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Since the 90s, western countries such as America and German have adopted switching mode power supply in newly established electric power plants and electricity substations.

The storage batteries are also changed from previous cadmium nickel battery into maintenance free plumbic acid storage battery. Because of the adoption of new circuit breaker

(vacuum switch and spring type energy storage), switching current falls obviously. Duplicatebusbar is gradually replaced by single busbar.

High frequency switching mode power supply suits the trend of modern power supply with many advantages such as its small volume, light weight, high efficiency, little output ripple,
module superposition, N+1 warm backup design and convenient computer management. In terms of computer, aerospace and communication, switching mode power supply has
been extensively applied. Recently, domestic power supply has been changed from switching mode power supply into phase controlled power supply. As the increasing application
of high frequency switching mode power supply in our electric power system, more and more regular DC power systems of electricity substations have been replaced by it. This trend
results in many manufacturers in DC power supply market. So, how to choose the DC power system you need?
1. Whether the equipment you choose are suitable or not?
When people choose high frequency DC power system device, many of them think it is better to choose a higher technique level and higher price one. But it is not necessarily right.
Any product has a process from trial to perfect. It demands customers’ continuous feedback in practical operation to help manufacturers improve the products. Besides, the theory
of high frequency switching mode power supply has already been mature. Most manufacturers choose classic circuit. So the manufacturer of the device you choose should has one
year successful experience in operation. Besides, you should consider the technique suitability of electricity substations. For example, in most rural electricity substations, there
always be someone on duty, so there is no need to choose a well appointed device with all remote metering, remote command, remote control, and remote regulating functions.
If you consider the later networking and communication, you could ask to keep the communication interface to convenient the remake later when ordering. Secondly, it is also very
important to choose battery. Batteries can be classified in acid proofed, sealed and totally sealed. Now we often choose the totally sealed one.
2. Interference immunity and dependability of device
With the development of technology, recently, the new fruit of microcomputer technology has been extensively applied in comprehensive automatic device in electricity substations,
which highly increases its automation degree. But the most prime and important demand of electric power system is the safety and dependability of equipment. Thus, when we
choose DC power supply device, we need pay attention to the measures of its interference immunity. For example, it is strictly examined about the anti high frequency interference
performance of charging generator and central control unit as well as the thunderproof function and system earth dependability. High frequency switching mode power supply
adopts microcomputer control. For example, some manufacturers use IPC, same use programmable controller and some use SCM. The technology of computer develops rapidly.
So it often comes up this situation: The most advanced product which stands for that year may lack necessary operation time. The dependability of it then becomes a question.
3. Whether it is convenient to operate and maintain
When users choose high frequency switching mode power supply, except its advanced function, we should pay attention to whether it is convenient to operate or to maintain. Thus,
no matter how complex and how advanced the control software of CCU is, the interface should be clear and convenient to operate. When a fault occurs, the display screen and
display device can display the nature, occurrence time, position and other main parameter of the fault. With strong selfexamined function, it is convenient for users to maintain.
So when we choose DC power system panel, we should pay attention to the software display of manufacturers, examined the operation and display of CCU with personal practical
situation in operation and maintenance.
4. The strength and sustainable development ability of manufacturers who produce the core part of DC power system.
Nowadays, companies with whole set of DC power system choose to configure the products from manufacturers who produce the core part of DC power system, which is also the
demand of modern industrialized work division. The dependability of the core part of DC power system decides 90% of the dependability of the whole system.
Core parts (including rectifier module, monitor unit, insulation status detector and battery detector) with high quality need a high comprehensive ability of manufacturers in phases
like research and development, supply chain management, process engineering and quality system. Besides, it need the guarantee of higher technology, more fund, accurate test
and production equipment, good technology condition and other resources. In recent years, there are many manufacturers producing DC power system spare parts. The quality
of the products is on various levels. The fault rate of some manufacturers far exceeds the industry demand and increases the maintenance cost of terminal users. Some companies
do not have the ability to develop sustainably in this field. Many companies went bankruptcy or change another career in 1 or 2 years. So the quality problem of core part of on-line DC power system cannot be maintained, so the companies have to change the DC power system in a short time with more investment cost. Nowadays, EMERSON is well
acknowledged for its best quality of DC power system core part. Then it comes to Ott, Increase. Other brands belong to the third or fourth level.
5. Whether DC power system has the management function to improve storage battery
DC power system offers high quality direct current for all circuit breaker operating mechanism and secondary circuit. At the same time, it manages smartly on whole
set storage batteries, including auto normal battery BC& timed battery BC management, current-limit boost charge management, temperature compensation, calculating the battery capacity change according to the battery charge/discharge situation and charging
protection of the batteries. Good storage battery management function can increase the working life of the battery. Previous battery investment cost nearly occupies
half of the system. The life cycle of DC power system panel charging cabinet and feeder cabinet are often over 10 years. If the weak smart management functions of storage
battery result in shorter working life, the purchase cost of storage battery of DC power system user in the service life is increased. Nowadays, the storage battery
management function of DC power management monitor units of some manufacturers on the market is still imperfect. Some inferior products are only with the
display function of floating charge and basic parameter. Thus, terminal users should follow the technical manual of storage battery management strictly when
choose DC power system. Fully test the management function of storage battery before the check as far as possible.
6. Whether the price is rational
Rational price is one of the factors most users consider. When they choose DC power system panels, they often get confused on the big difference between the prices
of different manufacturers. As a mater of fact, the price difference is resulted from the following reasons: First, the cost of high frequency switch module is different.
Some use imported elements with higher cost. Some use domestic component with lower cost. Second, the price of CCU is different. Some use PLC, which is widely
used by most manufacturers. The manufacturers of PLC are different, too. Domestic brands are with lower price and imported elements are with higher price. Third,
the output current of modules from different manufacturers are different. The smaller the output current is, the more modules they have.
7. After-sale service
The quality of aftersale service has direct influence on customers’ decision of choosing products. It decides the sales market of manufacturers. Some manufactures that
should have been succeeded pay little attention to after sale service, which result in its poor company image and shrinking market and give them a profound lessen. High frequency DC power system is high-tech products. When users, especially users with poor technique, make their first choice, they are suffering a certain risk. If the manufactures cannot give a good after-sale service, customers’ purchase activity will be influenced because of their worry, which will finally influence the spread and application of the products. As there are too
many inner information exchanges in electric power system, when customers choose the model, they could learn the usage situation and opinion from manufacturers,
which could be as a reference to choose manufacturers.