How to check for leakage in clamp ammeters
The tested circuit wire passing through the iron core becomes the primary coil of the current transformer, and the current is induced in the secondary coil through the current. So that the ammeter connected to the secondary coil has an indication - to measure the current of the tested circuit. The clamp meter can be changed to different ranges by shifting the gear of the switch. But it is not allowed to operate with electricity when shifting gears. The accuracy of clamp watches is generally not high, usually ranging from 2.5 to 5 levels. For ease of use, there are also conversion switches with different ranges in the meter for measuring different levels of current and voltage.
When using a clamp ammeter to detect current, be sure to clip in a wire (wire) being tested. If two parallel lines are inserted, the current cannot be detected. In addition, when using the center (iron core) of the clamp ammeter for detection, the detection error is small. When checking the power consumption of household appliances, using a circuit separator is more convenient. Some circuit separators can amplify the detection current by 10 times, so currents below 1A can be amplified before detection. When using a DC clamp ammeter to detect DC current (DCA), if the current direction is opposite, it displays a negative number. This function can be used to detect whether the car's battery is in a charging or discharging state.
At the distribution transformer, disconnect the neutral wire on the output side of the AC contactor that controls the low-voltage line, and then install the removed fuse core on one of the phases. Measure the phase with a clamp ammeter, and the measured current is the leakage current of that phase. Measure the leakage current of the remaining leakage phases in sequence using the same method. To prevent the occurrence of high current damage to the instrument due to phase grounding on the line (such as someone stealing electricity using the one line, one place method), first place the clamp type ammeter in the high current position during testing; If the detection value is very small, then switch the clamp ammeter gear to milliampere gear for detection.
After determining the phase line with leakage, the method to determine the location of leakage is: at the distribution transformer, insert a fuse core into the phase line to be checked, disconnect the neutral line and the fuses of the other two phases, and use a clamp ammeter to detect the live phase line and determine the leakage position. To improve efficiency, the pole can be mounted in the middle of the line, and the leakage position can be determined by detection whether it is in the front or back half of the line, and then detected in the suspected leakage section of the line. Similarly, narrow down the detection range. Finally, the pillar insulators of the phase line within the determined smaller range are tested, and the user's household line phase lines connected to the phase line within this range are tested (which can be done on the ground or simultaneously with insulation testing) to determine the specific location of leakage.
In the case of low-voltage power transmission, clamp ammeters can also be used to detect low-voltage user connection lines within the suspected range. When testing, the phase and neutral wires of single-phase users should be placed in the clamp of the clamp ammeter at the same time, and the three phase and neutral wires of three-phase users should also be placed in the clamp at the same time. If there is no leakage fault, the phasor sum of the load current magnetic flux is zero, and the indication of the clamp ammeter is also zero; If there is leakage current, the clamp ammeter can detect the leakage current.
The method of checking for leakage in the user's internal wiring and equipment is to use a clamp ammeter to measure the leakage current at the user's power inlet line, and at the same time, put the user's electrical equipment and lighting fixtures into and out one by one. By observing the changes in the leakage current detected by the clamp ammeter, the leaking equipment and lighting fixtures can be found. If all the equipment and lighting fixtures are in good condition, or if the equipment with leakage has been removed, but the clamp ammeter shows that the user still has leakage current, it is possible that the user's low-voltage circuit has leakage, and it should be handled according to the specific situation. For leakage faults in buried pipelines, only wire replacement or rewiring methods can be adopted.
