Precautions for the use of low-voltage circuit breakers

Industrial Control Abstract: If the line voltage is reduced to 70% of the rated voltage (known as the breakdown voltage), the motor will not start, the lighting fixtures will be dull, the resistance furnace will be insufficiently heated, and the operating motor will be reduced to 50 when its operating voltage is reduced. About % (referred to as the critical voltage), stalling (dragging the load and stopping the motor) occurs. The current of the motor is drastically long and reaches 6 IN. The time is slightly longer and the motor will be burned. In order to avoid the above-mentioned situation, it is required to install an undervoltage release on the circuit breaker. The operating voltage of the undervoltage release is set at (70% - 35%) rated voltage. Undervoltage release has instantaneous and delay type (with 1s, 3s, 5s... - .). Delay-type undervoltage release is used on main lines or important branches, and instantaneous type is often used on general branches. For areas with poor power supply quality, the voltage itself fluctuates greatly and approaches the upper voltage limit of the undervoltage release. This situation is not suitable for undervoltage releases.

The basic installation method of the circuit breaker is vertical installation. However, tests have shown that, when the thermal-action long-delay release is installed horizontally, although the heat dissipation conditions are somewhat different, its operation value does not change much. As an electromagnet for short-circuit protection, although the reaction has some relationship with gravity, the horizontal load is The error is only about 5% to 10%. Therefore, a molded case circuit breaker using a thermal-electromagnetic release can also be mounted horizontally or horizontally. However, if the tripping device is fully electromagnetic type (oil cup trip unit), the error value of the action value when mounted horizontally is as high as 20%-30%. In view of this, the molded case circuit breaker of the oil-filled cup trip unit can only be installed vertically. The universal type (frame type) circuit breaker can only be mounted vertically. This is related to the direction of its handle operation, and it is related to the energy storage operation of the spring, and the electromagnet release, closing device, under voltage release, etc. are related to the gravity compared with the plastic case. In addition, many types of universal circuit breakers have drawer-type installations, and they cannot be operated horizontally or horizontally. In this regard, all universal circuit breakers are required to be installed vertically, and the required tilt angle with the vertical plane is not greater than 5.

If the conductive connection (soft connection), tripping and moving, static contact, arc extinguishing chamber, arc exit, etc. are not in a plane, such as DZ5-20, TL-100C, TL-225B and DWl5-1600, 2500, 4000 And DW45 and other types of circuit breakers, they can be on the line (circuit breaker's "ON'' on the end of the power line, "OFF" the lower end of the load), but also under the line ("ON" on the termination of the load, "OFF" The lower end is connected to the power supply. However, most molded case circuit breakers (such as HSMl, DZ20, TO, TG, H series, etc.) can only enter the line and cannot enter the line. DWl 5-630 is also only able to enter the line. The reason is: When the short-circuit current is disconnected, there is no transient restoration voltage on the moving contact of the upper line, and the breaking conditions are good.When the lower wiring is connected, the front of the moving contact bar (when the upper line enters the line is the back) has soft connection and double Metals, heating elements, etc., have a recovery voltage on the movable contact, the breaking conditions are severe, and the arcing time is long, which may lead to a short-circuit between the phases.Because the moving contacts are mostly linked by a common axis, they are closely connected. Soft couplings and trips if they are disconnected due to a short circuit If the insulation is lowered by ionized gas or conductive dust, the phase-to-phase short circuit is likely to occur, and the circuit breaker that can only enter the line, if it is necessary to enter the line due to the installation conditions, must reduce the short-circuit breaking capacity and generally reduce it by 20%-30. % It is expected that the short-circuit current will be much lower and smaller and smaller.