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.

Overcurrent protection and overload protection are critical mechanisms in electrical systems, yet they serve distinct purposes. Overcurrent protection focuses on safeguarding against sudden, high-magnitude currents (e.g., short circuits), while overload protection addresses prolonged, slightly elevated currents (e.g., excessive loads). This guide details their core objectives, trigger conditions, action timelines, applications, and typical devices, helping clarify their roles in maintaining electrical safety.

Compact ring main units (RMUs) are widely used in urban areas, roads, residential communities, and other ring network distribution systems, as well as in industrial and mining enterprises for transmitting power to load centers. The hand-in-hand power supply method ensures continuous power supply. In gas-insulated RMUs, the high-voltage live parts are either completely sealed in gas-insulated chambers with IP67 protection or fully encapsulated by metal shielding and touchable solid insulation. As a result, except for the operating mechanism and secondary control protection equipment, the units are entirely unaffected by environmental conditions. The operating mechanism and secondary system compartments are sealed with high IP protection ratings, or their components are encapsulated using environmentally resistant materials, making them suitable for outdoor applications.

​Parallel operation​ involves connecting two or more independent AC power sources (e.g., generators, grids) to share electrical loads seamlessly. This process—synchronization—demands precise matching of voltage magnitude, frequency, and phase angles between systems before interconnection. Critical for grid expansion, backup power, and renewable integration, it enables redundant supply during failures.

A ring-closing operation involves closing a normally open switch within a closed-loop electrical network fed by a single power source. This creates parallel paths to redistribute loads without interruption, primarily for maintenance or network reconfiguration. Key prerequisites are voltage difference under 5%, phase angle alignment below 5 degrees, and pre-calculation of induced circulating currents to avoid equipment damage. Distinct from connecting independent systems, this procedure requires advanced monitoring but avoids synchronization complexity. Strict protocols using real-time sensors and simulations ensure safe execution, making it fundamental for resilient distribution networks like ring-main units (RMUs) in urban grids.

This article compares the ​synchronism check function​ in line protection devices and the ​synchronizing function​ in dedicated synchronizing equipment. The ​synchronism check function​ serves as a safety interlock for circuit breaker closing operations, while the ​synchronizing function​ enables precise generator synchronization and critical tie-line interconnections with active parameter regulation. Explore core principles, application scenarios, and technical distinctions between these critical power system components.

Transformer protection is critical for maintaining power system reliability. A well-designed ​transformer protection configuration​ must balance speed, selectivity, and sensitivity to prevent equipment damage and outages. ​Primary protection​ (e.g., differential and gas protection) acts instantly for internal faults, while ​backup protection​ (e.g., overcurrent, zero-sequence) provides redundancy for extended coverage. This guide covers key principles, settings, and coordination to optimize ​transformer protection​ schemes for different transformer types and voltage levels.