As an indispensable power supply protection system for data center, UPS is more and more widely used. However, for a long time, some users did not understand the composition, principle and characteristics of UPS, and did not pay attention to the management and maintenance of UPS, which shortened its service life and increased the failure rate. As a result, the performance of UPS was affected and led to UPS system failure. The passive failure of UPS system can be divided into usability failure and device or board level failure.

Usability failure of UPS

The so-called operational fault refers to the fault caused by the misoperation of operation and maintenance personnel, wrong judgment of fault phenomenon, improper measures taken and empirical diagnosis. The usability faults of UPS can be roughly divided into knowledge faults, operation faults, delay faults, maintenance faults, empirical faults, environmental faults, sudden power failure faults, UPS device or board level faults, etc.

1. knowledge fault

This kind of failure is mainly caused by the lack of basic theoretical knowledge of maintenance personnel. For example, a newly installed 30KVA UPS supplies power to a device. After the device is powered on, it is found that a power module in the device is burned out. Therefore, the user thought that it was caused by the zero drift of the three-phase voltage of UPS, and made representations to the ups manufacturer, requiring that the equipment be inspected or replaced immediately and that the damaged equipment be compensated. Since the user raised such a professional and serious problem, the manufacturer immediately sent technicians to inspect the ups. Through inspection, the three-phase output voltage is 220V, 219v and 219v respectively, with good symmetry and no zero drift. After careful inspection and analysis, it is confirmed that the damage of the power module of the equipment is due to its quality problem. After replacing the power module, the equipment operates normally.

Generally speaking, the deviation of three-phase voltage less than 2% can be ignored. At present, most ups have the ability to automatically adjust its voltage unbalance less than 2% when the three-phase load is 100% unbalanced. The so-called three-phase load 100% imbalance refers to the situation that one or two phases of UPS load are fully loaded while the other two or one phase is unloaded. For example, the full load value of one phase of 30KVA UPS is 10KVA (i.e. 10kva/220v=45a). It is not like what some people understand. When one phase current is 1a and the other phase is 2a, it is considered that their unbalance degree is 50%. In fact, it cannot be understood in this way. On the contrary, if the current of one phase is 1a and the current of the other phase is 0, their imbalance is also 100%. It seems to be correct to understand it literally, but the definition is not so.

For another example, some users configure the ups with a battery with a service life of 3-5 years, but the ambient temperature often exceeds 30 ℃ in summer, and the mains power has never been stopped for more than two years. After startup, the maintenance personnel have never conducted a verification or capacity testing discharge test on the battery, and the operation status of the battery is unknown. In case of power failure, the ups will shut down when the battery discharge time is less than 1/3 of the rated time. Therefore, the user sent a notice of claim to the manufacturer. After the manufacturer's maintenance engineer pointed out the cause of the fault, presented the relevant contents on battery maintenance in the operation manual and analyzed in detail the reasons for the reduction of battery capacity, the user could not claim any more, but the impact on the manufacturer's reputation was serious.

2. operational failure

Because of the importance of the load carried by UPS, in order to ensure the safe and reliable operation of UPS, various products have their own set of safe operation procedures, which are written into the manual for users' reference. However, some maintenance personnel don't think so. Instead of following the established procedures, they operate at will according to their own understanding. Sometimes, problems occur; There are also unintentional operation faults. For example, during the maintenance or repair period, the adjacent devices are not found because they are accidentally damaged during the disassembly of a device, and a secondary fault is formed during power on; Short circuit a certain two points when checking the fault; Wrong positive and negative electrodes when connecting external batteries; If one or several battery connecting strips are not tightened or battery switches are not closed, the battery cannot be discharged during mains power failure, resulting in UPS shutdown; If the power supply bureau makes a mistake in the original phase sequence during the transformation or maintenance of the mains line, it will also lead to UPS failure in startup or conversion; Forgetting to start the inverter after UPS is powered on will also cause shutdown in case of mains power failure; Rats are attracted by the personnel on duty placing food in the machine room. The rats bite the cables or flee into the machine, resulting in short circuit between cables or components; Unshielded remote signal cables are wired in parallel with AC lines, resulting in faults due to coupling interference.

3. delayed fault

Delayed fault refers to the ups fault caused by the negligence of maintenance personnel who fail to find out the hidden trouble in time, or find out but fail to take corresponding measures in time. For example, in the ups dual redundant parallel system, the load is equally divided into two ups. Sometimes one inverter is shut down due to some coincidence. At this time, all the load is transferred to the other ups. If the maintenance personnel find out in time, they can just restart the shut-down UPS inverter; If the maintenance personnel do not find it in time, it will become a single machine power supply in case of mains power interruption. On the one hand, the overload capacity will be weakened, and on the other hand, the backup time will be halved. At this time, once the load is overloaded, all the loads will be interrupted. For another example, when the battery operates under unsatisfactory conditions, the battery shall be maintained on time. Once a battery with significantly reduced capacity is found, it shall be replaced immediately. Because some of the battery damage is caused by gradual accumulation, and some of it occurs instantaneously, that is, it was still available yesterday, and it can not be discharged today. During the maintenance of storage batteries, this kind of situation will be encountered: during the last monthly inspection, although the floating charge voltage of some storage batteries was slightly low, it was not completely unusable. However, after the mains power outage in the current month, a group of storage batteries could not be discharged at all. Therefore, once the battery is found to be faulty, it should be replaced in time to avoid accidents.

4. maintenance failure

Although there are few periodic maintenance contents of UPS, these contents are very necessary, and these maintenance shall have a set of strict procedures. Failure to maintain the equipment regularly as required is an important cause of failure. For example, some ups are not maintained for a long time. Once it is found that the equipment is unstable, it has to ask for maintenance. When the chassis is opened, a thick layer of dust is accumulated on the circuit board and components. As long as the dust is removed with a blower and vacuum cleaner, the equipment can return to normal. For another example, after the maintenance of a UPS is completed, the maintenance personnel add the mains power to the input terminal and forget to start the inverter or close the battery switch. When the next mains power outage occurs, the ups will shut down because the inverter cannot be started.

Even the experience gained from several troubleshooting experiences should not be blindly copied. For example, a user with UPS operation experience of brand a operates the newly installed ups of Brand B without reading the manual, and directly starts the DC startup based on experience. Because UPS he is familiar with can be started by DC, but this machine has no DC start function. Of course, it cannot be started. So he opened the chassis and poked the relay with a screwdriver. Although the inverter was started, it immediately smoked and the power tube was damaged. He did not know that ups with DC startup function has certain procedures during startup: when the DC startup switch is turned on, the control circuit works first, and then the inverter is driven, that is, normal startup. However, this UPS has no DC start function. While the control circuit is working, the inverter is also starting. The unstable state in the transition causes the two power tubes of the inverter to be connected at the same time and burned out.

Other maintenance personnel think they have mastered the principle of UPS during training, so long as they learn some troubleshooting methods. However, in the short-term training, it is only possible to learn some judgment methods for simple faults. Specific faults should be analyzed in detail, and experience can only be used as a reference. For example, there are many reasons for UPS AC input fuse burnout, such as rectifier breakdown, filter capacitor breakdown, inverter breakdown, RC network short circuit at both ends of the input rectifier tube, and the resulting damage to the control circuit, which will cause fuse burnout. Of course, experience is useful for the judgment and elimination of some simple faults, but it should be applied flexibly and treated on a case by case basis.

5. environmental fault

Environmental failure is caused by the user's neglect of the equipment environment. For example, a 30KVA UPS has been placed in a warehouse full of sundries by users for a long time. The warehouse has no air conditioning and ventilation. In summer, the temperature is as high as 30 ~ 40 ℃, and the humidity is high. As a result, the performance of components in the UPS is reduced, and the battery capacity is greatly reduced. When the UPS is installed and put into use, failures occur frequently, and the battery capacity is far from meeting the requirements. For another example, a 20KVA UPS was installed in a simple roof room. After the wind and rain, the UPS inverter was shut down and the charging board was burned. It was found that the muddy water on the roof was poured into the machine through the upper air outlet. In other places, the power supply conditions are very poor, and the power is often cut off, resulting in a long-term power loss state of the battery and a sharp shortening of its service life; In some places, high interference voltage is often superimposed on the mains voltage. The secondary lightning arrester in the distribution cabinet is often burned, and sometimes the UPS is destroyed, thereby damaging the electrical equipment.

From the above points, it can be seen that a set of scientific and effective methods should be formulated and strictly followed for the maintenance of UPS, so that it is possible to avoid the above-mentioned man-made faults, so as to greatly reduce the failure rate of ups and truly provide safe, reliable and clean power supply for electrical equipment without interruption.

6. sudden power failure

Sudden power failure will cause great damage to UPS hardware and affect the operation of data center. The sudden power failure is mostly the automatic shutdown protection caused by the ups load exceeding the upper limit. In this regard, several unimportant equipment can be shut down to make the load rate of UPS lower than 90%.