Types of American standard medium voltage switchgear

The American standard medium voltage levels mainly include 5, 15 (15.5 outdoor), 27, and 38kV, which are applied to system voltages including 4.16, 8.23, 13.8, 15.5, 25, 27.6, 34.5kV, etc. Rated current of 1200/2000/3000/4000A, classified according to IEEE/UL standards, there are mainly five types of American standard medium voltage switchgear.

One is the IEEE C37.20.2 standard metal armored power switchgear, a primary power switchgear, air insulated, double-layer withdrawable circuit breaker design, with five high-voltage compartments completely separated by 3mm thick metal steel plates and no ventilation holes between compartments. Divided into internal arc type and non internal arc type, the internal arc type meets the IEEE C37.20.7 standard.

All functional units adopt a handcart structure, such as voltage transformer handcart, power transformer handcart, and fuse handcart.

The low voltage through type current transformer is installed on the primary contact box and requires maintenance and replacement in front of the cabinet. Do not use a grounding switch, use a grounding inspection handcart as grounding protection during switchgear maintenance.

The second is the IEEE C37.20.3 standard metal enclosed load switchgear, used for front-end operation protection of client transformers. There are four different functional units: load switch, load switch fuse combination, isolation switch with fixed circuit breaker, and withdrawable circuit breaker.

5～38kV， Rated current up to 4000A (load switch up to 1200A), air insulated, box structure, no partitions inside, manual operation of load switch. 3000/4000A is mainly used for generator outlet switchgear, using isolation switches and circuit breakers, or withdrawable circuit breaker structures.

The third is the IEEE C37.20.9 standard metal enclosed gas insulated switchgear, also known as gas filled cabinets, with a rated voltage of 5-38kV. SF6 gas insulation is the main type, and environmentally friendly gas insulation is also a development trend. The main circuit is sealed in a low-pressure insulating gas filled environment, using European or American standard cable connectors. The insulation withstand voltage level varies depending on the cable head, and visible measures must be taken to isolate the fracture surface, either through direct observation or by using a camera.

The fourth is IEEE C37.74 for underground, basement, and base mounted load disconnecting switchgear and fuse load disconnecting switchgear for AC systems of 38kV and below.

C37.74 is a distribution switchgear used in power supply system ring network applications. Outdoor applications include above ground, underground, and pry mounted switchgear, solid insulation, gas insulation, and oil insulation, all of which are sturdy, durable, simple, and reliable.

Ring network power supply, two inputs and two outputs, or two inputs and multiple outputs, with simple manual operation or external electric operation mechanism, and the latest intelligent distribution integrated intelligent terminal.

The fifth is the UL347 standard medium voltage motor control cabinet, which includes "medium voltage AC contactors, controllers, and control centers". Specially designed for industrial medium voltage motor operation control cabinet, with a voltage of generally 4.16/7.2kV and a maximum current of 720A. The isolation switch is equipped with a fixed installation fuse and a pull-out contactor handcart. The outer shell meets the C37.20.3 standard, and the internal arc fault meets the C37.20.7 standard.

Different applications have different standards for medium voltage switchgear. When inquiring about the price, it is important to first inform what standard of switchgear needs to be purchased. For the same 15kV 1200A 31.5kA air insulated switchgear, using the C37.20.2 standard results in a smaller overall width, higher height and depth, and a higher price. The C37.20.3 standard has a larger overall width but smaller height and depth, making it suitable for wall installation. With the same circuit breaker configuration and arc rating, the unit price for each outgoing circuit is only half of the C37.20.2 standard armored cabinet.