You may have heard some electricians say that frequency converters (VFD) can save power, but you have never understood why VFD can save power and how much power it can save at the same time. Is it high frequency or low frequency?

Some people may have the following questions:

1. If two identical motors work at 50HZ power frequency, one uses VFD and the other does not, and the speed and torque of the motors are at the rated state, can VFD still save power? How much can you save?

2. If the torque of the two motors does not reach the rated torque of the motor (the frequency and speed are still the same at 50HZ), how much power can the VFD one save?

3. Under the same conditions, how much money can be saved under no-load conditions? Which of these three conditions saves more?

Popular Science About vfd

Then the answer is:

It is an indelible fact that VFD can save power. In some cases, it can save more than 40% of electricity, but in some cases, it will be more wasteful than not connecting VFD!

VFDs save energy by reducing light load voltage. Because the drag torque load speed does not change much, even if the voltage is reduced, the energy saving is very weak, but it is different when used in a fan environment. When less air volume is required, the motor reduces speed. We know that the energy consumption of the fan is proportional to the 1.7th power of the speed, so the torque of the motor will drop sharply, and the energy saving effect is obvious. If we use it in the oil well, the return trip will waste a lot of electricity, but it will waste more electricity.

Of course, if the environment requires speed regulation, the energy saving effect of VFD is obvious. If the speed is not adjusted, the VFD will not save electricity, but will only improve the power factor.

Let’s go back to the first three questions:

1. If two identical motors work at 50HZ power frequency, one uses VFD and the other does not, and the speed and torque of the motors are at the rated state, can VFD still save power? How much can you save?

Answer: In this case, VFD can only improve the power factor, not save electricity.

2. If the torque of the two motors does not reach the rated torque of the motor (the frequency and speed are still the same at 50HZ), how much power can the VFD one save?

Answer: If the automatic energy-saving operation is used, the VFD can operate at a reduced voltage, which can save part of the power, but the power saving is not obvious.

3. Under the same conditions, how much money can be saved under no-load conditions? Which of these three conditions saves more?

Answer: The no-load state of dragging the load will not save much power.

For example, “closed-loop control”. I think there is room for discussion. The concept of closed loop in this paper is too narrow. Closed-loop control is not just feedback from the speed sensor, but also counting. The frequency control in the vector control is closed-loop control, and it is the closed-loop control inside the equipment. V/F control belongs to open-loop control, and PID regulator feedback controls physical quantities such as temperature, pressure, and flow. All belong to the category of closed-loop control. And it can be achieved by VFD adjustment. The concept of closed-loop control should not be interpreted so narrowly.

For example, the concept of brakes, that kind of explanation is like nonsense, playing with words, saying it is equivalent to not saying it.

1. Frequency conversion cannot save electricity everywhere. There are many occasions where frequency conversion does not necessarily save power.
2. As an electronic circuit, the VFD itself also consumes power (about 3-5% of the rated power).
3. It is a fact that VFD runs at power frequency and has power saving function. But his prerequisites are:
High power and fan/pump load;
The device itself has power saving function (software support);
 Long-term continuous operation. These are the three conditions that reflect the power-saving effect.

Also, it doesn’t really matter and doesn’t make sense to save power or not. It is an exaggeration or commercial hype to say that VFD power frequency operation is unconditional and energy-saving. Knowing the whole story, you will skillfully use him to your service. We must pay attention to the occasions and conditions of use in order to apply it correctly, otherwise it is blind obedience and credulity.

You may have heard some electricians say that frequency converters (VFD) can save power, but you have never understood why VFD can save power and how much power it can save at the same time. Is it high frequency or low frequency?

Some people may have the following questions:

1. If two identical motors work at 50HZ power frequency, one uses VFD and the other does not, and the speed and torque of the motors are at the rated state, can VFD still save power? How much can you save?

2. If the torque of the two motors does not reach the rated torque of the motor (the frequency and speed are still the same at 50HZ), how much power can the VFD one save?

3. Under the same conditions, how much money can be saved under no-load conditions? Which of these three conditions saves more?

Popular Science About vfd

Then the answer is:

It is an indelible fact that VFD can save power. In some cases, it can save more than 40% of electricity, but in some cases, it will be more wasteful than not connecting VFD!

VFDs save energy by reducing light load voltage. Because the drag torque load speed does not change much, even if the voltage is reduced, the energy saving is very weak, but it is different when used in a fan environment. When less air volume is required, the motor reduces speed. We know that the energy consumption of the fan is proportional to the 1.7th power of the speed, so the torque of the motor will drop sharply, and the energy saving effect is obvious. If we use it in the oil well, the return trip will waste a lot of electricity, but it will waste more electricity.

Of course, if the environment requires speed regulation, the energy saving effect of VFD is obvious. If the speed is not adjusted, the VFD will not save electricity, but will only improve the power factor.

Let’s go back to the first three questions:

1. If two identical motors work at 50HZ power frequency, one uses VFD and the other does not, and the speed and torque of the motors are at the rated state, can VFD still save power? How much can you save?

Answer: In this case, VFD can only improve the power factor, not save electricity.

2. If the torque of the two motors does not reach the rated torque of the motor (the frequency and speed are still the same at 50HZ), how much power can the VFD one save?

Answer: If the automatic energy-saving operation is used, the VFD can operate at a reduced voltage, which can save part of the power, but the power saving is not obvious.

3. Under the same conditions, how much money can be saved under no-load conditions? Which of these three conditions saves more?

Answer: The no-load state of dragging the load will not save much power.

For example, “closed-loop control”. I think there is room for discussion. The concept of closed loop in this paper is too narrow. Closed-loop control is not just feedback from the speed sensor, but also counting. The frequency control in the vector control is closed-loop control, and it is the closed-loop control inside the equipment. V/F control belongs to open-loop control, and PID regulator feedback controls physical quantities such as temperature, pressure, and flow. All belong to the category of closed-loop control. And it can be achieved by VFD adjustment. The concept of closed-loop control should not be interpreted so narrowly.

For example, the concept of brakes, that kind of explanation is like nonsense, playing with words, saying it is equivalent to not saying it.

1. Frequency conversion cannot save electricity everywhere. There are many occasions where frequency conversion does not necessarily save power.
2. As an electronic circuit, the VFD itself also consumes power (about 3-5% of the rated power).
3. It is a fact that VFD runs at power frequency and has power saving function. But his prerequisites are:
High power and fan/pump load;
The device itself has power saving function (software support);
 Long-term continuous operation. These are the three conditions that reflect the power-saving effect.

Also, it doesn’t really matter and doesn’t make sense to save power or not. It is an exaggeration or commercial hype to say that VFD power frequency operation is unconditional and energy-saving. Knowing the whole story, you will skillfully use him to your service. We must pay attention to the occasions and conditions of use in order to apply it correctly, otherwise it is blind obedience and credulity.

continue reading

Related Posts