Use clamp Ammeter to check the leakage and theft of low-voltage lines
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 on the output side of 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: at the distribution transformer, disconnect the neutral line at the outgoing line side of the AC contactor that controls the low-voltage line, 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 the phase. Measure the leakage current of the remaining leakage phases in sequence using the same method.
In order to prevent the instrument from being damaged by large current due to phase line grounding (such as someone stealing electricity by using the one line one place method) on the line, the clamp Ammeter gear shall be placed on the large current gear first during detection; If the detected 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: at the distribution transformer, insert the phase line to be checked into the fuse core, 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 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.
Under the condition of low-voltage line power transmission, clamp type Ammeter can also be used to detect the low-voltage user connection line within the suspected range. During detection, the phase line and neutral line of single-phase users shall be placed in the jaw of clamp Ammeter at the same time, and the three phase lines and neutral lines of Three-phase electric power users shall also be placed in the jaw at the same time. If there is no leakage fault, then the phasor sum of the load current magnetic flux is zero, and the clamp Ammeter indication is also zero; If there is leakage current, the clamp Ammeter can detect the leakage current.
4 Check whether the user's internal lines and equipment have leakage
The method is: measure the leakage current with a clamp Ammeter at the power incoming line of the user, put the user's electrical equipment and lamps into operation and out of service one by one, and find out the leakage equipment and lamps by looking at the clamp Ammeter to detect the change of leakage current. If all the equipment lamps are in good condition, or the equipment with leakage has exited, but the clamp Ammeter shows that the user still has leakage current, it may be that the user's low-voltage line has leakage, which 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.
