Medium-voltage switchgear available in markets such as Europe and Asia is manufactured according to International Electrotechnical Commission (IEC) standards. However, these switchgears feature rear-mounted cabling, making installation and maintenance difficult.

Furthermore, this type of switchgear uses rear-mounted "epoxy-pillared" current transformers, making field replacement impossible in case of failure.

According to IEC standards, complete shielding between compartments is not required, making cooling of the circuit breakers much easier through inter-compartment ventilation.

Medium-voltage metal-clad switchgear for the North American market, as per IEEE and ANSI standards, requires stringent requirements. Under these standards (UL testing is conducted to meet these standards), circuit breakers are tested internally within the switchgear, resulting in very limited cooling. Limiting temperature rise becomes a major challenge. Without modifications to adequately cool the circuit breakers, switchgear designed according to IEC standards must be used with significantly reduced capacity to comply with North American standards.

Furthermore, IEEE/ANSI designs require busbar insulation, making it more difficult to cool the critical current-carrying busbars in certain compartments of switchgear using circuit breakers. Alternatively, expensive heat sinks must be used to limit temperature rise. Adding heat sinks in a compact space is a daunting task and poses a significant challenge to meeting the required lightning impulse withstand voltage.

Recent advances in vacuum circuit breaker technology have improved the performance and reliability of vacuum circuit breakers. New vacuum interrupters utilize superior contact materials, such as chromium copper, and employ axial magnetic field (AMF) or radial magnetic field (RMF) field contact systems. Furthermore, these circuit breakers are permanently magnet driven (with solenoids), include built-in capacitors for storing operating energy, and electronic tripping mechanisms. Compared to mechanically (spring-operated) circuit breakers, these have fewer moving parts and have proven more reliable in enhanced life-cycle (torture) testing and installations worldwide. The ABB VM1 and Eaton VCP-TL are examples of such permanently magnet driven circuit breakers. These circuit breakers are designed to perform 100,000 operations without failure due to the significantly fewer moving parts.

These circuit breakers look almost identical to low-voltage circuit breakers, and if they meet ANSI/UL design challenges, the 15 kV metal-clad switchgear will have a footprint approximately 25% smaller than low-voltage switchgear handling the same power. The reliability of this medium-voltage switchgear will also be significantly higher. Such products will save substantial space in mission-critical data centers, marine, and other applications.

The following parameters were considered when designing the new metal-clad switchgear:

* Fully front-operated, installed, and serviced

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

* Arc resistant, Class 2A

* Infrared observation port and observation window

* Front access to 600V CT and front connection cables

* Withdrawn circuit breakers, PTs, and CPTs

* Fully insulated busbars

* UL and cUL listings (metal-clad and arc resistant) according to ANSI/IEEE standards

Based on experience, we knew that extensive simulation would be the best way to find a suitable solution to such a multi-dimensional optimization problem. IEM performed extensive mathematical analysis on the following:

(1) Thermal characteristics of the switchgear, to study temperature rise and hot spots under rated current;

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

(3) Dielectric analysis during lightning impulse tests;

(4) Analysis of arc and gas propagation, and the pressure generated in various switchgear compartments during arc faults.

The benefit of this extensive simulation is that it allows us to define an initial solution, which can then be used to build a prototype unit for testing. Without the benefits of extensive analysis, the solution would require extensive testing through trial and error, requiring a large sample size and very expensive testing costs.

Note that this product, while meeting the requirements of IEEE C37.20.2 standards such as fully insulated busbars, a temperature rise standard lower than 10k, complete isolation between compartments, internal arc resistance of 2A, and material surface treatment, abandons the traditional 36-inch wide double-layer circuit breaker design in the United States, adopting a 24-inch compact single-layer design with features such as front-mounted maintenance, spring mechanism circuit breakers, retention of US standard donut-shaped current transformer contact box installation, and infrared observation window. This user-friendly, new type of switchgear meets GB/IEC/UL standards and is suitable for various needs worldwide. Different types of instrument transformers can be installed according to project requirements. For the bus-side instrument transformers, IEC62271-102 standard grounding switches or ANSI IEEE C37.20.6 standard grounding test G&T trolleys can be installed as needed.