VFD - AC Variable Frequency Drives

Torrent Engineering and Equipment utilizes variable frequency drives (VFDs) to provide the best performance in motor, fan and compressor control systems. VFDs are used in any application when there is mechanical equipment powered by motors. The drives provide extremely precise electrical motor control, enabling the motor to be ramped up, down, and maintained at speeds required. This conserves energy, rather than running a motor at a constant (fixed) speed. Since motors consume a majority of the energy produced, the demand-based control of motors increases in importance as energy supplies become ever more strained. Additionally, end users of motors can realize 25 – 70% energy savings using motor controllers.

Here are 10 additional benefits users realize when operating motors with drives:

1. Controlled Starting Current - When an AC motor is started "across the line," it takes as much as seven-to-eight times the motor full-load current to start the motor and load. This current flexes the motor windings and generates heat, which will reduce the longevity of the motor. A VFD starts a motor at zero frequency and voltage and increases it as demand dictates. The reduced starting current extends the life of the AC motor, when compared to starting across the line. The customer payback is less wear and tear on the motor (motor rewinds) and extended motor life.

2. Reduced Power Line Disturbances - Starting an AC motor across the line with its initial high demand places an enormous drain on the power distribution system connected to the motor. Typically, the supply voltage sags, with the amplitude of the sag being dependent on the size of the motor and the capacity of the distribution system. These voltage sags can cause sensitive equipment, such as computers, sensors, proximity switches and contactors, connected on the same distribution system to trip offline due to the low voltage. Using a VFD eliminates this voltage sag.

3. Lower Power Demand on Start - Because VFDs reduce the power demand when equipment starts, industrial customers can avoid peak period surge charges designed to offset over-taxed power distribution systems.

4. Controlled Acceleration - A variable frequency drive starts at zero speed and accelerates smoothly on a customer-adjustable ramp. An AC motor started across the line is a tremendous mechanical shock both for the motor and connected load. This shock will, over time, increase the wear and tear on the connected load and the AC motor.

5. Adjustable Operating Speed - The VFD enables optimizing of a process, making changes in a process, starting at reduced speed, and remote adjustment of speed by programmable controller or process controller.

6. Adjustable Torque Limit - Use of a VFD can protect machinery from damage and protect the process or product with the accurate control of the torque applied to the motor. A variable frequency drive can be set to limit the amount of torque so the AC motor never exceeds limit.

7. Controlled Stopping - Controlled stopping reduces mechanical wear and tear due to shocks to the process or breakage loss.

8. Energy Savings - Centrifugal fan and pump loads operated with an VFD reduce energy consumption. Centrifugal fans and pumps follow a variable torque load profile, which has horsepower proportional to the cube of speed and torque varying proportional to the square of speed. If the speed of the fan is cut in half, the horsepower needed to run the fan at load is cut by a factor of eight. Energy savings can be sufficient to pay back the capitalized cost in a relatively short period of time, depending on the size of the motor.

9. Reverse Operation - The output phases to the motor can be electronically changed without any mechanical devices, eliminating the need for a reversing starter. Equipment costs, additional maintenance costs, and panel space are reduced.

10. Elimination of Mechanical Drive Components - Using a VFD can eliminate the need for mechanical drive components such as gearboxes. Because it can operate with an infinite variable speed, it can deliver the speed required by the load without speed-increasing or reduction devices between the motor and load. This eliminates maintenance costs, as well as reducing floor-space requirements.