According to the operation mode: there are electric operation, energy storage operation and manual operation;
According to the structure: there are universal type and plastic shell type;
According to the category of use: optional and non-selective;
According to the arc extinguishing medium: oil-immersed, vacuum and air;
According to the action speed: there are fast type and ordinary type;
According to the number of poles: there are unipolar, bipolar, tripolar and quadrupole, etc.;
According to the installation method: there are plug-in type, fixed type and drawer type.
A circuit breaker is generally composed of a contact system, an arc extinguishing system, an operating mechanism, a release, and a casing.
When a short circuit occurs, the magnetic field generated by the large current (usually 10 to 12 times) overcomes the reaction force spring, the release pulls the operating mechanism to act, and the switch trips instantaneously. When overloaded, the current becomes larger, the heat generation increases, and the bimetallic sheet deforms to a certain extent to promote the action of the mechanism (the larger the current, the shorter the action time).
Now there is an electronic type, which uses the transformer to collect the current of each phase and compares it with the set value. When the current is abnormal, the microprocessor sends a signal to make the electronic release drive the operating mechanism to act.
The function of the circuit breaker is to cut off and connect the load circuit, as well as cut off the fault circuit, prevent the accident from expanding, and ensure safe operation. The high-voltage circuit breaker needs to break 1500V arcs with a current of 1500-2000A. These arcs can be stretched to 2m and continue to burn without being extinguished. Therefore, arc extinguishing is a problem that high-voltage circuit breakers must solve.
The principle of arc blowing and arc extinguishing is mainly to cool the arc to reduce thermal dissociation. On the other hand, to lengthen the arc by blowing the arc to strengthen the recombination and diffusion of charged particles, and at the same time, the charged particles in the arc gap are blown away, and the dielectric strength of the medium is quickly restored.
Selection principles of low-voltage circuit breakers
How to choose a low-voltage circuit breaker correctly? The following five steps are essential:
(1) The rated current of the circuit breaker is determined by the calculated current of the circuit; (about 99% of the designers have done this).
(2) The short-circuit setting current of the circuit breaker should avoid the normal working starting current of the line. (About 30% of designers noticed this one).
(3) Check the breaking capacity of the low-voltage circuit breaker according to the maximum short-circuit current of the line; (about 10% of the designers noticed this).
(4) Check the sensitivity of the circuit breaker action according to the minimum short-circuit current of the line, that is, the minimum short-circuit current of the line should not be less than 1.3 times the short-circuit setting current of the circuit breaker; (about 5% of the designers noticed this).
(5) Check the rated short-circuit making capacity (expected peak value of the maximum current) of the circuit breaker according to the short-circuit impulse current on the line (that is, the maximum instantaneous value of the short-circuit full current), that is, the latter should be greater than the former.
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