Automatic fast arc suppression system with the hig

2022-08-06
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High short-circuit impedance transformer type automatic fast arc suppression system

Abstract: a new type of distribution neutral grounding mode is proposed: when a transient single-phase grounding fault occurs, the automatic tracking arc suppression coil is used to realize fast compensation; In case of non instantaneous single-phase grounding fault, the fault line can be correctly selected and tripped. The basic structure and principle of high short-circuit impedance transformer type controllable reactor are put forward. The high short-circuit impedance transformer type automatic fast arc suppression system developed based on this principle has the advantages of excellent volt ampere characteristic linearity, fast response, stepless continuous regulation from zero to maximum current, good compensation effect and strong adaptability to the system. It is an ideal equipment to realize a new grounding mode

key words: distribution arc suppression coil controllable reactor thyristor short-circuit impedance 1 new grounding mode

the selection of distribution neutral grounding mode is closely related to the safe and reliable operation of power system, and it is an important issue that must be paid attention to in urban and rural construction. However, it has not been satisfactorily solved for a long time. With the continuous development of electricity, there is less and less electricity that allows the neutral point to be ungrounded when the capacitive current is less than a certain value. Most of the neutral points of distribution adopt low resistance grounding or arc suppression coil grounding

although the low resistance grounding avoids the overvoltage problem of the system, the tripping rate is too high to meet the increasingly high requirements for power supply reliability, especially in the distribution of overhead lines and cables. At the same time, the huge grounding current during single-phase grounding will increase the ground potential. In serious cases, it will exceed the safety value. After the new machine is used for 1 hour, it may have an adverse impact on the communication lines, low-voltage electrical appliances and personal safety, which is a congenital defect of this method. With the increasing coexistence of power distribution system and telecommunication system, more and more sensitive components (computers, electronic control, power electronics, etc.) are used by users, and the reduction of international standards on the voltage withstand requirements of low-voltage equipment, the insurmountable defect of low resistance grounding mode is becoming more and more intolerable by the society. Especially in the case that the use of cables is gradually increasing and the power is rapidly expanding, resulting in a large increase in the capacitive current, it is very difficult to limit the single-phase grounding fault current to far less than the two-phase short-circuit current by using resistance and meet the overvoltage requirements at the same time, that is, it is very uneconomical to adopt the low resistance grounding method. Therefore, the low resistance grounding method is not only not suitable for the rural areas which mainly rely on overhead lines, but also for the cities which mainly rely on cables and whose capacity is expanding

the automatic tracking arc suppression coil grounding mode avoids a series of problems caused by the huge grounding fault current, and can automatically eliminate the transient grounding fault without affecting the power supply [1,2]. However, the regulations stipulate that the line is allowed to operate with fault for 2h when the line is single-phase grounded, which has high requirements on the insulation level of the system, so some imported equipment (especially cables) are threatened. At the same time, the long duration of fault current is not only harmful to personal safety, but also easy to expand non instantaneous grounding fault into phase to phase short circuit (especially cable). With the gradual replacement of overhead lines by cables, the traditional arc suppression coil grounding method, which does not trip regardless of transient and non transient faults during single-phase grounding, is no longer suitable

the new grounding mode of distribution neutral point is: in case of instantaneous single-phase grounding fault, the automatic tracking arc suppression coil is used to realize rapid compensation, so that the fault current is less than a certain value and the arc is automatically extinguished, so that the system can continue to operate normally without stopping the power supply; In case of non instantaneous single-phase grounding fault, the fault line can be correctly selected and tripped without affecting the normal operation of other non fault lines; At the same time, ensure that the duration of single-phase grounding fault is less than 10s, so that the insulation level of the system can be the same as that of low resistance grounding [3]. This grounding method has both the advantages of low resistance grounding and arc suppression coil grounding, and gets rid of their respective shortcomings. It is an ideal new grounding method that attaches importance to the innovation and utilization of disruptive technology and alternative technology

the realization of this grounding mode requires not only reliable, accurate and fast response small current grounding line selection device and corresponding tripping device, but also high-quality automatic tracking compensation device. The main requirements are: the arc suppression coil has good volt ampere characteristic linearity, fast response, continuous adjustment in a large range, good compensation effect, etc. The existing various types of automatic tracking compensation arc suppression coils, including turn adjustment type [4], air gap adjustment type [5], DC bias type [6], magnetic valve type [7], capacitance adjustment type [8], and other types [9, 10], have some disadvantages and can not meet the above requirements at the same time. This is also the reason why the application of arc suppression coil is limited at present. The new automatic fast arc suppression system composed of high short-circuit impedance transformer reactor described in this paper can meet the above requirements and make the above grounding mode possible

2 main composition of automatic fast arc suppression system

the system is mainly composed of high short-circuit impedance transformer arc suppression coil and controller, and small current grounding line selection device is used as supporting equipment

2.1 high short-circuit impedance transformer type arc suppression coil

the arc suppression coil is a new type of transformer type controllable reactor. The short-circuit impedance between the primary and secondary windings is very large (up to 100% or more), and the secondary windings are short circuited by thyristors. The short-circuit current in the secondary winding is adjusted by adjusting the conduction angle of the thyristor, so as to realize the controllable adjustment of the reactance value. Its principle structure is shown in Figure 1

a special filter circuit is set in the whole device to absorb the harmonic generated when the thyristor is switched on and off and make the reactor output power frequency current. Given that we have to operate and verify the trigger angle of thyristor once a time, wood plastic material has also made rapid development due to its excellent characteristics α When, the fundamental current output by the working coil is:

where IOM is the effective value of the current flowing through the working coil when the thyristor is fully conductive under the rated voltage. The arc suppression coil does not need to adjust the number of turns, the iron core does not need to have an air gap, and does not need a complex DC circuit and any mechanical transmission device. Therefore, the structure is very simple and the same as that of an ordinary transformer. Since the reactance value is adjusted by adjusting the thyristor, the arc suppression coil has extremely fast response speed and can realize stepless continuous adjustment from zero to rated current

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