Dec 11
9
A variable frequency drive is really a speed manage technique used for regulating the speed of an alternating present electric motor. The speed regulation is effected by varying the frequency of the electrical energy supplied towards the motor. Variable frequency drives find wide application in ventilation systems for big buildings, conveyors, pumps, elevator, machine tool drives, et cetera.
An alternating existing induction motor draws up to 6 times its rated present in the time of start up. The current continues to remain high till the motor approaches the full speed. When a variable frequency drive is used to start the induction motor, a low frequency and a low voltage are applied to the motor. Normally, the start-up frequency is two Hz or less. Given that the frequency is low, the current flow in the time of starting will also be low. When the motor is began employing the variable frequency drive, the applied voltage and frequency are increased at a controlled rate to ensure that the motor will not draw excessive present. This strategy of starting enables the motor to as considerably as 150% of its rated torque at much less than 50% of its rated existing consumption.
The variable frequency drive program consists of an AC motor, a controller and an operator interface. A controller is a solid state electronic power conversion device. AC input power is converted to DC intermediate power utilizing a three-phase bridge rectifier method. The DC power is then converted to quasi-sinusoidal AC power making use of an inverter switching circuit.
The rewards of a variable frequency drive are the following:
~ Saving in electrical energy consumption is by far the most essential benefit of employing variable frequency drives. For example, AC motors utilized in ventilation systems aren’t required to usually run at peak load. Variable frequency drives save energy by controlling the volume of air required for a specific technique demand.
~An induction motor employing a variable frequency drive will last longer. The maintenance expenses will also be lower. While classic starters commence the motors abruptly, variable frequency drives gradually enhance the speed to operating speed. This contributes to a reduction mechanical and electrical anxiety on the motor.
~A variable frequency drive enables greater process manage. This really is simply because variable frequency drives could be programmed to run the motor at the needed load, cease as per requirement and apply a specified quantity of torque.
There are three types of variable frequency drives. These are continuous voltage, constant present and cycloconverters. Probably the most crucial section of a variable frequency drive could be the inverter circuit. These units support boost power element and lessen harmonic distortion.
