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The variable frequency drive (VFD) is used for various purposes, such as change the speed of the motor. For example, it is used to change the speed of the AC induction motor for heating or cooling systems. VFD allows the user to alter the speed of the motor so that they can adapt the device to their level of comfort.
Variable frequency drive in simple words is a power conversion device. It transforms a standard fixed-frequency to a variable-voltage output for induction motor speed control.
The main purpose of the VFD is to change motor speed and to maintain the load at the desired speeds as per the required energy. The speed of an AC induction motor is variable with the change of the voltages input and the frequency at a constant relation. Thus, even at lower speeds, the motor will keep a constant torque.
Electric motor systems account for more than 60% of the energy consumption in the industry. The enhancement of motor control systems with VFD installation can reduce the power consumption by up to 70%.
VFDs can offer various advantages in addition to energy savings and better process control:
The purpose of installing VFD has some direct and indirect benefits:
Starting current for the AC motor
The installation of VFD provides complete control on AC motor starting current. The starting of the AC motor across the line, the motor start and load up to 7-8 time the total motor current. This current loosens up the motor windings and generates heat, thereby reducing the motor durability over time.
At zero frequency and voltage, a VFD drive starts a motor. This “magnetises” the motor windings as the frequency and voltage builds, which typically take 50-70% of the full-load motor current. The extra current above this point depends on the attached load, the speed and acceleration.
Lower demand for power at the start
If the current time voltage is proportional, the power required to start an AC motor across the line is significantly higher than that required by a VFD. This will be valid only at startup. The core problem is that in particular times of the day and certain electrical distribution systems may be regarded as peak hours. Once industrial customers start their motors in such peak hours, it is not unusual for customers to be paid for power increases at maximum hours. Such aspects of demand would not be an issue with VFD’S.
To adjust the operating speed with VFD
In contrast to the conventional stop-and-go motor, the use of VFD improves and makes changes in the process. It permits starting at a lower speed and allows the programmable controller or process controller to change speed remotely.
Torque limit can be adjustable
The use of a VFD can shield the machinery from damage and protect the process because the amount of torque applied can be accurately controlled, such as VFD on bulk material handling conveyors. When an AC motor is connected, the motor will still rotate till the overload device of the motor is turned on due to the excessive current derived from the large load. In addition, a VFD can be programmed to restrict the amount of torque (amp/current), so that the AC motor never reaches the limit.
Acceleration controlled
A VFD begins at zero speed and accelerates smoothly on a path that can be modified. In comparison, an AC motor started across the line causing greater mechanical shock loads for both the motor and load attached to it. Applications such as bottling line benefits considerably from a slow power ramp that allows the conveyor belt to accelerate smoothly rather than a hast.