Advantages and disadvantages
From the beginning of the industry, until today motors have been the main source of movement. From steam systems to the discovery of electric motors which provide electromotive force, the need has arisen to control this force through variation of speed while maintaining sufficient torque to mobilize large loads.
Controlling speed has been one of the main requirements in production processes and until not many years ago this variation was made thanks to mechanical systems such as gears, belts, pulleys and pinions.
Obtaining the desired speed as a result involved calculating the number of teeth, gear diameters, adequate belt tension, etc. This made it difficult to use and in many cases it was necessary to count on bulky mechanical rigs, which were constantly maintained, which implied downtime and increased production costs.
What advantages do we get using variable speed drives?
Using variable speed drives allows us to have many advantages, including:
- Reduction in the consumption of electrical energy due to the reduction of the starting torque peak.
- Improved profitability and productivity of production processes, due to the possibility of increasing production capacity by increasing the speed of the process.
- Motor Protection by having internal protection systems in addition to allowing longer motor life by reducing mechanical impacts through the allocation of acceleration and deceleration ramps for start and stop events.
- Savings in maintenance, due to the lack of mechanical parts that may suffer aging due to mechanical wear.
- Possibility of making control loops and interacting with the process thanks to the fact that currently many speed variators have PID control functions, in addition to activating alarm signals in case of process failure, among many other possibilities.
- Have the possibility of basic PLC functions and dynamic braking.
What disadvantages do we get using variable speed drives?
- Installation, programming and maintenance must be carried out by qualified personnel.
- Derivation of noise and interference in the electrical network, which could affect other nearby electronic elements.
- For simple applications it may involve more investment than a simple system (contactor-motor-starter), although in the long run the additional cost is amortized due to the energy saving and reactive power provided by the drive.
- Inverter faults cannot be repaired on site (must be sent to the house or technical service). In the meantime, another equivalent inverter must be available, or the installation must be left inoperative.
TECHNOLOGICAL FUNDAMENTALS OF ELECTRONIC SPEED REGULATION IN MOTORS
An electronic speed regulator is made up of circuits that incorporate power transistors such as the IGBT (insulated gate bipolar transistor) the basic principle of operation being to transform electrical energy of industrial frequency into electrical energy of variable frequency.
This frequency variation is achieved through two stages in series. A rectifying stage that transforms the alternating current into direct, with all the power in the so-called intermediate circuit and another inverter that transforms the direct current into alternating current, with an adjustable frequency and voltage, which will depend on the set points.The entire frequency converter assembly is called an inverter.
The working mode can be manual or automatic, depending on the needs of the process, given the enormous flexibility offered by speed regulators, allowing solutions to be found to obtain optimal working points in all types of processes, being able to be managed by computer, PLC, digital signals or manually.
Most brands include motor protections within the converter itself, such as protections against over current, over-temperature, fault against imbalances, earth faults, etc., in addition to offering starting and smooth braking processes using acceleration and braking ramps, which results in an increase in the life of the engine and the installations.
Regarding speed, converters usually allow two types of control:
- Manual speed control. The speed can be set or modified manually (operator display). Possibility of variation in the direction of rotation.
- Automatic speed control. Using feedback the speed can be adjusted automatically. This solution is ideal for installation in applications where the demanded speed varies continuously.
Application examples
Obtain different speeds and rotation change according to the product recipe.
A mini programmer can give the order to execute the sequence of product development; speed and direction of rotation are important factors in this. Carrying out these operations automatically is simple, the drive interacting with the mini PLC, which will send impulse signals in the drive’s input module, which will act according to the programmed set points.
- Constant pressure control in pumping systems.
- Product positioning on conveyor belt.
- Homogenization of liquids in tanks at controlled speed.
- Traction speed control in packaging machines.
- Speed control ramps on Strech Film tapes.
- Ventilation systems and / or gas extraction.
- Alternating pumping systems, among many other possibilities.