Use the light to check the three-phase motor winding for broken wires

If one phase in the stator winding of a three-phase motor is circuit-opened, a phase loss will occur inside the motor. For a three-phase motor with star (Y) connection, the consequences of internal phase loss and power supply phase loss are exactly the same. For motors with delta (△) connection, when one phase winding is disconnected, an open triangle is formed inside the three-phase motor. There is no current in the disconnected phase winding, and the currents in the other two phases are increased than normal values. Usually, three-phase motor open circuit faults mostly occur at the ends of the windings, or at the terminals of each winding component, or at the ends of the three-phase lead wires. These areas should be checked first during inspection. To check the open circuit of a small three-phase motor, you can use the R×1Ω block of a multimeter to measure it, or you can use a light to detect it. The method is as shown in the figure. The so-called "light" is composed of one electric bead, two large batteries (3V), and a pair of test leads. If the winding is normal, the bead H will light up; if the winding is disconnected, H will not light up.