Medium-voltage switchgear available in markets such as Europe and Asia is manufactured in accordance with International Electrotechnical Commission (IEC) standards. However, these switchgear units typically feature rear cable connections, making the installation and maintenance of such equipment difficult.

Furthermore, this type of switchgear utilizes "epoxy post-type" current transformers mounted at the rear; should a fault occur, these components cannot be replaced in the field.

According to IEC standards, full compartmentalization between sections is not required; consequently, cooling of the circuit breakers is significantly easier due to inter-compartment ventilation.

The Institute of Electrical and Electronics Engineers (IEEE) and American National Standards Institute (ANSI) standards—applicable to medium-voltage metal-clad switchgear in the North American market—impose rigorous requirements. Under these standards (and the UL testing designed to verify compliance), circuit breakers are tested while enclosed within the switchgear assembly, where cooling is severely restricted; consequently, limiting temperature rise becomes a major engineering challenge. Without specific modifications to ensure adequate cooling of the circuit breakers, IEC-designed switchgear units must be significantly de-rated (operated below their nominal capacity) to meet North American compliance requirements.

Additionally, equipment designed to IEEE/ANSI standards mandates insulation for busbars, which further complicates the cooling of critical current-carrying busbars located within specific compartments of the switchgear. Alternatively, expensive heat sinks must be employed to mitigate temperature rise. In compact switchgear footprints, the integration of heat sinks presents a formidable engineering challenge and poses significant hurdles regarding compliance with the required lightning impulse withstand voltage levels.

Recent advancements in vacuum circuit breaker technology have significantly enhanced both the performance and reliability of these devices. Modern vacuum interrupters feature superior contact materials—such as chromium-copper—and utilize contact systems based on either Axial Magnetic Field (AMF) or Radial Magnetic Field (RMF) principles. Furthermore, these circuit breakers are driven by permanent magnets (supplemented by solenoids) and incorporate built-in capacitors to store operational energy, alongside electronic tripping mechanisms. Compared to mechanically (spring-operated) driven circuit breakers, these devices possess fewer moving parts and have demonstrated superior reliability during rigorous lifecycle ("torture") testing, as well as in real-world installations across the globe. The ABB VM1 and Eaton VCP-TL serve as prime examples of this type of permanent-magnet-driven circuit breaker. Designed with significantly fewer moving components, these circuit breakers are engineered to perform 100,000 switching operations without failure. These circuit breakers bear a striking resemblance to low-voltage circuit breakers; provided they meet the rigorous design challenges set forth by ANSI/UL standards, 15 kV metal-clad switchgear would occupy a footprint approximately 25% smaller than that of low-voltage switchgear handling equivalent power loads. Furthermore, the reliability of such medium-voltage switchgear would be significantly higher. Products of this nature would yield substantial space savings for mission-critical data centers, maritime vessels, and various other applications.

During the design phase of this new metal-clad switchgear, the following parameters were carefully considered:

*   Complete front-access operation, installation, and maintenance capabilities

*   Target dimensions for the 1200A rating: 24 inches (609.6 mm) wide x 60 inches (1524 mm) deep x 96 inches (2438 mm) high

*   Arc-resistant design (Type 2A)

*   Integrated infrared (IR) viewing ports and observation windows

*   Front-accessible 600V Current Transformers (CTs) and front-connected cabling

*   Draw-out type circuit breakers, Potential Transformers (PTs), and Control Power Transformers (CPTs)

*   Fully insulated busbars

*   UL and cUL listed in accordance with ANSI/IEEE standards (covering both metal-clad and arc-resistant features)

Based on our extensive experience, it was abundantly clear that comprehensive simulation would constitute the optimal approach for identifying a suitable solution to such a multi-dimensional optimization problem. IEM conducted extensive mathematical analyses covering the following aspects:

(1)  The thermal characteristics of the switchgear, to investigate temperature rise and identify potential "hot spots" under rated current conditions;

(2)  Electromagnetic force analysis of the switchgear under fault conditions, such as short circuits;

(3)  Dielectric analysis during lightning impulse testing;

(4)  Analysis of arc and gas propagation, as well as the pressure generated within various switchgear compartments during arc-fault events.

The benefits derived from this extensive simulation process enabled us to define an initial solution, which was subsequently utilized to construct prototype units for physical testing. Had we not leveraged the advantages of such comprehensive analysis, arriving at a solution would have necessitated an extensive trial-and-error process—a method requiring a vast number of physical samples and incurring prohibitively high testing costs. Note: While fully complying with the requirements of the IEEE C37.20.2 standard—including fully insulated busbars, a temperature rise margin of 10°C below the standard limit, complete compartmental isolation, internal arc withstand capability (2A), and specialized material surface treatments—this product departs from the traditional American 36-inch-wide, double-tier circuit breaker design. Instead, it features a compact 24-inch, single-tier configuration. Key design features include front-access installation and maintenance, a spring-operated circuit breaker mechanism, retention of the American-standard "donut-type" current transformer mounting within the contact box, and the inclusion of infrared observation windows.

This user-friendly, innovative switchgear meets the requirements of GB, IEC, and UL standards simultaneously, making it suitable for diverse applications worldwide. Depending on specific project requirements, various types of instrument transformers can be installed; furthermore, on the busbar side, users may opt to install either a grounding switch compliant with the IEC 62271-102 standard or a Grounding and Testing (G&T) truck compliant with the ANSI/IEEE C37.20.6 standard.