DC screen is an important component of the normal operation of substation, which can continuously transmit the stable DC power to the substation, and meet the power demand of power equipment operation and operation. From the practical application, the performance of substation DC screen is difficult to meet the standard requirements in terms of service life and power supply, which restricts the performance of DC power supply operation system. It is found that the Super Capacitor DC screen can effectively solve the problem of DC power supply. The improved super capacitor DC screen has greatly improved in performance, life and stability. It has obvious advantages compared with the DC screen of battery.
The DC power supply operation system is referred to as "DC screen", which provides stable DC power to all kinds of power equipment in substations, and is also the core power source of modern substations. The DC screen not only protects the normal operation of the power system, but also plays a very good protective role for the stable control of other components. The deep analysis of the problems existing in the DC screen of substation can guarantee the continuous DC power supply, and create favorable conditions for the normal operation of power equipment and related modules. The active introduction of DC screen technology in the power industry can accelerate the automation and intelligent development of the substation, and improve the overall efficiency of the substation equipment operation.
First, the current substation DC screen problems
The DC screen used in domestic substations is composed of charging cabinet, charging module, monitoring module, battery pack and step down silicon chain. Each module plays an important role in DC power supply. From the perspective of industry development, DC screen is a DC system running under the digital control mode, which has many functions such as regulation, protection, management and monitoring for substation DC power supply. At present, the DC screen technology in substations has advanced functions such as remote monitoring and control, which facilitates the control of the operation of the power system by the staff on duty. However, some problems existing in DC screen should also arouse the attention of technicians. Cadmium nickel batteries and sealed lead-acid batteries are commonly used DC screens. The main problems are as follows:
(1) CD - Ni battery DC screen
1. performance problem. In order to maintain normal DC power control, a large number of battery modules need to be used in a substation to output power through a DC bus. In general, a large substation DC bus output 220V, the need to use about 200 battery combination module. But during the production process of Ni Cd battery, manufacturers can not guarantee that the charging and discharging performance of each battery is exactly the same. There will be obvious differences between 200 battery combinations. The CD - Ni battery DC screen is the same as the power supply connected by the DC power supply, and the load discharge is the same. This characteristic reduces the performance of the local cadmium nickel battery and reduces the function of the whole battery assembly module.
2. life problem. Due to defects in composite material of nickel cadmium battery, DC screen runs essentially in "floating state", the nickel cadmium battery DC panel use depending on the charger. According to the regulations of the industry standard, the manufacturer guarantees the cadmium nickel battery for more than 10 years, and the record of the specific use is only about 5 years. The reason for shortening the life of the DC screen of the battery is that 94 of the subduction current exceeds the standard, which causes the electrolysis of hydrogen and oxygen in the electrolyte. This is the fundamental reason for the battery explosion. If the cadmium nickel battery is used for DC screen, no special treatment is done, which is easy to cause accidents. Therefore, the long service life of the DC screen will be limited by other factors.
3. oxidation problem. The redox reaction will also occur during the use of the DC screen of the cadmium battery of the power plant, which will cause cadmium to react with cadmium to form cadmium oxide, which will decrease the effective area of the plate. In order to avoid the occurrence of redox reaction, the staff of the substation will regularly analyze the battery by "activation test". The battery is charged and discharged in the activation test. The operation of this stage will reverse the polarity and cause the battery to be discarded. In addition, oxidation-reduction reaction will destroy the performance of cadmium and nickel direct current screen, and will also cause hidden dangers to the stable operation of substation. For example, if the battery is completely installed in the cabinet, it will easily cause burnout, explosion and other safety accidents.
(two) the direct current screen of sealed lead-acid battery
With the impetus of science and technology, the technology of the DC screen in the domestic substation is developing continuously, and many new battery products are also widely used in the substation. Based on the shortcomings of the cadmium nickel battery DC screen, the enterprise began to adopt sealed lead-acid battery, referred to as "valve controlled battery". This product is superior to cadmium nickel battery in quality, performance, price, maintenance and so on. For example, the valve controlled battery does not need too much maintenance or water treatment, which provides a great convenience for the operators of the substation. But the DC screen is in the "full seal" state, and it also causes many problems. Especially when battery operation is observed and inspecting, it is difficult for maintenance personnel to update the device in time. In addition, due to the relatively backward technology of VRLA batteries, the life of products used in substations is not guaranteed, and the operation conditions of VDC batteries are very strict, which has caused great difficulties to the normal production of substations.
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