Basic principles of energy saving
Choice of electrical equipment An important and still very little used energy saving reserve is the correct choice of the main electrical equipment in the simplest, most massive and energy-intensive unregulated electric drive (electric drive systems)
European experts believe that the average engine utilization factor (ratio of average power per cycle to nominal power) is 0.6
As experience shows, in domestic conditions this coefficient is sometimes significantly lower. Often, the share of energy costs for manufactured products increases exorbitantly, which makes production unprofitable
In such cases, a simple replacement of equipment (motors) or the introduction of automation systems can have a significant effect, however, the correct solution of such a problem requires a fairly high qualification of personnel making rational decisions The experience of creating such programs has shown that despite the high costs, the effectiveness of this approach: in the hands of specialists is a powerful, convenient, very easy to master tool that allows you to quickly solve very difficult problems Reducing losses in engines In world practice since the mid-1970s years, the use of energy-saving motors is actively promoted. The idea is very simple: they design an asynchronous motor so that they put in them 25-30% more active materials (aluminum, iron, copper), while energy losses are reduced by 30% and efficiency increases - d about 5% in small engines (kW units) and up to 1% in engines with a power of about 70 100 kW There are many enthusiastic publications related to EEM In particular, it is believed that if all engines in Europe were replaced by EEM, then the energy savings would be equivalent to the closing of six 500 MW power plants However, this direction of energy saving contains a number of controversial and non-obvious circumstances
Firstly, we are talking about an unregulated electric drive, saving a few percent on losses in the motor, in the most massive and energy-intensive applications (pumps, fans, etc.) you can continue to lose ten times more in units serviced by an electric drive
Secondly, the calculated savings will be achieved only with a little changing and close to the nominal load. With a sharply variable load, for example, with a significant share of idling in the cycle, the savings will be significantly less than the calculated
Thirdly, savings can be noticeable (advertised 45%) if all elements of the power channel are correctly selected and configured. Thus, losses in a belt drive, often used, for example, in an electric fan drive, can vary from 5 to 10 12% only due to the irrational choice of transmission parameters and can increase sharply with incorrectly selected belt tension
Reducing losses in supply networks The problem of power losses arises due to low power factor The problem of reactive power compensation traditionally enjoys great (sometimes excessively) attention in domestic practice devices, etc.)
As we can see most of these techniques are focused on an unregulated electric drive, and sometimes a very underloaded electric drive with asynchronous motors with a squirrel-cage rotor
Other ways to save energy in an unregulated electric drive include:
- decrease idle time;
- switching windings according to schemes during idling or light loads;
- changing the type of braking in electric drives with frequent starts and stops
Transition from an unregulated electric drive to an adjustable one This transition is the general direction of energy saving, adopted all over the world and giving the greatest effect both in terms of saving electricity and in other indicators of the technological process. For this, an additional element of an electric energy converter is included in the power channel, to the asynchronous motor voltage with adjustable amplitude and frequency (using frequency converters) As a result, the required (or optimal) power is supplied to the end user and large losses in the valve are excluded One of the quantities - water flow - changes uncontrollably, since it is determined by the currently open taps , and the second one is set by the pump and, therefore, can be controlled
In other technological processes, both power-generating quantities are free to control. So, when sawing logs, cutting metals, there are optimal modes determined by the best combination of speed and cutting force in particular cases: It should be emphasized that in the case under consideration, along with the main effect, there is a significant By reducing losses in the technological machine serviced by an electric drive and in other elements of the power channel, a number of additional, often no less important effects are achieved: the entire technological process is rationalized, other resources are saved, the service life of the main equipment is increased, noise is reduced, etc. it is essential to choose a method that is rational from a technical and economic point of view to control the value (values) that form the power consumed by technological machines
Until the mid-1980s, the only available solution was a DC electric drive. Its well-known disadvantages - an expensive machine and the need for maintenance - limited its use to cases where it was impossible to do without an adjustable electric drive (machines, metallurgical units, powerful excavators, etc.)e), an unregulated electric drive with asynchronous motors with a squirrel-cage rotor absolutely prevailed there. Now the situation has changed radically: perfect and affordable electronic frequency converters have appeared on the wide market. They are produced by dozens of foreign and domestic companies, have almost the same structure (uncontrolled rectifier-filter-autonomous amplitude module (PWM inverter)) and an advanced microprocessor control system that provides wide functionality, reliable drive protection and other important user functions common fleet of controlled electric drives, have become the main (and so far practically the only) means of implementing a high-quality adjustable asynchronous electric drive in mass applications
At the same time, attempts were made to use simpler thyristor voltage regulators to control the speed of an asynchronous motor with a squirrel-cage rotor in continuous mode (pumps, etc.). These devices are widely and successfully used for soft start and stop of an electric drive ("soft" starters) , with rare exceptions, cannot be used effectively for continuous continuous speed control
They require, even with the most favorable fan load, an increase in engine power by 2-3 times, a special design of the rotor (increased slip), intensive independent cooling, and at the same time they have low reliability and low energy performance. Other methods of regulation are just as inefficient speeds of an induction motor with a squirrel-cage rotor, based on a change in voltage at a constant frequency (special "tricky" asynchronous motors, slip clutches, etc.)
Multi-speed asynchronous motors are also becoming inefficient. They are heavy, expensive, require a lot of contact equipment, the cost of the drive is commensurate with the cost of the system. frequency converter — serial motor Entry into the wide market of electronic frequency converters poses a new challenge — creation of asynchronous motors with a squirrel-cage rotor
Here, apparently, it will be possible to significantly save active materials, reduce costs, etc. So, the electronic frequency converter system - an asynchronous motor with a squirrel-cage rotor becomes the main technical solution for a mass controlled electric drive in the coming years. It is especially attractive at the modernization stage, since all existing equipment is retained, but a new element — frequency converter that radically changes the entire technical and economic appearance of the system