How to Judge the Leakage and Stealing of Low Voltage Lines with Clamp Ammeter
Clamp Ammeter is composed of current transformer and Ammeter.
The iron core of the current transformer can be opened when the wrench is tightened; The wire through which the measured current passes can pass through the open gap of the iron core without cutting it off. When the wrench is released, the iron core closes. The tested circuit wire passing through the iron core becomes the primary coil of the current transformer, where the current is induced in the secondary coil through the current. Thus, the Ammeter connected with the secondary coil can indicate - measure the current of the line under test.
Usually, when measuring the current with an ordinary Ammeter, the Ammeter can be connected for measurement only after the circuit is cut off and shut down, which is very troublesome, and sometimes it is not allowed to do so for a normal running motor. At this time, it is much more convenient to use the clamp Ammeter, which can measure the current without cutting off the circuit.
Clamp Ammeter is the best tool to check the leakage of low-voltage lines or the theft of electricity.
1、 Determine if there is a problem with the residual current operated protector itself
Detection method: At the distribution transformer, disconnect the fuse on the phase line of the AC contactor on the output side of the low-voltage line. 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 which phase line has leakage
Test method: 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.
3、 After determining the phase line with leakage, determine the location of the leakage
Detection method: 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 to determine the leakage position. To improve efficiency, the climbing position of the pole can be selected in the middle of the line. Through detection, it can be determined whether the leakage position is in the first or second half of the line, and then it can be detected in the suspected leakage section of the line. By analogy, narrow the detection range.
Finally, the pillar insulators of the phase line within a determined small range shall be tested, and the user's household line phase lines connected to the phase line within this range shall 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
