Based on his many years of working experience, the author systematically elaborates the most common contactors. The experience gained from them is worth learning from.
The correct selection of AC contactors The mobile division of Shanghai Coking Co., Ltd.
Abstract: AC contactor is the most commonly used low-voltage electrical component. It directly controls the electrical and mechanical equipment on the site. The particularity of chemical companies put forward various requirements for their correct selection. This article starts from the basic idea of ​​the design and manufacture of AC contactors, and elaborates some points of use and experiences in combination with relevant national standards and relevant technical parameters.
Keywords: AC contactor use category national standard working system rated capacity rated voltage operating coil
The AC contactor is the most commonly used low-voltage electrical appliance in the chemical industry, and is mainly used for frequent connection and breaking of AC circuits below 380 volts. Its main control object is the electric motor, and is also commonly used in lighting, electric heating and other types of equipment. The correct choice of AC contactor directly affects the work quality of electrical maintenance and the operating status of electrical equipment, and then affects the normal production and safety and stability of the entire device. Taking seriously the issue of the selection of AC contactors is of practical significance to improving the overall electrical operation level and management level of chemical companies.
First, the use of AC contactors According to the AC contactor main contact control object, the national standard GB1497-85 "basic standard for low voltage electrical appliances" will be divided into four types of AC contactor use: AC-1, AC-2, AC -3, AC-4 (Table 1), obviously AC-4 is the most demanding use condition. It is rare that the situation is really long in the AC-4 use category. Due to the wide variety of equipment, large-scale chemical companies, in addition to the commonly used contactors belonging to the AC-3 and AC-1 categories, some important equipment such as the cranes, gantry cranes and coking machines of our company are also used by ACs. -2 Use a contactor of the category. However, these devices are busy and important. Their high failure rate and hidden dangers of equipment do not quickly reflect the surface characteristics. These devices are more prone to sick work and evolve into continuous AC-4 use categories. This is especially true for dock cranes and gantry cranes for lifting equipment. The type of use has a great influence on the electrical life of the contactor. Take the CJ20-63 type contactor as an example. If the type of use is AC-3, the electrical life can reach 1.2 million times, and when the type of use is AC-4, the electrical life Only 50,000 times. Therefore, we should avoid contactors working on AC-4 work systems that are very harmful to their life. For coke-making equipment and mining machinery and equipment, we must pay special attention to preventing the work of electrical wiring and the direct starting of winding motors. (ie AC-4 work category) appears.
Use Category Typical Job Type
AC-1 Non-inductive or micro-inductive load, resistance furnace, electric heating equipment, etc.
Starting and breaking of AC-2 wound induction motor
Disconnection of AC-3 Squirrel Cage Asynchronous Motor during Starting and Running
AC-4 Squirrel Cage Asynchronous Motor Start, Reverse Brake or Reverse Run, Jog II, AC Contactor Work System According to GB GB14048.4-93 "Low-voltage Switchgear and Control Equipment Low-voltage Electromechanical Contactors and Motors "Starter" stipulates that AC contactors can be divided into four types of work systems according to working hours:
(1) Eight-hour work system This is the basic work system. The contractual thermal current parameters of the contactor are determined according to this working system. Under normal circumstances, all series of contactors are applicable to the eight-hour working system. A contactor of this type of operation can achieve thermal equilibrium when its main contact passes the rated current in a closed condition, but should be broken after eight hours.
(2) Uninterrupted work system This type of work system is a long-term work system, in which the main contact is kept closed and a steady current of more than eight hours (several weeks or even years) is maintained and the current is not interrupted. The contactor can easily oxidize and accumulate dust when the contactor is in a constant working condition for a long period of time. These factors will lead to deterioration of heat dissipation conditions, phase and phase, and relative insulation decrease, and creepage phenomenon or even short circuit will easily occur. When working conditions require the contactor to work in this kind of working system, the AC contactor must be derated or used for special design. It is better to use a model with dust that does not gather easily and has a large creepage distance. Dust and corrosive gas environments should pay special attention to this issue.
(iii) Short-time work systems in which the main contacts of the contactors are kept closed for insufficient time to bring the contactors into thermal equilibrium. The loaded period is separated by the idle period, and the idle period is sufficient for the contactor temperature. Return to the initial temperature (ie cooling medium temperature). The standard value of the contact time for the contacts of the short-time working system is 3, 10, 30, 60 and 90 min.
(4) Intermittent-cycle work system Intermittent-cycle work system, that is, repeated short-time work system, means that the time for the contactor to close and open is too short to allow the contactor to reach the thermal equilibrium working system. Obviously the main factor affecting the contactor's time span is the cumulative number of operations. The main parameters that describe the intermittent cycle work system are the power continuity rate and the operating frequency. The standard value of the power continuity rate is 15%, 25%, 40%, and 60%. The operating frequency is divided into 8 levels (1, 3, 12). , 120, 300, 600, 1200). The number of each level represents the rated operating frequency per hour of the contactor. The equipment with an operating frequency of 100 times per hour or more is a heavy duty equipment. Typical equipment includes work machines (cars, drills, milling, grinding), lifting equipment, rolling mill equipment, and centrifuges. The coke ovens in the coking industry are also heavy vehicles. Task intermittent cycle work system. The equipment whose operating frequency exceeds 600 times/h belongs to special heavy duty equipment. Such equipment is mainly the port lifting equipment similar to our company's unloader and certain devices on the rolling mill.
Different working systems put forward completely different requirements for AC contactors, and the different aspects considered when choosing a product are naturally different. The conditions for limiting the use of contactors in the “8-hour working system†and “short-term working system†equipment are limited. Only consider that the rated current of the contactor is greater than the actual working current, and the equipment is properly put in a margin when it is important. When the contactless device is used in the “non-stop working†equipment, it must first consider the ability of dust prevention, anti-climbing and anti-overheating. It is not appropriate to use a compact contactor (if necessary, use a circuit breaker instead). To prevent overheating, the contactor capacity should be magnified by more than 20%. This is the case for most of the electrical equipment of large chemical production facilities. When the contactor is used for heavy duty and extremely heavy duty equipment, the contactor must first consider the electrical life of the contacts and the mechanical life of the actuators. The CJ12 series (especially for winding motors) and CJ20 should be selected. Series or vacuum series contactors can greatly increase the electrical life of the contactor due to the use of derating. The starting current of the motor can be simply used as the rated current of the selected contactor to increase the safety and reliability of the production device.
Third, the AC contactor to control non-motor load when the choice of capacitors, centralized lighting control devices, electric heating devices and other equipment when selecting the contactor should fully consider the impedance characteristics of the load, consider possible over-current, such as lighting and electric heating The cold impedance of the equipment is much smaller than the thermal impedance, and the closing surge may be large when the capacitor is put into operation. The first thing to consider when selecting a contactor for a motor-type device is the ability to break the contactor, and the first thing to consider for a load such as a capacitor and a large number of incandescent lamps is the ability to turn on. The general practice is: when the large-scale lighting device uses the contactor, the rated capacity is doubled. When the capacitive load is contained, the CJ16 series capacitor special-purpose contactor should be used or the CJ20 series contactor can be derated by half.
Fourth, the AC contactor operating voltage coil level AC contactor operating coil rated voltage AC (36V, 110V, 220V, 380V, 660V), DC (24V, 110V, 220V) and many other, most commonly used in industrial and mining enterprises The operating coil voltage is AC 220V and 380V two contactors, and a few contactors that require the use of safe voltage such as driving and humid environments also use AC 36V or DC 24V operating coil voltage. In general use is the choice of 220V operating coil or the use of 380V operating coil seems to be purely to comply with the original habits and control lines, is not the case.
The operating voltage of the control coil with AC 220V is equal to the ground due to its working zero line and earth potential. The working zero line is often designed as a multi-purpose bus, which makes the design and wiring of the control line more flexible, and the number of cores required for the control cable is obtained. Reduce, maintenance is also convenient.
The control circuit with the operating coil voltage of 380 volts AC has unique advantages in the environment of poor humidity, high failure rate, poor grounding, prone to short circuit or low insulation. Because the coil control signal corresponding to the contactor is transmitted between two single cores, the influence of the surrounding environment on the interference of the electrical components is small, the probability of occurrence of a malfunction is greatly reduced, and the remote control overcomes the influence of the distributed capacitance. The capacity is also greatly enhanced, and smaller line drop losses are also easily controlled over long distances. Therefore, it can be said that most of the large-scale chemical enterprise's low-voltage electrical line is more suitable for the 380-volt control line should be selected coil voltage of 380 volts AC contactor.
V. Several types of AC contactors commonly used by chemical companies Comparing model series Arc extinguishing contact materials Load current rating (A) Structure and technical points Applicable range
CJ10 series clay longitudinal seam (less than 20A) Silver base 5, 10, 20, 40, 60, 100, 150 Mainly small size, older model, low price. General small load
CJ20 series clay longitudinal seam or grid silver base 6.3,10,16,25,40,63,100,160,250,400,630 specifications, in line with IEC international standards for AC-3, AC-1 based The use of the category can be used for 660V or even 1140V systems, with a higher cost performance. Currently the most widely used product, but not suitable for heavy duty equipment in the AC-2, AC-4 use category.
CJ12 series of longitudinal joints, cutting, magnetic blowing or combination of copper 100,150,250,400,600 product specifications, mainly used in AC-2 based use category, more auxiliary contacts and normally open normally closed Transform. Large volume, large energy consumption, large sound of action, easy to damage the arc extinguishing cover and other parts need to be regularly adjusted exchange, electrical life and mechanical life is lower. It is mainly used to control motors that are frequently started by rolling mills, cranes, etc.
B series closed type (except B460) silver base 8.5, 11.5, 15.5, 22, 30, 37, 44, 65, 85, 105, 170, 245, 370, 460 BBC company's technology is introduced in Germany. It conforms to IEC standards and has specifications. The maximum operating voltage of 660V, technical performance and CJ20 similar, lighter weight, lower cost performance than the CJ20 is also the most widely used contactor, its ability to use the AC-2, AC-4 use category is not as good as the CJ20 series contactor.
3TB series closed-type silver base 9,12,16,22,32 Siemens technology is introduced, mainly small size, compact structure, small heat, terminal cover, and T-type thermal relay with better, but the overload capacity weak. Good for small loop control environment.
CKJ Series (mainly CKJ-5) Vacuum Molybdenum-based 250, 400, 600 Rated voltage up to 1140V, compact structure, small operating shock, high operating frequency, high electrical life and mechanical life ratio, operating coil with built-in rectifier bridge DC power supply, low maintenance, high price, non-intuitive operation position, creepage distance is small. It is especially suitable for equipment that is frequently used in the AC-4 use category, and is also suitable for explosion-proof and corrosive gas applications.
Six, a few points of experience 1 to purchase the need to explain the number of poles, operating coil voltage, manufacturers.
2 It is never wrong to put a certain amount of margin when selecting the rated current.
3 The mechanical life of the contactor is generally much higher than the electrical life of the contact, and the ratio between the two is roughly about 5 to 1.
4CJ12 series contactor arc extinguishing cover, electromagnetic iron, main contact, operation coil is the most vulnerable parts. The CJ12 series contactor must constantly check the three-phase simultaneity of the main contact movement, and at the same time check whether the arc extinguishing cover hangs and affects the work of the contact.
5 The instantaneous grid fluctuation will release the AC contactor. When the production device does not allow this to happen, the operation coil DC operation plus capacitor energy storage can be adopted.
2001/2/12
References: "China National Standard Classification" (Electrical Edition) China Standard Press, 1993 "Motor Engineering Manual" (Volume 5) Machinery Industry Press, February 1984