In the actual electrical and electrical operation, many masters have strong operational ability and high practical operability, but the accumulation of basic knowledge of electricity is relatively weak. In some occasions, sometimes it is unavoidable to make the electrical master embarrassed, and it is also important to master the necessary basic knowledge.
1. What is the purpose of current transformer?
The current transformer converts the large current into a small current in a certain proportion, provides the current for various instrument use and relay protection, and isolates the secondary system from the high voltage. It not only ensures the safety of people and equipment, but also simplifies and standardizes the manufacture of instruments and relays and improves the economic benefits.
2, what are the wiring modes of current transformer?
Wiring modes of current transformers include using two current transformers two-phase V-shaped wiring and two-phase current difference wiring; There are three - phase Y - type wiring, three - phase △ - type wiring and zero - sequence wiring using three current transformers.
3. How many kinds of reactive power sources are there in the power system?
The reactive power sources in the power system are:
1. Synchronous generator; 2. Adjust the camera; 3. Shunt compensation capacitor;
4. Series compensation capacitor; 5. Static compensator.
4, why install a group of ZnO arrester between the power capacitor and its short circuit?
The ZnO arrester can prevent the operation overvoltage which may occur when the power capacitor is in pull or close operation, and ensure the safe operation of the electrical equipment.
5. Why must the secondary side of the VOLTAGE transformer and current transformer be grounded?
The secondary side grounding of the voltage transformer and current transformer belongs to the protection grounding. If the insulation of the primary, secondary, and secondary sides is damaged, the high voltage from the primary side is connected to the secondary side, which threatens the safety of the human body and equipment. Therefore, the secondary side must be grounded.
6. What are the functions of shunt reactor and series reactor?
Line shunt reactor can compensate the capacitive charging current of the line, limit the increase of system voltage and operation overvoltage, and ensure the reliable operation of the line.
Bus series reactors can limit short circuit current and maintain high bus residual voltage. The capacitor bank series reactor can limit the high harmonic and reduce the reactance.
7. What are the characteristics of the connection mode of single bus section?
Single bus sectional connection can reduce the influence range of bus fault and improve the reliability of power supply. When a bus fault, subsection circuit breaker in the relay protection with automatic trip, remove the fault, so that the non-fault bus to maintain normal power supply. For important users, the power supply can be obtained from different segments to ensure that the power supply is not interrupted.
8. What are the disadvantages of double bus connection?
Dual bus has the following disadvantages:
1. The wiring and operation are complicated, and misoperation is easy to occur when switching operation.
2. There are many bus disconnecting switches and the structure of power distribution device is complicated, so the economy is poor.
9, what is the compensation degree of arc suppression coil, what is residual flow?
The ratio of the difference between the inductance current and capacitance current of the arc suppression coil and the capacitance current of the grid is called compensation degree. After the inductor current of the arc suppression coil compensates the capacitor current, the residual current flowing through the ground point is called residual current.
10. When the neutral point of the system is grounded through the arc suppression coil, is there a voltage on the arc suppression coil?
During the normal operation of the system, there is a certain voltage between the network neutral point and the ground due to the unbalance of the three relative ground capacitors of the line, and the voltage value is directly related to the unbalance of the capacitance. Under normal conditions, the voltage generated at the neutral point shall not exceed 1.5% of the rated phase voltage.
11. Why does the battery discharge?
Battery self-discharge as long as the cause is due to the plate containing impurities, the formation of local small battery, and the formation of short circuit at the two poles of the small battery, causing battery self-discharge. In addition, due to the different density of the battery electrolyte, the electromotive force of the plate is not equal, which will also cause the battery self-discharge.
12. Why should the battery be charged and discharged regularly?
Regularly check the charge and discharge, also called the charging and discharging is on operation of float charging battery, after a certain time to make the plate material on a larger charge and discharge reaction, in order to check the battery capacity, and can be found in aged cells, timely maintenance process, in order to ensure the normal operation of the battery, charge and discharge is usually not less than once a year on a regular basis.
13. What is the unbalanced current of the transformer? What are the requirements?
The unbalanced current of the transformer refers to the current difference between the three - phase transformer windings. In the three-phase three-wire transformer, the unbalance degree of each phase load shall not exceed 20%, and in the three-phase four-wire transformer, the neutral line current caused by the unbalance current shall not exceed 25% of the rated current of the low-voltage winding. If the above requirements are not met, the load should be adjusted.
14. Which part of the winding is hottest during normal operation of the transformer?
The temperature of windings and cores is high at the top and low at the bottom. For oil-immersed transformer windings of general structure, experience has proved that the hottest temperature is 70%-75% in the direction of height, one-third of the transverse winding from the inner diameter of the winding, and the hottest spot of each transformer winding should be determined by test.
15. What causes the abnormal sound of the transformer?
The main reasons are as follows: 1. Over load. 2. Internal contact is bad, discharge ignition. 3. Some parts are loose. 4. There is grounding or short circuit in the system. 5. The starting of a large motor makes the load vary greatly.
Why is the integrated reclosing device installed on the 16,220 kV line?
220kV line is the neutral direct grounding system, because the single-phase grounding fault of the system is the most, so the circuit breaker is equipped with phase separation operating mechanism. When single-phase grounding fault occurs, the protection action only jumps off the circuit breakers on both sides of the faulty line, and the phase without fault does not trip, which can prevent the operation of overvoltage, improve the stability of the system; When the phase fault occurs, the protective device action jump off the two sides of the three-phase circuit breaker, on the other hand, when the need for single-phase trip single-phase coincidence, three-phase trip three-phase coincidence, can also be completed by comprehensive reclosing.
17. How many operation modes does the comprehensive reclosing have? How does each work?
Comprehensive reclosing is realized in three ways by switching switch QK.
1. Comprehensive reclosing mode. After a single-phase fault trips, the single-phase overlaps. The three-phase phase overlaps on a permanent fault, and the three-phase phase overlaps on a phase-phase fault. The three-phase phase overlaps on a permanent fault.
2. Three phase reclosing mode. If any type of fault occurs, the three phases are skipped and the three phases overlap (check the same period or no voltage). If the fault occurs on a permanent fault, the three phases are skipped.
3. Single-phase reclosing mode. After a single-phase fault jumps off, the single-phase overlaps. When the single-phase fault overlaps on a permanent fault, the three-phase fault jumps off. When the phase-phase fault jumps off the three-phase fault, the three-phase fault does not overlap.
18. What is surface discharge?
In actual insulation structures, solid dielectric is often surrounded by gas or liquid dielectric, such as line insulators filled with air, and oil-immersed transformer solid insulation surrounded by transformer oil. In this case, the discharge tends to occur along the interface of the two dielectric, such a discharge is called surface discharge.
19. What are the factors affecting the surface discharge voltage?
Factors affecting surface discharge voltage are as follows: 1. Uniformity of electric field. 2. The difference degree of dielectric coefficient of the dielectric surface. 3. Rain or no rain. 4. Degree of filth.
20. What parts does the theoretical line loss in the power loss consist of?
1. Variable loss, the size of which varies with the load, is proportional to the quadratic power or current of the load through the components of the network. Including all levels of voltage overhead transmission, distribution lines and cable conductor copper loss, transformer copper loss, regulator, voltage regulator, reactor, wave stopper and arc suppression coil and other equipment copper loss.
2. Fixed loss, it has nothing to do with the current of the load power through the element, and is related to the voltage added to the power network element, it includes the iron loss of the transmission and distribution transformer, the iron loss of the regulator, voltage regulator, reactor, arc suppression coil and other equipment, the corona loss of 110kV and above voltage overhead transmission line; Dielectric loss of cable capacitor, leakage loss of insulator, iron loss of current and voltage transformer; Loss of voltage windings and other accessories of customer's electricity meters.