KYN28 air-insulated metal-clad switchgear dominates the domestic 12 kV AIS segment, representing more than 80% of installed demand. It is equally prevalent across IEC-governed markets. Yet, despite its maturity and widespread adoption, the standard KYN28 design cannot be directly deployed in North America. Divergent standards, application philosophies, and safety criteria necessitate structural, electrical, and material modifications before this equipment can be considered compliant with North American expectations.

The following sections analyze the essential gaps and articulate the adaptations required for KYN28 switchgear to meet IEEE, ANSI, and North American utility specifications.

Voltage Ratings and Dielectric Performance Requirements

The first challenge arises from the disparity in voltage classifications. North American medium-voltage systems frequently operate at 15 kV, with a Basic Insulation Level (BIL) of 95 kV. This exceeds the BIL used for 12 kV IEC switchgear. In practical terms, this difference mandates that dielectric validation be performed using equipment originally designed for the 24 kV IEC class, whose insulation capability aligns more closely with ANSI requirements.

Consequently, a KYN28 platform intended for the U.S. or Canadian market must adopt 24 kV-grade components, undergo dielectric testing at the elevated BIL, and incorporate reinforced internal clearances.

Compliance with IEEE C37.20.2: Compartmentalization and Ventilation

Although KYN28 is fundamentally a metal-clad design, it must be fully compliant with IEEE C37.20.2. This standard stipulates that high-voltage compartments shall not contain ventilation openings, except for designated cable-routing penetrations. Under the IEC/GB framework, IP2X-rated ventilation slots between compartments are typical and permissible; however, under ANSI rules they are prohibited.

For large-current applications—particularly 2,000 A and above—this absence of airflow in the busbar compartment creates formidable thermal challenges. Heat dissipation must therefore be achieved through optimized conductor sizing, enhanced insulation systems, and thermal modeling to mitigate excessive temperature rise.

Temperature-Rise Limits: Stricter Than IEC

Another key distinction concerns thermal performance. ANSI/IEEE imposes a maximum conductor temperature rise of 65 K for tin- or silver-plated copper busbars. This is 10 K lower than the limits prescribed by IEC/GB standards. Lower permissible temperature rise necessitates thicker conductors, expanded cooling surfaces, and improved arrangement of busbar phases.

Furthermore, IEEE C37.20.2 requires full insulation of the main busbar system. This requirement is technically compatible with the KYN28 architecture but may necessitate different insulation materials or encapsulation processes to withstand higher dielectric stresses and maintain stable thermal characteristics.

Structural Requirements for Metal-Clad Switchgear (MC Switchgear)

Material selection and sheet-metal thickness requirements differ significantly between IEC and ANSI designs. IEEE standards specify:

• Main compartment barriers and vertical section dividers: Not less than MSG 11 gauge steel (nominal 3 mm / 0.1196 in).

• All other doors, covers, and panels: Not less than MSG 14 gauge steel (nominal 1.9 mm / 0.0747 in).

These requirements serve to enhance rigidity, reduce deformation under short-circuit forces, and ensure adequate mechanical robustness.

If the manufacturer chooses aluminum instead of steel, the thickness must be increased by 50% to achieve equivalent stiffness due to the lower yield strength of aluminum alloys. This requirement must be integrated into both cabinet design and structural analysis.

Current Transformer Mechanical Ratings and Withstand Requirements

North American CTs must satisfy mechanical withstand requirements corresponding to the instantaneous current capability of the upstream interrupting devices. When current-limiting fuses are used in the primary circuit, CTs must withstand the maximum let-through current permitted by the fuse, as specified in IEEE C37.40.

The duration of the withstand requirement defaults to 10 electrical cycles, unless the protective device provides a shorter guaranteed limit.

This impacts CT selection in noticeable ways:

• Wound-type or bar-type CTs with small ratios must be selected according to mechanical withstand tables in the standard.

• Through-type (toroidal) CTs inherently avoid the mechanical issue as they do not experience the same primary conductor forces, simplifying conformity.

TOC and MOC Requirements for ANSI Switchgear

Two auxiliary mechanisms—mandatory in ANSI switchgear—must be addressed:

Truck Operated Contacts (TOC)

These contacts correspond to the functional equivalent of S8/S9 position switches on a KYN28 breaker truck. According to IEEE standards, TOC devices must be mounted within the stationary enclosure, actuated via a mechanical interface with the breaker truck.

Mechanism Operated Contacts (MOC)

MOC devices are auxiliary switches actuated by the breaker mechanism itself. They must also be installed in the stationary portion of the switchgear and driven through a linkage that interfaces with the breaker mechanism.

Both TOC and MOC requirements necessitate redesign of the breaker compartment’s mechanical interlocking systems and mounting provisions.

Corrosion Protection and Surface Treatment Requirements

Corrosion mitigation is treated with high priority in North America. IEEE standards require:

• All metal surfaces must be corrosion-resistant.

• Preferred base materials include 304-grade stainless steel or higher, or aluminum alloys that require no additional finishing.

• Outdoor equipment constructed from non-stainless or non-aluminum steel must undergo organic coating.

• Indoor surfaces and the interior of outdoor enclosures must be either galvanized or organically coated.

• The preferred surface color is ANSI Light Gray No. 61, corresponding to Munsell 8.3 G 6.10/0.54 (ASTM D1535).

Before coating, steel surfaces must be thoroughly cleaned. Both internal and external surfaces require at least one coat of corrosion-resistant organic material unless they are already compliant with the inorganic-coating qualification in Section 6.2.8.1.

If bending or forming operations damage coated surfaces, additional coating must be applied locally. Coating is considered damaged if flaking or cracking is visible at 25× magnification. Simple cuts, sheared edges, and punched holes do not require retouching.

Summary: Pathways for KYN28 Adaptation

To penetrate the North American market, KYN28 switchgear must undergo a substantive technical transformation:

• Alignment to 15 kV / 95 kV BIL insulation classes through adoption of 24 kV components.

• Full compliance with IEEE C37.20.2 metal-clad switchgear rules, including sealed compartments, thicker sheet metal, and complete busbar insulation.

• Redesigned thermal pathways to accommodate tighter 65 K temperature-rise limits.

• ANSI-rated CTs with mechanical withstand capabilities suitable for fuse-limited or breaker-limited systems.

• Integration of TOC and MOC devices into the breaker compartment architecture.

• Adoption of ANSI corrosion-protection and coating requirements.

Through meticulous redesign and rigorous verification, KYN28 switchgear can be transformed into a product fully compatible with North American regulatory, safety, and operational expectations.