The three-phase asynchronous motor was created at the end of the XIX century and at this stage of human development is one of the indispensable elements in modern industrial production. To ensure a smooth start and stop of such an engine, a special device is used.
It is called - frequency converter or chastotnik, if simpler. For large engines with high power the presence of such a converter is especially important. With the help of chastotnikov, starting currents can be regulated, which implies the implementation of such manipulations as control and limitation of their value.
- 1 The principle of operation of the frequency converter
- 2 Choice chastotnika
3 Connecting the frequency converter to the motor
- 3.1 Terminals
- 4 findings
The principle of operation of the frequency converter
Exclusively mechanical current control leads to energy losses and reduced equipment life. Indicators of this current will be several times greater than the nominalthat will adversely affect the normal operation of the equipment.
The principle of operation of the frequency converter is that the current is controlled electronically. This provides a soft start, smooth control of the drive, by respecting the relationship between frequency and direction according to a special pre-set formula.
The frequency converter has a number of advantages, which very positively characterize the operation of this device. One of these advantages is the fact that chastotnik helps save energy consumption. Savings of approximately 50%, which in itself is a very big plus. By the way, taking into account the needs of specific production, there is the possibility of regulating the energy that is consumed in the process of equipment operation.
The essence of this device is the principle of double voltage conversion. The very essence can be described through the schedule of just two points, which will allow to follow and realize the whole principle:
- Network voltage subjected to rectification and filtration system of capacitors.
- After that, electronic control directly enters the work.that is to form a current with a frequency that has been pre-programmed.
At the output, rectangular pulses are emitted that are amenable to the stator winding of the motor, after which they become close to a sine wave.
Manufacturers of such devices focus on the cost of frequency converters. From this it follows that many of the options that are available in more expensive models, on the cheap models of converters will no longer be present. Before selecting the desired device should pay attention to the technical characteristics of all available models presented in the range, as well as the basic requirements for a specific use.
- Management can be done in two ways.: vector and scalar. Vector control provides the ability to fine tune. The principle of scalar control is to maintain a single relationship between the voltage and the output frequency specified by the user. Scalar control is not suitable for complex devices and is used on simpler devices like a fan.
- The higher the power indicated in the specifications, the higher the versatility of the converter. This means that it will provide interchangeability. In addition, the maintenance of such a device will be easier.
- You should certainly pay attention to the specified voltage range. It should be as wide as possible, which will ensure safety in case of differences in its norms. And one can not fail to mention the fact that raising is much more dangerous than lowering. If increased, the line capacitors may explode.
- The specified frequency must meet all production needs.. The lower limit is indicated by the speed control range of the drive. When the need for a wider should resort to vector control. Practical application involves the use of frequencies such as: from 10 to 60 Hz. Rarely, but there are up to 100 Hz.
- Implementation management involves the use of various inputs and outputs.. The more of them, the, of course, better. But you need to take into account that with a larger number of inputs and outputs, the cost of the frequency converter increases significantly, and its configuration becomes more complicated.
- Attention should also be paid to the control bus of the connected equipment.. It should coincide with the possibility of the scheme of chastotnik by the number of inputs and outputs. Also, do not forget that it is better to have a small smell for a possible upgrade.
- Do not forget about the overload capabilities of the device. It is recommended to choose a frequency converter with power that will be 15% more than the power of the engine used. It is strongly recommended to read the instructions attached to the chastotnik included. Manufacturers certainly indicate in the documentation for the device all its basic parameters. In the event that peak loads are important, then when choosing a device, attention should be paid to real current values and values indicated as peak loads. In this case, you need to choose a converter with peak current indicators, which will be 10% higher than those specified in the documentation.
Connecting the frequency converter to the motor
- For single phase wiring (220 V), that is, for use in the home, the connection must be made by the user by performing a "triangle" scheme. In no case should the output current exceed 50% of the nominal! It is very important!
- For industrial use (three-phase wiring at 380V) it is recommended to connect the frequency converter to the motor according to the star circuit.
The frequency converter has a certain number of terminals, which are indicated by different letters, and which are needed for different connections:
- R, S, T - wires of the network are connected to these terminals, moreover, the sequence does not matter
- U, V, W - An asynchronous motor is turned on to these terminals. In the event that the motor rotates in the opposite direction, you just need to change any of the wires connected to these terminals
- One terminal is provided. for grounding
Recommendations for operation and maintenance of the inverter for the asynchronous motor.
In order to extend the life of the converter, you should follow a number of requirements and follow the tips that will help extend the life of the device:
- It is highly recommended to clean the inside of the transducer from dust.. You can do this and a vacuum cleaner, but here it should be noted that such cleaning will be incomplete and insufficient, since dust tends to condense, which will create additional difficulties for a vacuum cleaner, with which it will not always be able cope. Therefore, it is better to use the compressor. For cleaning of this kind, it is better suited.
- It should periodically replace the nodes. It is very important to do this on time.. The operation of electrolytic capacitors is designed for a period of five years, while fuses have a service life of two times longer - a full ten years. Cooling fans must be replaced by the user after two to three years of operation. Internal loops should also change after a certain period, their life expectancy is calculated for six years of use.
- It is necessary to monitor the internal temperature and voltage on the DC bus. An increase in temperature entails very unpleasant consequences. This is the drying of thermally conductive paste, and the destruction of capacitors. Thermal paste should be changed regularly - about once every three years and in no case less often.
- Be sure to adhere to all prescribed operating conditions.. Ambient temperature should not be higher than 40 degrees. High humidity and dusty air are not allowed.
Asynchronous motor control is not an easy process. It is required to possess certain knowledge in order to successfully carry out all manipulations involving both connections and operations.
Converters that were made handicraft can be used at home and for domestic purposes. In addition, there are such chastotniki significantly less than industrial counterparts. But it is not recommended to use such converters for work in production. For such conditions should choose chastotniki, which were collected in factories. Work on such devices and their maintenance should be entrusted to personnel who are well versed in these devices and have sufficient knowledge to work with chastotniki.
Asynchronous electric motors are superior in many parameters to DC motors. The superiority of this applies to the device and reliability. Therefore, in many cases, users choose precisely asynchronous motors, guided precisely by considerations about their superiority over other devices.
Mechanical current control causes some negative consequences, since when using this control option it is impossible to be sure of the 100% and high-quality operation of the equipment. The use of frequency converters for asynchronous motors has its very important advantages, which are important in many aspects of working with engines. One of the main advantages of using electronic control and chastotnikov is the fact that these devices allow you to save energy consumption. In addition, the power will be more.
Frequency should be chosen, taking into account the many characteristics that are written in the documentation attached to the device. Hand-made frequency converters can be useful in living conditions, but you should not use them in production.
Operation of converters should be carried out correctly, in accordance with all the recommendations and rules. This will improve the quality of the equipment. In addition, many tips will extend the work of the engine and converter. It is highly recommended to monitor the voltage. In the event of a critical overvoltage, capacitors may explode. Frequency should be used with an eye on all the basic safety rules. It is recommended not to take up work with them in the absence of all the necessary knowledge in this area.