Common Faults and Defects of Disconnecting Switches and Their Prevention

I. Common Defects and Fault Analysis

During system operation, disconnecting switches experience many defects and faults, involving various quality issues. The most threatening to safe operation is the fracture of porcelain insulators, followed by overheating of contacts, sluggish movement, jamming of mechanisms, incomplete closing or opening, and flashover of porcelain insulators. The common faults of disconnecting switches mainly include the following:

1. Porcelain insulator fracture fault. The CT volt-ampere characteristic and ratio comprehensive tester only needs to set the test voltage/current value, and the equipment can automatically boost voltage/current and quickly display the volt-ampere characteristic curve or ratio, polarity and other test results of the transformer. Porcelain insulator fracture is related not only to product quality but also to the overall quality of the disconnecting switch and the operation method. Improper control during the firing process of porcelain insulators may cause issues such as incomplete firing, uneven density, and poor cementing of the porcelain parts. Coupled with lax quality inspection, some low-quality porcelain insulators may be assembled into products and put into operation, posing a great threat to safety. Improper operation methods or excessive force when operators open or close the disconnecting switch can also easily cause damage to the porcelain insulators.

2. Overheating of the conductive circuit. Abnormal heating of the conductive circuit often occurs during operation, mostly due to fatigue of the compression springs of the stationary contact fingers, deterioration of their characteristics, single-side contact of the stationary contact fingers, and increased contact resistance after long-term operation. During operation, the compression springs of the stationary contact fingers are under long-term compression. If the working current is large and the temperature rise exceeds the allowable value, their elasticity will deteriorate, creating a vicious cycle and causing burnout. This is the main cause of contact overheating. In addition, poor silver plating process on contacts, easy wear exposing copper, dirty contact surfaces, insufficient insertion of contacts, and corrosion of bolts leading to reduced pressure on the contact surfaces of the wire clamp are also causes of overheating.

3. Mechanism problems. Mechanism problems manifest as operational failures, such as refusal to operate or incomplete closing or opening, often occurring during switching operations, affecting the safe operation of the system. Due to poor sealing of the mechanism box or corrosion and water ingress, the mechanism becomes severely corroded, lubrication dries up, and operational resistance increases. This makes operation difficult and can also cause damage to components, such as fracture of transmission gears and bending of connecting rods.

4. Transmission difficulties. Corrosion of the transmission system of the disconnecting switch causes high transmission resistance, and even refusal to open or close. For example, during operation, the base bearing may rust and seize, making operation impossible. This is caused by dry copper sleeves on the main shaft of transmission components, dirty bearings, and dried-up grease.

　

II. Prevention and Control of Common Defects and Faults

The causes of the above defects or faults in disconnecting switches include not only manufacturing processes and material selection quality issues, but also improper maintenance. To ensure the safe operation of disconnecting switches, ensuring their initial quality is key. How to ensure initial quality can be approached from the following two aspects:

1. Strengthen type selection work

It is necessary to extensively collect information on the operation of disconnecting switches in the system, and select products with reasonable structure, excellent design, and high overall quality.

2. Carry out technical transformation

(1) The problem of porcelain insulator fracture must be comprehensively addressed. First, ensure the overall structure of the disconnecting switch is reasonable. Second, strengthen the selection of porcelain insulator manufacturers. It is possible to designate that disconnecting switch manufacturers use products from porcelain insulator manufacturers with good quality and reputation. In addition, non-destructive testing technology can be carried out to regularly inspect porcelain insulators. Operating personnel should strengthen monitoring, especially observation of the cemented surfaces of porcelain insulators. During operation, methods should be appropriate; for example, avoid forced operation when difficulties are encountered.

   (2) Overheating of the conductive circuit and flashover of porcelain insulators seriously affect the safe operation of equipment. The compression springs of the stationary contact fingers can be replaced with stainless steel springs, and stainless steel bolts or hot-dip galvanized high-strength bolts can be used and tightened with a torque wrench; adjust the insertion depth of contacts and clean the contact surfaces, or use self-cleaning contacts similar to those of Siemens. At the same time, use infrared thermometry to regularly detect heating in conductive parts, and handle problems promptly when found.

(3) Corrosion is the primary issue affecting the safe and reliable operation of disconnecting switches. Regular anti-corrosion treatment should be carried out, and lubricants should be applied to all transmission parts, especially molybdenum disulfide lubricant, which has better performance than grease. Brass bushings should be replaced with steel-based surface sintered bronze composite bushings with modified polytetrafluoroethylene, and the outer surface and ends should be tin-plated to prevent corrosion. The mechanism box should use high-quality stainless steel products. The base of the disconnecting switch should be modified by drilling holes in the base, and molybdenum disulfide should be added regularly during operation to ensure the bearings do not rust.

　

III. Periodic Maintenance of Disconnecting Switches

The traditional maintenance method for disconnecting switches is periodic maintenance. Periodic maintenance is based on past experience in equipment operation and maintenance, and a maintenance cycle is predetermined. For example, the overhaul cycle for disconnecting switches is 6 years. When the specified maintenance cycle is reached, the equipment is maintained according to plan.