How to find the cause of the air switch tripping using a multimeter
There are three usual causes of air switch tripping. Short circuits, overloads and malfunctions.
Short circuits are not dosage, there are obvious or even loud acoustic and optical phenomena. This cause of tripping, as long as the cause of the short circuit is excluded, and then check that the contacts of the air switch have not been burned by the short-circuit current. Disconnect the upper power supply, so that the air switch is in an absolutely uncharged state, close the air switch, with a multimeter ohm file to measure the three-phase inlet and outlet terminals of this switch, if the conduction is good, you can power up to try it out. If the phase is missing, needless to say, replace the air switch.
The air switch that has short-circuited, the terminals have the possibility of being pierced, you can use a shaking table to measure the insulation resistance between the terminals (you can also use a multimeter with more than 20K gear measurement, remove the air switch on both sides of the incoming and outgoing wires). If the needle of the rocking meter quickly deflects to the right when you first shake the meter, this means that the phase-to-phase insulation of the air switch has been broken down and cannot be used. If the insulation resistance is large, several megohms or more, it can be powered up for trial.
The procedure of power-on trial is as mentioned before, disconnect the power supply of the previous level, close the overhauled air switch, and then close the power switch of the previous level, if the power supply is normal, there is no abnormal sound and odour, the air switch can continue to be used.
Overload. Overload is one of the causes of frequent tripping of air switches. When you touch an overloaded tripped air switch with your hand, it usually feels like the case is hotter, even to the point of scalding. This causes the air switch to generate a protective action from the internal thermal original.
Measure the operating current of the air switch with the AC current gear of a multimeter. If the operating current exceeds the rated current of the air switch and it continues to operate, the air switch should be replaced with one of a larger class according to the actual magnitude of the operating current.
Malfunction. When the inlet and outlet wires of the air switch are aluminium wires, it is easy to have an oxidation reaction with the copper terminals of the air switch, resulting in heat generation at the terminals. The thermal protection device inside the air switch is deformed by the heat and produces a protective action. This is a typical malfunction. This problem can be solved by pressing the copper and aluminium terminals on the aluminium wires and tightly bonding them to the air switch terminals.
