How to use multimeter to detect the cause of empty open trip
There are usually three reasons for air switch tripping. Short circuit, overload and misoperation.
Short circuit does not use much, and there are obvious or even huge acousto-optic phenomena. For tripping caused by this reason, as long as the short-circuit reason is eliminated, check whether the contact of the air switch is burned by short-circuit current. Disconnect the superior power supply to make the air switch in an absolutely dead state, close the air switch, and measure the three-phase incoming and outgoing terminal of the switch with a multimeter. If the conduction is good, you can try it on. If the phase is missing, needless to say, replace the air switch.
If the air switch has a short circuit, the terminals may be punctured. You can measure the insulation resistance between the terminals with a shaking table (you can also measure the insulation resistance with a multimeter over 20K, and remove the incoming and outgoing wires on both sides of the air switch). If the shaking table is shaken at first, the pointer of the shaking table will quickly deflect to the right, indicating that the interphase insulation of the air switch has been broken down and cannot be used. If the insulation resistance is large, more than a few megaohms, it can be powered on for trial use.
The procedure of power-on trial is as mentioned above: disconnect the front-stage power supply, close the overhauled air switch, and then close the front-stage power switch. If the power supply is normal and there is no abnormal sound and smell, the air switch can be used continuously.
Overload. Overload is one of the reasons for frequent tripping of air switches. Touching the air switch that is tripped by overload usually makes the shell feel hot or even hot. This will cause the thermal element inside the air switch to produce protective action.
Measure the working current of the air switch with the AC current gear of the multimeter. If the working current exceeds the rated current of the air switch and continues to run, the air switch with a larger level should be replaced according to the actual working current.
Misoperation. When the inlet and outlet wires of the air switch are aluminum wires, it is easy to have an oxidation reaction with the copper tip of the air switch, resulting in heating at the terminal. The thermal protection device inside the air switch is deformed by heat, resulting in protective action. This is a typical misoperation. This problem can be solved as long as the copper-aluminum terminal is pressed on the aluminum wire and closely combined with the air switch terminal.
