High-voltage switchgear assemblies are equipment units supplied as complete sets by the manufacturer and assembled on-site to form a high-voltage power distribution system. This system segments the main electrical circuit into several distinct units; within each unit, components such as circuit breakers, disconnect switches, instrument transformers, as well as protection, control, and measurement devices, are centrally mounted within a single integrated cabinet. Multiple such switchgear cabinets can be combined to construct the complete power distribution systems for power plants and substations. The product design aims to ensure the safe, reliable, and efficient operation of the equipment. Its design necessitates a comprehensive consideration of factors including electrical performance, mechanical structure, safety protection, and environmental adaptability. Among these considerations, the "Five Preventions" interlocking function stands as a critical measure for safeguarding both equipment and personnel, while effectively preventing operational errors.
A high-voltage switchgear assembly typically consists of several main compartments: the busbar compartment, the circuit breaker compartment, the relay compartment, and the cable compartment. The busbar compartment serves to aggregate and distribute electrical energy; the circuit breaker compartment houses the core switching devices; the cable compartment facilitates the connection of outgoing cables; and the relay compartment accommodates the protection and control equipment.
The "Five Preventions" associated with high-voltage switchgear assemblies include: preventing the opening or closing of disconnect switches (or isolating plugs) while under load; preventing the accidental opening or closing of circuit breakers; preventing the closing of a circuit breaker while the grounding switch is in the closed position; preventing the accidental closing of a grounding switch while the circuit is energized; and preventing accidental entry into an energized compartment.
The "Five Preventions" interlocking mechanisms can be broadly categorized into three types: mechanical, electrical, and integrated systems. These mechanisms are primarily implemented through mandatory mechanical interlocks-or, alternatively, electromagnetic locking systems-that coordinate the operation of the circuit breaker, disconnect switches, grounding switches, and cabinet doors. Specifically, for draw-out type circuit breakers, the "Five Preventions" interlocking features include: allowing the insertion or removal of secondary plugs only when the breaker carriage is positioned in the "test" position; preventing the withdrawal of the breaker carriage from the "working" position once the circuit breaker has been closed; locking the breaker carriage to prevent its entry into the "working" position whenever the grounding switch is closed; interlocking the grounding switch with the cable compartment cover plate to ensure that the cabinet door can be opened only after the circuit has been properly grounded; and utilizing automatic shutters to mechanically isolate the draw-out circuit breaker from the stationary contacts of the energized busbar section.
The normal operating conditions for complete sets of high-voltage switchgear typically include: an upper limit for ambient temperature generally not exceeding 40°C, and a lower limit generally at -5°C (which may extend to -15°C in severe cold regions); an altitude generally not exceeding 1000 meters; a daily average ambient humidity not exceeding 95%, and a monthly average not exceeding 90%; a seismic intensity not exceeding magnitude 8; and installation in locations free from fire hazards, explosion risks, severe pollution, chemical corrosion, or intense vibration.
The primary electrical components housed within the switchgear cabinet mainly include: high-voltage circuit breakers (such as vacuum or SF6 types), disconnectors, current transformers (CTs), voltage transformers (PTs), earthing switches, surge arresters, high-voltage fuses, load switches, and similar devices. The secondary components (auxiliary equipment) within the cabinet are primarily utilized for monitoring, control, measurement, and protection; common examples include: relays, energy meters, ammeters, voltmeters, wattmeters, microprocessor-based integrated protection devices, signal lamps, pushbuttons, fuses, and the like.
The operational procedures for complete sets of high-voltage switchgear primarily encompass power-on (energizing) and power-off (maintenance) operations. The general steps for a power-on operation are as follows: confirm that the earthing switch is open → push the withdrawable unit (trolley) into the test position and connect the secondary plugs → push the withdrawable unit into the service position → close the circuit breaker. The general steps for a power-off (maintenance) operation are as follows: open the circuit breaker → withdraw the unit to the test position → disconnect the secondary plugs → withdraw the unit completely out of the cabinet → close the earthing switch.
The product design of complete high-voltage switchgear assemblies typically features the following characteristics: electrical equipment is housed within a metal enclosure, resulting in a compact structure and a small footprint; the units undergo integrated factory assembly, minimizing on-site installation workload and shortening the overall construction cycle; and they offer high operational reliability combined with convenient maintenance.
