Three cases teach you how to use a clamp gauge to measure motor faults
Case 1
Phenomenon: A mineral crusher with a dragging motor of 15kW. After the major overhaul of the motor, it operates normally without load, but cannot carry load. When a load is added, the motor will overload and trip. After inspection, the mechanical and power supply are all normal. The DC resistance of the motor coil is measured to be 2.4 Ω, 3.2 Ω, and 2.4 Ω, respectively; Using a clamp ammeter to measure the three-phase no-load currents of 9A, 5A, and 8.8A respectively, it can be confirmed that there is a fault in the motor coil.
Analysis: After removing the motor end cover, it was found that one of the wire ends of one phase winding had been loosened, and the solder had melted. The motor is wound in parallel with two wires, one of which is disconnected while the other is still connected, resulting in a decrease in torque. It can only rotate without load, but cannot carry the load.
Case 2
Phenomenon: There is a motor with a rated power of 13kW. After rewinding the coil and testing the machine, the motor operates normally at no load. However, after being loaded, the motor speed is very slow and even does not rotate. The measured power supply voltage and resistance of each phase are normal. The three-phase no-load current is basically balanced when measured with a clamp meter, but the current values are relatively small.
Analysis: It can be concluded that the winding connection is incorrect. Opening the end cover, it was found that the motor, which was originally connected by △, was mistakenly connected to Y connection, causing the normal operating torque to be too small and unable to carry the load, because the torque of Y connection is one-third of that of △ connection.
Case 3
Phenomenon: A certain machine tool uses a 4kW motor, but when the power is turned on, the motor does not rotate and only makes a buzzing sound. Remove the motor wire, measure that there is electricity on the power side, the three-phase voltage is normal, the DC resistance of the winding is balanced, the insulation is qualified, and the mechanical rotation is flexible. Afterwards, a clamp ammeter was used to measure the no-load current on the motor lead under the switch, and the results showed that there was current in both phases and no current in one phase.
Analysis: It indicates that there is a fault in the wire inside the conduit. Pulling out the wire inside the steel pipe, it was found that a section of the wire had basically broken, facing like two needle tips, and there was white oxide powder at the end of the wire. This is due to the excessive pulling force when threading the pipe, causing the wire to be stretched and stretched, and the prolonged electrification current to generate heat and oxidize at the seemingly unbroken point. At this point, voltage can still be measured on the wire head, but current cannot be passed through.belong to desktop intelligent digital multimeters.
For example, GMC multimeter products: METRAHit 30M nbsp; The reading of a 6 1/2 high-precision digital multimeter should be ± 1999999 (six and a half digits)
