What to do with the leakage clamp ammeter?
The leakage current clamp meter is mainly composed of impedance transformation, range transformation, AC-DC transformation, amplification, indicating device and so on. Some also have over-current protection, acousto-optic alarm circuit and test voltage regulating device, and their indicating devices are divided into analog and digital. According to the American UL standard, leakage current is the current that can be conducted from the accessible part of household appliances, including capacitive coupling current. The leakage current includes two parts, one is the conduction current i1 through the insulation resistance; The other part is the displacement current I2 passing through the distributed capacitor. The capacitance reactance of the latter is XC=1/2pfc, which is inversely proportional to the power frequency. The distributed capacitor current increases with the increase of the frequency, so the leakage current increases with the increase of the power frequency. For example, if power is supplied by silicon controlled rectifier, its harmonic component will increase the leakage current.
If the insulation performance of a circuit or a system is assessed, this current should include not only all currents flowing into the earth (or conductive parts outside the circuit) through insulating substances, but also currents flowing into the earth through capacitive devices in the circuit or system (distributed capacitors can be regarded as capacitive devices). Longer wiring will form larger distribution capacity and increase leakage current, which should be paid special attention to in ungrounded systems.
Precautions for leakage of clamp ammeter:
1. The principle of leakage current measurement is basically the same as insulation resistance, and measuring insulation resistance is actually a kind of leakage current, but it is expressed in the form of resistance. However, the AC voltage is applied to the normal measurement of leakage current, so the components of leakage current include capacitive components.
2. During the withstand voltage test, in order to protect the test equipment and test according to the specified technical indicators, it is also necessary to determine a large current value that is allowed to flow through the tested equipment (insulation material) without damaging the high electric field strength of the tested equipment (insulation material). This current is usually also called leakage current, but this method is only used in the above specific situations. Please pay attention to the difference.
3. Leakage current is actually the current flowing through the insulation part of the electrical circuit or equipment without fault and applied voltage. Therefore, it is one of the important signs to measure the insulation of electrical appliances, and it is the main index of product performance.
4. The leakage current tester is used to measure the leakage current irrelevant to work generated by the working power supply (or other power supply) of electrical appliances through insulation or distributed parameter impedance, and its input impedance simulates the impedance of human body.
5. Connect the measured object to the measuring terminal, start the instrument, raise the test voltage to 1.06 times (or 1.1 times) of the rated working voltage of the measured object, switch the phase change switch, read the secondary readings respectively, and select the reading leakage current value with large value. When the change-over switch K is connected to the neutral line, what the tester samples is the leakage current between the neutral line and the shell. When K is connected to the phase line, the leakage current between the phase line and the shell is tested.
6. It must be noted that the leakage current is not necessarily the same when K is connected to the neutral line or K is connected to the phase line. This is because the position of insulation weakness of household appliances is random. Therefore, the leakage current test should be conducted by K-switching polarity, and the larger value should be taken as the leakage current value of the electric heating apparatus to be tested.
