High voltage direct current refers to high voltage current that does not undergo periodic changes in direction and time, but the magnitude of the current may not be fixed, resulting in waveform generation. Also known as constant current. The circuit passed through is called a DC circuit, which is a closed conductive circuit composed of a DC power source and a resistor. High voltage direct current refers to a type of battery where the size (voltage level) and direction (positive and negative poles) do not change over time (within a relative range), such as a dry battery. Pulsating direct current refers to the direction (positive and negative poles) that remains unchanged, but its magnitude changes over time. For example, we obtain a typical pulsating direct current by rectifying a 50Hz alternating current through a diode, a half wave rectification produces a 50Hz pulsating direct current, and a full wave or bridge rectification produces a 100Hz pulsating direct current. They only become smooth direct current after being filtered (using an inductor or capacitor), Of course, there are still pulsating components (called ripple coefficients), which depend on the filtering effect of the filtering circuit. The circuit through which high-voltage DC passes is called a DC circuit, which is a closed conductive circuit composed of a DC power source and a resistor. In this direct current circuit, a constant electric field is formed. Outside the power supply, positive charges flow from high potential to low potential through a resistor. Inside the power supply, they overcome the electrostatic force through the non electrostatic force of the power supply, and then travel from low potential to high potential, forming a closed current line. So, in a DC circuit, the function of the power supply is to provide a constant electromotive force that does not change over time, supplementing the energy consumed by the Joule heat on the resistor. The common name of DC screen is Intelligent Maintenance-free DC Power Supply Screen, abbreviated as DC screen, and the general model is GZDW. Simply put, a DC screen is a device that provides stable DC power supply. (When there is a 380V power supply input, it is directly converted to 220V. When there is no input (mains and backup power), it is directly converted to battery power supply - DC 220V: in fact, it can also be said to be an industrial dedicated emergency power supply). The power operation power supply in power plants and substations nowadays uses DC power supply, which provides power for control loads, power loads, and DC accident lighting loads. It is the foundation of contemporary power system control and protection. The DC screen is composed of AC distribution unit, charging module unit, step-down silicon chain unit, DC feeding unit, distribution monitoring unit, monitoring module unit, battery detection unit, and insulation monitoring unit. Mainly used in small and medium-sized power plants, hydropower stations, various substations, and other users who use DC equipment (such as petrochemical, mining, railway, computer rooms, etc.) in the power system, suitable for instruments, meters, relay protection, and fault lighting in switch opening and closing and secondary circuits