The AC impedance of a 3-kilowatt three-phase asynchronous motor is: 3×380×380÷3000=19.2 ohms; the
DC resistance is the DC resistance of the winding copper wire, generally in a fraction of a few ohms.
Resistance, in middle school physics definition, is the ability of a component in a circuit to block the flow of current. However, this definition is obviously not very strict.
Measuring its resistance can determine whether the winding has an inter-turn short circuit. Generally, the DC resistance of the motor winding is very small, and it needs to be measured with a milliohmmeter or a double-arm bridge.
For a 3000 watt motor, if calculated according to the standard, the rated current is 3000 times 220 times 0.8 times 0.8 (power factor and efficiency) ≈ 8.7A, calculated as pure resistance, that is, 3000÷220≈13.6A, the difference is still slightly larger.
Generally, the braking resistor should be selected so that the braking current Is does not exceed the rated current Ie of the inverter, and the maximum power Pmax of the braking resistor is less than 1.5 times the inverter power, and then multiplied by the overload factor.
It is used to measure the insulation resistance of the motor between phases and between phases to the ground, not less than 0.5 megohms. Use a 500V megohmmeter to measure the insulation resistance greater than 0.5M, indicating that it is good, and less than 0.5M indicating that the motor is broken.
The resistance value of a resistive element is generally related to temperature, material, length, and cross-sectional area. The physical quantity that measures the resistance to temperature is the temperature coefficient, which is defined as the percentage of the resistance value that changes when the temperature increases by 1°C.
The regenerative resistor is actually what we often call the servo braking resistor, the servo braking resistor. When the servo motor is driven in generator mode, the power returns to the servo amplifier side, which is called regenerative power.