2. Operational malfunctions
Because of the importance of the loads carried by UPS, in order to ensure the safe and reliable operation of UPS, various products have their own set of safe operating procedures, which are written into the instruction manual for users to refer to and follow. However, some maintenance personnel disregard this and operate according to their own understanding instead of following established procedures, sometimes resulting in problems. There are also unintentional operational malfunctions, such as accidentally damaging nearby components during disassembly without noticing, leading to secondary faults when powering on; accidentally short-circuiting two points with the meter probes during fault diagnosis; incorrectly connecting the positive and negative terminals when connecting external batteries; loose battery connectors or battery switches, causing the UPS to shut down when the mains power fails; incorrect phase sequence during mains line modifications or repairs by the power company, preventing the UPS from starting or causing conversion failure; forgetting to start the inverter after powering on the UPS, leading to shutdown when the mains power fails; rats attracted by food left haphazardly in the machine room, causing short circuits between cables or components; and unshielded remote signal cables running parallel to AC lines, causing coupling interference and malfunctions.
3. Delay-related failures
Delayed failures refer to UPS malfunctions caused by maintenance personnel’s negligence in failing to detect potential faults in a timely manner, or by failing to take appropriate measures after detection. For example, in a dual-unit redundant parallel UPS system, the load is evenly distributed across two UPS units. Sometimes, due to some coincidence, one of the inverters shuts down, and the load is completely transferred to the other UPS. If maintenance personnel detect this in time, they can simply restart the shut-down UPS inverter. However, if they fail to detect it in time, a power outage will result in a single-unit power supply, weakening the overload capacity and halving the backup time. In this case, an overload will cause a complete power outage of the supplied load. Another example is that when batteries are operating under suboptimal conditions, they should be maintained regularly, and any battery with a significantly reduced capacity should be replaced immediately.
Battery damage can occur gradually or suddenly; a battery that worked yesterday may fail to discharge today. This can happen during battery maintenance: during the last monthly inspection, some batteries may have slightly low float voltages but weren’t completely unusable. However, after a power outage that month, one group of batteries may completely fail to discharge. Therefore, if a battery malfunction is detected, it should be replaced promptly to prevent accidents.