How to use a clamp meter to find motor faults is demonstrated in three examples.
Case 1
An ore crusher with a 15kW drive motor is a phenomenon. The motor functions normally without a load following an overhaul, however it cannot be loaded. The motor will trip due to overload once the load is introduced. The mechanical and power supply have been examined, and everything is in order. The three-phase no-load current recorded by the clamp ammeter is 9A, 5A, and 8.8A, respectively. The DC resistance of the motor coil is 2.4, 3.2, and 2.4 accordingly. The motor coil definitely has a fault.
Analysis: After removing the motor's end cover, it was discovered that one of the phase windings' wire ends had become loose and the solder had melted. The motor has two wires, one of which is removed while the other is still in place, reducing the torque, allowing it to revolve but not bear a weight.
Case 2
Phenomenon: A motor with a 13 kW rated power exists. The motor runs at a normal speed when there is no load after the coil has been rewound and checked. When a load is applied, the motor rotates very slowly or not at all. While the three-phase no-load current measured with a clamp meter is essentially balanced and the recorded power supply voltage and phase resistance are both normal, the measured current values are all quite low.
Conclusion: The winding connection is incorrect, according to the analysis. Opening the end cover revealed that the motor with the connection had been connected incorrectly to the Y connection, resulting in a normal running torque that was too low to support the load due to the Y connection's torque being one-third that of the connection.
Case 3
Phenomenon: A 4kW motor is used by a machine tool. The motor just hums after the power is turned on; it does not revolve. Disconnect the motor wires and check that there is power on the supply side, that the three-phase voltage is normal, that the DC resistance of the winding is balanced, that the insulation is suitable, and that the mechanical rotation is flexible. Finally, use a clamp ammeter to measure the no-load current on the motor leads on the switch's lower side. As a result, current flows through two phases while stopping in a third.
Analysis: It shows that the wire conduit has a problem. When the steel pipe's inner wire is removed, it is discovered to be practically fractured, with two needle-like points facing each other, and to have white oxidized powder at the wire's end. The wire becomes thinner and longer as a result of the pipe's extreme tension, and the long-term energized current warms up and oxidizes where it appears to be broken. At this point, the electrified wire head can still be used to detect voltage, but current cannot flow.
