Motor power calculation

Power multiplied by the power factor is the actual power factor.

Check a basic electrical engineering book or an electrical engineering manual. Power should be equal to 1.732 * voltage * current * power factor.

The three-phase current values detected by MCC cannot be used to calculate the motor’s power, as the rated power is not achieved under normal operating conditions.

The rated power can be calculated using the formula P = 1.732 × UXIX for the power factor

The current in a motor can also vary depending on the number of poles, but once the capacity of a three-phase motor is known, its rated current can be calculated using this formula: divide the capacity by the voltage in kilovolts, and then multiply the result by 0.76. Note: (1) This mnemonic is applicable to the calculation of the rated current of three-phase motors at any voltage level. Both formulas and mnemonics show that motors with the same capacity but different voltage levels have different rated currents; in other words, when the voltage in kilovolts varies, dividing by the same capacity yields different \"quotients.\" When these different quotients are multiplied by the same coefficient of 0.76, the resulting current values also differ. If the above mnemonic is referred to as a general mnemonic, then special calculation mnemonics can be derived for determining the rated current of motors operating at voltage levels of 220 V, 380 V, 660 V, and 3.6 kV. When using these special calculation mnemonics to find the rated current of a three-phase motor, the relationship between capacity in kilowatts and current in amperes is based on simple multiplication; there is no need to divide the capacity by the voltage in kilovols, nor to multiply the resulting figure by the coefficient of 0.76. Three-phase 220V motor, 3.5 kilowatts and 3.5 amperes. The commonly used motor is a 380V model, with one kilowatt and two amperes. Low-voltage 660 motor, 1.2 kilowatts and amperes. High-voltage 3,000-volt motor, four kilowatts one ampere. High-voltage 6,000-volt motor, eight kilowatts one ampere. (2) When using mnemonic c, the capacity unit is kW, the voltage unit is kV, and the current unit is A; this point must be kept in mind. (3) The coefficient 0.76 in formula c is a comprehensive value derived from calculations taking into account the motor’s power factor and efficiency, etc. The power factor is 0.85 and the efficiency is 0.9; these two values are more suitable for motors with a capacity of several dozen kilowatts, while they appear to be on the high side for commonly used motors with a capacity of less than 10 kW. In this case, the rated current of the motor calculated using formula c differs from the value indicated on the motor’s nameplate; this difference has little impact on motors of 10 kW or less, as it affects the switch, contactor, wires, etc., based on the rated current. (4) Use mnemonic calculation techniques. To calculate the rated current of a common 380V motor using a mnemonic, first divide the motor’s connected supply voltage of 0.38 kV by 0.76; then multiply the resulting quotient by the motor’s capacity in kW. For larger 6kV motors, if the capacity in kW is exactly a multiple of 6kV, the capacity is divided by the voltage in kV, and the resulting figure is multiplied by a coefficient of 0.76. (5) Error. The coefficient 0.76 in formula c is derived by assuming a motor power factor of 0.85 and an efficiency of 0.9; as a result, calculating the rated current for motors with different power factors and efficiencies leads to errors. The multiples of capacity (kW) and current (A) for the 5 specialized formulas derived from formula c are the quotient of the voltage level (kV) value divided by the 0.76 coefficient. Special mnemonics are simple for mental calculation, but it should be noted that their error margin increases. Generally, for units with a higher power rating, the calculated current is slightly higher than that indicated on the nameplate ； For those with a lower kilowatt rating, the calculated current is slightly lower than that indicated on the nameplate. Therefore, when calculating the current, if it reaches ten or several dozen amperes, there is no need to consider values beyond the decimal point. It can be rounded off to take only the integer value; this is simple and does not affect its practical use. For smaller currents, it is sufficient to consider one decimal place. This is from the electrical worker’s quick calculation mnemonics