As the core equipment of modern power metering system, the accuracy and reliability of smart meters are crucial to the billing and service quality of power companies. However, in some cases, in order to ensure that the smart meter can accurately measure high current or high voltage electrical energy, it is necessary to install a transformer to assist the measurement. This paper will discuss in detail in which cases smart meters need to install transformers, and explain the principle and technical requirements behind it.

Hall current sensor based on the magnetic balance Hall principle, according to the Hall effect principle, from the control current end of the Hall element into the current Ic, and in the Hall element plane normal direction to apply magnetic induction intensity of B magnetic field, then perpendicular to the current and magnetic field direction (that is, between the Hall output end), will produce a potential VH, called Hall potential. Its magnitude is proportional to the control current I.

Zero sequence current transformer is a device that detects the current value called zero sequence current in a three-phase AC power supply. The sum of the current vectors flowing through the phases of a three-phase AC power supply is usually symmetric and therefore zero, but if the ground current flows, the balance will be disrupted and the sum will have a non-zero value. If a ground problem occurs, the zero-sequence current transformer kicks in, instantly disconnecting the fault location from the surrounding circuit. Therefore, it is pre-built into the leakage circuit breaker to play a role in constantly discovering accidents.