Electric motors are the most common electrical machines in the world. Not a single industrial enterprise, not a single technological process can do without them. Rotation of fans, pumps, movement of conveyor belts, movement of cranes - this is an incomplete, but already significant list of tasks solved with the help of engines.
However, there is one nuance in the operation of all electric motors without exception: at the moment of start, they briefly consume a large current, called starting current.
When voltage is applied to the stator winding, the rotor rotation speed is zero. The rotor must be moved and spun to the rated speed. This requires significantly more energy than what is needed for the nominal operating mode.
Under load, inrush currents are higher than at idle. The mechanical resistance to rotation from the mechanism driven by the engine is added to the weight of the rotor. In practice, they try to minimize the influence of this factor. For example, for powerful fans, the dampers in the air ducts automatically close at the time of startup.
At the moment the starting current flows from the network, significant power is consumed to bring the electric motor to its nominal operating mode. The more powerful the electric motor, the more power it needs to accelerate. Not all electrical networks tolerate this regime without consequences.
Overloading the supply lines inevitably leads to a decrease in network voltage. This not only makes starting the electric motors even more difficult, but also affects other consumers.
And the electric motors themselves experience increased mechanical and electrical loads during startup processes. Mechanical ones are associated with an increase in torque on the shaft. Electrical ones, associated with a short-term increase in current, affect the insulation of the stator and rotor windings, contact connections and starting equipment.
Methods for reducing inrush currents
Low-power electric motors with inexpensive ballasts start quite well without the use of any means. Reducing their starting currents or changing the rotation speed is not economically feasible.
But, when the influence on the operating mode of the network during the startup process is significant, the inrush currents require reduction. This is achieved through:
- application of electric motors with wound rotor;
- using a circuit to switch windings from star to delta;
- use of soft starters;
- use of frequency converters.
One or more of these methods is suitable for each mechanism.
Electric motors with wound rotor
The use of asynchronous electric motors with a wound rotor in work areas with difficult working conditions is the most ancient form of reducing starting currents. Without them, the operation of electrified cranes, excavators, as well as crushers, screens, and mills, which rarely start when there is no product in the driven mechanism, is impossible.
Reducing the starting current is achieved by gradually removing resistors from the rotor circuit. Initially, at the moment the voltage is applied, the maximum possible resistance is connected to the rotor. As the time relay accelerates, one after another they turn on contactors that bypass individual resistive sections. At the end of acceleration, the additional resistance connected to the rotor circuit is zero.
Crane motors do not have automatic stage switching with resistors. This happens at the will of the crane operator moving the control levers.
Switching the stator winding connection diagram
In the brno (winding start distribution block) of any three-phase electric motor there are 6 terminals from the windings of all phases. Thus, they can be connected either in a star or in a triangle.
Due to this, some versatility in the use of asynchronous electric motors is achieved. The star connection circuit is designed for a higher voltage level (for example, 660V), and the triangle connection for a lower voltage level (in this example, 380V).
But at a rated supply voltage corresponding to a delta circuit, you can use a star circuit to pre-accelerate the electric motor. In this case, the winding operates at a reduced supply voltage (380V instead of 660), and the inrush current is reduced.
To control the switching process, you will need an additional cable in the electric motor, since all 6 winding terminals are used. Additional starters and time relays are installed to control their operation.
Frequency converters
The first two methods cannot be applied everywhere. But the subsequent ones, which became available relatively recently, make it possible to smoothly start any asynchronous electric motor.
A frequency converter is a complex semiconductor device that combines power electronics and elements of microprocessor technology. The power part rectifies and smoothes the mains voltage, turning it into constant voltage. The output part of this voltage forms a sinusoidal one with a variable frequency from zero to the nominal value - 50 Hz.
Due to this, energy savings are achieved: the units driven into rotation do not operate with excessive productivity, being in a strictly required mode. In addition, the technological process has the opportunity to be finely tuned.
But what is important in the spectrum of the problem under consideration: frequency converters allow a smooth start of the electric motor, without shocks and jerks. There is no starting current at all.
Soft starters
A soft starter for an electric motor is the same frequency converter, but with limited functionality. It works only when the electric motor accelerates, smoothly changing its rotation speed from the minimum specified value to the nominal one.
To prevent useless operation of the device after the acceleration of the electric motor is completed, a bypass contactor is installed nearby. It connects the electric motor directly to the network after the start is complete.
When performing equipment upgrades, this is the simplest method. It can often be implemented with your own hands, without the involvement of highly specialized specialists. The device is installed in place of the magnetic starter that controls the start of the electric motor. It may be necessary to replace the cable with a shielded one. Then the parameters of the electric motor are entered into the device’s memory, and it is ready for action.
But not everyone can handle full-fledged frequency converters on their own. Therefore, their use in single copies is usually meaningless. The installation of frequency converters is justified only when carrying out a general modernization of the electrical equipment of the enterprise.
How to start a three-phase asynchronous motor from a single-phase network?
The easiest way to start a three-phase motor as a single-phase one is based on connecting its third winding through a phase-shifting device. Such a device can be an active resistance, inductance or capacitor.
Before connecting a three-phase motor to a single-phase network, you must make sure that the rated voltage of its windings corresponds to the rated voltage of the network. An asynchronous three-phase motor has three stator windings. Accordingly, the terminal box should contain 6 terminals for connecting power. If we open the terminal box, we will see the motor boron. 3 motor windings are connected to the boron. Their ends are connected to terminals. The motor power is connected to these terminals.
Each winding has a beginning and an end. The beginnings of the windings are marked as C1, C2, C3. The ends of the windings are marked C4, C5, C6, respectively. On the terminal box cover we will see a diagram for connecting the motor to the network at different supply voltages. According to this diagram, we must connect the windings. Those. if the engine allows the use of voltages 380/220, then to connect it to a single-phase 220V network, it is necessary to switch the windings to a delta circuit.
If its connection diagram allows 220/127 V, then it must be connected to a single-phase 220 V network in a star circuit, as shown in the figure.
Circuit with starting active resistance
The figure shows a single-phase connection circuit for a three-phase motor with a starting active resistance. This circuit is used only in low-power motors, since the resistor loses a large amount of energy in the form of heat.
The most common circuits are those with capacitors. To change the direction of rotation of the motor, a switch must be used. Ideally, for the normal operation of such an engine, it is necessary that the capacitance of the capacitor varies depending on the speed. But this condition is quite difficult to fulfill, so a two-stage control circuit for an asynchronous electric motor is usually used. To operate the mechanism driven by such an engine, two capacitors are used. One is connected only at startup, and after the startup is completed it is turned off and only one capacitor is left. In this case, there is a noticeable decrease in its useful power on the shaft to 50...60% of the rated power when connected to a three-phase network. This type of engine starting is called capacitor starting.
When using starting capacitors, it is possible to increase the starting torque to a value of MP/Mn = 1.6-2. However, this significantly increases the capacity of the starting capacitor, which increases its size and the cost of the entire phase-shifting device. To achieve the maximum starting torque, the capacitance value must be selected from the ratio, Xc = Zk, i.e. the capacitance is equal to the short circuit resistance of one stator phase. Due to the high cost and dimensions of the entire phase-shifting device, capacitor starting is used only when a large starting torque is required. At the end of the starting period, the starting winding must be turned off, otherwise the starting winding will overheat and burn out. An inductance inductor can be used as a starting device.
Starting a three-phase asynchronous motor from a single-phase network, through a frequency converter
To start and control a three-phase asynchronous motor from a single-phase network, you can use a frequency converter powered from a single-phase network. The block diagram of such a converter is shown in the figure. Starting a three-phase asynchronous motor from a single-phase network using a frequency converter is one of the most promising. Therefore, it is it that is most often used in new developments of control systems for adjustable electric drives. Its principle lies in the fact that by changing the frequency and supply voltage of the engine, it is possible, in accordance with the formula, to change its rotational speed.
The converter itself consists of two modules, which are usually housed in one housing:
— a control module that controls the operation of the device;
— a power module that supplies the engine with electricity.
Using a frequency converter to start a three-phase asynchronous motor. allows you to significantly reduce the starting current, since the electric motor has a strict relationship between current and torque. Moreover, the values of the starting current and torque can be adjusted within fairly large limits. In addition, using a frequency converter, you can regulate the speed of the engine and the mechanism itself, while reducing a significant part of the losses in the mechanism.
Disadvantages of using a frequency converter to start a three-phase asynchronous motor from a single-phase network: the rather high cost of the converter itself and its peripheral devices. The appearance of non-sinusoidal interference in the network and a decrease in network quality indicators.
Question: What is a barno of an electric motor and what does the abbreviation BARNO stand for?
Answer:
BARNO
Abbreviation – Distribution Unit Started Windings. It would be more correct to say the terminal box.
BRNO
When in the literature on electrical engineering or on forums one encounters terms such as “electric motor brake,” the decoding becomes a fascinating excursion into the history of the development of electrical engineering.
It should be noted right away that now this term is used extremely rarely.
You can hear it from elderly electricians of the old school who trump this word, knowing in advance that they are unlikely to be understood by those to whom they are addressing. But this gives them the opportunity to “teach the youth.”
Technical version of the origin of the name
Regarding the origin of this term, there are two versions, each of which is quite plausible.
According to the first, most common, Brno is an abbreviation that stands for “ the disconnection (or distribution) unit has started windings”. This decoding is quite acceptable, since the term “motor frame” refers to the terminal box installed on its body, and in it the terminals of the ends of the electric motor windings are actually connected in a certain way (disconnected).
Historical and linguistic version
According to the second version, the term comes from the name “born or borns”.
Here is what the Brockhaus and Efron dictionary says about this: “Borns (otherwise called terminals) - in electrical engineering mean copper clamps on dynamoelectric machines and other electrical devices for securing wires (conductors, wires).” If we take this version as the main one, then other pronunciations of the name of the terminal box become clear - “electric motor burner”, or “burner box”.
Destination Brno
The BRN of an electric motor is a terminal box in which the terminals of the windings of an asynchronous electric motor are connected. The way these terminals are connected determines the circuit in which the motor will be connected - star or delta.
The choice of switching circuit depends on the design of the motor and the supply voltage. Structurally, currently produced domestic motors are designed for connection to a three-phase 220/380 V network in a star configuration. If we consider all the options, we get the following:
127/220 V network (a standard used in the USSR until the 60s and almost not preserved) - modern engines are connected in a triangle.
network 220/380 (230/400) V (produced in Western Europe) - connected to our networks only with a triangle;
Single-phase 220 V network - when connecting a three-phase asynchronous electric motor to a single-phase network, using capacitors, the windings are connected in a triangle.
In rare cases, a combined connection to a 220/380 V network is used, when during start-up, to reduce starting currents, the engine is turned on as a star, and after the stator and a set of revolutions, it switches to a triangle. In this case, the ends of the windings are led out into the control cabinet and not used.
Regardless of the origin of the term “Brno”, or its variants “Barno” or “Born”, we are talking about the terminal box of the electric motor in which the ends of the windings are switched.
How to choose a diesel generator
To select a generator based on its power, add up the power indicators of all electrical appliances that can be simultaneously connected to the generator set. At the same time, take into account the peak power of consumers, not the rated power. The generator power should be 20-30% greater than the resulting sum of power. This excess is necessary both to ensure load uniformity and to have a reserve for connecting additional consumers in the future.
Pay attention to the number of phases of the generator set. The choice between a three-phase, two-phase and single-phase generator depends on the type of electrical appliances being connected. When connecting consumers directly to the station, it is important that the difference in the power of electrical appliances in different phases does not exceed 20-25%. This significantly affects the installation resource. With a certain connection, a three-phase power plant is capable of producing a voltage of 220 V.
Make a choice between a synchronous and asynchronous generator. The first type of generators is less accurate in maintaining voltage and is suitable for powering equipment that is insensitive to voltage changes and inductive consumers (pumps, power tools, electric motors). Asynchronous generators can power equipment that is sensitive to voltage surges and active consumers of electricity (light bulbs, computers, electronics).
Cooling system (air or liquid). Diesel generators with a liquid cooling system have an increased resource and are able to operate around the clock for a long time. Stopping is required only for refueling and maintenance. On the other hand, air-cooled diesel generators have lower cost and weight and dimensions.
Depending on where the diesel generator is operated, increased noise protection may be required. The presence of a special noise-protective casing is absolutely necessary in rooms and places with noise level requirements. By design, noise-absorbing means can be either anti-noise casings or mufflers for the exhaust system.
In addition, depending on the climatic conditions of operation, a special design of the installation may be required, as well as a container that protects the generator from environmental influences. This can be a simple weatherproof container, a shelter casing, or an arctic container that allows the generator to be used in temperatures down to -60ºC.
Depending on your financial capabilities and needs, choose additional equipment for a diesel generator. It could be: the ability to automatically start, liquid crystal information
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General Motors has presented three modifications of the new EN-V concept car.
The prototypes were developed jointly with GM's Chinese partner SAIC, but each was designed by a different studio.
The overall length and width of each version of the EN-V prototype is on average 1.22 meters, and the height is 1.83 meters. The concept cars, whose bodies are made of plastic and carbon fiber, have two seats and are driven by two three-kilowatt electric motors located in the wheels and powered by a set of lithium-ion batteries.
According to GM representatives, the EN-V's range with fully charged batteries will be about 40 kilometers, and the maximum speed will not exceed 40 kilometers per hour. According to engineers, such characteristics are quite suitable for cars of the future, which will be used in busy cities in 20-30 years. The prototypes are equipped with an “electronic” control system, and are also capable of exchanging data between cars using the capabilities of the GPS global positioning system. Electric cars use special video cameras to monitor the space around the car and analyze the movements of each of the neighboring cars. GM hopes that in the future, such safety systems will completely eliminate accidents. The developers note that concept cars can operate in fully automatic mode, reaching the desired destination without driver intervention. For example, a car can independently take the owner to work, then stop by for recharging and at a certain time return for the driver to take him home.
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Icona Fuselage
(“Science-Auto”)
Design studio Icona Shanghai was founded in early 2010 by European designers who were attracted by the huge market of China and Asia. The company is entirely based in Shanghai, but its “ears” grow from Turin: almost all of its key employees built their careers here, and engineering support for the Italians is provided by Tecnocad Progetti and Cecomp.
At the “home” auto show in Shanghai, the studio showed a spectacular Fuselage concept: a memorable silhouette, complex surfaces, interesting details. The designers of Icona Shanghai, unlike many of their colleagues, resisted the temptation to “decorate” the front of the concept with many air intakes: only a decorative panel with a wavy texture. Pay attention to the transparent polycarbonate wheels.
The Fuselage is driven by electric motors located next to the wheels and has all-wheel drive. The battery pack, weighing 360 kg, is located in the central tunnel. The Icona Fuselage accelerates to 100 km/h in 4.5 seconds, with a top speed of 200 km/h.
At the beginning of October, a small Czech town called Brno will host Coffee Week. The celebration will begin on the first of October, namely on International Coffee Day. More than 80 city cafes will take part in the event, where visitors will be offered to try different types of coffee for free or for a nominal fee throughout the week. In addition, guests of this kind of coffee festival will be able to take part in master classes and compare different methods of preparing this aromatic drink.
Nikola Tesla
Open circuit
After the break with Edison, Tesla was taken in by the famous industrialist George Westinghouse, founder of the Westinghouse Electric company. While working for the company, he received patents for multiphase electrical machines, an asynchronous electric motor, and a system for transmitting electricity through alternating polyphase current.
And at the same time he is developing new, unprecedented ways of transmitting energy. How do we connect any electrical appliance to the network? A plug - i.e. two conductors. If we connect only one, there will be no current - the circuit is not closed. And Tesla demonstrated power transmission through a single conductor. Or no wires at all.
During his lecture on the high-frequency electromagnetic field to scientists at the Royal Academy, he turned on and off the electric motor remotely, and the light bulbs in his hands lit up by themselves. Some didn't even have a spiral - just an empty flask. It was 1892!
After the lecture, physicist John Rayleigh invited Tesla into his office and solemnly proclaimed, pointing to a chair: “Please sit down. This is the great Faraday's chair. After his death, no one sat in it.”
Visitors to the 1893 World's Fair in Chicago watched in horror as a thin, nervous scientist with a funny name passed an electric current of two million volts through himself every day. In theory, there shouldn’t be even a coal left from the experimenter. And Tesla smiled as if nothing had happened, and electric lamps burned brightly in his hands. Now we know that it is not voltage that kills, but current strength, and that high-frequency current passes only through the surface integument. At the time, this trick seemed like a miracle.
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The Latvian company Dartz Armored Cars is engaged in car armoring. She also loves to create somewhat absurd projects - with the latest one, called Jo-Mojo, she has outdone herself. This is an electric open two-seater sports car with... an armored body and built-in solar panels!
We do not undertake to understand the logic of the creators of this project, so we will simply talk about the features of the unusual concept. The body of the compact car resembles a large go-kart or Ariel Atom roadster. Swedish designers from the Gray Design company helped the Latvians in its design. The chameleon effect color changes depending on different lighting conditions.
The body panels are lightly armored and the tires are bulletproof. The passenger compartment is closed by a movable automatic curtain, on the upper surface of which there are flexible solar panels. After all, the creators see the main habitat of their car... The Cote d'Azur of France! We're not sure if it's customary to shoot at car tires there, but there's definitely enough sun to recharge your batteries on the French Riviera.
Under the hood of the Jo-Mojo Roadster is an 80-horsepower electric motor. It provides the recreational sports car with a maximum speed of 200 km/h and acceleration from 0 to 100 km/h in 9.5 seconds. The creators of the car promise future buyers excellent handling due to the low center of gravity and wheels located at the corners of the body. Yes, yes, buyers! After all, the first driving prototypes will appear in the middle of next year, after which the Latvians intend to establish small-scale production and sell the new product at a price of about $40,000.
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There are no limits to design thoughts and ideas. But designer Roman Mistyuk was apparently inspired by the science fiction film “Minority Report,” where cars could move along the walls of houses. From his pen came the Metromorph masterpiece under the Peugeot brand, which not only rolls on vertical surfaces, but also serves as an elevator and even a balcony. This miracle machine by Roman Mistyuk solves the problem of parking and the need to climb to the upper floors of a residential high-rise in one fell swoop. Such buildings must be equipped with special doors so that people can get directly from the car into the apartment. The car itself, when “parked,” serves as a kind of balcony. The car interior is designed in such a way that when vertically ascending or descending, the seats can occupy the desired positions. The Metromorph's door opening principle is a bit reminiscent of a Lamborghini. The miracle of technology is driven by two electric motors located on the rear axle shafts.
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BMW i8 Spyder concept car presented by designer Sonny Lim. This two-seater car weighs 1630 kg, is equipped with two engines - a 96-kilowatt electric motor (131 hp), responsible for driving the front axle, and a three-cylinder internal combustion engine with a volume of 1.5 liters and a power of 223 hp.
The electric motor charge is enough for 30 km without recharging. Effectively use the power of two engines simultaneously. Thanks to this mode of operation, the car spends no more than three liters of gasoline per 100 km. The gas tank capacity is 100 liters.
The design of the most unusual city cars. Twike is a “frivolous” city car. We usually use the word “hybrid” to describe a car that has a motor that combines an internal combustion engine and an electric motor. But the car called Twike can move both thanks to an electric motor and the power of human legs. This car is compact, lightweight and economical (it costs only 2.4 US dollars to drive it 300 miles).
The hardware in the new F30 is very interesting. There are many modifications: you can choose a manual or automatic, 6 or 8 gear shift steps, interior design variations, gasoline, diesel or gasoline with an electric motor - choose what you like.
Under the hood, the new three-ruble car from BMW 2012 model year can have either a turbodiesel or a gasoline engine paired with an electric motor. The latter option will be of particular interest to those who like to save fuel, although it is difficult to believe that such people could be among the owners of cars of this iconic brand.
Citroën has unveiled the new Tubik car, which attracts the attention of onlookers with its futuristic design. The minivan is only 4.8 meters long and 2.05 meters high and can accommodate up to 9 passengers, who can sit on three rows of seats. Tubik is powered by a new hybrid electric-diesel engine, the diesel part of which drives the front axle of the wheels, and the electric motor pushes the rear axle.
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