifier circuit, if there is a two stage short circuit, open circuit or reverse connection, what will happen?Answer: in the single-phase bridge rectifier circuit, if there is a di

47、ode short circuit, will become half wave rectification, the other half wave power supply circuit; if there is a diode circuit breaker, it will form a half wave rectifier, if there is a diode connected in reverse, the circuit can not afford rectification, no current flows through the load.2. What are

48、 the main functions of transformers in power systems?Answer: the main function is to replace the voltage to facilitate the transmission of power. When the voltage is raised by the step-up transformer, the loss of the line can be reduced, the power supply economy can be increased, and the aim of tran

49、smitting the power over long distance can be achieved, and the voltage drop can satisfy the users need of using voltage at all levels.3. What are the main parameters of the transformer?Answer: (1) (2) rated voltage; rated current; rated capacity; (3) (4) (5) no-load current; no-load loss; short circ

50、uit loss (6); (7) impedance voltage; (8) winding connection diagram, phase diagram and connection symbol.4. Why is the temperature rise of transformer winding set at 65?Answer: Transformer in operation to produce iron loss and copper loss, the two parts of the loss of all converted to heat, so that

51、the core and winding insulation aging. Affect the service life of the transformer, so the national standard stipulates that the insulation of transformer windings adopts class a insulation and the temperature rise of winding is 65 degrees centigrade.5 、 what is the harm to the operation of the break

52、er when its speed is too high or too low?Answer: points, closing speed is too high,Will cause the running mechanism or related parts to bear more than enough mechanical stress to cause damage to parts or shorten service life.The brake speed is too low, especially the brake initial speed low, unable

53、to clear the fault quickly, if the closing speed is too low, the circuit breaker to short-circuit fault, can not overcome the effect of closing contact power, contact caused by vibration or stagnant, can make the contact loss.6, voltage transformer should pay attention to what?Answer: (1) Y-Y- wirin

54、g; (2) Y-Y wiring; (3) V-V wiring.7, the use of voltage transformers should pay attention to what?Answer: should pay attention to the following points:(1) the band should first protect the voltage transformer and automatic device, to prevent misoperation can be related to the protection and automati

55、c device disabled; (2) if the automatic switch device or manual switching device is provided with a voltage transformer, the protection belt and automatic device can not stop; (3) discontinued the voltage transformer, the two side fuse should be removed to prevent reverse charge.8, what role does th

56、e DC system play in the substation?A: DC system provides reliable DC power supply for control signal, relay protection, automatic device and accident lighting in substation, and also provides reliable operation power supply for operation. The reliability of the DC system plays an important role in t

57、he safe operation of the substation, and it is also the guarantee of the safe operation of the substation.9 、 What are the requirements for the installation of contactors?Answer: (1) before and after the inspection installation of contactor contactor coil voltage is in accordance with the actual req

58、uirements, and then wipe the rust proof oil to electromagnetic pole core.Active part and hand split and close contactor, check the contact is good, the pressure is uniform, no blocking phenomenon; (2) the contactor is installed, and the bottom of the incline of the ground should be less than 5 degrees; (3) the contact of the contactor does not allow oil.10. What is reverse bra