Motor winding resistance analysis: How much is considered qualified?
What should the resistance of the stator winding of a three-phase asynchronous motor be considered normal depending on the capacity? (As for using a bridge and calculating the resistance based on the wire diameter, it is a bit unrealistic.) For motors below 10KW, the multimeter only measures a few ohms. For 55KW, the multimeter shows a few tenths. Ignore the inductive reactance for now. For a 3kw star-connected motor, the multimeter measures the winding resistance of each phase to be around 5 ohms (according to the motor nameplate, current: 5.5A. Power factor = 0.8. It can be calculated that Z=40 ohms, R=32 ohms). The difference between the two is also too big.From the motor startup to the early stage of full load operation, the motor runs for a short time and the temperature is not high. After running for 1 hour, the temperature naturally rises to To a certain extent, will the motor power drop a lot after one hour? Apparently not! Here, I hope experienced electrician friends can introduce how you measure it. Friends who are also confused when repairing motors can share how you understand it?Add a picture to see:The resistance of the three-phase winding of the motor is measured as follows:1. Untie the connecting piece between the motor terminals.2. Use the low-resistance range of a digital multimeter to measure the resistance at the beginning and end of the three windings of the motor. Under normal circumstances, the resistances of the three windings should be equal. If there is an error, the error cannot be greater than 5%.3. If the motor winding resistance is greater than 1 ohm, it can be measured with a single-arm bridge. If the motor winding resistance is less than 1 ohm, it can be measured with a double-arm bridge.If there is a large difference in resistance between motor windings, it means that the motor windings have short circuits, open circuits, poor welding and errors in the number of winding turns.4. The insulation resistance between windings and the insulation resistance between windings and shells can be measured by:1) The 380V motor is measured with a megohmmeter with a measuring range of 0-500 megohms or 0-1000 megohms. Its insulation resistance cannot be less than 0.5 megohms.2) Use a megohmmeter with a measuring range of 0–2000 megohms to measure the high-voltage motor. Its insulation resistance cannot be lower than 10–20 megohms.