What is the efficiency of the electric motor? How to increase the efficiency of the electric motor?
Electric motors have appeared for a long time, buta great interest in them arose when they began to represent an alternative to internal combustion engines. Particularly interesting is the efficiency of the electric motor, which is one of its main characteristics.
Each system has some coefficientuseful action, which characterizes the effectiveness of its work as a whole. That is, it determines how well the system or device transfers or converts energy. The value of the efficiency does not matter, and most often it is represented as a percentage or a number from zero to one.
Parameters of efficiency in electric motors
The main task of the electric motor is reducedto the transformation of electrical energy into mechanical energy. The efficiency determines the efficiency of this function. The formula for the efficiency of the electric motor is as follows:
- n = p2 / p1
In this formula, p1 is the sum ofelectric power, p2 - useful mechanical power, which is produced directly by the engine. Electrical power is determined by the formula: p1 = UI (voltage multiplied by the current strength), and the mechanical power value by the formula P = A / t (ratio of work to unit of time). This is how the calculation of the efficiency of the electric motor looks. However, this is the simplest part of it. Depending on the purpose of the engine and the scope of its application, the calculation will differ and take into account many other parameters. In fact, the formula for the efficiency of the electric motor includes many more variables. The above was the simplest example.
Decrease in efficiency
The mechanical efficiency of the motor mustmust be taken into account when choosing a motor. A very large role is played by losses that are associated with engine heating, power reduction, reactive currents. Most often, the drop in efficiency is due to the release of heat, which naturally occurs when the engine is running. The reasons for the release of heat may be different: the motor can be heated during friction, as well as for electrical and even magnetic reasons. The simplest example is the situation when 1000 rubles were spent on electric energy, and the work was done for 700 rubles. In this case, the efficiency will be 70%.
For cooling electric motorsFans are used that blow air through the created gaps. Depending on the class of motors, heating can be carried out to a certain temperature. For example, Class A engines can be heated to 85-90 degrees, class B - up to 110 degrees. In the event that the temperature exceeds the permissible limit, this may indicate a stator closing.
Average efficiency of electric motors
It is worth noting that the efficiency of a direct current (and alternating current) motor varies depending on the load:
- At idle, the efficiency is 0%.
- At a load of 25%, the efficiency is 83%.
- At a load of 50%, the efficiency is 87%.
- At a load of 75%, the efficiency is 88%.
- At a load of 100%, the efficiency is 87%.
One of the reasons for the fall in the coefficient of usefulthe action is the asymmetry of the currents when a different voltage is applied to each of the three phases. If, for example, the first phase is 410 V, the second - 403 V, and the third - 390 V, then the average value will be 401 V. The asymmetry in this case will be equal to the difference between the maximum and minimum voltage in the phases (410 -390), that is 20 V. The formula of efficiency of the electric motor for calculation of losses will have a form in our situation: 20/401 * 100 = 4.98%. This means that we lose 5% of the efficiency at work because of the voltage difference in the phases.
Total loss and fall in efficiency
Negative factors that affecta drop in the efficiency of the electric motor, very much. There are certain methods that allow them to be determined. For example, you can determine if there is a gap through which the power from the grid is partially transmitted to the stator and then to the rotor.
Losses in the starter also take place, and they consist of several values. First of all, it can be losses related to eddy currents and magnetization reversal of the stator cores.
If the motor is asynchronous, then there areadditional losses due to teeth in the rotor and stator. Vortex currents can also occur in separate engine nodes. All this in total reduces the efficiency of the electric motor by 0.5%. Asynchronous motors take into account all losses that can occur during operation. Therefore, the range of efficiency can vary from 80 to 90%.
History of development of electric motorsbegins with the discovery of the law of electromagnetic induction. According to him, the induction current always moves in such a way as to counteract the cause that causes it. It was this theory that formed the basis for the creation of the first electric motor.
Modern models are based on the same principle,However, they differ radically from the first specimens. Electric motors have become much more powerful, more compact, but most importantly - their efficiency has increased significantly. We have already written above about the efficiency of the electric motor, and in comparison with the internal combustion engine this is an amazing result. For example, the maximum efficiency of an internal combustion engine reaches 45%.
Advantages of electric motor
High efficiency is the main advantage of such a motor. And if the internal combustion engine spends more than 50% of the energy for heating, then in the electric motor, a small part of the energy is spent for heating.
The second advantage is the low weight andcompact size. For example, the company Yasa Motors has created a motor with a weight of only 25 kg. It is capable of delivering 650 Nm, which is a very decent result. Also, such motors are durable, do not need a gearbox. Many owners of electric cars talk about the economy of electric motors, which is logical to some extent. After all, when working, the electric motor does not emit any combustion products. However, many drivers forget that coal, gas or enriched uranium must be used to produce electricity. All these elements pollute the environment, so the environmental friendliness of electric motors is a very contentious issue. Yes, they do not pollute the air in the process of work. For them, power plants produce electricity.
Increasing the efficiency of electric motors
Electric motors have someDeficiencies that have a negative effect on performance. This is a weak starting torque, high starting current and inconsistency of the mechanical torque of the shaft with a mechanical load. This leads to the fact that the efficiency of the device is reduced.
To increase efficiency,Engine load up to 75% and higher and increase power factors. Also there are special devices for regulating the frequency of the supplied current and voltage, which also leads to increased efficiency and increased efficiency.
One of the most popular devices to increaseThe efficiency of the electric motor is a soft starter that limits the rate of growth of the starting current. It is also appropriate to use frequency converters to change the rotational speed of the motor by changing the frequency of the voltage. This leads to a reduction in power consumption and provides a smooth start-up of the engine, high accuracy of adjustment. The starting torque is also increased, and at a variable load the speed of rotation is stabilized. As a result, the efficiency of the motor increases.
Maximum efficiency of the electric motor
Depending on the type of construction, the coefficientuseful in electric motors can vary from 10 to 99%. It all depends on what kind of engine it is. For example, the efficiency of a piston pump motor is 70-90%. The end result depends on the manufacturer, the structure of the device, etc. The same can be said about the efficiency of the electric motor of the crane. If it is equal to 90%, it means that 90% of the consumed electricity will go to perform the mechanical work, the remaining 10% - for heating the parts. Still, there are the most successful models of electric motors, the efficiency of which is close to 100%, but not equal to this value.
Is the efficiency more than 100% possible?
It's no secret that electricengines whose efficiency exceeds 100% can not exist in nature, since this contradicts the basic law on the conservation of energy. The fact is that energy can not come from nowhere and disappear in exactly the same way. Any engine needs an energy source: gasoline, electricity. However, gasoline is not eternal, like electricity, because their reserves have to be replenished. But if there was a source of energy that did not need replenishment, then it would be possible to create a motor with an efficiency of over 100%. Russian invent Vladimir Chernyshov showed a description of the engine, which is based on a permanent magnet, and its efficiency, as the inventor himself claims, is more than 100%.
Hydroelectric power station as an example of perpetual motion
For example, take a hydroelectric power plant, whereenergy is produced by falling from a high water height. Water rotates the turbine, and it produces electricity. The fall of water is carried out under the influence of the Earth's gravity. And although the work on electricity production is done, the gravity of the Earth does not become weaker, that is, the force of attraction does not decrease. Further, the water under the action of sunlight evaporates and again enters the reservoir. This concludes the cycle. As a result, electricity is generated, the costs for its production are renewed.
Of course, we can say that the sun does not last forever, it'sso, but it will last a couple of billions of years. As for gravity, it constantly does work, drawing moisture out of the atmosphere. If we generalize strongly, the hydroelectric power plant is the engine that converts mechanical energy into electrical energy, and its efficiency is more than 100%. This makes it clear that the search for ways to create an electric motor, the efficiency of which can be more than 100%, should not be stopped. After all, not only gravity can be used as an inexhaustible source of energy.
Permanent magnets as energy sources for engines
The second interesting source is a permanent magnet,which from nowhere receives energy, and the magnetic field is not wasted even when the work is done. For example, if a magnet attracts something to itself, it will do the work, and its magnetic field will not become weaker. This property has been used more than once to create the so-called perpetual motion machine, but so far nothing more or less normal has come of it. Any mechanism is worn out sooner or later, but the source itself, which is a permanent magnet, is practically eternal.
However, there are specialists who claim,that in time permanent magnets lose their strength as a result of aging. This is not true, but even if it were true, then it would be possible to bring it back to life with only one electromagnetic impulse. The engine, which would require recharging once in 10-20 years, although it can not claim the role of the eternal, but very close to this is suitable.
There have been many attempts to create a perpetual motion machinebased on permanent magnets. So far, there have been no successful decisions, unfortunately. But given the fact that the demand for such engines is (it simply can not be), it is possible that in the near future we will see something that very closely approaches the model of the perpetual motor that will operate on renewable energy.
The efficiency of the electric motor is the most important parameter,which determines the efficiency of a particular motor. The higher the efficiency, the better the motor. In an engine with an efficiency of 95%, almost all the energy expended goes to work and only 5% is spent unnecessarily (for example, heating parts). Modern diesel engines can achieve an efficiency of 45%, and this is considered a cool result. The efficiency of gasoline engines is even less.