Schneider inverter has misunderstandings in practical applications

Myth 1: Whether the inverter can complete power saving

The use of inverters can save electricity Some literature claims that inverters are power-saving control products, giving people the impression that only the use of inverters can save electricity. In practice,

The reason why the inverter can save electricity is that it can regulate the speed of the motor. If the frequency converter governor is a power-saving control product, then all the speed control equipment can also be said to be a power-saving control product. The inverter governor is just slightly higher in power and power factor than other speed control equipment.

Whether the inverter can complete power saving is determined by the speed regulation characteristics of its load. For centrifugal fans, centrifugal pumps and other loads, 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 valve is originally used to control the flow, and it is not a full-load operation, it is changed to speed control, which can complete the power saving. When the rotational speed is reduced to 80% of the original speed, the power is only 51.2% of the original power. It can be seen that the application of frequency conversion governor in this type of load has obvious power-saving effect. For loads such as roots blowers, the torque is independent of the size of the speed, i.e. the constant torque load. If the method of releasing the remaining air volume by using the air release valve was originally used to adjust the air volume, and the speed control operation was changed, the power saving could also be completed. When the rotational speed drops to 80% of the original, the power is 80% of the original. It is much smaller than the use of centrifugal fans and centrifugal pumps. When it comes to constant power loads, power has nothing to do with the rotational speed. Constant power load of cement plant, such as batching belt scale, under the condition of setting the flow rate, when the material layer is thick, the belt speed slows down; When the material layer is thin, the belt speed accelerates. The application of frequency converter governor in this type of load cannot save electricity.

Compared with the DC speed regulation system, the DC motor has higher power and higher power factor than the AC motor, and the power of the digital DC governor is equal to that of the frequency conversion governor, and even the power of the digital DC governor is slightly higher than that of the frequency conversion governor. Therefore, the claim that the use of AC asynchronous motors and variable frequency governors is more energy-efficient than the use of DC motors and DC governors, and theory and practice have proved that this is not correct.

Schneider inverter has misunderstandings in practical applications

Schneider inverter has misunderstandings in practical applications

Myth 2: The capacity of the inverter is selected only based on the extra power of the motor

In relation to the motor, the price of the inverter governor is more expensive, so it is very meaningful to reasonably reduce the capacity of the inverter governor under the premise of ensuring safe and reliable operation.

The power of the variable frequency governor refers to the power of the 4-pole AC asynchronous motor to which it is suitable. Because of the same capacity of the motor, its

The number of poles is different, and the additional current of the motor is different. With the increase of the number of poles of the motor, the additional current of the motor increases. The capacity selection of the inverter governor cannot be based solely on the additional power of the motor. Together, for retrofit projects that did not originally use frequency converters, the capacity selection of frequency converters cannot be based solely on the additional current of the motor. This is because the capacity selection of the motor should take into account factors such as load, affluence coefficient, motor specification, etc., and industrial motors often operate under 50%-60% additional load. If the capacity of the inverter governor is selected based on the extra current of the motor, the amount of wealth is too large, which forms an economic waste, and the reliability has not been improved.

For squirrel cage motors, the capacity selection of Schneider inverter should be based on the principle that the additional current of the inverter is greater than or equal to 1.2 times the normal operating current of the motor. Regarding heavy-duty starting, high-temperature environment, winding motor, synchronous motor, etc., the capacity of the inverter should be appropriately increased.

In the design of the inverter from the beginning, it is understandable that the selection of the inverter capacity is based on the additional current of the motor. This is because the capacity of the inverter cannot be selected based on the actual operating conditions at the moment. Of course, in order to reduce investment, in some cases, it is also possible to determine the capacity of the inverter first, and then select according to the actual current after the equipment has been running for a period of time.

Schneider inverter has misunderstandings in practical applications

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