A situation where the no-load current of a three-phase asynchronous motor was measured using a clamp ammeter
The clamp ammeter's feedthrough current transformer's primary winding is the measured wire that travels through the transformer's center, and the secondary winding is wound on an iron core and connected to the clamp ammeter's AC ammeter. The wrench's job is to open and close the moveable section of the through-type transformer's core so that it may clamp the wire being tested. The knob is essentially a range selection switch.
When measuring current, press the wrench, open the jaws, and place the current-carrying wire under test in the middle of the feed-through current transformer. A current is induced in the side winding, and the current passes through the coil of the electromagnetic ammeter, causing the pointer to deflect, and the measured current value is indicated on the dial scale.
After inserting the test wire into the window via the core button, pay attention to how well the jaws fit together on either side and avoid allowing any other objects to obstruct the opening;
The clamp meter's minimum range is 5A, thus measuring a tiny current will result in a bigger display error. This outcome can be calculated by winding the energized wire on the clamp meter for a number of weeks, dividing the reading value acquired by the number of turns, and adding the results together.
A case of using a clamp ammeter to measure the no-load current of a three-phase asynchronous motor
instance 1
a crusher for ore with a 15 kW drive motor. 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. One of the wire ends of one of the phase windings had become loose, and the solder had melted, it was discovered after the motor end cover had been removed. 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.
Example 2 A motor with a 13 kW rated power is present. The coil is examined and wound again. When there is no stress on the motor, it rotates normally. The motor turns very slowly or not at all once the load is applied. When the three-phase no-load current is measured using a clamp meter, the measured power supply voltage and the resistance of each phase are both normal, and the current readings are all modest, it is determined that the winding connection is incorrect.When the end cover was opened, it was discovered that the motor with the connection had been inadvertently linked with 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.
Example 3: 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.shows that there is a bad wire in the conduit. 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.
