How to Check the Leakage of Low-Voltage Lines with Clamp Ammeter
The single-phase power supply uses a clamp ammeter to clamp the neutral wire and the live wire at the same time, and if there is an indication, there is leakage. Three-phase power supply without a neutral line uses a clamp ammeter to hold three live wires at the same time, and if there is an indication, there is leakage. Three-phase four-wire power supply uses a clamp ammeter to clamp four wires at the same time, and if there is an indication, there is leakage.
How to use a clamp ammeter to check low-voltage line leakage and electricity theft?
A clamp ammeter is a combination of a current transformer and an 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 gap opened by the iron core without being cut off, and the iron core is closed when the wrench is spread out.
The measured 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. Then the ammeter connected to the secondary coil has an indication-measure the current of the line under test.
The clamp ammeter can be changed to different ranges by shifting the switch. However, it is not allowed to operate with electricity when shifting gears. Clamp meters are generally not high in accuracy, generally 2.5 to 5 grades.
For the convenience of use, there are switches of different ranges in the meter for the function of measuring different levels of current and measuring voltage.
When using ordinary ammeter to measure current, it is necessary to cut off the circuit and shut down the circuit before connecting the ammeter for measurement. This is very troublesome, and sometimes the normal operation of the motor does not allow this.
At this time, it is much more convenient to use a clamp ammeter, which can measure the current without cutting off the circuit. The clamp ammeter is the best tool to check the leakage of low-voltage lines or check the electricity theft.
1. Determine whether there is a problem with the residual electrical activity protector itself
Measures: At the distribution transformer, disconnect the fuse on the phase line on the outlet side of the AC contactor that controls the low-voltage line. If the residual current operation protector can be put into operation normally at this time, it is confirmed that the residual current operation protection The appliance is good. Otherwise, the residual electrical activity should be checked and replaced.
2. Check to determine which phase and phase line are leaking
Method: At the distribution transformer, disconnect the neutral wire on the outlet side of the AC contactor that controls the low-voltage line, and then install the removed fuse core on one of the phases, and measure the voltage with a clamp ammeter. phase, the measured current is the leakage current of that phase. Measure the leakage current of other leakage phases sequentially in the same way.
In order to avoid phase line grounding on the line (if there is no partial discharge power frequency test transformer, automatic ratio tester, ground conduction resistance tester, frequency conversion series resonance test device, wireless high-voltage phase nuclear device adopts the one-line-one-local method Electricity, etc.) A large current will damage the instrument. When testing, first put the clamp ammeter gear on the high current gear; if the detection value is small, then switch the clamp ammeter gear to mA gear for detection. From: Home of Electrical Technology
3. After determining the phase line with leakage, determine the location of leakage
Method: At the distribution transformer, insert the phase wire to be checked into the fuse core, disconnect the neutral wire and the other two-phase fuses, and use a clamp ammeter to detect the live phase wire to determine the leakage position. In order to improve efficiency, the location of the boarding pole can be selected in the middle of the line. Through detection, it can be judged whether the leakage site is in the first half or the second half of the line, and then the line section with suspected leakage is detected. By analogy, the detection limit is reduced.
Finally, test the phase line post insulator within the determined smaller limit, and test the phase line of the user connection line connected to the phase line within the limit (it can be carried out on the ground, or when the insulator is tested Also carried out) to determine the detailed location of the leakage.
