In ECO (Economy) mode, the UPS prioritizes energy efficiency. When the mains (bypass) power supply is stable and within the acceptable voltage and frequency range, the UPS powers the load directly through the static bypass path. The inverter remains in a standby state, ready to take over instantly if the mains power fails or deviates from the set parameters. This avoids the power loss associated with the double-conversion process (rectifier and inverter), thus increasing overall efficiency.

A. Battery mode is activated only when the mains power fails, not when it is stable.

B. Normal mode involves continuous double-conversion (AC-DC-AC), which is bypassed in ECO mode for efficiency.

D. Maintenance bypass is a manual switch used to isolate the UPS for service, not an automatic operational mode.

1. Huawei UPS5000-H-(300 kVA-1200 kVA) V100R001C00 User Manual, Section 2.2, "Working Modes". The description for ECO mode states, "When the bypass power supply is normal, the load is powered by the bypass."

2. Huawei FusionPower6000 & UPS5000-H Technical White Paper, Section 3.2, "High Efficiency". It explains that in ECO mode, the system bypasses the rectifier and inverter, supplying power through the static bypass to achieve efficiencies up to 99%.