Misunderstanding 1 The use of frequency converters can save electricity Some literature claims that the frequency converter is a power-saving control product, giving the impression that as long as the inverter is used, it can save electricity.

In fact, the inverter can save power because it can speed the motor. If the frequency converter is a power-saving control product, then all speed-control equipment can also be said to be a power-saving control product. The frequency conversion governor is only slightly more efficient than Other speed control devices and the power factor.

Whether the frequency conversion governor can achieve power saving is determined by the speed regulation characteristics of its load. For loads such as centrifugal fans and centrifugal pumps, the torque is proportional to the square of the speed, and the power is proportional to the cube of the speed. As long as the original use of the valve to control the flow, and not full-load work, to speed operation, can achieve energy savings. When the speed drops to the original 80%, the power is only 51.2% of the original. It can be seen that the application of frequency converters in such loads has the most obvious effect of power saving. For a load such as a Roots blower, the torque is independent of the speed, that is, a constant torque load. If the original air vent valve is used to remove the excess air volume to adjust the air flow rate and change to speed control, it can also save electricity. When the speed drops to the original 80%, the power is 80% of the original. Compared to centrifugal fans and centrifugal pumps, the energy saving effect is much smaller. For constant power loads, the power is independent of the speed. Cement plant constant power load, such as batching belt weigher, under a certain set flow conditions, when the material layer is thick, the belt speed is slowed; when the material layer is thin, the belt speed is faster. The use of frequency converters in such loads cannot save power.

Compared with DC speed control systems, DC motors are more efficient than AC motors and have higher power factor. Digital DC speed regulators are comparable to inverters, and even digital DC speed regulators are slightly more efficient than inverters. Therefore, it is claimed that the use of AC asynchronous motors and frequency conversion governors is more energy-efficient than the use of DC motors and DC governors. This is not true in theory and practice.

Misunderstanding 2 The capacity of the inverter is based on the rated power of the motor. Compared with the motor, the price of the inverter is relatively expensive. Therefore, under the premise of safe and reliable operation, it is very reasonable to reduce the capacity of the inverter. Significant.

The power of the frequency converter is the power of the 4-pole AC asynchronous motor to which it applies.

Because the same capacity of the motor, the number of poles, the motor rated current is different. As the number of motor poles increases, the rated current of the motor increases. The capacity of the inverter cannot be selected based on the rated power of the motor. At the same time, for the retrofit projects that originally did not use the inverter, the capacity of the inverter was not selected based on the rated current of the motor. This is because the capacity of the motor is selected taking into consideration factors such as the maximum load, the affluence factor, and the motor specification, and the amount of leanness is often large, and the industrial motor is often operated at a rated load of 50% to 60%. If the capacity of the inverter is selected on the basis of the rated current of the motor, the amount of surplus is too large, resulting in economical waste, and the reliability is not improved as a result.

For squirrel-cage motors, the capacity of the inverter should be selected based on the principle that the rated current of the inverter is greater than or equal to 1.1 times the maximum normal operating current of the motor, so that capital can be saved as much as possible. For heavy load starting, high temperature environment, winding motor, synchronous motor and other conditions, the capacity of the frequency conversion governor should be appropriately increased.

For the design that uses the frequency converter from the beginning, the choice of the capacity of the frequency converter is based on the rated current of the motor. This is because the drive capacity cannot be selected in actual operation at this time. Of course, in order to reduce investment, in some occasions, the capacity of the inverter may also be uncertain, and after the actual operation of the equipment for a period of time, the actual current may be selected.

In a 2î€4Ã—13m cement grinding secondary grinding system of a cement company in Inner Mongolia, there is a domestically produced N-1500 O-Sepa high-efficiency classifier with motor type Y2-315M-4 and motor power of 132kW. However, FRN160-P9S-4E type inverters are used. This type of inverter is suitable for 4-pole, 160kW motors. When it is put into operation, the maximum operating frequency is 48Hz, and the current is only 180A, which is less than 70% of the rated current of the motor. The motor itself has a considerable amount of wealth. The inverter selection specifications are one step larger than that of the drag motor, causing undue waste, and the reliability will not be improved as a result.

Anhui Chaohu Cement Plant No. 3 limestone crusher, its feeding system uses 1500 Ã— 12000 plate feeder, drag motor selection Y225M-4 AC motor, motor rated power 45kW, rated current of 84.6A. Before carrying out frequency conversion speed regulation reformation, through tests, it was found that when the plate feeder is running normally, the three-phase average current is only 30A, and only 35.5% of the rated current of the motor. In order to save the investment, choose ACS601-0060-3 type frequency converter, the rated output current of this frequency converter is 76A, apply to 4 poles, the power is 37kW electric motor, have obtained better use effect.

These two examples have been described one by one. It is shown that, for retrofit projects that have not previously used inverters, the selection of inverter capacity based on actual operating conditions can significantly reduce investment.

Misunderstanding 3 Use apparent power to calculate reactive power compensation Energy-saving benefits Use apparent power to calculate reactive energy compensation Energy-saving effect. For example, when the original system fan power frequency is full load, the motor running current is 289A. When using variable frequency speed regulation, the power factor is about 0.99 at 50Hz full load and the current is 257A. This is due to the internal filter capacitor of the inverter. Improve the power factor effect. The energy-saving calculation is as follows: Î”S=UI=Ã—380Ã—(289-257)=21kVA

Therefore, this article believes that its energy-saving effect is about 11% of stand-alone capacity.

The actual analysis: S means that the apparent power, that is, the product of voltage and current. When the voltage is the same, the apparent power saving percentage and the current saving percentage are one and the same. In a reactance circuit, the apparent power only reflects the maximum allowable output capability of the power distribution system and does not reflect the actual power consumed by the motor. The actual power consumed by the motor can only be represented by active power. In this example, the actual current is used, but the apparent power is calculated instead of the active power. We know that the actual power consumed by a motor is determined by the fan and its load. The increase of power factor did not change the load of the fan, nor did it improve the efficiency of the fan. The power actually consumed by the fan did not decrease. After the power factor is increased, the operating state of the motor is not changed, the stator current of the motor is not reduced, and the active power and reactive power consumed by the motor are not changed. The reason for the increase in power factor is that the inverter's internal filter capacitor generates reactive power that is used by the motor. As the power factor increases, the actual input current to the frequency converter is reduced, thereby reducing the line losses from the grid to the frequency converter and the copper losses of the Transformer. At the same time, the load current is reduced, and the power distribution equipment such as transformers, switches, contactors, and wires that supply power to the inverter can carry more loads. It should be pointed out that if the line losses and the copper consumption of the transformer are not taken into consideration as in this example, and considering the loss of the frequency converter, the frequency converter will not only fail to save energy but also consume electricity when operating at full load of 50Hz. Therefore, it is not correct to use the apparent power to calculate energy-saving effects.

A cement plant centrifugal fan drive motor model Y280S-4, rated power 75kW, rated voltage 380V, rated current 140A. Before the frequency conversion speed control reform, the valve was fully opened. It was found through testing that the motor current was 70A, only 50% load, the power factor was 0.49, the active power was 22.6 kW, and the apparent power was 46 î€ 07 kVA.

After adopting the variable frequency speed control transformation, when the valve is fully open and the rated speed is running, the average current of the three-phase power network is 37A, and it is considered that the power saving (70-37)Ã·70Ã—100%=44.28%. This calculation seems to be reasonable. It is still based on the apparent power calculation energy-saving effect. After further testing, the plant found that the power factor was 0.94, the active power was 22.9 kW, and the apparent power was 24.4 kVA. It can be seen that the increase in active power not only does not save electricity, but also consumes electricity. The reason for the increase in active power is to consider the loss of the frequency converter without considering the line loss and the copper consumption of the transformer. The key to this kind of error lies in not considering the influence of the increase of power factor on the current drop, the default power factor does not change, thus exaggerating the energy-saving effect of the frequency converter. Therefore, in calculating the energy-saving effect, active power must be used, and apparent power cannot be used.

Article link: Gongkong (100 stations) Com/Tech_news/detail/62738. Html

In fact, the inverter can save power because it can speed the motor. If the frequency converter is a power-saving control product, then all speed-control equipment can also be said to be a power-saving control product. The frequency conversion governor is only slightly more efficient than Other speed control devices and the power factor.

Whether the frequency conversion governor can achieve power saving is determined by the speed regulation characteristics of its load. For loads such as centrifugal fans and centrifugal pumps, the torque is proportional to the square of the speed, and the power is proportional to the cube of the speed. As long as the original use of the valve to control the flow, and not full-load work, to speed operation, can achieve energy savings. When the speed drops to the original 80%, the power is only 51.2% of the original. It can be seen that the application of frequency converters in such loads has the most obvious effect of power saving. For a load such as a Roots blower, the torque is independent of the speed, that is, a constant torque load. If the original air vent valve is used to remove the excess air volume to adjust the air flow rate and change to speed control, it can also save electricity. When the speed drops to the original 80%, the power is 80% of the original. Compared to centrifugal fans and centrifugal pumps, the energy saving effect is much smaller. For constant power loads, the power is independent of the speed. Cement plant constant power load, such as batching belt weigher, under a certain set flow conditions, when the material layer is thick, the belt speed is slowed; when the material layer is thin, the belt speed is faster. The use of frequency converters in such loads cannot save power.

Compared with DC speed control systems, DC motors are more efficient than AC motors and have higher power factor. Digital DC speed regulators are comparable to inverters, and even digital DC speed regulators are slightly more efficient than inverters. Therefore, it is claimed that the use of AC asynchronous motors and frequency conversion governors is more energy-efficient than the use of DC motors and DC governors. This is not true in theory and practice.

Misunderstanding 2 The capacity of the inverter is based on the rated power of the motor. Compared with the motor, the price of the inverter is relatively expensive. Therefore, under the premise of safe and reliable operation, it is very reasonable to reduce the capacity of the inverter. Significant.

The power of the frequency converter is the power of the 4-pole AC asynchronous motor to which it applies.

Because the same capacity of the motor, the number of poles, the motor rated current is different. As the number of motor poles increases, the rated current of the motor increases. The capacity of the inverter cannot be selected based on the rated power of the motor. At the same time, for the retrofit projects that originally did not use the inverter, the capacity of the inverter was not selected based on the rated current of the motor. This is because the capacity of the motor is selected taking into consideration factors such as the maximum load, the affluence factor, and the motor specification, and the amount of leanness is often large, and the industrial motor is often operated at a rated load of 50% to 60%. If the capacity of the inverter is selected on the basis of the rated current of the motor, the amount of surplus is too large, resulting in economical waste, and the reliability is not improved as a result.

For squirrel-cage motors, the capacity of the inverter should be selected based on the principle that the rated current of the inverter is greater than or equal to 1.1 times the maximum normal operating current of the motor, so that capital can be saved as much as possible. For heavy load starting, high temperature environment, winding motor, synchronous motor and other conditions, the capacity of the frequency conversion governor should be appropriately increased.

For the design that uses the frequency converter from the beginning, the choice of the capacity of the frequency converter is based on the rated current of the motor. This is because the drive capacity cannot be selected in actual operation at this time. Of course, in order to reduce investment, in some occasions, the capacity of the inverter may also be uncertain, and after the actual operation of the equipment for a period of time, the actual current may be selected.

In a 2î€4Ã—13m cement grinding secondary grinding system of a cement company in Inner Mongolia, there is a domestically produced N-1500 O-Sepa high-efficiency classifier with motor type Y2-315M-4 and motor power of 132kW. However, FRN160-P9S-4E type inverters are used. This type of inverter is suitable for 4-pole, 160kW motors. When it is put into operation, the maximum operating frequency is 48Hz, and the current is only 180A, which is less than 70% of the rated current of the motor. The motor itself has a considerable amount of wealth. The inverter selection specifications are one step larger than that of the drag motor, causing undue waste, and the reliability will not be improved as a result.

Anhui Chaohu Cement Plant No. 3 limestone crusher, its feeding system uses 1500 Ã— 12000 plate feeder, drag motor selection Y225M-4 AC motor, motor rated power 45kW, rated current of 84.6A. Before carrying out frequency conversion speed regulation reformation, through tests, it was found that when the plate feeder is running normally, the three-phase average current is only 30A, and only 35.5% of the rated current of the motor. In order to save the investment, choose ACS601-0060-3 type frequency converter, the rated output current of this frequency converter is 76A, apply to 4 poles, the power is 37kW electric motor, have obtained better use effect.

These two examples have been described one by one. It is shown that, for retrofit projects that have not previously used inverters, the selection of inverter capacity based on actual operating conditions can significantly reduce investment.

Misunderstanding 3 Use apparent power to calculate reactive power compensation Energy-saving benefits Use apparent power to calculate reactive energy compensation Energy-saving effect. For example, when the original system fan power frequency is full load, the motor running current is 289A. When using variable frequency speed regulation, the power factor is about 0.99 at 50Hz full load and the current is 257A. This is due to the internal filter capacitor of the inverter. Improve the power factor effect. The energy-saving calculation is as follows: Î”S=UI=Ã—380Ã—(289-257)=21kVA

Therefore, this article believes that its energy-saving effect is about 11% of stand-alone capacity.

The actual analysis: S means that the apparent power, that is, the product of voltage and current. When the voltage is the same, the apparent power saving percentage and the current saving percentage are one and the same. In a reactance circuit, the apparent power only reflects the maximum allowable output capability of the power distribution system and does not reflect the actual power consumed by the motor. The actual power consumed by the motor can only be represented by active power. In this example, the actual current is used, but the apparent power is calculated instead of the active power. We know that the actual power consumed by a motor is determined by the fan and its load. The increase of power factor did not change the load of the fan, nor did it improve the efficiency of the fan. The power actually consumed by the fan did not decrease. After the power factor is increased, the operating state of the motor is not changed, the stator current of the motor is not reduced, and the active power and reactive power consumed by the motor are not changed. The reason for the increase in power factor is that the inverter's internal filter capacitor generates reactive power that is used by the motor. As the power factor increases, the actual input current to the frequency converter is reduced, thereby reducing the line losses from the grid to the frequency converter and the copper losses of the Transformer. At the same time, the load current is reduced, and the power distribution equipment such as transformers, switches, contactors, and wires that supply power to the inverter can carry more loads. It should be pointed out that if the line losses and the copper consumption of the transformer are not taken into consideration as in this example, and considering the loss of the frequency converter, the frequency converter will not only fail to save energy but also consume electricity when operating at full load of 50Hz. Therefore, it is not correct to use the apparent power to calculate energy-saving effects.

A cement plant centrifugal fan drive motor model Y280S-4, rated power 75kW, rated voltage 380V, rated current 140A. Before the frequency conversion speed control reform, the valve was fully opened. It was found through testing that the motor current was 70A, only 50% load, the power factor was 0.49, the active power was 22.6 kW, and the apparent power was 46 î€ 07 kVA.

After adopting the variable frequency speed control transformation, when the valve is fully open and the rated speed is running, the average current of the three-phase power network is 37A, and it is considered that the power saving (70-37)Ã·70Ã—100%=44.28%. This calculation seems to be reasonable. It is still based on the apparent power calculation energy-saving effect. After further testing, the plant found that the power factor was 0.94, the active power was 22.9 kW, and the apparent power was 24.4 kVA. It can be seen that the increase in active power not only does not save electricity, but also consumes electricity. The reason for the increase in active power is to consider the loss of the frequency converter without considering the line loss and the copper consumption of the transformer. The key to this kind of error lies in not considering the influence of the increase of power factor on the current drop, the default power factor does not change, thus exaggerating the energy-saving effect of the frequency converter. Therefore, in calculating the energy-saving effect, active power must be used, and apparent power cannot be used.

Article link: Gongkong (100 stations) Com/Tech_news/detail/62738. Html

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