Advantages of clamp ammeters_ Measuring three-phase current with a clamp ammeter
Advantages of clamp ammeters
The biggest advantage of a clamp type ammeter is that it can measure current without interruption. Clamp type ammeters are mainly divided into two categories: pointer type and digital type. Clamp type ammeters can be divided into specialized AC clamp type ammeters and electromagnetic clamp type ammeters for both AC and DC purposes based on their results and purposes.
Usually, when measuring current, it is necessary to disconnect the circuit under test in order to connect the ammeter or primary winding to the circuit under test. By using a clamp type ammeter, the measured current can be measured without disconnecting the circuit under test. Although the accuracy level of clamp ammeters is not high, usually 2.5 or 5.0, they have been widely used due to their convenience in use. Clamp type ammeters are generally used to measure load currents with a voltage not exceeding 500V. The commonly used clamp type ammeters are divided into two types according to their different structural forms: transformer type and electromagnetic type. Among them, there are t301 clamp type ammeters that only measure AC current, t302 clamp type ammeters that measure both AC current and AC voltage, and mg series AC DC dual purpose clamp type ammeters.
Measuring three-phase current with a clamp ammeter
The three-phase current needs to be detected phase by phase, as there is a phenomenon of three-phase current imbalance.
1. Firstly, select the voltage level of the clamp type ammeter correctly, check its appearance for good insulation, damage, flexible pointer movement, and rust on the jaw. Estimate the rated current based on the motor power to select the range of the meter.
2. Before using a clamp type ammeter, it is necessary to carefully read the manual and determine whether it is an AC or DC dual purpose clamp type ammeter.
3. Due to the low accuracy of the clamp ammeter itself, the following method can be used when measuring small currents: first, wrap the wires of the circuit being tested a few turns, and then place them in the clamp of the clamp ammeter for measurement. At this point, the current value indicated by the clamp meter is not the actual value being measured, and the actual current should be the reading of the clamp meter divided by the number of coils wound on the wire.
4. When measuring, the jaws of the clamp type watch should be tightly closed. If there is any noise after closing, the jaws can be opened and reset once. If the noise cannot be eliminated, the joint surfaces on the magnetic circuit should be checked for smoothness. If there is dust, it should be wiped clean.
5. The clamp meter can only measure the current of one phase wire at a time, and the measured wire should be placed in
In the center of the clamp shaped window, it is not allowed to clamp all multiphase wires into the window for measurement.
6. The voltage of the tested circuit should not exceed the value indicated on the clamp meter, otherwise it may cause grounding accidents or electric shock hazards.
7. Measure the working current of the cage asynchronous motor during operation. Based on the current level, it is possible to check and determine whether the motor is working properly to ensure safe operation and extend its service life.
8. When measuring, it is possible to measure once in each phase or once in three phases. At this point, the number on the meter should be zero (due to the sum of the three-phase current phasors being zero). When there are two phase lines in the clamp, the value displayed on the meter is the current value of the third phase. By measuring the current of each phase, it can be determined whether the motor is overloaded (the measured current exceeds the rated current value), Is there a problem with the power supply voltage inside the motor or the device that converts other forms of energy into electrical energy, that is, whether the three-phase current imbalance exceeds the 10% limit.
9. Before measuring with a clamp meter, the magnitude of the measured current should be estimated before deciding which range to use. If it is impossible to estimate, the maximum range range can be used first and then reduced appropriately to obtain accurate readings. Small current ranges cannot be used to measure large currents. To prevent damage to the instrument.
