Using a clamp ammeter to check for low voltage line leakage and theft
1. Determine if there is a problem with the residual current operated protector itself
The method is to disconnect the fuse on the phase line of the AC contactor controlling the low-voltage line at the distribution transformer. If the residual current operated protector can be put into operation normally at this time, it proves that the residual current operated protector is good. Otherwise, the residual current operated protector should be repaired and replaced.
2. Check and determine which phase line has leakage
The method is to disconnect the neutral wire on the outlet side of the AC contactor controlling the low-voltage line at the distribution transformer, and then install the removed fuse core on one of the phases. Use a clamp ammeter to measure the phase, 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, determine the location of the leakage
The method is to insert a fuse core into the phase line to be inspected at the distribution transformer, disconnect the neutral line and the fuses of the other two phases, and use a clamp type ammeter to detect the live phase line on the pole to determine the leakage position. To improve efficiency, the pole mounting position can be selected in the middle of the line, and the leakage position can be determined by detecting whether it is in the first or second half of the line, and then to detect the suspected leakage section of the line. By analogy, narrow the detection range* Afterwards, the pillar insulators of the phase line within a determined small range will be tested, and the user's household line phase lines connected to the phase line within this range will be tested (either on the ground or simultaneously during insulation detection) to determine the specific location of leakage.
In the case of low voltage line power transmission, clamp type ammeters can also be used to detect low-voltage user connecting wires within the suspected range. During detection, the phase and neutral wires of single-phase users should be placed in the jaws of the clamp ammeter at the same time, and the three phase and neutral wires of three-phase electrical users should also be placed in the jaws at the same time. If there is no leakage fault, then the phase 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 it.
4. Check the user's internal wiring and equipment for leakage
The method is to use a clamp ammeter to measure the leakage current at the user's power input line, and at the same time, put the user's electrical equipment and lamps into and out one by one. By checking the clamp ammeter to detect changes in the leakage current, locate the leaking equipment and lamps. 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 pre buried and concealed pipelines, only replacement or rewiring methods can be adopted.
