What Are the Types and Common Faults of HV Switchgear?

High-voltage switchgear is a critical electrical device in power systems. Deterioration in switchgear operating conditions is one of the main causes of power system failures. So, what are the common faults in high-voltage switchgear?

I. Classification of High-Voltage Switchgear

(1) Outdoor and Indoor Types

Based on installation location, high-voltage switchgear can be classified as outdoor or indoor types. Indoor switchgear is commonly used for systems at 10 kV and below. According to primary circuit configurations, they can be further categorized as incoming/outgoing line switchgear, tie oil-switchgear, bus section switchgear, etc. In 10 kV incoming/outgoing switchgear, oil-immersed or vacuum circuit breakers are typically installed. These breakers are usually equipped with spring-operated or electromagnetic operating mechanisms, although some use manual or permanent magnet mechanisms. Different switchgear designs vary significantly in structure, which affects sensor selection and installation.

(2) Fixed and Withdrawable Types

Based on usage, high-voltage switchgear can be divided into fixed and withdrawable (draw-out) types. Historically, power plants preferred withdrawable switchgear for station service systems, while fixed types were more common in utility power supply systems. With technological advances and new product development, traditional practices are evolving. For example, metal-clad withdrawable switchgear has evolved from conventional fixed switchgear. This type features a fully enclosed design with functionally separated compartments. It offers improved operational safety, enhanced interlocking against misoperation, easier maintenance, and significantly increased operational reliability.

(3) Development of High-Voltage Switchgear

In recent years, with the development and widespread adoption of compact vacuum circuit breakers, medium-mounted switchgear (also known as switchgear with circuit breakers mounted in the middle compartment) has rapidly advanced as a new type of metal-enclosed, armored, withdrawable switchgear. Medium-mounted switchgear offers many advantages, the most important being the miniaturization of the draw-out unit and the mechanization of manufacturing processes, resulting in higher precision in trolley and guide rail fabrication.

Some manufacturers even ship the trolley (including the main circuit breaker) and the switchgear cabinet separately, enabling easy on-site assembly and commissioning with guaranteed smooth insertion and withdrawal. Due to excellent interchangeability, performance is minimally affected by uneven floor conditions at the site. This type of metal-clad withdrawable switchgear offers safe, reliable operation and convenient maintenance, leading to its increasing adoption in power supply systems.

II. Analysis of Common Faults in High-Voltage Switchgear

Fault analysis shows that most switchgear failures originate from insulation, conduction, and mechanical issues.

(1) Failure to Operate or Maloperation

This is the most common fault in high-voltage switchgear, with causes falling into two categories. The first is mechanical failure in the operating mechanism and transmission system, such as mechanism jamming, component deformation, displacement or damage, loose or stuck tripping/closing solenoids, broken or loose pins, and latch failure. The second category arises from electrical control and auxiliary circuits, including poor contact in secondary wiring, loose terminals, incorrect wiring, burned-out closing/tripping coils (due to mechanism jamming or faulty selector switches), inflexible auxiliary switch operation, and failures in control power supplies, closing contactors, and limit switches.

(2) Switching and Closing Failures

These faults originate from the circuit breaker itself. In oil-immersed circuit breakers, common issues include oil spraying during short circuits, arc chamber damage, insufficient breaking capacity, and explosions during closing. In vacuum circuit breakers, typical problems are vacuum interrupter or bellows leakage, reduced vacuum level, restriking when switching capacitor banks, and ceramic housing fractures.

(3) Insulation Failures

Insulation performance involves balancing various voltages (including normal operating voltage and transient overvoltages), protective measures (e.g., surge arresters), and insulation strength to achieve a safe and economical design. Insulation faults mainly manifest as: external insulation flashover-to-ground, internal insulation flashover-to-ground, phase-to-phase flashover, lightning overvoltage flashover, flashover, pollution flashover, puncture or explosion of porcelain or capacitor bushings, insulator post flashover, and flashover, puncture, or explosion of current transformers (CTs), as well as porcelain insulator fractures.

(4) Current-Carrying Faults

For switchgear rated 7.2–12 kV, the primary cause of current-carrying faults is poor contact at the isolation stabs, leading to overheating and melting of contacts.

(5) External Forces and Other Faults

These include impacts from foreign objects, natural disasters, short circuits caused by small animals, and other unpredictable external or accidental faults.