Introduction to the function and use of DC system

The DC system is a very important part of the substation. Its main task is to provide power to the relay protection device, circuit breaker operation, and various signal circuits. The normal operation of the DC system is related to the correct operation of the relay protection and circuit breakers, and will affect the safe operation of the substation and the entire power grid. The DC system consists of charging equipment, storage batteries, DC screens, DC split screens, insulation monitoring devices, loads, etc.

Why do substations use DC systems, and what are the advantages compared with AC systems?

1. The voltage is stable, and it is not affected by the grid operation mode and grid fault. Unipolar grounding can still operate.
2. A single set of DC system generally has two AC inputs (automatic switching), and another set of battery packs, which is equivalent to three power supplies, and the power supply is highly reliable.
3. Because there is no electromagnetic vibration, no AC impedance, the DC relay has small loss, can be miniaturized and is easy to integrate.
4. If the AC power supply is used, when a short-circuit fault occurs in the system, the voltage will be reduced due to the short-circuit, and the secondary control voltage will also be reduced. In severe cases, the circuit breaker cannot be opened due to the low voltage!

The role of the DC system

1. The DC system is a power supply device that provides DC power for signal and remote control equipment, protection and automatic devices, emergency lighting, and circuit breaker (switch) opening and closing operations. The DC system is an independent power source. When the external AC power is interrupted, the battery pack continues to provide DC power to ensure the normal operation of system equipment.
2. The power load of the DC system is extremely important, and the reliability of the power supply is very high. The reliability of the DC system is one of the decisive conditions to ensure the safe operation of the substation.
3. In the case of a system failure and an interruption of station power, if the DC power supply system cannot reliably provide DC working power to the working equipment, unpredictable losses will occur.

The use of DC system: widely used in hydropower, thermal power plants, various substations and other users who use DC equipment (such as power plants, substations, distribution stations, petrochemicals, steel, electrified railways, real estate, etc.), as signal equipment, Protection, automatic devices, emergency lighting and circuit breaker opening and closing operations provide DC power supply. It is also widely used in communication departments, computer rooms, hospitals, mines, hotels, and reliable emergency power supplies for high-rise buildings. It has a wide range of uses. The heart of the DC system is the battery, and scientific maintenance of the battery is the core work of the DC system.

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