American standard air-insulated switchgear, rated voltage 5/15/27/38kV. Corresponding system voltages include 4.16/8.23/13.8/24.9/25.8/34.5kV, etc.

27kV is the voltage level in North America; some regions, such as South Korea, also use 27kV (system voltage 25.8kV). This differs from the 24kV defined in the IEC 62271-1 standard (power frequency withstand voltage 50kV, lightning impulse withstand voltage 125kV), and also differs from the 24kV defined in the GB/T 11022 standard (power frequency withstand voltage 50/65kV, lightning impulse withstand voltage 125kV). The 27kV defined in the North American IEEE standard has a power frequency withstand voltage of 60kV and a lightning impulse withstand voltage of 125kV.

Traditional North American 27kV switchgear is designed identically to 15kV, featuring a double-layer circuit breaker design. Current transformers are housed in the primary contact box, with two transformers installed on the top and two on the bottom, allowing for four windings per phase.

Regardless of whether the current rating is 1200A or 2000/3000A, North American 27kV switchgear has a standard width of 36 inches (914mm), a height of 95 inches (2413mm), and a depth of 130 inches (3305mm).

The 27kV circuit breaker dimensions are similar to the 15kV circuit breaker, except for a slightly larger swing-in distance. Therefore, it also uses a double-layer circuit breaker arrangement. The through-type low-voltage current transformer is not limited by voltage and is installed in the contact box.

27kV voltage transformers (VT) and power transformers (CPT) are much larger than 15kV transformers. Therefore, unlike 15kV transformers, a single switchgear cannot accommodate one circuit breaker truck, one VT truck, and one CPT truck simultaneously. Instead, it can only accommodate a circuit breaker and one auxiliary function truck.

Switchgear with internal arc protection features has a separate instrument compartment (inst cmpt) located in the middle of the switchgear. The auxiliary function truck contains VT voltage transformers and D/O fuses. For power transformers ≤15kVA, they are installed in a separate compartment on the truck and pushed in from the front of the cabinet for connection.

Power transformers >15kVA (CPT) are fixedly installed in a compartment at the rear of the switchgear, controlled and protected by a D/O fuse truck. This design requires mechanical interlocking to ensure the CPT secondary power supply is disconnected before the fuse truck can be withdrawn, typically achieved through a mechanical key interlock.

The 27kV switchgear has the same width (36 inches) and height as the 15kV switchgear, but its depth is slightly greater.

The structural and feature requirements are the same for both 15kV and 27kV systems. The circuit breaker compartment must have TOC/MOC (Total Operating Control/Modular Operating Control) and other similar features.

The circuit breaker is equipped with TOC (Total Operating Control) and MOC (Modular Operating Control) drive units to drive the auxiliary switches installed in the circuit breaker compartment. Additionally, it features ASD (Automatic Energy Discharge) and Trip-free operation. ASD allows the circuit breaker to automatically release energy from the energy storage spring when pulled out of the switchgear compartment.