The DC current indication is on the high side, and the power number is inconsistent with the product of DC voltage and current

May 11, 2022

Fault phenomenon: the equipment operates normally and the DC current indication is high. If the current is set at the rated value, the voltage is too low, and the indicated value of the power meter is inconsistent with the product of DC voltage and DC current, which was consistent before.

Fault analysis and treatment: the reason for this fault is that the indication of DC ammeter is inaccurate, which gives people an illusion that the current is large.

The cause of this fault is relatively hidden and difficult to find at the moment. If carefully analyzed, it can be found that the indicated value of power is inconsistent with the product of voltage and current, indicating that the displayed value of the instrument may be wrong. The voltage value can be calibrated with the DC voltage block of the multimeter. The current value can be calibrated by measuring the incoming current with a clamp ammeter and dividing it by 0.816. If not, the indication of ammeter is inaccurate.

The value of DC ammeter is taken from the 75my voltage signal generated on the diverter. Under the conditions of long service time and harsh service environment, there is dirt or oxidation between the wiring on the diverter and the diverter, and the contact resistance increases, which increases the voltage generated on the diverter, which is greater than 75my, resulting in the larger indication of DC ammeter.

Treatment method: deal with the dirt and oxide layer between the shunt and its wiring.