In order to meet the demand of high voltage DC power supply, a high voltage DC power supply was developed to simulate high voltage power consumption conditions.

 

500kW load bank
 

When purchasing other brands of power supplies, engineers sometimes use DC power supplies and DC electronic loads to control "analog battery systems" through custom application software, according to customers. This is a system that can be charged and discharged like a rechargeable battery. This system is sent to the customer for acceptance. After connecting with the customer's test equipment, there was a problem in operation that the ammeter showed a value below the set value. The difference in this value is slightly higher than the allowable error of the galvanometer. After completing a series of inspection items, it was found that the system was operating in full compliance with the requirements, but there was a question as to why the current value was set at a different value than that shown by the ammeter.

Later, the checks were often repeated, and it was found that it was neither the customer's own equipment nor the HVDC power analog battery system, but the difference in the current detection values. Therefore, it is decided to investigate the surrounding environment of the current detection circuit. The current detection circuit uses a shunt resistor inserted at the negative end of the power line. The reason is that the grounding end of the wire is grounded.

After careful examination of the circuit diagram of the customer's equipment, it was found that the conductor ground terminal of the circuit was grounded. Moreover, the system's circuit detection circuit of the wire ground terminal is also grounded.

The meaning of a wire grounding terminal (GND) is the reference point of potential. In English, it means "Ground = ground", but in electronic circuits, the grounding end of the wire does not have to be ground. But, in general, grounding equipment is a matter of common sense for the sake of safety and interference elimination. In this sense, whether the customer's equipment, or the company's system, "run alone" is a reasonable approach.

However, the customer's equipment and the HVDC power analog battery system need to be connected together. After the ground terminals of each wire are connected to the ground, a path through the current is formed at the negative end of the power line except for the shunt resistor. In other words, the charging current is diverted. The difference in the value shown by the ammeter is the result of subtracting the shunt current.