Reasons for the introduction of frequency converters
With the transition to a market economy, the issues of energy and resource saving in all spheres of industry and communal services in Russia have acquired special importance. In our time, practically all the mechanical energy for the operation of machines and mechanisms is obtained by electric energy, using electric drives for this purpose. They consume more than 65% of all electricity produced in the country. The growth of tariffs forces us to look for ways to reduce electricity costs. After all, even now the cost of electricity consumed annually by an average electric motor is almost 5 times greater than its own cost. Elimination of irrational expenditure of funds is increasingly being solved today with the help of high technologies. One of the main directions here is the introduction in various industries and utilities of regulated electric drives based on a frequency converter or inverter.
What is a frequency-controlled electric drive
The frequency-controlled electric drive consists, in general terms, of a three-phase AC motor and inverter, which provides, at a minimum, a smooth start of the electric motor, its stopping, changing the speed and direction of rotation. The possibility of such regulation improves the dynamics of the electric motor and, thereby, increases the reliability and durability of the technological equipment. Moreover, the inverter allows the automation of virtually any process. In this case, a feedback system is created where the inverter automatically changes the speed of rotation of the motor in such a way as to maintain various parameters of the system at a given level, for example pressure, flow, temperature, liquid level, etc.
Due to the optimal control of the electric motor depending on the load, the power consumption in pumping, fan, compressor and other units is reduced by 40-50%, and the starting currents, which are 600-700% of the rated current and are a scourge for start-up equipment, disappear completely. Thus, the use of adjustable electric drives based on frequency converters allows the creation of a new energy-saving technology, in which not only the electric energy is saved, but the service life of electric motors and technological equipment as a whole also increases.
What is a frequency converter?
Frequency converter, or international terminology - an inverter, is an electronic static device designed to control an asynchronous or synchronous AC motor. At the converter output, an electrical voltage with a variable amplitude and frequency is generated. The very name of the "frequency converter" is due to the fact that the regulation of the engine speed is carried out by changing the frequency of the supply voltage supplied to the motor from the converter. Thus. the inverter converts the voltage of the supply network 220V / 380V at a frequency of 50Hz into an output pulse voltage, which generates a sinusoidal current in the motor windings from 0 to 400 Hz and higher.
Two ways to control the speed of the motor with an inverter
By increasing the frequency and amplitude of the voltage supplied from the inverter to the windings of the induction motor, it is possible to provide a smooth control of the speed of rotation of the motor shaft. Changing the frequency of the motor supply voltage leads to a deviation from the calculated values of the maximum and starting torque of the engine, efficiency, power factor. Therefore, in order to maintain the required performance of the engine, it is necessary to change the amplitude of the voltage simultaneously with changing the frequency. Such a fairly simple method of speed control is called scalar. In existing converters with scalar control, the ratio of the maximum motor torque to the moment of resistance on the shaft is kept constant. Those. when the frequency is changed, the amplitude of the voltage changes the current, the ratio of the maximum motor torque to the current load moment remains unchanged. This ratio is called the overload capability of the engine. With constant overload capacity, the nominal power factors and efficiency the engine over the whole range of speed control is practically unchanged. The scalar method of control is expedient for realizing at low requirements to the range of regulation of the engine speed and stability of maintaining the specified parameters. An important advantage of the scalar method is the possibility of simultaneous control of a group of electric motors. Scalar control is sufficient for most practical applications of a frequency-controlled electric drive with a speed control range of up to 1:40.
For high-speed drives, vector control may be required. It allows to significantly increase the control range and the accuracy of control, but it is much more expensive than the scalar one. Vector control provides direct control of the motor torque. The torque is determined by the current of the stator, which creates an exciting magnetic field. With direct torque control, it is necessary to vary the amplitude and phase of the stator current, in addition to the amplitude. vector of current. This is the reason for the term "vector control". It provides a control range of up to 1: 1000 and higher, speed control accuracy - hundredths of a percent, accuracy by the moment - a unit of percent. The share of such drives is gradually increasing and today it is about 5% of the total number.
Frequency converters provide:
Frequency converter control methods
The frequency converter can be controlled from the built-in or remote control panel, or via external signals. In the second case, the rotation speed is set by the analog signal 0-10 V or 4-20 mA, and the start, stop and change of the rotation modes are given by digital signals.
The rule of selecting a frequency converter
As a rule, the power of the frequency converter is selected equal to the power of the electric motor. This rule applies to electric motors with a nominal speed of 1500 and 3000 rpm. When using other motors or in some special applications, the choice of the frequency inverter (inverter) must meet the following condition: the rated output current of the frequency converter must be not less, but better slightly higher than the rated current of the motor.
Areas of application of the advantages of frequency converters:
The economic effect of the use of frequency converters:
Translation of cranes to the frequency drive Krasnodar
Krasnodar as the capital of the Kuban is a rapidly developing region of Russia. The recent large-scale construction projects showed the need for economical use of energy resources. The upcoming major projects for the construction of modern communication and transport channels with the new region of Russia-Crimea are setting tasks for contractors requiring rational and frugal use of resources. Balanced decision to reduce energy resources is offered by the company "EMR" whose specialists provide a full range of services for the introduction of frequency converters in Krasnodar and the Krasnodar Territory as well as throughout the territory of Russia. Based on the technologies of frequency re-education offered by our company, it is possible to implement the following projects: