Motor output power problem
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Does the rated power of the motor refer to the rated output power? If the actual current is known, can the actual output power be calculated using the following formula: Actual output power = rated power × actual current / rated current. Also, is the rated power calculated by the following formula?: Rated power = 1.732 × line current × line voltage × power factor × efficiency This post was last edited by rmxg on 2009-4-13 21:30 ]
Both formulas have problems. 1. I have never seen the actual output power calculated like this, but there is a simple way to know that even if your formula is true, there are still range requirements, such as the motor is close to full load. For example, when the motor is no-load, there should actually be no output, but the current may reach 50% at this time. 2. This formula seems familiar. But it seems that efficiency should not be used as a multiplication coefficient. It seems that dividing by efficiency is more reasonable.
The actual output power you gave is a theoretical calculation formula； The rated power calculation formula is correct!
The output power of the motor P=M* ω. M is torque, ω is angular velocity. Angular velocity can be converted from rotational speed or rotational frequency: ω=1/f. Torque detection is a bit difficult. But it can be obtained in the following ways: a. Measure it with a torque meter (but for general loads, measuring with this precision instrument is a bit overkill). b. Calculate backwards through the motor's drag load, that is, divide the motor's drag load by the transmission efficiency of the connection, which is the actual output power of the motor. c. When the accuracy requirements are not very high, it is generally assumed that the motor is rated at full load output, and the rated value of the motor is calculated as the actual value of the output. (This has an advantage: if the calculated efficiency of the motor deviates too much from the rated efficiency - usually low, it means that the motor may have insufficient output, or there may be a problem with the transmission connection.)
Actual output power = rated power × actual current / rated current. The power mentioned by the poster should refer to active power. The rated active power is related to the power factor. If it is a motor load, when the motor is running under a light load, the power factor is low, which is commonly known as a large horse-drawn cart. Therefore, if it is calculated accurately, the formula does not hold. But it can be used as a rough estimate. Rated power = 1.732 × line current × line voltage × power factor × efficiency. For three-phase motors, it is the power output part, and the rated power has no efficiency.
The second one is correct, actual power = operating current x machine terminal voltage x efficiency.