1. Selection of DC battery

As a device that provides uninterrupted power supply, the DC battery is the core of the DC system. The common lead-acid battery is used in the early stage of the DC system, but because of its low overload capacity and acid corrosion, it has been replaced by alkaline cadmium tweezers battery 80 years later. The alkaline cadmium tweezers battery has the following advantages compared with the original lead-acid battery.

1) small volume, good mechanical strength, and will not be damaged by large shock and strong column vibration.

2) the pressure drop is small, and the loss of energy caused by self discharge is small.

3) overdischarge capacity is strong and can withstand a large amount of overload in a short time.

4) the overcharge resistance is strong, and the internal short circuit will not be caused by overcharge.

5) the discharge voltage is stable, the life span is longer, and if the use is better, it can reach more than 3000 use cycles.

At present, alkaline cadmium tweezers battery is still a good DC battery, but it also has some shortcomings, such as low battery voltage, large quantity of battery usage, large battery maintenance workload, complicated maintenance work and high maintenance requirements. In view of the above problems, there is another maintenance free valve regulated lead-acid battery entering the market. Its biggest advantage is its small maintenance quantity, high monomer voltage and small number of batteries. It is easy to monitor battery monomer. But there are still excessive discharge current ratio is low, lack of low temperature performance is slightly worse, life is also slightly shorter battery cadmium tweezers, the battery can not be restored after aging, and in the use of close life prone online aging, capacity drop, if the inspection is not timely, easily become accidents.

In view of the above comparison, if the load of the DC system is heavy and the overload may be large, such as the operation power of the electromagnetic operation mechanism, the environment of the installation location is good, the ambient temperature is not high and the maintenance force is strong, it is recommended to choose the alkaline cadmium tweezers battery. Conversely, if the load is lighter and the overload may appear to be lower than the bottom (such as the operation power supply as the spring energy storage switch operation mechanism), the installation environment is generally weak, and the maintenance power is weak, it is recommended to use the maintenance free lead-acid battery.

Two, the selection of the charging system

In charge of equipment, is currently using more thyristor phase controlled DC charging system, charging of the battery charge and floating charge is divided into two stages, the charge current of large current and strong charge trickle in two ways. The common control methods include thermal sensor method, timing method, negative sequence voltage slope method, volt ampere method and so on. In recent years, many manufacturers of the DC system, mainly in the improvement of control technology, such as integrated circuit technology, PLC technology, computer monitoring, "three remote" communication technology, continuous integration of them, so that the reliability of phase controlled charging equipment system continue to improve, so this kind of DC mesh screen system, reliability and practicability the product can basically satisfactory.

However, the phase control charger still has the disadvantages of large harmonic output voltage, large current ripple, and more difficult to improve the precision of steady current. At the same time, in some cases, the reliability of the system is still not enough. So, overseas gradually adopt a high-frequency switching power supply is relatively new in some higher requirements for DC power supply, the overall structure of the module combination, the module principle diagram is as follows, namely the first phase controlled rectifier for three-phase AC DC, then transform into high-frequency alternating current, high frequency AC by full bridge rectifier, and transformer isolation converted to stable DC output filter. The main characteristic of this DC power supply is high precision, small ripple and low harmonic distortion. It is a kind of high quality DC power supply. When the DC system is made up, the DC output can be provided by the combination of N modules, so the degree of backup is high and the overall reliability of the DC system is high. The DC power supply of existing domestic manufacturers, but in the overall appearance and was less than that of traditional phase controlled DC screen, enterprises can compare the trade-offs in the selection of DC power supply.

Three, DC screen system maintenance

The following problems should be paid attention to in the use of nickel cadmium batteries:

1) regularly charge and discharge the battery group with high power to activate the chemical substances inside the battery, reduce the battery inertia and restore the battery capacity.

2) regularly check the battery level and adjust the high and low level of the battery level in time when the battery is full.

3) regularly check the concentration of the battery solution, make up the alkaline solution or add water when the specific gravity changes, and reprepare the electrolyte when necessary.

4) check the battery terminal voltage regularly one by one, and "activate" the battery that has a large drop in the individual voltage.

5) to pay attention to the environment temperature of the battery, it is best to make the battery run at the temperature below 40 C, so as to avoid the self discharge of the battery and cause the battery capacity to decrease.

6) keep the battery clean and the environment dry, so as to avoid the battery creeping, resulting in the decrease of the battery capacity and the decrease of the insulation of the DC system. The alkaline solution spillover to the battery should be cleaned in time with dry cloth during maintenance and maintenance, and the battery can not be washed with water.

2, maintenance of maintenance free lead acid battery

Maintenance free lead-acid battery maintenance workload small operation, usually only need to pay attention to check the battery connection intact, stay connected without rust, corrosion; observation of whether there is swelling, cell deformation; sealing valve is in good condition; there are no signs of melting electrode column; and keep clean and dry battery and so on. At the same time check the battery end voltage, discover the battery failure.