Clamp Multimeter Field Test Electric Energy Meter and Current Transformer
It is simple and convenient to use a portable clamp-type multimeter to detect the change of the current transformer and the error of the electric energy meter in the field, and the judgment is accurate.
Without dismantling any original circuit and without affecting the power supply, it can quickly measure the current and sensor transformation ratio and the accuracy of the electric energy meter's disk revolutions per minute. This is a technical anti-stealing measure for electricity business inspection.
The shunt is: use a portable clamp multimeter to test on-site in AC gear. First, measure the primary load current and the secondary current after the CT ratio, and then according to the test data. After a simple operation, the CT transformation ratio and the error coefficient of the electric energy meter can be obtained immediately.
Test the CT ratio calculation formula n=I1/I2.
where n——CT magnification
I1 - measured - secondary load current
I2——The secondary current of the CT under test
Example 1: Calculate CT transformation ratio.
A certain measuring box CT ratio scale is 150/5, and the load current measured by the clamp-type multi-purpose performance field is 90A. The secondary current is 2A, and the CT ratio is calculated.
①Calculate the actual multiple of CT:
Substitute into the formula n′=I1/I2=90/2=45
It is known that the original calibration CT transformation ratio is n=150/5=30 magnification. However, the actual magnification of the CT calculated by the field test is 45 times.
It can be seen that the standard value of the original transformation ratio of 150 / 5 may be wrong. Or there is an error in the measurement wiring, and further inspection is required.
Example 2: Calculate the number of revolutions of the electric energy dial. A-metering box electric energy meter is 5A (three three-phase four-wire), rated voltage is 220V, and the constant is 1200 rpm/kW. h·CT is 100/5, and the primary current of a certain phase is 70A measured with a clamp-type performance field. Then - observe the electric energy meter turn 38 circles in one minute, and calculate how many circles the meter should make. (Power factor is taken as 0.8)
① Calculate the CT primary and secondary side power P
Clamp Multimeter
②Calculate the number of revolutions of the electric energy meter 1 watt 1 minute
Solution: Known to be 1200 revolutions per kWh. Then: the number of disk revolutions in 1W1 minute is n=1200(1000×60)=0.02(week)
③ Under the load, the electric energy meter should run for several weeks
n=616×0.02=12.32(week)
According to the on-site load measurement, the table should turn 12.32 weeks within 1 minute. In the field observation, the electric energy meter only turned for 8 weeks in 1 minute. In this way, the meter leaks 35% of the electricity.
Through the above method, various technical means of stealing electricity can be effectively prevented.
For example: privately replace the CT inner core, increase the transformation ratio, change the number of turns of the CT secondary coil, and reduce the secondary output current; short-circuit the number of turns of the CT secondary coil to reduce the secondary output current, turn the energy meter negative, etc .
