Common mode and differential mode

    When the changes in voltage and current are transmitted through wires, there are two forms, which we refer to as "common mode" and "differential mode". The power line of a device, communication line of a telephone, etc., and communication line exchanged with other devices or peripheral devices must have at least two wires, which serve as round-trip lines to transmit power or signals. But there is usually a third conductor outside these two wires, which is the "ground wire". There are two types of interference voltage and current: one is that two wires are used as round-trip transmission lines; The other method is to use two wires as the destination and the ground wire as the return path for transmission. The former is called "differential mode", while the latter is called "common mode". For differential amplifiers, if the two input interference signals are of unequal size or in different directions, they are considered differential mode interference signals.

    Usually, the electrical appliances we use are two wires, one live wire (L) and one neutral wire (N). The neutral wire is considered the neutral wire of three-phase electricity, and there is also a grounding wire called the ground wire,. The interference between the zero wire and the live wire is called differential mode interference, while the interference between the live wire and the ground wire is called common mode interference. It is considered that there is no voltage between the ground and the zero line, or it can be considered that the zero line has no voltage and cannot drive the electrical appliance. Therefore, it is considered that there is no interference between the zero line and the ground line.

    Common mode voltage: The average value of the phasor voltage that occurs between each conductor and a specified reference point (often ground or frame). Alternatively, the part of the input voltage that is simultaneously applied between the two measuring terminals of the voltmeter and the specified common terminal.

    Differential voltage: The voltage between any two charged conductors in a specified set. Differential mode voltage, also known as symmetrical voltage.

    In the specified waveform, the nominal discharge current impacts the zinc oxide valve plate, and the voltage peak measured at both ends of the valve plate is called residual voltage. The ratio of residual voltage to voltage sensitive voltage, residual voltage ratio. Lightning strikes can generate instantaneous high voltage and high current on input/output power lines, affecting the stable operation of user equipment, and in severe cases, causing equipment damage. Lightning arresters can be divided into two types according to their connection methods: common mode connection and differential mode connection. The connection of lightning arresters between phase lines or between phase lines and zero lines is called differential mode connection, which is also known as lateral protection. The connection of lightning arrester between phase line and ground line or between zero line and ground line is called common mode connection, which is called longitudinal protection.