How do you get more torque out of a VFD?

How do you get more torque out of a VFD?

A novel way to provide constant torque at higher-than-base speeds is to run a 230-volt motor on a 460-volt VFD. In these applications, the drive is programmed to provide full voltage at 120 hertz and then reduces voltage proportionally as speed is reduced.

How does a VFD affect torque?

A VFD cannot increase the voltage above its supply voltage. This causes the current to decrease as frequency increases, thus decreasing the available torque. Theoretically, torque is reduced by the ratio of the base speed divided by the higher speed (60 hertz / 90 hertz = 67%).

How does VFD control motor torque?

VFDs are designed to maintain a constant V/Hz ratio and torque up to 60 Hz. As Table 1 shows, the V/Hz ratio decreases at above 60 Hz because VFDs are designed to maintain constant voltage above 60 Hz. When the V/Hz ratio decreases, the air-gap flux decreases, causing a decrease in the torque.

Does a VFD provide constant torque?

Constant torque is achieved because the VFD is increasing the voltage to the motor as it increases the speed. This relationship keeps the current and torque to the motor relatively constant. Typical applications are: Traction Drives, Compressors, Conveyors, Mixers, and Hoists.

What is Variable torque?

VARIABLE TORQUE LOADS: Many types of loads require reduced torque when driven at speeds less than the base speed of the load. Conversely, such loads may require increased torque when driven at speeds greater than the base speed of the load. These are classified as variable torque loads.

How does frequency affect motor power?

A frequency higher than the rated frequency usually improves the power factor but decreases locked-rotor torque and increases the speed and friction and windage loss. At a frequency lower than the rated frequency, the speed is decreased, locked-rotor torque is increased, and power factor is decreased.

What is a variable torque application?

VTL (variable torque load) drives are designed to deal with alternating torque demands and can range their speed/torque from low to high. Think about HVAC fans and sump pumps. Though the drive may need to run the motor at intermittent torque and speed, the application will not be at full capacity 100% of the time.

How can we increase the starting torque of an induction motor?

There are three ways to improve the starting torque of Single phase induction Motor

1. Internal Rotor Resistance. The across the line starting torque at low speed can be increased by increasing the rotor resistance.
2. External Rotor Resistance.
3. Variable Voltage/Frequency.

How do you calculate torque in a VFD?

Block diagram of VFD for hardware Torque Calculation The Full load torque for induction motor is given as T fl =9550*P VA /N r *1000 (1)

Which of the following is an example of variable torque equipment?

Variable torque loads include most centrifugal and axial pumps, fans and blowers and many mixers and agitators. As the speed is decreased, the torque will decrease by the square of the speed decrease and the horsepower required decreases by the cube of the speed decrease.

Is a pump constant torque or variable torque?

Variable torque loads are loads that startup under no load. Typically these are fans and clean water (centrifugal) pumps. Constant torque loads are those that startup under a load. Typically these are positive displacement pumps, conveyors and general machining applications.

How does a variable frequency drive affect torque?

Once a Variable frequency drive reaches the point of delivering full motor voltage, increasing the frequency does not increase torque on the motor shaft because voltage cannot be increased further to maintain the V/Hz ratio. See Figure 1. Figure 1. Controlling the volts-per-hertz ratio (V/Hz) applied to an AC motor controls motor torque.

How does hp and torque change with frequency?

HP and torque changes with different frequencies When a VFD increases frequency above 60 hertz, HP and torque do a complete flip flop. HP remains at 100 percent, and torque decreases as frequency increases. The torque reduction occurs because motor impedance increases with increasing frequency.

How does a variable frequency drive control speed?

Variable frequency drives control frequency applied to a motor over the range 0 Hz to several hundred Hertz. Variable frequency drives are programmed for a minimum operating speed and a maximum operating speed to prevent damage to a motor or driven load. Damage occurs when a motor is driven faster than its rated nameplate speed.

How are horsepower and torque affected by VFD?

At 60 hertz (base motor speed), both HP and torque are at 100 percent. When the VFD reduces frequency and motor speed, it also reduces voltage to keep the volts/hertz ratio constant. Torque remains at 100 percent, but HP is reduced in direct proportion to the change in speed.