North American outdoor switchgear

According to the IEEE C37.20.2 standard, North American switchgear comes in two forms: indoor and outdoor. Outdoor switchgear is further divided into outdoor box type switchgear with an operating corridor and outdoor switchgear without an operating corridor. In fact, not only medium voltage switchgear has indoor and outdoor types, UL1558 low-voltage switchgear, UL891 low-voltage distribution panel, etc. also have outdoor and indoor product definitions.

The outdoor switchgear with corridors is basically similar to the prefabricated warehouse structure in China. The indoor switchgear is placed inside the prefabricated warehouse, and the internal arc fault heat effect can be transmitted to the outside of the prefabricated warehouse through the pressure release channel.

Equipped with maintenance channels, other electrical equipment can also be installed, and basic facilities such as air conditioning and lighting can be provided. Prefabrication work such as installation and wiring can be completed before leaving the factory. It can be transported as a whole or transported separately for on-site assembly and installation of auxiliary equipment. As shown in the figure below, the right part is the main body of the switchgear, while the left part is the operational corridor component assembled on site.

For those without corridors, there is no outer box. Instead, based on the switchgear body, the front and top frames are added to install the front door panel, rain and snow cover plate on the top, and the rear cover plate of the switchgear. Measures such as adding sealing strips can meet the NEMA 3R protection level.

The size of the American standard switchgear itself is relatively large, and adding an outdoor box separately makes the size even larger, which is not conducive to transportation. And with a separate outdoor switchgear structure, single or several cabinets can be assembled and transported, with small size, light weight, and easy on-site assembly and installation of single cabinets. No need for separate casing, more compact size, standardized outdoor switchgear design, no need for additional engineering design

NEMA 3R requires the enclosure to withstand external solid foreign objects entering the charged body, prevent rain and snow from entering, and meet outdoor anti-corrosion applications. Generally, the salt spray test requirement is greater than 600 hours.

The basic structure is still a switchgear, which can be operated and maintained by opening the cabinet door. As there are protective, indicating, and controlling devices installed on the switchgear, an additional door is added in front to protect these devices, while there are no electrical appliances at the back, so no protection is required. The rear cover plate is used as the outer shell of the outdoor switchgear, which is sealed with sealing strips and other seals. Removing the cover plate allows direct access to the high-voltage busbar and cables in the cable room.

The American standard switchgear has a double-layer circuit breaker or functional handcart structure. The non arcing cabinet does not have a separate instrument room. The comprehensive protection, indication and other components are installed on the door of the circuit breaker compartment. The secondary terminals, micro breakers, fuses and other components are installed in the upper, lower, left and right spaces of the front of the circuit breaker compartment. Generally, terminal blocks are installed on both sides. The upper part is equipped with micro breakers or switches, contactors and other devices, and the lower part is equipped with power transformers, capacitor devices for opening, etc.

Therefore, opening the front door of the outdoor switchgear allows for control and status check of the switches. The operation of the circuit breaker requires opening the door of the circuit breaker compartment.

The outdoor application design adopts a steel plate splicing structure, without using thick materials such as profiles. The two switch cabinets are overlapped and covered with each other, and the top cover plate design is similar to that of a transformer box. There are ventilation holes at the front and rear of the cabinet top, and the outermost cover plate blocks rainwater from entering.

It should be noted that the minimum operating temperature for American standard switchgear is minus 30 degrees Celsius, which is five degrees Celsius lower than the minimum temperature required by IEC. Generally, it is necessary to test and verify the working performance at low temperatures, such as whether lubricating grease will solidify, which may cause the operating parameters of the mechanism to exceed the standard.

The bottom plate of American standard switchgear generally requires the use of waterproof sealing rings for cable entry. The cable bottom plate of the switchgear is made of thickened aluminum plate, and holes are arranged according to the diameter of the cable sealing ring on site.

Due to its ability to be directly placed outdoors, outdoor switchgear is widely used in industrial and mining enterprises such as chemical plants, infrastructure such as shopping centers, and vehicle mounted mobile switchgear. Generally, after the base is constructed, the switchgear can be placed on top and cables can be connected.