Which of the following statements are true?

Statement A is FALSE: When a UPS operates in normal mode (online mode), directly turning on the maintenance bypass switch without proper procedure is dangerous and incorrect. The proper procedure requires first transferring the load to static bypass mode, then engaging the maintenance bypass switch. This ensures uninterrupted power to the load during maintenance operations.
Statement B is TRUE: When operating in static bypass mode, if the mains input experiences a sudden outage, the UPS automatically switches to battery mode to maintain power to the critical load. This is a fundamental feature of UPS systems to ensure continuous power availability.
Statement C is TRUE: The Huawei UPS5000-H is designed as a modular UPS system that supports hot-swappable power modules. This allows failed modules to be replaced online without interrupting power to the critical load, ensuring high availability and maintainability.
Statement D is TRUE: When mains and bypass inputs share the same power source, a mains outage affects both inputs simultaneously. Since bypass mode relies on the bypass input being available, the UPS cannot operate in bypass mode during a mains outage when both inputs are from the same source. The UPS would need to operate in battery mode instead.

- Statement A is incorrect because it violates proper UPS maintenance procedures and could cause load interruption or equipment damage.

1. Huawei UPS5000-H Series (25-800 kVA) User Manual, Section 4.3 "Operation Modes," pages 78-82, describing the automatic transfer capabilities between different UPS operating modes.

2. Huawei UPS5000-H Series Technical Specifications Document, Section 2.4 "Modular Architecture," page 15, detailing the hot-swappable module design and online replacement capabilities.

3. IEEE Standard 2030.1.1-2021, "IEEE Standard Technical Specifications for a DC Quick and Bidirectional Charger for Use with Electric Vehicles," Section 6.2.3, providing general UPS bypass operation principles applicable to modular systems.

4. Huawei UPS5000-H Installation and Commissioning Guide, Section 5.2 "Bypass Operations," pages 92-95, explaining the relationship between mains and bypass inputs and operational limitations.

5. IEC 62040-3:2021 "Uninterruptible power systems (UPS) - Part 3: Method of specifying the performance and test requirements," Section 5.3.4, defining standard UPS transfer characteristics and bypass operation requirements.