1. 2 low pressure breakers
Breakers are a mechanical switch that can be connected, carried and separated under normal circuit conditions, and can be connected under the prescribed irregular circuit conditions (e. G. Short circuit conditions), carrying a certain amount of time and cutting off the current, which was previously called an automatic air switch and renamed a circuit breaker to conform to iec (international electric committee) standards。
Low pressure breaker
(1) functions of low-pressure breakers
Low-pressure breakers are appliances that combine the functions of controlling and protecting appliances, with graphics and text symbols as shown in the figure. Under normal conditions, it is often used as an infrequent and disconnected circuit and as a start-up and stop-over of electrical motors. It is often used as a total power switch or as a power switch for some circuits。
Graphics and text symbols for low-pressure breakers
The action value of the breaker can be adjusted, with overloading and both protective functions, to automatically cut the circuit when the circuit has malfunctions, such as loading, short circuits or pressure failure, and to effectively protect electrical equipment attached behind it. The ease of installation and the high break-up capacity, particularly after the break-up of the malfunctioning power, generally do not require replacement of spare parts, which is not an advantage for most smelters. As a result, the use of low-pressure breakers has become increasingly widespread. Low-pressure circuit breakers can function as both thermal relays and breakers。
(2) structure and working principles of low pressure breakers
Although there are many types of low-pressure breakers, the structure is essentially the same and consists mainly of contact systems and arc silencers, various detachors and operators, and free detachments. Various kinds of deductors include transients, depressure (depressure) debutors, thermal debutors, etc. The anticlaves vary according to the type of breaker, often using narrow and deionic anticlaves, and plastic case-like anticlaves are made of hard steel cardboard slabs。
When the circuits are short-circuited or run-off, the trans-deductor's electromagnetic inhaler is wired, removing the hooks of the free-deductor institution, separating the automatic switch contact point from the spring force, and effectively and in a timely manner removing the failure currents up to dozens of times the rated current. When the circuit passes, the thermal elements of the heat-deductor heat up, bending on the double-metal plate and promoting free-deductive institutional movements. Deductors are used as remote controls, which, in normal working hours, are electrically disabled, and when distance control is required, press the start button, so that the loop is electrocuted, and the cortex drives the free-deductive agency action, and the main contact point is disconnected. The main contact point of the switch is the operator's manual or electric gate, which is capable of connecting and breaking up the currents of work in normal working conditions. If the electricity grid is too low or zero, the electromagnetic iron is released, the free-deductive agency moves to separate the breaker's contact point, thereby ensuring the safety of the circuit and the equipment in the circuit in the event of passover and zero pressure。
Chart of working principles for low-pressure breakers (overflow protection)
1- spring; 2-deductive apparatus; 3-emagnetic wire rings; 4-tangles
Chart of working principles for low-pressure breakers (overload protection)
1- spring; 2-deductive apparatus; 3-bimetal tablets
4-touch
(3) typical products of low-pressure breakers
The main classification method for low-pressure breakers is classified in structural form, with two types of opening and installation. The opening form is also called a framework or an all-power model, and the device form is also called a plastic shell (known as a plastic shell). There are other classifications, such as distribution by use, motor protection, domestic and similar sites, leak protection and special uses; unipolar, bipolar, tripolar and tetrapolar by extreme number; and vacuum and air by endar media。
1 installed breakers。
Currently, the commonly used devices are dzl5, dz20, dzx19, dz47, c45n (now upgraded to c65n) series of products. The t series, which introduces japanese products, is equivalent to the domestic dz949, and applies to ships. Series h is the introduction of western house products from the united states. The 3ve series, which introduces siemens' products, is equivalent to the domestic dz108 and applies to the protection of electrical motives. The c45n (c65n) series introduces products from the french company melan zhiland, equivalent to the domestic dz47 breakers, which have small sizes, high break-up capacity, limited flow performance, operational light and full model specifications, and can easily combine on a unipolar basis the advantages of diodes, tripolares, quadratic breakers, etc., with extensive use of civilian lighting sub-lines and sub-routines in 60a and below (many access and commercial lighting feeders) or motorized power distribution systems and line overload and short circuit protection。
Main technical parameters for low-pressure breakers in the dz47-63 series
Main technical parameters for low-pressure breakers in the dz15 series
One-size-fits-all breakers, previously known as frame breakers, typically have a steel framework (which is also made up of small quantities of plastic floors plus metal stubs), the main components are within it and are generally naked, the one-size-fits-all breakers generally have a large capacity, with rated currents generally ranging from 630 to 6300a, with high short-circuit break-ups and high mobility stability. Applicable to main protection as a distribution trunk in a distribution network of 50 hz or 60 hz and a rated voltage of 380 v or 660 v。
The universal circuit breakers consist mainly of the contact system, the operator, the perfunctory detachor, the detachor and the unpressure detachor, accessories and frames, all of which are insulated and placed in the frame structure base。
At present, the country has commonly used a series of universal circuit breakers such as dw15, dw45, me, ae, ah etc. The dw15 series of breakers are self-developed and produced in the country, with a full range of 1000a, 1500a, 2,500a, 4000a, etc. The products produced by the me series (the me series switch current class ranges from 630 to 5000a, with 13 classes) are equivalent to the dw17 series in the country. The ae series is equivalent to the domestic dw18 series for products produced for the introduction of mitsubishi technology in japan and is used primarily for distribution protection. The ah series, produced for the introduction of japanese technology, is equivalent to the domestic dw914 series, used in general industrial power lines。
Smart breakers are new products that introduce new technologies such as microelectronics, sensory, communication and electrical and electronic technologies into circuit breakers. The smart breakers are characterized by the introduction of smart controls (smart breakers) centred on microprocessors or single-piece machines, which, on the one hand, have the function of circuit breakers and, on the other hand, can achieve two-way features with centrally controlled computers, consisting of intelligent online surveillance, self-regulation, measurement, testing, self-diagnosing, communication, etc., capable of displaying, setting and modifying action parameters for various protective functions, and failure parameters for the protection of circuit operations can be stored in non-disable storage devices for search purposes。
Currently, domestically produced smart circuit breakers are in the frame and plastic shell formats. Framework smart circuit breakers are used primarily for the main circuit breakers in the smart automatic distribution system, and plastic shell smart breakers are used mainly for the distribution of electrical power in the distribution network and for the control and protection of circuits and power supply equipment, as well as for the control of three-cage walk-through motors. In the country, smart frame breakers such as dw45, dw40, dw914 (ah), dw18 (ae-s), dw48, dw19 (3we), dw17 (me) and smart plastic shell breakers are equipped with st-series smart controllers and accompanying accessories, and st-series smart controllers are equipped with building-block packages that can be installed directly in the breaker body without the need to repeat secondary connections and have multiple packages。
(4) technical parameters for circuit breakers
The main technical parameters for circuit breakers are extremes, current types, rated voltage, rated currents, rated passivity, circuit rated voltage, permissible operating frequencies, mechanical lifetime, electrical lifetime, type of use, etc。
1 the rated working voltage. Under the prescribed conditions, the working voltage to which the circuit breaker is exposed for long periods of time shall be greater than or equal to the rated voltage load. Usually the maximum working voltage is the rated voltage, usually the wire voltage. The rated voltage values commonly used for straight-through breakers are 110 v, 220 v, 440 v and 660 v, etc. The rated voltage values commonly used in communication breakers are 127 v, 220 v, 380 v, 500 v and 660 v, etc。
2 the rated work current. Under the prescribed conditions, circuit breakers may pass the current value for a long period of time, also referred to as the deductor rated current。
3 short-circuit ability. Short-circuit current values that breakers can connect and divide under specified conditions。
Electrical and mechanical life. Electrical life means the number of load operations that are not required for repair or replacement of circuit breakers under the prescribed normal working conditions. Mechanical lifetime means the number of unloaded operations carried by an institution whose circuit breaker does not require repair or replacement. The mechanical life of circuit breakers now exceeds 10 million times, and electrical life is about 5-20 per cent of the mechanical life。
(5) selection principles for low-pressure breakers
1 the type and form of protection of circuit breakers should be determined in accordance with the requirements of the line for protection, e. G. Universal or plastic-hull breakers, usually more than plastic-hull breakers when the current is below 600a, and, of course, there is now a rated breaker of over 600a。
2 the rated voltage of the breaker u idgencharoverride-4 shall be equal to or greater than the rated voltage of the protected route。
3 the circuit breaker shall have a rated voltage equal to that of the protected route。
The rated current of the circuit breaker and the pass-deductor shall be greater than or equal to the calculated current of the protected circuit。
5 the circuit breaker's maximum breaker capacity shall be greater than the effective value of the maximum short-circuit current of the line。
The protective features of upper- and lower-level breakers in the distribution lines shall be coordinated, and the protective characteristics of the lower level shall be located below and not intersect。
7 long-duration deductive currents of circuit breakers shall be smaller than the continuous current allowed by the guide。
In selecting breakers, consideration is given to the use of breakers, such as those used to protect electrical motives, distribution or lighting. This is mentioned later in the example。
In direct current control circuits, the nominal voltage of the direct flow breaker shall be greater than that of the direct line. In the case of reverse brakes and reversals, the nominal voltage of the direct-flow breaker shall be greater than two times the direct-flow line voltage。
(6) attention
1 when connected, the end of the line above the low-pressure breaker shall be connected to the power line and the end of the line below shall be connected to the load line。
2 type c is often selected for the instant-deductible current type of lighting circuit。
For example, there is an illumination circuit with a total load of 1. 5 kw and a suitable breaker is selected as its total power switch。
As the lighting circuit was rated at 220 v, the rated voltage for the circuit breaker was 230 v. The rated current for the lighting circuit is: the rated current for the selected breaker is 10a. The circuit breakers in the dz47-63 series are more suitable for instant-activated currents of 6 to 20 times the rated current for lighting circuits, as can be seen from the checklist, type c is appropriate, so the final choice of low-pressure breakers is dz47-63, c10 (10a rated currents of type c)。
For example, the ca6140a bed is equipped with three three-stage different paced electric motors with a primary power of 7. 5 kw, a rapid electric motor power of 275 kw, a cooling motor power of 150 w and control of circuits of approximately 500 w, with the appropriate power switch。
As the electric motor rated voltage was 380v, the rated voltage for the circuit breaker was 380v. The rated current for circuits is: in=p/u=(7500+275+150+500)/380=22. 2a and 40a for circuit breakers may be selected. The circuit breakers in the dz15-40 series are more suitable for use as power switches, so the final choice of low-pressure breakers is dz15-40/40。
