Three-phase current measurement with clamp ammeter
The three-phase current needs to be detected one by one, after all, there is a phenomenon of unbalanced three-phase current.
1. First of all, correctly select the voltage level of the clamp ammeter, check whether its appearance insulation is good, whether it is damaged, whether the pointer swings flexibly, whether the jaw is rusted, etc. Estimate the rated current according to the motor power to select the range of the meter.
2. Before using the clamp ammeter, you should read the instructions carefully to find out whether it is an AC or AC-DC dual-purpose clamp meter.
3. Due to the low precision of the clamp ammeter itself, the following method can be used when measuring small currents: first wind the wire of the circuit under test several times, and then put it into the jaw of the clamp meter for measurement. At this time, the current value indicated by the clamp meter is not the actual value being measured. The actual current should be the reading of the clamp meter divided by the number of turns of the wire.
4. The jaws of the clamp meter should be closed tightly during measurement. If there is any noise after closing, you can open the jaws and repeat it again. If the noise still cannot be eliminated, you should check whether the joint surfaces on the magnetic circuit are smooth and clean. Wipe clean.
5. The clamp meter can only measure the current of one phase wire at a time, and the wire to be tested should be placed in the center of the clamp window, and multi-phase wires cannot be clamped into the window for measurement.
6. The voltage of the circuit under test cannot exceed the value marked on the clamp meter, otherwise it may easily cause a grounding accident or cause an electric shock hazard.
7. Measure the working current of the cage-type asynchronous motor in operation. According to the magnitude of the current, it can be checked to determine whether the motor is working normally, so as to ensure the safe operation of the motor and prolong its service life.
8. When measuring, you can measure once for each phase or once for three phases. At this time, the number on the meter should be zero (because the phasor sum of the three-phase current is zero). When there are two phase wires in the jaw, the meter should be zero. The value displayed on the screen is the current value of the third phase. By measuring the current of each phase, it can be judged whether the motor is overloaded (the measured current exceeds the rated current value). Whether there is a problem with the power supply voltage, that is, whether the three-phase current imbalance exceeds the limit of 10 percent .
9. Before measuring with the clamp meter, you should first estimate the magnitude of the measured current, and then decide which range to use. If it is impossible to estimate, you can first use the maximum range file and then change it to a smaller one to get an accurate reading. It is not possible to use the low current gear to measure large currents. to prevent damage to the meter.
