工厂供电答案What is the computational load and how is the calculated load calculated at different time limits?A: the calculation load is the maximum assumed load that isexpected to be fixed based on the capacity of the known plant.Load curve and its function in calculating load.Answer: the load curve represents the variation of the power load over time, which reflects the characteristics and laws of the user's electricity.What is a short circuit? What are the types of short circuits? What causes the short circuit failure? What is the harm of short circuit?"Short circuit" refers to the connection between the phase and phase of the electrical system, or between the phase and the ground (or neutral).The short circuit type of three-phase ac system mainly has three phase short circuit, two phase short circuit, single phase short circuit and two phase field short circuit.The main reason for the short circuit is: (1) the insulation damage (2) error (3) lightning stroke or over-voltage breakdown of the electrical equipment.The damage of short circuit: when short circuit temperature rises sharply: can make the insulation accelerate ageing or damage. Generate large electrical power to deform or damage the current ofthe device, considering the stability of short circuit current. Produces a lot of pressure drop: the short circuit current on the nearer the short-circuit point of bus bar, the more powerful the voltage drop, influence and busbar connection of motor or other equipment normal operation of the line.What is an infinite capacity system? What are its features? Why do you think of the power supply as an infinite capacity system when there is a short circuit for the distribution system?Unlimited capacity system: a system with constant voltage, no internal impedance and unlimited capacity.Characteristics of infinite: the infinite capacity of the system voltage constant through your fingers, no internal impedance and capacity infinite system. Its features are: the system capacity is infinite. System impedance is zero and the voltage of the system remain unchanged during the process of short circuit. In fact, any power system has a certain capacity, and has certain internal impedance. When the power supply and distribution system capacity of the power system capacity, when the electric power system has a capacity of 50 times better than the user power supply system, power system impedance is less than the short circuit loop 5% ~ 5% of total impedance, short-circuit point or from the power of the electric distance is far enough, when the short-circuit power system bus voltage is very small, the power system can be considered infinite system.What is a transient short-circuit current? What is a shock short circuit current? What is a steady state circuit current? Them with a shortWhat is the relationship between the effective values of the current periodic component?Transient short circuit current: the effective value of the short circuit current period component in the first cycle after the short circuit.Shock short circuit current: the maximum instantaneous value of short circuit current.Steady state short circuit current: short circuit current of short circuit current after decay.What are the equipment for power distribution?A: a device is divided into the following categories(1)the production and transformation equipment: including motor converts mechanical energy to electrical energy, transform voltage rating of the transformer, high voltage, large current is converted to a low voltage and small current for measurement of transformer secondary equipment, etc.(2)the switch equipment: used to control a circuit on and off, including high voltage circuit breaker, isolating switch, load switch, clutch, breaking magnetic starter, etc.(3)protection equipment: used for circuit over-voltage or over-current protection device, including the short circuit current limiting reactor, high and low voltage fuse, lightning arrester and so on.(4) a current conductor: a soft, hard conductor that transports current, such as various types of overhead lines and power cables.Compensation equipment: used to compensate for reactive power, such as parallel capacitor.(6) complete sets of equipment, will be the primary equipment and secondary equipment, the scheme of circuit connection, combination of electrical devices, such as high and low voltage switchgear, low voltage distribution box, etc.What are the principles of choice for a power distribution device? How to select transformer capacity and table number?A: there are three principles that apply to electrical equipment regardless of its use and work environment.Choose the principle according to the normal working conditionsAccording to the principle of short-circuit conditionPrinciple of effectiveness of cut-off capability of switch equipmentWhat is the basic requirement of the electrical master connection design?Answer: to the electrical 〃> electric main connection design requirement has:(1)the reliability of power supply.(2)it has operational security and flexibility.(3)simple and easy to operate.(4)the economy of construction and operation.The possibility of future expansion should be considered.What are the functions of the secondary loop of the variable match? What is the role of the various parts?Answer: the secondary circuit is divided by function, the circuit breaker control circuit, the signal circuit, the measuring circuit, the relay protection circuit and the automatic device loop etc. Circuit breaker control circuit's main function is to pass circuit breaker operation, when the line fault occurs, the corresponding relay protection movement, the switching circuit breaker tripcircuit of control circuit, the circuit breaker tripped, start signal sound and light signal; The power supply is supplied to circuit breaker control circuit, relay protection device, signal circuit, test system and other secondary circuit.What is the use of current transformer? What items are needed to check for current transformer?Answer: use the note: the second side of the work is not to open; It is also not allowed to use a secondary circuit breaker or a disconnecting switch. The secondary connection leads shall adopt the larger copper wire of the area, and the secondary side of the current transformer shall be shortened by the short wiring in the repair and check. The secondary side has to be grounded on one end.What are the tasks and requirements of the relay protection device?A: relay protection:(1)automatically, rapidly, selectively, the fault device is removed from the power supply system, and the other non-fault parts quickly return to normal power supply.(2)to correctly reflect the abnormal running condition of the electrical equipment and to issue a warning signal so that the operator can take measures to restore the normal operation of the electrical equipment.(3), and the power supply and distribution system of automatic device, such as automatic reclosing and standby power automatic input device, etc.) to improve the power supply reliability of power supply and distribution system.Requirements for secondary protection:According to relay protection, secondary protection should be selective, reliable, quick-acting and sensitiveWhat is the compensation method of 9. 3 capacitor? What are the characteristics of each?Answer: local compensation, group (dispersion) compensate and centralize compensation 3 kinds.High voltage centralization compensation: easy to run management and adjust, and high utilization, and can improve the capacity ofpower transformer.:low pressure group compensation can compensate the low voltage bus bar in front of the high voltage power grid users, regional power grid, and the entire power system reactive power, users can obtain considerable economic benefits, compensation investment is not big, operation maintenance and management is also very convenient.Dispersion compensation on the spot: it is consistent with the stop of electrical equipment, transport, but it can，t use a set ofcontrol devices, with the compensation effect is ideal, but investment is larger, at the same time increase the inconvenienceof administration, and the efficiency is low.What is a short circuit? What are the causes of short circuit failures? What is the harm of short circuit to the power system?Short circuiting means the conductive part of a different potential, including the low resistance of the conductive partto the ground.The cause of short circuit: insulation damage, overvoltage, damage of external forces, violation of operating regulations, animal causing etc.The damage of short circuit to the power system: great power, high temperature, and damage of components. The voltage stops, affecting the normal operation of the electrical equipment; Failure of power and power system stability; Unbalanced current, unbalanced inverse magnetic field, electromagnetic interference etc.What are the forms of short circuit? What type of short circuit is the most likely? Which short circuits are the most harmful?Short circuit: three phase short circuit, two phase short circuit, single phase short circuit. Single phase short circuit is the most likely. The short-circuit current of three-phase short circuit is the largest, so the damage is greatest.What is the power system of unlimited capacity? What are its features? How does the short-circuit current change when a short circuit occurs in an infinite capacity system? Can it suddenly increase?The power system of unlimited capacity is the power system with a large capacity relative to the user's power supply system. The characteristic is that when the load change of the user's power supply system even has a short circuit, the voltage on the feeder bus of the power system transformer is basically unchanged. When a short circuit occurs in an infinite capacity system, due to the load impedance and part line impedance is short-circuited, the circuit current is suddenly enlarged according to ohm，s law. But due to the electric inductance in the circuit, the current can not mutate, causing an excessive process, which is the transient transient process. The short circuit current reaches a new stable state.How does the short circuit current period component and the non-periodic component occur? What is the law?The short circuit current period component is caused by the sudden decrease of the circuit impedance of the circuit after the shortcircuit, and the current of a lot of times should be increased by the ohm，s law.Short circuit current aperiodic component is due to short circuit circuit inductance, and produced according to lenz，s law to maintain circuit current moment from at the beginning of mutation of a reverse offset inp and attenuation of current according to the law of exponential function.5, what is short circuit shock current ish? What is a short circuit transient current I? What is short circuit steady current I infinity?After a short circuit, the ik reaches the maximum, the shortcircuit current is the short circuit current.The practical value of short circuit transient current, which is the effective value of the short circuit current cyclecomponent of the first cycle after the short circuit.Short circuit steady current is the short circuit full current after the short circuit current is decayed.What is short circuit calculating voltage? What does it have to do with the line rating voltage?Because of the most severe short-circuit in the first circuit of the circuit, the voltage of the short circuit is 5% higher than the line rated voltageWhat are the functions of high voltage isolating switches? What are the structural features?Isolate high-voltage power supply, ensure the safety of equipment and line. Disconnect visible disconnect after clearance, there isno specific arcing device, do not allow the loading operation, can be on and off of no more than 2 a no-load transformer, capacitor current is not more than 5 a racing line, used with high voltage circuit breaker.6, fuse, high voltage switch, high voltage circuit breaker and low voltage knife switch in selecting, which need to check the ability to break current? Which need to check short circuit and heat stability?What are the conditions for the power transformer to run in parallel?(1)the secondary rated voltage of the transformer must correspond to the same.(2)the impedance voltage of the transformer (short circuit voltage) must be equal.(3)the connection of the transformer must be the same.(4)the capacity of the transformer is as identical or similar as possible, with maximum capacity of less than 3:1.Does current transformer and voltage transformer use time notice?Considerations for current transformers:(1)the second side of the work may not be opened,(2)one side of the secondary side must be grounded,(3)when the current transformer is connected, pay attention to the polarity of the terminal.Use of voltage transformer:(1)the second side of the job may not be short-circuited,(2)the secondary side has to be grounded,(3)the transformer is aware of the polarity of the terminal when connected.What are the basic requirements for the main wiring in the factory? What are the drawing methods for the main wiring diagram of the transformer distribution? What are the applications for?The basic requirements for the main wiring of the factory transformer are safe, reliable, flexible and economical.Master wiring diagram: system master wiring diagram - used for the operation of transformer distribution.Device type master wiring diagram - used in the construction drawings for changing distribution.Which conditions should be considered in the selection of theswitch site?General principles of choice of address:It is near the center of the load center without violent vibrationor high temperatureIt is convenient for dust and no corrosive gasesIt's close to the side of the power supplyEquipment is easy to transport without explosive hazardsWhat is the connection of the high and low voltage circuit?The wiring method is: radial, trunk, ring.The composition of overhead lines and cable lines.Composition: wire, pole, insulator, line, gold, etc.What are the conditions for the selection of wire and cable?Heating conditions, voltage loss conditions, economic current tight, mechanical strength.The basic requirements of power supply in factories:Safety: personal accidents and equipment accidents should not occur in the supply, distribution and use of electricity.Reliable: meet the requirement of electric power users for the reliability of power supply.Quality: meet the requirement of electric power users on the quality of voltage and frequency.Economy: there is less investment in the power supply system, lower operating costs, and minimized the consumption of non-ferrous metals.What is the operating mode of the power source of the power system in the three-phase ac power system? What are the characteristics of a neutral grounding system and a neutral grounding system?Neutral running mode:Neutral ground system, neutral ground system, neutral grounding system.The two relative voltage increases to the square root of three times when the neutral grounding system is neutral. The single-phase ground capacitance current is three times that of the capacitance current at the normal running time.When the neutral ground system is grounded by the impedance grounding system, the other two relative voltage increases to the square root of three times, reducing the ground current. In a power system with a single-phase grounded capacitance current greater than a certain value, the neutral point of the power supply must be operated in an arc.When the neutral ground system of neutral ground system is grounded, the other two relative voltage is constant, and it becomes asingle-phase earth short circuit.。
