Type testing of medium voltage switchgear in accordance with IEC standards may involve two scenarios: First, testing at domestic accredited testing stations in compliance with the IEC 62271 series standards, resulting in test reports that conform to IEC 62271. Second, testing at international STL (Short-Circuit Testing Liaison) testing stations according to IEC standards and STL guidelines.

A 400V PV Low-Voltage Grid-Connection Cabinet is a critical interface device that connects the photovoltaic (PV) power generation system to the low-voltage grid. It is a dedicated distribution panel integrating protection, monitoring, metering, and control functions. It is primarily composed of the following core components:

Switchgear requires the use of many fastening standard parts such as bolts, nuts, washers, and rivets. It is essential to select appropriate standard parts based on different applications to ensure functional requirements are met while enhancing product safety and cost-effectiveness.

  Incoming Line Configuration: Marine switchgear systems are powered by multiple diesel generators operating in parallel. Each incoming line must be equipped with voltage transformers for accurate voltage measurement on the supply side.

   The typical service life of medium-voltage switchgear is approximately 20 years. After prolonged operation, various issues may arise, such as insulation aging, increased temperature rise, circuit breaker mechanism jamming, and loss of vacuum, all of which pose significant risks to continued operation. Replacing entire units requires substantial financial investment and time, whereas retrofitting offers a rapid solution to address safety hazards, revitalize the equipment, and ensure continued safe operation.

 Even for the same voltage level, different standards may require verification of both power frequency withstand voltage and lightning impulse withstand voltage. For instance, some regions like Southeast Asia and Australia require 11/12 kV switchgear with a power frequency withstand voltage of 28 kV but a lightning impulse withstand voltage of 95 kV. Standard domestic 12 kV switchgear cannot meet this requirement; enhanced insulation type, high-altitude type products, or using a higher-rated switchgear (e.g., 24 kV) to substitute for a lower one ("using a higher rating to cover a lower one") may be necessary.

  High-voltage electrical equipment carries voltages ranging from several thousand to millions of volts. These high voltages are conducted through busbars, which must be isolated from the ground and supported by non-conductive insulation components. In addition to the normal operating voltage, high-voltage systems are subject to switching overvoltages and lightning impulse overvoltages, which can be 3 to 8 times the operating voltage. Insulation components must therefore withstand both the normal operating voltage and these overvoltage conditions while maintaining insulation integrity.

Gas-insulated switchgear (GIS) primarily refers to a cabinet for housing switching devices, enclosed by a metal steel plate shell with doors or cover panels to allow access for installation and operation. The switchgear includes various components such as disconnectors, load switches, earthing switches, etc., each serving specific functions.

The design of switchgear must account for numerous factors, with insulation being paramount. An insulation scheme must be established, determining the method of insulation—whether air insulation, gas insulation, solid insulation, or air compound insulation, among others. For pure air insulation, the applicable standards for air insulation clearance distances must be met.

In regions with high humidity, condensation frequently occurs. While the primary circuit is sealed within the gas compartment and remains unaffected, protective measures must be implemented for the operating mechanism, secondary circuits, and special attention should be paid to condensation in the fuse compartment. For instance, an industrial user in Australia installed a ring main unit (RMU) inside an outdoor enclosure. The unit was powered on in the morning and switched off at night, resulting in no load during non-operational hours. One day, during a fuse replacement, severe corrosion was found on the fuse holder. Although the fuse compartment cover and the compartment itself were fully sealed, meeting IP67 requirements, and the compression of the silicone rubber ensured the power-frequency withstand voltage between the high-voltage fuse and the cabinet, it was initially perplexing how moisture could have entered the fuse compartment.