Circuit breakers are usually connected online, but often due to installation occasions, circuit breakers are required to be connected offline. For example, the power supply is located below the distribution cabinet, which is convenient for the power supply to enter the load end of the circuit breaker; Two or two rows of circuit breakers are also installed at the top and bottom of the cabinet, and the power incoming line is introduced from the middle, and the upper and lower two or two rows of circuit breakers are connected, which are respectively the connection mode of lower incoming line and upper incoming line. There is also a special occasion, no matter what measures are taken, the way of descending line is avoided, which is a classic bus connection form in building electricity, as shown in figure 1.
The three circuit breakers qf 1, 1F2 and QF3 in figure1are connected with each other, and only two circuit breakers can be closed at the same time, and one circuit breaker must be open. In practice, three locks and two keys are often used to ensure the reliability of their interlocking. For example, HSW 1 series intelligent universal circuit breakers have this function. All three circuit breakers have the same lock, which can reliably lock the tripping position of the mechanism. Three circuit breakers can only be equipped with two identical keys. When the key is inserted and unlocked, the mechanism of the circuit breaker can operate and make the circuit breaker close normally. During normal operation, QF3 is not equipped with a key, and the circuit breaker QF3 is in the off position. When either power supply fails, such as QF2, and the key of QF2 is moved to QF3, then QF2 is turned off and QF3 can be turned on, and all loads are powered by the same power supply through QF 1 and QF3. QF3 is online at this time. When QF 1 fails to supply power, all loads are supplied by the same power supply through QF2 and QF3, and QF3 is downward. So for the circuit breaker QF3, no matter what connection mode, there is always an online mode and an offline mode for the two power supplies, so the offline mode must be adopted in this occasion.
Third, different structures have different feeding methods.
Can all circuit breakers meet the requirements of up and down incoming lines at the same time? According to GB 14048.2-94 "Low-voltage Circuit Breakers for Low-voltage Switchgear and Control Equipment", the power terminal and load terminal (if necessary) shall be indicated on the nameplate of the circuit breaker or in the relevant materials provided by the manufacturer. DW 15-200, 400 and 630 universal circuit breakers clearly point out in the manufacturer's samples or instructions that the connection mode of the circuit breaker is the upper lead, and the user cannot connect the power end and the load end reversely. The industrial standard JB589- 1997 of DZ20 series molded case circuit breakers stipulates: "Circuit breakers are marked with power terminals and load terminals, 1, 3 and 5 represent power terminals respectively, and 2, 4 and 6 represent load terminals." . Some manufacturers directly engrave Arabic numerals "1, 3,5" and "2,4,6" on the dies of DZ20 series product covers. There are also some molded case circuit breakers. The words "Line" and "Load" in English are directly pressed on the plastic cover, or the words "power end" and "Load end" in Chinese are pressed, and there are also self-adhesive signs with the words "Line (power end) and load end" on them, which indicate that the circuit breaker can only be wired. Most general circuit breakers are specified in samples or manufacturing instructions. If there is no such identification or description, it means that they can be the power end and the load end. It is also DW 15 series, and the circuit breakers with shell current greater than 630A, such as those with shell currents of 1600A, 2500A and 4000A, can be connected not only, but also. The specifications used in HSW 1 series and DW45 series intelligent universal circuit breakers can be wired up and down. Why can some circuit breakers only go online but not offline, while others can go online and offline? This is mainly related to the structure of the product. The distance from the static contact to the terminal of the circuit breaker is short, and the distance from the welding of the tripping driven contact to the connecting rod to the connecting end is long. The traditional circuit breaker design always takes the terminal connected to the static contact as the power supply terminal, and fully considers the measures of isolating the arc extinguishing system between the static contact and the power supply terminal in the design. When the moving and static contacts and connecting parts of the circuit breaker have been insulated and isolated, as long as the arc suppression system goes out normally, but when the circuit breaker with lower feeder is short-circuited, the connecting parts of each moving contact are charged. In a long area, such as there is a gap in the tripping area between shafts, most of the arc generated during limit breaking is extinguished in the arc extinguishing system due to the action of electrodynamic force and arc extinguishing chamber, but there is always a small amount of charged free gas meeting with adjacent charged bodies, which may lead to interphase short circuit and destroy the normal breaking of the circuit breaker. In DW 15 series, the shell current is 1600A and above. Because the phase-to-phase spacing is larger than that of the circuit breaker with the shell current of 630A, and the isolation and insulation measures are taken, although they are both DW 15 series, they can meet the requirements of upper and lower incoming lines at the same time. In the structure of HSW 1 and DW45 series, each phase is divided into independent chambers by plastic shell structure, so the specifications used can be put into the upper line and the lower line.