Common formulas for measuring three-phase motors with multimeters
1. Determine the head and tail ends of three-phase motor stator windings by DC method
Three-phase motor winding, judged by head and tail DC method. The multimeter dials the milliampere, and the DC power supply is dry battery. One phase winding is connected to the meter, and the other phase winding is connected to the battery.
When the power is turned on, the hands turn and the positive pole is reversed. If the wiring is not reversed, the residual phase winding is judged in the same way.
2. The residual magnetism method is used to determine the head and tail ends of the stator windings of the three-phase motor
The motor that has been run is judged by the residual magnetism method at the beginning and end. Three-phase winding outlet, marked and connected in parallel. Turn the multimeter to the milliamp range and connect the common point in parallel.
Slowly turn the motor shaft while watching the gauge needle. There is no obvious movement of the pointer, and the three heads and three tails are connected in parallel. The pointer swings to the left and right, with two heads and one tail at one end.
Swap the head of one-phase winding, and then use the same method to measure and identify. Until the hands do not swing, the head and the tail are respectively connected to one end.
3. The circulating current method determines the head and tail ends of the stator windings of the three-phase motor
The motor that has been run is judged by the head-to-tail circulation method. The three-phase winding outlet ends are connected in series to form a triangle. Turn the multimeter to the milliamp gear and connect it to the three-phase winding in series.
Evenly turn the motor shaft while watching the gauge needle. The pointer basically does not swing, and the windings are connected end to end. The pointer swings greatly, and the first phase winding head is reversed.
The two connection points and the two wire ends are both the first end and the tail end.
4. Use a multimeter to measure the speed of the three-phase motor
Three-phase motor speed, use a multimeter to judge. Open the motor terminal box and remove the terminal lugs. Connect the multimeter to the milliamp gear and bridge any phase winding.
Turn the rotor around once and watch the pointer swing a few times. The two-pole motor swings once, and the synchronous speed is three thousand whole. The four-pole motor swings twice, and the synchronous speed is one thousand and five.
Judging the speed in this way, the speed is slightly lower than the synchronous speed.
