UPS uninterruptible power supply systems, both leakage current protection and uninterruptible power supply capability are required. Therefore, some users have adopted a 3kVA high-frequency online UPS and a 30mA timed leakage current circuit breaker in each power supply system. During the commissioning of one power supply system, the following phenomenon occurred repeatedly: when the mains power was normal, the high-frequency online UPS started under no-load. When the output relay activated, cutting off the bypass and connecting the inverter circuit, the leakage current protection of the mains circuit breaker tripped, thus cutting off the mains power. This seems to verify a current claim that circuit breakers with leakage current protection cannot be installed at the front end of a UPS . Therefore, this issue was investigated.
A malfunction of the leakage current protection in a UPS was discussed. This included an examination of the power filter, the leakage current protection, and the transient process when they are used together.
1. UPS starts up and works normally.
When the mains power is normal, the high-frequency online uninterruptible power supply (UPS) starts under no-load conditions. Upon receiving the start-up command, the start-up circuit begins operation. The main circuit first outputs through the bypass. Once the CPU detects that the inverter is working normally, it sends a control signal to drive the output relay, disconnecting the bypass and connecting the inverter circuit, thus completing the UPS start-up process. In the eight power supply systems we developed, the UPS in seven systems operated normally during startup.
2. UPS Uninterruptible Power Supply Repair: Symptoms of UPS Leakage Protection Triggering
In the power supply system we developed, the phenomenon described in the introduction occurred, making it impossible to use mains power. It should be noted that this leakage current protection tripping of the UPS did not occur every time the UPS started. In the eight power supply systems, it only occurred multiple times in one system.
3. Analysis of UPS leakage causes
3.1 Circuit diagram of the uninterruptible power supply output section
Initially, we suspected a problem with the UPS ‘s main circuit board and control board. However, the issue persisted after replacing them. We then replaced the charging board and input filter board, but the problem remained. We suspected a problem with the output power filter. Removing the output power filter allowed the UPS to start normally, indicating the problem was likely related to the output power filter.