The 38kV ring main unit adopts the American standard

Ring main unit is mainly used for power supply in domestic power supply bureaus, and in the United States, it is also used for corresponding ring main unit power supply. Load switches are used as ring in and out switches, and load switches and fuses are used for outgoing lines. The product standard names are underground, dome and pad load disconnect switchgear and fused load disconnect switchgear. The ANSI/IEEE C37.74 standard is the requirement for this product.

As a switch equipment used in power supply bureaus, the product requirements are extremely high, and only local enterprises such as G&W, Schneider Electric, Cooper (Eaton Electric) produce it. Other enterprises such as the three major ones rarely have this standard ring main unit entering this field. The product has a compact structure, a common box type, and different designs such as oil insulation, solid insulation, and other insulation. It has high reliability and is completely maintenance free. DEAD FRONT, including the operating mechanism, is completely sealed and not affected by the environment, with a lifespan of over 50 years.

The other part of the ring network application is the medium voltage switchgear in front of the user side transformer, which adopts the standard IEEE C37.20.3, that is, box type load switchgear products. Most of them use air insulated switchgear, with single in single out, two in one out DUPLEX, and multiple parallel cabinet LINE-UP application solutions.

The majority of switchgear in C37.20.3 standard are load switch and load switch fuse schemes, as well as load switch+circuit breaker schemes and withdrawable circuit breaker switchgear schemes. They are air insulated and have a large size. The width of the 38kV load switch cabinet is 60 × 25.4=1524mm, with clear and visible isolation switches. They are inexpensive and easy to operate and maintain.

Due to the introduction of compact gas insulated ring main units such as Schneider and ABB, which do not meet the C37.74 standard and cannot enter the power supply bureau system, they have been used in the front-end application of user transformers. The size is small, initially as an air insulated ring main unit, later as a compact ring main unit. The C37.20.3 standard is an air insulated metal enclosed switchgear. The SF6 load switch or switch plus circuit breaker gas box of the compact ring main unit is used as a component in the air insulated switchgear, and the gas insulated ring main unit is tested according to the C37.20.9 standard gas insulated switchgear.

Compared with traditional box type cabinets, this type of box type load switch cabinet has significantly reduced size, but is expensive and has a high threshold for operation and maintenance. Therefore, it is only used in emerging markets such as data centers and new energy. Traditional transformer front-end protection still tends to use air insulated knife switch load switch box type cabinets.

The volume of 38kV gas insulated ring main unit has significantly decreased, and there is a huge demand for data centers and other areas, with many market opportunities. The rated voltage is 38kV, the rated frequency is 60Hz, the rated current is 600A, and the rated short-circuit breaking current is 20kA. For new energy applications, the C37.20.4 standard load switch is generally not used, but a three position switch with a vacuum circuit breaker. Therefore, it has the same structure as the inflatable cabinet scheme and is tested according to the C37.20.9 inflatable cabinet standard.

Visible fracture is required, and the circuit breaker equipped complies with C37.04 standard. The voltage transformer and current transformer comply with C57.13 standard. The material used for insulation meets the requirements of C37.20.9 standard and has passed the corresponding type test.