IEC 61225:2025

Overview - What IEC 61225:2025 covers

IEC 61225:2025 (Edition 4.0) defines performance and functional characteristics for low‑voltage static uninterruptible power supply (SUPS) systems used in nuclear power plants (NPPs) and nuclear facilities. It covers both DC and AC static UPS solutions (systems without rotating parts) that draw, store and deliver electrical energy to maintain uninterrupted power to instrumentation, control and electrical power systems. Component‑level design (detailed battery or inverter internals) is excluded and handled by referenced IEC standards.

This edition expands and clarifies requirements to ease application to small modular reactors (SMRs) and passive designs.

Key topics and technical requirements

• System requirements and boundaries - definitions of SUPS scope, system divisions and interfaces with plant power systems.
• Functional requirements - requirements for SUPS supporting systems important to safety; specifications for batteries, battery chargers, inverters, bypass switches, converters (DC/DC, AC/DC) and associated performance.
• Distribution systems - load allocation, electrical characteristics, earthing/grounding, and architecture examples for redundant divisions.
• Supply quality and load effects - immunity to voltage/frequency variations, transients, open‑phase and asymmetrical conditions, electromagnetic interference (EMI) and load current impacts.
• Monitoring, protection and control - continuous monitoring, alarms, electrical protection requirements, and human factors considerations.
• Qualification, ageing, testing and maintenance - qualification criteria, aging mitigation, test procedures and maintenance practices to ensure long‑term reliability.
• Informative annexes - examples of voltage variations (Annex A), sample specifications (Annex B) and specific guidance for SMRs/passive plants (Annex C).

Practical applications and who uses this standard

IEC 61225:2025 is used to:

• Specify SUPS performance for safety‑related and non‑safety I&C equipment in NPPs.
• Inform procurement and vendor requirements for static UPS, batteries and converters.
• Guide system architects and electrical engineers on distribution design, redundancy and earthing for uninterrupted DC/AC supplies.
• Support safety assessors, licensing authorities and plant operators in demonstrating robustness against grid disturbances and ageing.
• Provide test, qualification and maintenance criteria for engineering, commissioning and long‑term plant operation.

Typical users: NPP electrical/I&C engineers, plant designers, equipment manufacturers, safety analysts, regulatory bodies and maintenance teams.

Related standards

IEC 61225:2025 is to be used with IEC 61513, IEC 60709, IEC 60880, IEC 62138, IEC 62855, IEC 63046 and other normative references covering component‑level design, software, and qualification of nuclear I&C and electrical systems.

Keywords: IEC 61225:2025, static uninterruptible power supply, SUPS, UPS, nuclear power plants, NPP, DC power, AC power, SMR, passive design, batteries, inverters, distribution, EMC, testing.