The electromagnetic actuator (solenoid actuator) - automatic switching device windings tend induction motor. Puskozaschitnoy relay refrigerator is permissible to include the specified device class.
need to apply
By the 60th year of the XX century 40% of the electricity consumed in the country asynchronous motors. class of devices is designed so that an adjustment is required during operation. This resistance circuits cage rotor (rheostats), actuating single-phase motor winding, reverse and so on. As a result of the use of the principle of induction, open Arago and Foucault, it is difficult without the automation equipment.
Not surprisingly, the production capacity of the electromagnetic actuators great. For well-chosen material should thank Ermolaeva NN and a group of people who wanted to release a series of electrician Library. A qualitative presentation of the material appreciated.
Brief Classification and Labeling
In view of the existing diversity may lead set criterion for the division into groups, we mention only general:
- As the functionality: reversible and non-reversible.
- Rated voltage of the indoor units.
- According to the power of the connected load.
- Of hull designs: open and closed.
- According to the number of poles, contacts, additional nodes of the auxiliary contacts.
Labeling of electromagnetic actuators is typical:
- Brand name or manufacturer's name.
- Type of.
- The working voltage of the equipment being protected.
- Current consumption of the protected equipment.
- Application category.
- Electrical parameters of the internal control circuit (the relay).
- hull protection by IP, with the exception of the complete absence of (IP00). Device for mass weighing more than 10 kg. Allowed to specify the item in the documentation, and do not apply to the case.
- Date of manufacture.
- GOST or W, according to which the electromagnetic actuator is made. Allowed paragraph does not refer to the body, and placed in the documentation.
Separately marked the electromagnetic coil starter relay. Here are duplicated information on the current, voltage, power frequency, to facilitate the repair and partial replacement. The diameter of the wires, the brand and the number of turns required for rewinder is correct and complete reconstruction of the inductor. If the coil is too small, the marking includes only electrical parameters. Others experienced winder is able to determine on their own.
Electromagnetic actuator is designed to match the engine, paired with that work. The component parts of the equipment are considered the contactor and the starter relay. Sometimes part of the added thermal protection on the basis of bimetallic plates. Contactor becomes a part of the executive and is an electromagnetic relay. Distinguish open (open-frame) and closed (cabinet) the starter performance. Certain products according to the process conditions consist in explosion proof enclosure.
The fixed portion is formed by winding. Mobile armature of a ferromagnetic alloy is used directly for the contact closure. At first glance, the design seems to be waning, but remember that Sir Joseph Henry in 1831 raised almost a ton electromagnet powered by a voltaic pile. It turns out that such a design speed trudnovoobrazima. He said the scientist in 1837 year discussed the novelty with Wheatstone, and little has changed:
- The anchor is of a forward (Henry).
- Anchor - turning (Wheatstone, Schilling, Amps).
The moving contacts are provided with a spring mechanism, an accelerating operation, their connection with the anchor are not always rigid. In addition, the design includes a lock-latch. Relays are normally closed, normally open. Start up frequently refer to the last family of electromechanical devices.
Part magnetic actuators for remotely controlled, being automated, others contain the housing controls. Often, the control signals are transmitted through the intermediate relay. Thus, the contactor is considered an actuating device, it shall be included in the equipment under consideration.
Thermal relay sometimes absent. His appointment to disconnect the load when input current is too large. The bimetallic plate affects the total transmission device charge carriers. Contactor not normally controls, demonstrating its own circuit, connected in series. This has a profound meaning: the engine is switched frequently, and the protection is triggered rare. Therefore, the circuit breaker requirements vary. If the bimetallic relay sparkled, it is rare and does not play a big role.
The sensitive plate at one end sometimes welded to the current-carrying part of the chain, forming an eternal connection. for starters materials come from unified:
- Iron-nickel alloy (from 36 to 40% nickel content) has a low coefficient of thermal expansion.
- The second element of an alloy or pure metal: brass, copper, steel and so forth.
Bimetal or chain engine serves directly or heated special spiral, where part of the current branches. The main thing is to correctly were calculated thermal conditions. In both cases, a Joule-Lenz, describes heating conductors under the influence of an electric current flowing. Resistance is a bimetallic plate directly (direct heating) or metal spiral heater (indirect heating). Upon reaching a certain threshold temperature occurs clicking protection tripped. The bimetal plate is bent and breaks the contact.
There are relays, wherein the mixed heating - are used simultaneously both methods of temperature control. Contact protection sometimes reinforced by a spring to suppress sparking and arcing. Thermal relay normally controls only two of the three phases in a circuit voltage of 380 V. Starting relay sometimes only contains two pairs of contacts.
From the above it follows that not every electromagnetic actuator provides reverse. Changes in the shaft direction by adding an additional contactor unit. In fact, the phase switching is performed to change the rotational direction of the magnetic field inside the stator. Special mechanical lock excludes the simultaneous operation of contactors, which immediately led to networks 380 to the line (interfacial) short circuit. Not allowed on the remote while pressing the buttons "forward" and "back".
Sometimes locking is performed electrically, one contactor is supplied via additional, normally closed contacts of the second.
- Durability is primarily determined by the mechanical contact resistance. If you look at the characteristics of any electromagnetic relay, it is easy to note that the service life is given two types. Indeed, the second characteristic is the electrical durability characterizes success standoff devices burning arc.
- Switching capacity determines what the maximum current is able to activate or deactivate the relay, not to disturb the declared characteristics of durability. Example: most people can pick up on your biceps 8 kg 10 times. Excess over eight kilograms would be going beyond the switching capacity, if you do not manage to complete 10 repetitions.
- Clarity response shows how the contacts are moving slowly. If progress stops at a particular point, the arc formed cook group, the device instantly becomes corrupted. Running smoothness directly affects the electrical durability and mechanical indirectly by determining and switching capacity. This characteristic is considered to be a base defining other parameters of the electromagnetic actuator.
- Power consumption is spent for the work switch and the thermal relay.
- thermal protection parameters protect the motor windings from the operation in intense temperatures. This measure is designed to extend the life of equipment and prevent failure from overheating.
Frequency on and off in the hundreds or thousands of operations per hour (maximum speed recognized important characteristic). The service life is sometimes replaced by a number of operations. Durability is important, repair or replacement of parts during the operation almost impossible. Usually it is a few million cycles. But electric durability on the order of (say, 5 times) lower than the mechanical.
It is considered good electromagnetic actuator that withstands 10 Mill. positives. The number is chosen the lower of the two figures shown in the characteristics. If required, specifies the possibility of replacing the electrical contacts. Most modern (2016) fulfill the requirements. This indicates that more important than in the starter extinguish the arc, rather than improve the mechanical part that rarely causes product failure.
For orientation, the duration of the products literature (NN Yermolaev Magnetic actuators AC) leads calculation:
"Apparatus with 10 Mill. cycles will last 5 years in the following environments:
- Two full shifts - 16 hours a day;
- 300 switching operations per hour: medium intensity mode ".
Sold in the market device with a limit of 2 million. It is therefore possible to estimate roughly on the resulted calculation, whether the choice is suitable to the operating conditions. The durability of mechanical impact:
- Anchor magnetic system wear, bag fluff, broken rivets, torn shorted turns.
- Friction surfaces are at increased risk.
In the electric arc impact wear conditions. As stated above, this is considerably inferior mechanical, often provides an opportunity to replace the contacts. The electrical durability depends on the mains voltage and the type of load that affects the conditions for the occurrence of the arc. Induction motors consume very large current at start-up. Doug is growing with increasing power. Studies have shown that contact wear is proportional to the square of the electric current, because switching mode is the most intense.
As a result, the difference of damage during start up to 3-4 times the damage when the engine is off. Disastrous considered bouncing mode when the contactor makes a series of damped amplitude shocks as a result of the impact. The situation is complicated when the above movable part mass, greater speed and less than the pressing force.
The arc is extinguished when the motor is turned off at the moment when the voltage through zero. Usually it comes quickly, at a frequency of 50 Hz, a similar situation occurs 100 times per second. Stop has little effect in the end the result of measures to protect the relay and does not require separate and special measures. Have a good electric strength of silver contacts:
- Contact silver well kept comparatively low alternating current.
- Sintered contact (composition of oxides and silver) works well with high currents.
According to the requirements of normative acts of the actuator is required to withstand the currents indicated in Table 6 of IEC 12434-83. According to the category starter ratio overcurrent dial worker to vary, typically it is at least 6. In general, the term is treated, for example, as the ability to switch the current at 7 times the worker 50 consecutive times and always to remain in operable condition. Expected nominal voltage and the cosine of the phase angle (see. Reactive power) equal to 0.3.
On switching capacity directly affects the design of the extinguishing chamber and any action taken in the described direction. Partially influenced by the form of contacts. The switching capacity is closely related to the electrical durability, the nature of the contact movement depends on the durability of the product and the maximum switching current.
The graph below shows the characteristics of the motion of the armature magnetic switch with two springs: the contact and returnable. Countering shown in Figure 1. This force that occurs in a particular coordinate the movement of the contact group. It coincides with the return force of the linear anchor. The springs need to as quickly as possible to break the contact, providing fast and efficient quenching arc by increasing the resistance of the gap, reducing the density and increasing the potential difference of length combustion. It is assumed that the relay of the electromagnetic actuator in the normal state is open.
Characteristics armature movement
Other lines indicate the tractive force of the electromagnet by direct (2, 3) and reverse (4, 5) during anchor. It is clearly seen that the lines 3 and 4 cross the graph of reactive force. In a direct course to the closing of contacts, at some points of the electromagnet force hard enough to overcome the spring tension. Anchor will continue to move in including through inertia. In practice, this means that there is a breakthrough, the rate of change, which adversely affects the clarity and response to mechanical and electrical durability of the product. The curve of the forward stroke is obliged at all points remain above the counter line. Let it will not provide a constant speed, but will contribute to an early switch, reducing the power of the arc.
On the way back below the electromagnet force is expected to counter the line. The current from the coil must vanish any way earlier than start reverse motion under the action of springs. Otherwise, contact group stuck on the return stroke. It will not last long in human terms - of a second - but the welder to quickly create a seam. It turns out, the arc during this time will burn the contact group, reducing the electrical resistance to wear and the resulting electromagnetic starter relay in disrepair. The winding is constructed so that the current time to come loose, and the curve of return at each point is below the line counter.
Thus, the response is higher in sharpness magnetic actuator with characteristics 2 and 5. Manufacturers have calculated standards, taking into account the tolerance on the supply voltage (GOST 13109) is 10% in both directions, magnetic actuators must operate precisely:
- On the forward stroke at a voltage not higher than 80-85% of the nominal.
- On the return stroke at a voltage not more than 40-50% of the nominal.
The parameters of thermal protection
The design and general operating principles of the thermal protection section illustrated in Fig. The basis is the bimetallic strip, is shown Warming Nichrome spiral. The spring mechanism can be omitted if the current passes directly over the sensitive part. The active is generally chosen edinsvtenny metal expands when heated. The back button is not always included in the design: puskozaschitnoy relay refrigerators do not require constant monitoring (an obvious fact).
Nominal starter current is not minimum threshold bimetal protective mechanism. The private video A. Zemskov thoroughly discusses the properties of circuit breakers mains apartment. Their operating principle is similar to the magnetic actuators, components identical. The tables show that the number of known classes of automata, each with specific characteristics, but there is a common feature (Alexey specifically focused its animated red arrow):
- Overcurrent 13% triggers thermal protection more than an hour appearance dangerous situation.
- Overcurrent 45% heat triggers a protection of less than one hour from the time of occurrence of a dangerous situation.
Link to the video shown is not in vain. BUT. Zemskov says plainly that series machines D and, to a lesser extent, K are not suitable for the home. Alex dropped a phrase about the powerful induction motors. Thus, household series circuit breakers D and to a lesser degree K may assume magnetic starters. Actually, in the first approximation is what they are, but devoid of the remote control, the possibility of reversing, and other qualities. However, the above stated that the product structure is different, but the magnetic switch maintains its own essence.
Thermal relays (see. above) are triggered due to the bending of the bimetallic plate from excessive heating. The process obeys Joule and proceeds with the gradual accumulation of heat. engineers design is calculated to perform operation conditions. As stated above, preheating the three methods lead to the same result - the bending of the bimetallic plate. The engineer simply chooses the scheme more relevant in a particular situation.
The basis of the supposed protective qualities preventing operation of the motor windings in hazardous conditions. Not everyone is aware of the importance of the approval. A simple increase in temperature causes an impact the aging of insulation that reduces the life of the equipment. The second critical point temperature becoming deformation windings. As a result of the friction forces cause mechanical destruction of wire insulation damage. Ferromagnetic alloys positive in constant expansion and contraction is not to accumulate fatigue.
Table of books Ermolaeva NN, perhaps a little dated, but it shows evidence of the above reasoning, conscious 50 years ago. Data are given by the condition that the motor is operated for at least 10,000 hours. Already knew that the time to reach a dangerous condition differs from the current design of the engine and other factors. So industrial starters differ from the domestic circuit breakers, discussed A. Zemskov: excess interest over the working value for a similar response times vary depending on the type of equipment to be protected. Because such machines criticality classes of order 7, then the relay puskozaschitnoy refrigerator engine usually operates with one or two types of compressors.
To assess the adequacy of the overload protection plotting engine performance. Line thermal protection ideally coincides with this simple curve. This ensures both the safety of the equipment and the most intense mode of operation. Will not have the need of repair, vdobavok- manufacturer is able to drive the machines even in three shifts. The main thing - not to go beyond the protective curve.
Since the ideal is unattainable valid schedule relay must lie below the characteristic line of the engine. Above it are potentially dangerous regimes, leading to the consequences described above. Overcurrent occurs when the shaft jamming that recognized a potentially dangerous situation. Starters are not engaged in the regulation of the speed, are the other electrical circuits operate control. Therefore, the current consumption is not a priori a constant and sometimes exceeds the face value. Important to the duration of the event is not exceeded interval bounded schedule.
Relay operation consumes power. Firstly, constantly heated thermal relay, regardless of the fact whether the Nichrome spiral or current should pass on a bimetallic plate. Experts estimate that at constant rates of growth in industrial consumption share falls starters millions of kilowatt-hours of energy. Of course, Russia is not yet threatened, but in the developed countries under the existing requirements, saving starters will constantly improve.
Task voiced follows. It would be nice starter enclosed in an insulating outer sheath, saving energy and making nichrome spiral thinner (but longer), may consume less power. But it turns out to calculate the thermal resistance of the housing beyond the power of modern science. The result of operation becomes unpredictable. And when the bimetallic strip is known in the agreed management conditions (where the engine is protected), triggering at the right time assured.
So, Nichrome spiral warms workers, premises, sometimes outside. This is not a positive result. But the calculation of thermal modes for difficult housing. Perhaps the situation will correct microprocessor control in the future. As a result, now the starter casing looks much more bulk than the required dimensions of the device. This is a fee for the predictable thermal relay mode and leads to additional inconveniences and spending.
It comes to that the actuator must be placed in premises with limited climatic conditions that the temperature provided inside stabilized (e.g., 35 degrees Celsius). The above concerns thermal relay, but the main part of the electromagnetic energy consumption (up to 60%):
- Heat generation in the ohmic resistance of the coil.
- Losses on closed loop whose purpose is to mitigate vibration of contacts when switching the system (due to the induced induction).
- Losses in the anchor such as those who suffer transformer cores. This eddy current and magnetic reversal.
Last complexity partially eliminated the manufacture of electrical steel anchors, but the stacked it does not always look the best idea. Insulating Varnish not able to withstand shock loads and crack. In addition, contacts are going to complex packages, the mechanical strength is not easy to provide. For example: starter three-phase network with a load capacity of up to 28 kW consumes 80 watts. It is easy to calculate that a percentage of this amount to 0.3%. Given that the annual consumption of the country (the Russian Federation), measured in billions of kilowatt-hours, the figures are in the range of millions. Translated into monetary value goes Residential high-rise annually. A similar amount is worth the effort and thoughts on how to increase the efficiency of the magnetic actuator.
As for burdening, it is economically feasible to use it for a small relay with a relatively weak electromagnetic field of the coil, when the blow slack or amortized.