As an indispensable power protection system for data centers, UPS is increasingly widely used. However, for a long time, due to some users’ lack of understanding of the composition, principles, and characteristics of UPS, and their neglect of UPS management and maintenance, the service life of UPS has been shortened and the failure rate has increased. As a result, the performance of UPS has been affected, leading to UPS system failure. Passive failures of UPS systems can be divided into usage failures and component or board-level failures.
UPS Usability Faults
Usability failures refer to malfunctions caused by operator or maintenance personnel’s misoperation, incorrect judgment of the fault phenomenon, inappropriate measures taken, and experience-based diagnosis. UPS usability failures can be broadly categorized into knowledge-based failures, operational failures, delay failures, maintenance failures, experience-based failures, environmental failures, sudden power outages, and UPS component or board-level failures.
1. Knowledge-based fault
These types of malfunctions mainly occur due to maintenance personnel lacking basic theoretical knowledge. For example, a newly installed 30kVA UPS was supplying power to a device. After the device was connected and powered on, it was discovered that one of the power modules was burnt out. The user assumed this was due to zero-point drift in the UPS’s three-phase voltage and contacted the UPS manufacturer, demanding immediate inspection or replacement of the equipment and compensation for the damaged parts. Given the user’s complex and serious concern, the manufacturer immediately dispatched technicians to inspect the UPS. The inspection revealed that the three-phase output voltages were 220V, 219V, and 219V respectively, with excellent symmetry and no zero-point drift. After careful inspection and analysis, it was confirmed that the power module’s damage was due to a quality issue; replacing the power module resolved the problem and the device operated normally.
For three-phase voltage, a deviation of less than 2% is generally negligible. Currently, most UPS systems have the capability to automatically adjust the voltage imbalance to less than 2% even when the three-phase load is 100% unbalanced. A 100% unbalanced three-phase load refers to a situation where one or two phases of the UPS are fully loaded, while the other two or one phase is unloaded. For example, the full load value of one phase of a 30kVA UPS is 10kVA (i.e., 10kVA/220V=45A). It’s not as some people understand it: if one phase current is 1A and another phase current is 2A, it’s not considered a 50% imbalance. Conversely, if one phase current is 1A and another phase current is 0, wouldn’t their imbalance also be 100%? While this seems correct literally, the definition is not accurate.
For example, some users configure their UPS systems with batteries that have a service life of 3-5 years. However, the ambient temperature often exceeds 30°C in summer, and the mains power has never been interrupted for over two years. Maintenance personnel have never conducted any verification or capacity testing discharge tests on the batteries after startup, so the battery’s operating condition remains unknown. In the event of a power outage, the UPS shuts down before the battery has discharged for even less than one-third of its rated time. The user then issues a claim to the manufacturer. After the manufacturer’s maintenance engineer identifies the cause of the malfunction, provides the relevant battery maintenance information from the instruction manual, and analyzes in detail the reasons for the reduced battery capacity, the user can no longer file a claim. However, the damage to the manufacturer’s reputation is severe.