Star multi-branch parallel three-phase motor winding open circuit inspection circuit

The stator windings of three-phase motors above 10kW mostly use multiple enameled wires wound in parallel and multiple branches connected in parallel. In a certain phase winding, if one or several windings are broken, or even all of the windings are broken, it is difficult to judge with a light. The three-phase current balance method can be used for detection. As shown in the figure, the circuit is powered by a single-phase AC arc welding machine transformer T, and three ammeters A1, A2, and A3 are connected in series with windings U1, V1, and W1 respectively. After powering on, observe the current values ​​of the three ammeters. Normally, the values ​​indicated are basically the same. If the phase difference is greater than 5%, the phase with the smaller current is the open winding.