Why is volts and Hertz used instead of constant voltage?
In order to keep the magnetic flux constant, the V/Hz ratio must remain constant. This keeps torque production stable, regardless of frequency. V/Hz control of a VFD drive avoids this variation in the magnetic field strength by varying the voltage along with the frequency, in order to maintain a constant V/Hz ratio.
What is volts per hertz ratio?
The Volt/Hz ratio is calculated by taking the rated voltage of the drive (such as 460 Volts) and dividing by the line frequency (typically 60 Hz or 50 Hz). For example, a 460 Volt drive running on 60 Hz has a ratio of: 460 V / 60 Hz = 7.67 V/Hz.
What is the difference between constant and variable torque?
Many variable torque loads decrease with the square of the speed. As the speed changes, the load torque remains constant and the horsepower changes linearly with speed. Constant torque loads cause motors to draw relatively high current at low speeds when compared to variable torque applications.
What is the difference between VFD and Vvvfd?
Most commonly, the terms VFD and VSD are interchangeable. The term VVVF is often used in the mining industry – it refers to a variable voltage variable frequency drive. It describes exactly the same AC drive as the term VFD – any AC drive will automatically control voltage to suit the frequency it is running at.
Why is volts per hertz important?
The output torque for a motor is determined on the basis of the ratio of the motor’s applied voltage and applied frequency, known as the volts per hertz (V/Hz) ratio. Thus, for a motor to produce its rated torque at variable speeds, it also is necessary to control the voltage and frequency supplied to the motor.
What does constant torque mean?
Constant torque loads require the same amount of torque at low speeds as at high speeds. Torque remains constant throughout the speed range, and the horsepower increases and decreases in direct proportion to the speed. With constant torque loads, the torque is not a function of speed.
What do you understand by constant torque and constant power drive?
Constant torque and Power Operations: Fig: Region of continuous operation in the torque–speed plane. When the field flux is at its full value the speed corresponding to full armature voltage and full current (i.e. the rated full-load condition) is known as base speed.
Why it is required to maintain the ratio of VF is constant in the control of induction motor?
From above equation ratio V/f is directly proportional to maximum value of flux as N is constant for the motor. Magnetic material of core of stator gets saturated if flux is increasing beyond limit. This is the reason to keep V/f ratio constant so that magnetisation of core remain same.
Is a VSD and VFD the same?
VSD is the acronym for variable speed drive. This all-encompassing term describes drives which are used for controlling both AC and DC motors, and technically, even mechanically control. It’s commonly used in the context of AC or DC electric drives. VFD is the term for a variable frequency drive.