Friday, March 18, 2011

【 Weak current College 】 resolution UPS application errors 】

UPS uninterruptible power supply, that is, although the information construction of behind-the-scenes hero, but its role is absolutely not to be ignored, especially with the growing information technology to the socio-economic aspects of life, its value is becoming more and more obvious, however, after all, this is a very specialized area, there are many users on UPS fuzzy or even erroneous understanding.
UPS brand variety performance setups, this will give the user raises the question: what is the best UPS? what kind of UPS at the best price? is there an objective standard? of course, there is an objective standard, that is UPS performance indicators. However, since UPS is a professional strong areas, many users though uses UPS over the years, these indicators on the ups or not clear. The following author combined with the user in the use of common issues, the indicators for analysis, but also on user in the use of a lot of fuzzy understanding clarification for readers to choose UPS products.
Price does not mean that the price is high.
Price and product quality
For many years, users of a UPS price pressure and pressure, forcing a lowering of prices UPS go further, so some users have formed the habit of a down: no matter what product, no matter under what conditions, if not down will suffer, but also think that even the price pressure is low, the supplier also profitable. This small power products especially prominent. On the other hand, the UPS supplier in order to open up markets, on the user's down "policy" is also used, in case of not losing it gradually give way, this seems to be a "harmonious" State. But the price is always the bottom line, when the price was to a certain extent, the supplier can not afford, the situation has changed.
UPS supplier in order to bid or entering a trade, although it will accept a lower price, but since prices are indeed has been compacted to unsustainable levels, but to "open short cut" to the user laid.
Manufacturers which responses? manufacturers the most common means from UPS host has to a significant reduction in the original price, but to the user laid. For example, past ups overload capacity generally: overload to 125% for 10 minutes, you can stick to 150% overload may persist in 30 seconds. But these prices after the product overload capacity significantly lower (see table below), from here we can see why the price of the machine. Machine prices down, accident.
Select cheap battery, and reduced quality of service and is also the approach taken by manufacturers often. As a result of poor battery, the battery needs to be replaced frequently, this involves the UPS shutdown problems in those UPS a day 24-hour continuous service, giving users out of the problem, stop loss to users.
Therefore, users of products too low, what is generally not a good result, in the long term, this approach should think twice.
Because of the capacitor voltage capacity is insufficient, the actual use is often less than nominal input voltage range.
UPS input voltage and frequency
Input voltage range has always been very concerned about the user, the user always want UPS allows input voltage range, the larger the better, this time in small power has formed a habit, especially off line UPS. In the small power to implement a wide range of input voltage is usually easy, because power is smaller to use a multi-tap transformer with relay contacts for regulating many off-line UPS allows input voltage variation ± 30% and even wider. But this kind of use tapped transformer and relay adjustment input voltage method is only suitable for very small power, Max will not 5kVA power. Otherwise, the high-power devices must use contactor, and high-power transformer combination will enable UPS to grow very large, the price will increase significantly. Thus, the General will not adopt it.

While in high power UPS, universal is 380V three-phase three-wire bridge rectifier, Silicon controlled rectifier full use of phased approaches to maintain the stability of the AC input voltage. It claimed that allows input voltage variation ± 30% or more of the products, are generally based on the principle of Silicon phased regardless of exceptions, which although meet user's expectations, but they have hidden causes a capacitance explosion occurred repeatedly. In view of this, the pursuit of the input voltage range of the user not to blindly believe manufacturers propaganda, be sure to know the capacitance of the pressure resistance, because as the capacitor voltage increase and the cost of the machine up. In other words, the price is also the elevation.
In the output voltage frequency, normal work situations the UPS output voltage frequency always track the input, the input voltage frequency range is too wide to load does not benefit, in particular the frequency down. Such as UPS claims that it allows input frequency range ± 10Hz, actually this formulation of the basis does not fully or not necessary, the bottom line is:
1. the national standard GB/T15545-1995 "power system frequency tolerance": power system normal operation frequency tolerance value of ± 0.2Hz, when the system capacity is low, its deviation can relax to ± 0.5Hz. In fact, some of the large area of the system is capable of maintaining normal frequency deviation value within ± 0.1Hz.
2. General diesel generators in the frequency of such changes, the output voltage is very unusual.
3. input frequency range is wide, the greater impact on output characteristics. Because many load is nonlinear, not sentimental is capacitive.
Overload capacity is the most crucial indicator of the ups.
UPS overload ability
Overload capacity is the key to performance UPS because in AC and load properly, UPS just as regulator and filter function, but this function with a cheap AC regulator is completely achievable. Therefore, if a UPS only so little actionIt's not worth it. So UPS points in: power UPS to when exceptions can continue uninterrupted, load exception UPS to be discretionary, i.e. for general overload you want to be able to stand up, not a ready to go bypass overload, because the emergency power supply bypass belonging to the "emergency" contains "hasty meet" mean, since the "rush to meet", which means that the quality and reliability is not guaranteed. Therefore, minimize switch to bypass the chance is to guarantee the supply of reliable supply of critical, overload capacity is an important indicator.
Overload capacity reduction caused by how? mainly due to the reduced price of expensive power component level. Because the size of the overload capability directly subject to the power component module temperature, the temperature is too high is causing power devices fail. As shown in Figure 6, power component modules, the heat capacity, if the module (a) reach 150 degrees 10 minutes, power modules (b) because the device power levels low, small heat capacity, and (a) the amount of equivalent overload, as long as 1 minutes make module temperature reaches 150 ° c, if not timely switch to bypass a risk of burn-out devices. If the same is imported famous brand 40kVA ups, have adopted the IGBT module 300A, also have adopted the IGBT module, 150A at power on almost doubled with the cost! also dropped. The same product, the user does not, of course, this to 150A, but do not know the internal power device specifications, especially the machine before you buy, then it is only through the products of overload capacity to judge the internal power device specifications, but this technique is very accurate.
The use of lower power device specifications to achieve price objectives, to reduce the machine's reliability, and also to the user's work have implications.

UPS switching time is only meaningful for off-line.
System switching time
UPS conversions in several situations: AC exception, load exception, circuit exception, load exception and the exception when the circuit to eliminate. But no matter what kind of exception, all hope is not interrupted power supply UPS, discussed below, respectively.
Many users of commercial exception is most concerned about is the commercial power supply switching time when exceptions to ensure zero. For on-line ups, power circuit when the exception is not carried out any corresponding switch switching, so there is no switching time, then why do some users also very worried about this? this has to go back to off line UPS, in the early days of PC use, there is very little need for bulk-UPS, and most probably less than the off line UPS 1kVA. In the commercial power supply failure, backup UPS must switch from AC power switch to the inverter power supply, as shown in Figure 2. This switch is used as intermediate relay, the original products will this switch within the time limit in 3ms, but actually in testing the switching time has reached 45ms. General and little less than 10ms switching time of products. Therefore in these user's consciousness in either on-line or off-line, as long as the UPS are like this. Because there was no difference between on-line and off-line circuit structure differences, so the AC power switch time also becomes a major concern though.
Load exception when load current or short circuit, because the inverter can no longer bear the burden of this you will need to switch to bypass the power supply. Due to overload a time limit, at this time in addition to the original overload of frequency tracking phase, the voltage amplitude began tracking utility to enable in-phase voltage amplitude when switching as close as possible to the closer the voltage amplitude, switch smoother. More UPS overload, would result in increases the more time tracking, track, the better the effect, but also the more guarantee zero switching. Switch has two modes: one is the static inverter switch on the back of the revocation of the trigger signal triggered at the static bypass switch, it sometimes appears circulation; the other is static inverter switch on the back of the revocation of the trigger signal after a time delay to ensure that the static switch entirely due to trigger after the static bypass switch to avoid the emergence of the circulation. But this delay must be appropriate to delay short still appears circulation, extended duration and discontinuous phenomena can occur.
Circuit exception includes circuit components, circuit failure is a serious situation, in particular lead to inverter fault suddenly stopped working, so that the voltage rise time tracking. If the event listing of electrical voltage frequency transients and undermined the frequency and voltage track adjust switch is not capable of doing, but to continue to supply, UPS has a forced switch link, then there will be a continuous time, generally the time control in 5ms.
Load exception and the exception when the circuit to eliminate this is a power switch to the inverter. Inverter resumes: load exception elimination or circuit after troubleshooting, the inverter to restart (automatic or manual start), there are two voltage waveform are not synchronized and you want to track for a period of time. Generally this time are relatively affluent, easy to realize zero switching.
UPS can truly redundant parallel direct improve system reliability and capacity.
UPS parallel capacity
In order to improve the reliability of power supply, redundant parallel technology available ex-often using hot backup serial connection, this approach is characterized by a flexible application, no additional equipment, even from different manufacturers, different types of UPS, as long as static bypass, and capacity, you can do this kind of connection and has redundant functionality. Shortcomings are not compatible, a machine overload to another is also overloaded, which means little more than two examples of the connection. Parallel redundancy programme, effectively addresses the issue of capacity and redundancy, and until now is still a best programme. It not only can you accurately for load sharing, but also at times of overload capacity. But with the expansion of the range of applications, also showed some deficiencies, such as the bulk of IDCIn some situations or environments, the load is long row display cabinet, but also very long. Especially the UPS itself parallel poor performance, and redundancy functionality had to use the backup method of the switch, this is redundant structure of dual-bus. On the other hand, because the number of parallel UPS is limited, there is a maximum of 9 units, in the capacity of large and require redundancy of big occasions, also had to adopt this proposal. There is also a place that is, the user requirements for reliability, a high bulk power system, but a few years is available full capacity, the use of dual-bus structure also has its advantages.
You can see from the above, the dual-bus redundancy programme is from in-line hot backup redundant connection developed an improved solution. 1. in-line hot backup and dual-bus in the middle of the redundant connection has a synchronization toggle switches, the difference is in-line hot backup connection switch is one-way, that is, you cannot back up each other; and dual bus switch of redundant connection is bidirectional and can be the backup, this is it.
2. dual-redundant connections did not jump out of the bus-line hot backups, so a machine overload, even over the past still overload that machine while increased several times, but no overload capacity and increases.
3. Since the middle of the two has a synchronization toggle switch to form the "bottleneck", so how much does not increase system reliability, and the synchronization toggle switch prices almost and one with capacity ups equivalent, or even more expensive, allowing users to increase investment.
4. dual-bus capacity of redundant connection system must be a double, such as adding a UPS1 20kVA UPS2 parallel single, must also be increased by a parallel single 20kVA, allowing users of investment multiplied and increased user load.
5. it is clear that parallel redundant connection scenarios because no formation "bottleneck" of the toggle switch, whether from intuitive or theoretical calculations are its reliability than the former two higher one to several times the conclusions, overload capacity also increased significantly, but do not have to be double the capacity.
From the above simple comparison can be seen, the dual-bus performance redundant connection is in-line hot backup connection a lot better, but still doesn't work with parallel redundancy in the United States, but in some cases is the last resort, or from the other perspective so that some of the more appropriate. Means that in certain circumstances this programme is a good idea to sell this scenario instead of occasions, it may not be able to play out its advantages, even up to the opposite effect.

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