System scheme and primary structure of American standard medium and low voltage switchgear

The system scheme for power distribution comprehensively reflects the direction of power flow, current distribution, short-circuit protection, etc. from top to bottom. The current distribution and switching device of the primary circuit, as well as the system measurement and protection type of the secondary auxiliary circuit, can be clearly seen.

The primary structural design of a switchgear is centered around the power distribution system scheme, which means that what kind of system power distribution needs to be implemented initially and what kind of structure of switchgear is required to meet the requirements, such as large enterprise main power distribution, multiple types of power input and output lines, complex systems, complete protection functions, high safety requirements, flexible layout, easy operation, and safety and reliability.

Then it is necessary to have switch equipment that meets its system requirements, and the layout of the switch cabinet should be directly and clearly consistent with the system layout, rather than adjusting the system scheme too much to meet the structural requirements of the switch cabinet. The switchgear is designed to meet the needs of the power distribution system, and the design of the power system cannot be changed around the structural requirements of the switchgear.

For medium voltage primary distribution, the IEEE C37.20.2 standard metal armored power switchgear is of utmost importance. Circuit breakers, current transformers, auxiliary switches, instrument protection, etc. are located in the same compartment, making it easy to achieve control and protection functions. The metal armored power switchgear has a rated voltage of 4.16/8.25/15/27/38kV, a rated current of 600/1200/2000/3000/4000A, and a short-circuit current of 25/31.5/40/50/63kA.

Low voltage main distribution system scheme, high current, short-circuit capability, perfect system protection, complex system configuration. The installation density is high, and the secondary control protection circuit is also installed in the same compartment as the circuit breaker for easy inspection and maintenance.

The switchgear requires a primary power distribution equipment - IEEE C37.20.1/UL1558 standard metal enclosed power switchgear, standard four layer withdrawable circuit breakers, and system level protection. Rated voltage 240/480/600V, maximum current up to 6000A, short-circuit current 200kA.

For the user side, it is simple, efficient, practical and economical. The distribution circuit is simple. Isolation protection cabinet in front of medium voltage transformer, transformer, and switch cabinet for low voltage users. The front-end operation protection isolation switch cabinet of the transformer can use different schemes such as load switch+fuse, load switch+circuit breaker, withdrawable circuit breaker, etc.

The load switch has functions of isolation, load disconnection, and short-circuit closing, and can operate transformers. High voltage fuses are used for transformer short-circuit protection. It can be single in single out or two in one out. Current 600/1200A.

Medium voltage can also be a C37.20.3 metal enclosed switchgear using withdrawable circuit breakers. The circuit breaker compartment is designed according to the C37.20.2 standard, with busbar isolation and a maximum current of 2000A.

The low voltage side adopts UL891 low voltage distribution panel, Dead front enclosed cover design, direct panel operation, completely sealed, compact size, and economic efficiency. The incoming line adopts a fixed frame circuit breaker or ICCB as the incoming line isolation switch, and the current can reach 6000A 100kA. The outgoing line adopts group installation of plastic shell circuit breakers, and the outgoing cable is connected through the cable connector provided by the circuit breaker.

Insulated Case Circuit Breaker is a product category that falls between Molded Case Circuit Breakers (MCCBs) and Low Voltage Power Circuit Breakers (PCBs), primarily used in medium to high current distribution systems. ICCB balances the compactness of MCCB with the high reliability requirements of PCB. Some ICCBs use energy storage operating mechanisms that support remote operation and O-C-O (on-off) operation, with fast action speed. Good performance, low cost, and low daily maintenance requirements.