1. Selection of DC screen battery

    As a device that provides uninterruptible power supply, DC storage battery is the core of DC system. Early DC systems mostly used ordinary lead-acid batteries, but due to their low overload capacity and prone to acid corrosion, they were gradually replaced by alkaline cadmium tweezer batteries after the 1980s. Alkaline cadmium tweezer batteries have the following advantages over original lead-acid batteries:

    1) Small size, good mechanical strength, will not be damaged by large impact and strong vibration.

    2) Small voltage drop, small energy loss caused by self-discharge.

    3) Strong over-discharge capacity, can withstand large overload in a short time.

    4) Strong overcharge resistance, no internal short circuit caused by overcharge.

    5) Stable discharge voltage, long life, if used properly, can reach more than 3000 cycles.

      At present, alkaline cadmium tweezers battery is still a good DC battery, but it also has some shortcomings, mainly such as low battery cell voltage, large number of uses; large battery maintenance workload; cumbersome maintenance work, high maintenance requirements. In response to the above problems, a maintenance-free valve-controlled sealed lead-acid battery has now entered the market. Its biggest advantage is that it has low maintenance, high battery cell voltage, small number of uses, and easy battery cell monitoring. However, there are still some shortcomings, such as low discharge overcurrent multiples and slightly poor low-temperature performance. The lifespan is also slightly shorter than that of cadmium tweezer batteries. The battery cannot be restored after aging, and it is prone to online aging when it is close to its lifespan. The capacity drops sharply. If the inspection is not timely, it is easy to become a hidden danger of accidents.

      Based on the above comparison, if the DC system load is heavy, the overload may be large (such as the operating power supply of the electromagnetic operating mechanism), the installation site environment is good, the ambient temperature is not high, and there is strong maintenance force, it is recommended to consider using alkaline cadmium tweezer batteries. On the contrary, if the load is light, the possibility of overload is low (such as the operating power supply of the spring energy storage switch operating mechanism), the installation environment is general, and the maintenance force is weak, it is recommended to use maintenance-free lead-acid batteries.

    2. Choice of charging system

      In terms of charging equipment, the thyristor phase-controlled DC charging system is currently used more. The battery charging is divided into two stages: main charging and floating charging. The charging current is divided into two methods: high current strong charging and trickle charging. The common control methods include thermal sensor method, timing method, negative sequence voltage slope method, volt-ampere method, etc. In recent years, many manufacturers have continuously improved this type of DC system, mainly in its control technology, such as integrated circuit technology, PLC technology, microcomputer monitoring, "three remote" communication and other technologies, so that the reliability of the phase-controlled charging equipment system is continuously improved. Therefore, the reliability and practicality of this type of DC screen system are basically satisfactory.

      However, the phase-controlled charger still has the shortcomings of large output voltage harmonics, large current ripple, and difficult to improve the current stabilization accuracy. At the same time, since it generally adopts the master-slave backup mode, in some occasions, the system reliability is still a little bit lacking. Therefore, in some places where DC power supply is required to be high, a relatively new type of high-frequency switching power supply is gradually adopted abroad. The overall structure adopts a module combination mode. The module schematic diagram is as follows, that is, the three-phase AC is first rectified into phase-controlled DC, and then converted into high-frequency AC. The high-frequency AC is then isolated by a transformer, rectified by a full bridge, and filtered to be converted into a stable DC output. The biggest feature of this DC power supply is high current stabilization accuracy, small ripple, and small harmonic distortion. It is a high-quality DC power supply. When forming a DC system, a combination of N unit modules can be used to provide DC output, so the backup degree is high and the overall reliability of the DC system is high. This type of DC power supply is currently produced by domestic manufacturers, but it is slightly inferior to the traditional phase-controlled DC panel in terms of overall appearance. Enterprises can make comparisons when choosing a DC power supply.  

     3. DC panel system maintenance

     Cadmium nickel batteries should pay attention to the following issues when using:

     1) Regularly charge and discharge the battery pack at high power to activate the chemical substances inside the battery, reduce the battery inertia, and restore the battery capacity.

     2) Check the battery liquid level frequently, and adjust the battery liquid level that is too high or too low in time when the battery is full.

     3) Check the battery solution concentration regularly, add alkali solution or water when the specific gravity changes, and re-prepare the electrolyte if necessary.

     4) Check the battery terminal voltage regularly one by one, and perform "activation" treatment on individual batteries with large voltage drops.

     5) Pay attention to the battery ambient temperature. It is best to operate the battery at a temperature below 40℃ to avoid aggravating the self-discharge of the battery and causing the battery capacity to decrease.

     6) Keep the battery clean and the environment dry to avoid battery alkali creep, which will cause the battery capacity to decrease and the insulation of the DC system to decrease. During normal times and maintenance, the alkali solution overflowing from the battery should be wiped clean with a dry cloth in time, and the outside of the battery must not be rinsed with water.

    2. Maintenance of maintenance-free lead-acid batteries

    Maintenance of maintenance-free lead-acid batteries requires less maintenance work during operation. Usually, you only need to check whether the battery connections are intact and keep the connections free of rust and corrosion; observe whether the battery is swollen or deformed; whether the sealing valve is intact; whether the electrode column has signs of melting; and keep the battery clean and dry, etc. At the same time, regularly check the battery cell terminal voltage to promptly detect and deal with failed batteries.

     3. Other maintenance of DC system

    The main maintenance work in DC system is battery maintenance. In addition, the following should be noted during the operation of DC system:

    1) Keep the DC system dry and clean, especially to avoid battery leakage from contaminating wires and devices, which may cause the insulation of DC system to decrease and DC grounding to occur.

    2) Regularly check the functions of DC panel system, such as equalization charging, floating charging, insulation monitoring, fault monitoring, alarm and other functions, to ensure that the equipment is in good condition.

    3) Regularly check the status of components of the system, especially pay attention to common problems such as overheating of thyristor components and DC melting of contacts of feeder switch components.