Measured safety requirements

In the work regulations for electrical safety, it is stipulated that two persons shall perform the duty measurement personnel's use of the clamp ammeter in the high-voltage circuit. When measuring on a high-voltage circuit, it is strictly forbidden to measure the meter from the clamp ammeter. When measuring, the operator should wear insulating gloves and stand on the insulation pad. Do not touch other devices to prevent short circuit or grounding.

When measuring the current of the high-voltage cable, phase separation can only be performed at the cable head, and the phase distance of the measured cable head must be more than 0.3 m to ensure that the combined spacing insulation strength formed by the clamp-shaped ammeter is qualified; the insulation medium of the measured cable Should be free from defects and should be able to tolerate neutral ground

The effect of the phase voltage is doubled. For the entire cable, the weak points of insulation are often located around the cable head. When the line voltage and the system overvoltage are applied, the cable head is most likely to be punctured and short-circuited first for explosion. First, when there is a phase ground in the circuit under test, measurement must be strictly prohibited. Once a single-phase ground fault occurs in the measurement, the measurement should be stopped immediately and the job should be immediately exited.

The measurement of currents in low-voltage busbars and electrical components in distribution devices is not as high as that of high-voltage measurement, but the distance between the lines of low-voltage busbars is not large, and some clamp-type ammeters have a large size, and they are measured during measurement. Open jaws may cause phase short circuit or grounding. If the surveyor's posture is unstable or the arm is shaken, accidents can easily occur. Therefore, prior to the measurement, the busbars and the electrical components should be isolated with a qualified insulating material, and care should be taken not to touch other live parts.

When measuring the current of the bare wire, if the distance between the wires of the different phases and between the wire and the ground is small, if the jaw insulation is not reliable, it is easy to cause a short circuit between the phase and the phase, and between the phase and the ground. Therefore, it is usually not allowed to use a clamp ammeter to measure the current of the bare wire. If it is necessary to measure, the bare wire should be insulated and insulated to prevent accidents.

Measurement accuracy requirements

The clamp ammeter realizes the current measurement according to the electromagnetic field generated in the jaws of the measured wire. If there is some electromagnetic interference at the measurement site, it will inevitably interfere with the normal conduct of the current measurement and affect the accuracy of the measurement. Therefore, interference sources should be avoided as much as possible to prevent interference factors of various electromagnetic properties. The clamp current meter gear selection should be appropriate, it is best to make the watch drop to more than one-third of the scale, because the watch's deflection angle is too small, not only the scale value is not easy to distinguish, and the meter in this range of measurement accuracy Relatively low.

The orientation of the wire under test in the jaw is also emphasized. The correct operation should make the wire under test perpendicular to the center of the jaw. When the wire is too skewed, the magnetic induction intensity generated by the measured current in the jaw core will change greatly, which directly affects the measurement accuracy. The measurement error caused by the improper position of the measured wire in the jaw can reach 2-5%.

When the conductor to be tested is clamped into the jaws and the clamp core is closed, the electromagnetic noise emitted from the jaws should not be heard. The hand grasping the clamp ammeter should also not feel a slight vibration. Otherwise, it means that the end face of the jaw is not tightly jointed, that is, the end surface of the jaw is not fully consistent, and the jaws should be re-tensioned and clamped once. If the noise is still present, check whether there is any dirt or rust on the end surface of the jaw. It should be removed until the jaws are well combined to ensure the accuracy of the measurement.

For digital clamp ammeters, although the battery level was checked before use, the battery level should be observed at any time during the measurement process. If the battery voltage is found to be insufficient (if a low-voltage warning symbol appears), it must be replaced. Continue to measure after the battery, otherwise it will directly affect the accuracy of the measurement.

When the measurement site temperature is abnormal or changes drastically, it will affect the accuracy of the measurement. The reason that the clamp ammeter is influenced by the temperature is mainly because: As a result of the temperature change, the result of the performance of the material constituting the key structural member of the meter is changed. For example, if the ambient temperature changes, the elasticity of the balance spring, which often causes the instrument to produce a reaction torque, changes, which in turn causes changes in the instrument's display value. It also allows the magnetic properties of the permanent magnets that form the magnetic field to change, causing the magnitude of the applied torque to change. .

In addition, due to changes in the ambient temperature, the resistances of the lines that make up the instrument, as well as the parameters of various electronic components and semiconductor devices, will change, and the final result will affect the accuracy of the measurement.

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