Addtime：2023-06-05 13:40:06 Resource：ShenGaosuo Electric Co., Ltd.

The disconnector plays an important role in the power system such as isolating the power supply, changing the operation mode of the system, separating the small load current, and performing reverse operation. Due to its simple operating principle and structure, there is usually no strict overhaul cycle regulations, and it is generally carried out with the overhaul of the main equipment according to the convention. However, with the oil-free transformation of circuit breakers, the transformation of unmanned substations and the gradual transition of substation equipment from regular maintenance system to state maintenance system in recent years, the overhaul cycle of main equipment is gradually extended, so the problems of outdoor disconnectors in operation have risen sharply, directly affecting the power supply reliability and safety of the system. This article analyzes some fault problems of AC disconnectors, and proposes solutions based on the problems.

1. Technical requirements for high-voltage AC disconnectors

In the power grid, high-voltage AC disconnector is used to combine and divide non-load circuits and electrical equipment, and its functions mainly include the role of transmitting power and safety isolation, that is, in the closed state can reliably pass the normal working current and the abnormal (fault) current in a specified short time, and in the open state, there is an insulation distance and obvious disconnection point between the contacts that meet the specified requirements, so that the load-side power equipment and the power supply are safely isolated. The functional requirements for the disconnector are relatively small, so its structure is relatively simple, there is no arc extinguishing device, and it cannot be used to turn on and off the load current. High voltage AC disconnector is an outdoor structure, most of which operate under relatively harsh outdoor conditions, directly exposed to the atmospheric environment to work, vulnerable to environmental and climatic conditions, product design and manufacturing should fully consider this factor, to ensure that rain, wind, ice, snow, dust, cold and heat and other conditions can work reliably.

2. Common faults of disconnector switches

The common types of faults in the operation of the disconnector are as follows: porcelain bottle breakage failure, mechanism problems, and conductive circuit heating. In the operation of the system, the disconnector has many defects and failures, involving many problems. It can be summarized as mechanism problems, including operation jamming and closing and opening gate is not in place, rust, water ingress and moisture, lubrication dryness, mechanism jamming, auxiliary switch failure, etc., these defects to varying degrees lead to abnormal switch opening and closing, refusal and closing opening is not in place; Secondly, the poor contact of the conductive system makes the conductive circuit heat abnormal, the reason is that the switch contact spring fails to make the contact poor or the closing is not in place, as well as the conductive circuit is loose, cracked, etc., and there is also the problem of poor conductive circuit structure; The biggest threat to safe operation is the broken failure of porcelain bottles, which has the most serious impact.

2.1 Porcelain bottle breakage failure

The disconnector that occurs this kind of fault is especially 220kV level, some develop into major accidents, so the impact is great, pillar insulator and rotating porcelain bottle fracture problems have occurred over the years, some are old products that have been in operation for many years, and some are new products that have just been put into operation for more than a year.

Insulator fracture is related to the quality of the product of the electroporcelain factory, but also related to the overall quality of the disconnector, the uneven pouring of the insulator, and the problem of cement glue. In addition, the lack of strict quality inspection methods also leaves hidden dangers to the operation, defective and hidden insulators are not detected, and after being assembled into products, they pose a great threat to safe operation.

In addition to supporting the insulator, the rupture failure of the rotary insulator also occurs from time to time, and the rotating insulator is mainly affected by torsion during operation, and the porcelain bottle fracture accident can not be effectively prevented so far.

The problem of porcelain insulator fracture, must be comprehensively treated, first from the source, insulator manufacturers to strict process, stable production process, each insulator should be carefully inspected, to ensure that qualified products can leave the factory, disconnector manufacturers to do a good job of purchased parts, strengthen inspection, improve the overall quality of disconnectors. Compare the operating torque of the same type of disconnector during manual operation, and avoid forced operation if it is difficult to operate. A better way is to carry out the pilot and promotion of the new technology of defect detection of porcelain bottles with the disconnector pillar, and further research and develop online monitoring of porcelain bottle defects. It is recommended that during minor repair or overhaul inspection, the number of no-load mechanical operations should be appropriately increased to improve the probability of porcelain bottle defects exposed in power failure operations, and some maintenance is only operated 2~3 times, which is too little.

2.2 Institutional issues

Mechanism problems are manifested as refusal or disconnection and closing are not in place, which often occur during reverse operation. In many cases, the fault will not expand, and temporary maintenance and treatment can be carried out on site, which of course will delay the power transmission time. Most of the problems occur with the old GW4 and GW7 switches, and the GW6 disconnector has had automatic opening failure after closing (mainly due to poor balance spring material and workmanship, and even the balance spring rust during operation); GW10 and GW11 products have had incorrect adjustment of the angle of the three-phase arm of the gate knife, the angle of the output shaft flange of the mechanism is not adjusted in place, and the sector gear burst teeth, resulting in the joint joint flange and the mechanism flange connection screw being cut off, the limit switch cast of the mechanism being interrupted, and the closing gate not in place.

When the disconnector is put into production at the factory or just after installation, the closing and opening operation is still relatively normal. But it won't be long before a year or two later, and all kinds of problems will arise. Some of them cannot turn during operation due to water ingress of the mechanism, some will bend the connecting rod during operation, and even twist the twist between the rotating porcelain bottle and the sliding spool, and some will break at the welding of the connecting rod and cannot be operated. In short, various failures can be caused due to the problem of mechanism jamming.

Operation failure is first of all mechanical transmission problems, the early use of the mechanism box is easy to enter water, condensation and moisture, rotating bearing waterproof performance is poor, and can not add lubricating oil, long-term non-operation, mechanism jamming, bearing rust, forced operation often leads to component damage and deformation. In addition, the transmission structure design of the product is unreasonable, and the operating resistance is also an important reason. Some products have improper matching of the closing limit of the conductive rod with the motor, which causes turbine cracking during operation. Some GW4 type disconnector switch gate knife mechanism transmission spindle is connected with the vertical drive shaft, using a semi-cylindrical anastomosis structure, in the electric operation due to the half-cylindrical deformation of the relative displacement, so that the closing gate is not in place. There is also a rust of the grounding knife, which makes the shaft pin break and cannot be operated. In addition, there are auxiliary switch problems, including switching is not in place or poor contact contact, resulting in electric operation failure, such problems, in the design and manufacturing stage to carry out careful analysis and experimental research, and responsible for the factory test of each switch, must not leave defects to the operation site.

Water ingress in the disconnector mechanism box and water ingress in the bearing part are common. The rust problem of metal parts is also very serious, including housings, connecting rods, shaft pins, springs, etc. The rain cover on the intermediate box of the existing GW6 switch will be rusted to the point that it cannot be touched. The operating mechanism box shell will also be severely rusted. Coupled with improper lubrication measures, the mechanical transmission fails, and the conductive contact system causes poor contact. Improvement measures such as switching the mechanism box to stainless steel, adopting a dry lubrication process for the contact system, and making the rotating part fully sealed and waterproof to achieve lifelong maintenance-free.

2.3 Conductive circuit heating

2.3.1 Causes and characteristics of disconnector heating

(1) Long operating years, equipment tends to age, static contact finger compression spring characteristics deteriorate, may also be static contact finger unilateral contact, contact clamping spring loose deformation, clamping force is not enough to cause some contacts and moving contacts do not contact, so that the contact surface between the contact between the finger and the moving contact is reduced, there is dirt in the dynamic and static contacts, and the material is easy to oxidize after long-term operation, the contact resistance is too large, and there are obvious burn pits on the fingers. (2) The closing is not in place or the scissor clamp structure is poorly clamped. There is a deviation in the closing angle, resulting in insufficient contact surfaces, insufficient tightening of connecting bolts or excessive bolt breakage. (3) Frequent fever during peak summer load. (4) It is in a stable and large load state all year round.

2.3.2 Treatment of heat generation of disconnectors

(1) Carry out temperature monitoring, and decide whether it is necessary to apply to the dispatch to change the operation mode or reduce the load according to the heating temperature and development speed. (2) Change the way it operates. (3) Overhaul: Disconnector maintenance generally replace static contact spring clamp and burn contact, remove the oxide layer of dynamic and static contact, clean dynamic and static contact, apply conductive glue, tighten bolts, and the thorough way is to replace static contact. The use of moving contact two-step movement rotary or plug-in contact structure will improve product quality, users strengthen maintenance and adhere to infrared monitoring is an effective means to reduce and find conductive circuit heating failure. The operation department should also continue to sum up experience, hoping that through the joint efforts of manufacturers and users, the product quality and operation level of domestic high-voltage disconnectors can be improved.