The structure principle, advantages and disadvantages of the current disconnector are analyzed and compared. According to the characteristics of my country's power grid and the mechanism of arrester failure and damage, the technical performance requirements that the disconnector should meet are proposed. A thermal explosion breaker with a new structural principle is designed, and its application is explained. This kind of disconnector has reasonable structure principle, high operational reliability, perfect technical performance, and can be popularized and used.
As a supporting product of the lightning arrester, the disconnector is used in series with the arrester. When the arrester manufacturer fails and is damaged, it can move away, isolate the damaged arrester from the system in time and give a clear label, so as to ensure the normal operation of the system and facilitate the fault point. Find and repair and replace the lightning arrester.
In foreign countries, power distribution type, power station type and line type arresters operating in power grids in countries and regions such as Europe, America, Japan and Southeast Asia have been generally equipped with disconnectors. In China, only a few areas are currently used, and they are mostly used for power distribution. Type lightning arrester. The reasons for this phenomenon are nothing more than two aspects: on the one hand, the performance and function of the current disconnector are not yet recognized and familiar with users, on the other hand, the rationality of the structure principle, the reliability of operation of the current disconnector and our country There are deficiencies and defects in many aspects such as the applicability of the power grid characteristics and the compatibility with the failure mechanism of the arrester, which cannot meet the requirements of use.
In order to make the structure principle of the disconnector reasonable, reliable in operation, compatible with the characteristics of my country's power grid and match with the failure damage mechanism of the arrester, so as to make the popularization and application of the disconnector possible and expand its application range, a new type of product is designed and applied. It is very necessary to use the structure principle of the disconnector and the arrester in conjunction.
1. Structural principle and characteristics
There are two types of separators: thermal explosion type and hot melt type, among which the most commonly used in the world is the thermal explosion type separator.
1.1 Thermal explosion type disconnector
Since GE's silicon carbide valve arrester was introduced into my country in 1984, it has developed from an integrated type to an accessory type, but its structural principle has not been improved.
The structure principle is: a capacitor is connected in parallel with the discharge gap, and the thermal burst tube is placed in the lower electrode of the discharge gap. When the arrester is working normally, the voltage drop of the lightning and operating impulse current on the capacitor is not enough to cause the discharge gap to break down and discharge, and the disconnector will not operate; when the arrester is damaged, the voltage drop of the power frequency fault current on the capacitor will be The discharge gap is broken down and the arc continues to heat the thermal explosion tube. When the thermal explosion tube heats up to about 400 ℃, the separator will act.
Silicon carbide valve arresters must have a series gap due to the lack of non-linearity of the silicon carbide valve, and the power frequency freewheeling value after the arrester is large, and its failure and damage means the complete failure of the arrester, so the silicon carbide valve arrester The failure damage has the characteristic of sudden change. The metal oxide arrester has excellent non-linearity due to the metal oxide resistor, and the power frequency freewheeling value is extremely small after the arrester is activated. Its failure and damage are mainly manifested in two aspects: the arrester collapses due to the gradual aging of the metal oxide resistor , And the internal insulation of the lightning arrester decreases due to poor sealing, which leads to internal insulation flashover. It can be seen that the failure and damage of the metal oxide arrester has the characteristics of gradual change and sudden change.
Therefore, the structural principle of the European type cable joint thermal explosion disconnector matches the failure damage mechanism of the silicon carbide valve arrester and the sudden change in the failure damage mechanism of the metal oxide arrester, but it matches the failure damage mechanism of the metal oxide arrester. The gradual change characteristics in the system do not match, and are not suitable for the characteristics of my country's power grid.
The power systems of 35 kV and below in my country are mostly neutral-point ineffective grounding systems, which is different from the neutral-point effective grounding systems in foreign countries. The single-phase ground fault capacitance current of the neutral point non-effective grounding system generally does not exceed 20 A, most of which are below 10 A, and the small capacity system is even below 2 A, while the neutral point effective grounding system ground fault current is generally up to 100~ 1000A [1]. The ampere-second characteristic curves specified by national standards [2, 3], international standards [4] and American standards [5] all start from 20A with cold-shrinkable cable terminations. Obviously, this is only applicable to neutral-point effective grounding systems. This kind of structural principle of the thermal explosion type disconnector can not ensure the action under the small power frequency fault current, so it is not suitable for the neutral point non-effective grounding system.
1.2 Hot melt disconnector
The structural principle of the hot melt disconnector is: use solder to weld the action rod to the metal oxide resistance piece, and cooperate with the pre-tension spring to form the action mechanism, and use the resistance piece as the heat source. When the arrester is working normally, the lightning and operating impulse current is not enough to make the energy absorbed by the resistance piece melt the solder joints, so the disconnector does not operate; when the arrester fails and is damaged, the power frequency fault current continues to heat the resistance piece, and when the resistance piece heats up When the solder joint is melted to about 200 ℃, the detacher will act.
This kind of structure principle of the hot-melt disconnector uses metal oxide resistors as the heating source, which can achieve successful operation under small power frequency fault currents. Therefore, it is compatible with the characteristics of the neutral point ineffective grounding system and is compatible with metal oxide The gradual characteristics in the damage mechanism of the arrester are matched; but under large power frequency fault currents, it takes a certain time for the resistance piece to heat up to the temperature required to melt the solder joints, which cannot achieve the requirement of rapid action, so it is effectively grounded to the neutral point The characteristics of the system are not applicable, and do not match the mutation characteristics in the failure mechanism of the metal oxide arrester.
1.3 New thermal explosion type disconnector
The thermal explosion type disconnector has the advantages of rapid breaking once it is activated, good arc extinguishing effect and high operational reliability. If the action function under small power frequency fault current can be added to the design of the structural principle, the disconnector can be The technical performance is improved.
The new thermal explosion type disconnector uses a resistor made of conductive silicon rubber in parallel with the discharge gap, which is not only the leakage current channel of the arrester, but also the heat source that operates under the small power frequency fault current of the disconnector, which can make the structure principle of the disconnector It is reasonable, reliable in operation, compatible with the characteristics of my country's power grid and matched with the failure damage mechanism of the arrester.
2. Technical performance requirements
When the disconnector is used in series with the arrester, its technical performance should meet:
a) The normal use conditions should be the same as the arresters used in series;
b) It should have the same withstand characteristics as the arrester;
c) It should have good operating ampere-second characteristics, suitable for the characteristics of my country's power grid and matching with the failure damage mechanism of the arrester;
d) It should have appropriate mechanical strength.
3. Design and calculation
3.1 Structural design
The new thermal explosion type disconnector uses a resistor made of conductive silicon rubber in parallel with the discharge gap. In order to reduce the size of the disconnector, the resistor is made into a ring shape, and the upper and lower electrodes of the discharge gap are respectively placed on the upper and lower end faces of the resistor, and the resistor is compressed by 30% to 40% to achieve tight electrical contact. And play a sealing role, and form a discharge gap at the axis of the ring resistor. The thermal explosion tube is placed in the lower electrode of the discharge gap and is in close contact with the bottom surface of the lower electrode to facilitate heat transfer.
The structural design realizes the miniaturization of the volume, and can be conveniently made into integrated and accessory products.
3.2 Electrical calculation
3.2.1 Discharge gap distance value
The distance value of the discharge gap is proportional to the arc energy after the discharge gap breaks down. For the withstand characteristics of the disconnector, the distance value of the discharge gap should be smaller, and for the operating characteristics of the disconnector, it is desirable to discharge The distance value of the gap is better. The distance value of the discharge gap is generally 0.5 to 3 mm. After the distance value of the discharge gap is determined, the heat transfer between the lower electrode and the heat burst tube can be adjusted through the structural design, so as to achieve the difference between the withstand characteristics and the action characteristics of the separator Unity.
3.2.2 Starting current value of action
The following factors should be considered when determining the initial current value of the disconnector:
a) Under the continuous operating voltage of the metal oxide arrester, if the power-frequency current flowing through the resistor column reaches a few milliamperes, the resistor begins to heat up, showing signs of aging, reaching tens of milliampere hours, it will start When its irreversible aging reaches hundreds of milliamps, its aging speed is obviously accelerated, and when it reaches several amperes, it quickly collapses;
b) Under the action of transient power frequency overvoltage of the metal oxide arrester, when the equivalent salt density is 0.03 g/mm2 (level Ⅲ pollution), the leakage current value of the jacket surface can be as high as hundreds of milliamperes;
c) Small-capacity neutral point ineffective grounding system has a small capacitance current for single phase-to-earth fault, which can be below 2A.
Taking the above factors into consideration, it is appropriate to take 0.5 A for the starting current of the disconnector.
3.2.3 Resistance of resistor
The test shows that the heating value of the resistor 300W is the minimum heating value required for the reliable operation of the disconnector. According to the calculation of P=I2R, in order to make the disconnector operate reliably under 0.5 A power frequency fault current, the resistance value of the resistor should be 1.2 kΩ. When the distance value of the discharge gap is 1mm (its power frequency breakdown voltage is about 2.4 kV), it can be calculated according to I=U/R, so that the power frequency fault current of the discharge gap breakdown discharge is 2A. In this way, the power frequency fault current below 2A all flows through the resistor, and only the resistor is used as a heating source to heat the heat burst tube, so as to realize the reliable operation of the disconnector under the small power frequency fault current; and the power frequency fault current exceeding 2A The voltage drop on the resistor causes the discharge gap to break down and discharge, and the gap arc is used as the main heat source to quickly heat up the thermal burst tube, so that the disconnector can quickly operate under large power frequency fault currents.
The resistance value of the resistor is related to the structure size of the resistor and the volume resistivity of the conductive silicone rubber used. After the structure size design is determined, the required volume resistivity can be obtained by adjusting the formulation process of the conductive silicone rubber to obtain the required volume resistivity. The required resistance.
4. Application of European-style cable glands
The use of the disconnector and the arrester in series can ensure the safe operation of the system and realize the maintenance-free of the arrester. The new thermal explosion type release device has perfect technical performance, which makes it possible to popularize and apply.
The TLB-1 disconnector is suitable for 10kV and below voltage level arresters and the rated voltage of 36kV and below the outlet lightning arrester; the TLB-2 type disconnector is suitable for 35kV, 110kV, 220kV voltage level power station type and line type arresters.
The installation of the disconnector should enable the disconnector to move freely and form a sufficient air gap, so that the lightning arrester damaged by the fault can be reliably isolated from the system, so as to ensure that it does not affect the normal operation of the system.
(a) Used for lightning arresters for voltage levels of 10kV and below, and outlet lightning arresters for rated voltages of 36kV and below;
(b) For 35kV, 110kV, 220kV voltage level power station type arresters;
(c) Line type arrester for 35kV, 110kV, 220kV voltage level
The application of the disconnector can avoid system accidents caused by the failure and damage of the arrester, and realize the maintenance-free of the arrester. It is a necessary equipment to ensure the safe operation of the system; the designed new thermal explosion-type disconnector has a reasonable structure and high operational reliability. The characteristics of my country's power grid are compatible with the mechanism of lightning arrester failure and damage. The technical performance is perfect and can be promoted. The arresters of different voltage levels and used in different occasions should be used with suitable disconnectors, and appropriate installations should be adopted. the way.
Yichang Hengyuan Technology Co., Ltd. is a professional manufacturer of European-style cable connectors, plug connectors, cable branch boxes, American elbow connectors, high-voltage vacuum circuit breakers, high-voltage load switches, lightning arresters, zinc oxide arresters, tank arresters, overvoltage protectors, Counters, monitors, heat-shrinkable cable accessories, cold-shrinkable cable accessories, T-shaped heads, wall bushings, European cable accessories, American cable joints, transformer neutral point protection devices, fuses, isolating switches, PT cable heads, elbows Manufacturers of type cable joints, 10kV outdoor terminals, switch cabinets, cable intermediate joints, cable accessories and other products
