IEC 61225:2019

Overview

IEC 61225:2019 is an international standard published by the International Electrotechnical Commission (IEC) that sets the requirements for static uninterruptible DC and AC power supply systems specifically used in nuclear power plants. This third edition replaces the 2005 version and broadens the scope to include all static uninterruptible power supplies (SUPS) in nuclear facilities, not just those serving Instrumentation and Control (I&C) systems.

A static uninterruptible power supply is a critical electrical system that provides continuous and reliable power by drawing energy from a source, storing it, and maintaining the output without interruption. Unlike other types, static UPS systems do not contain rotating parts, enhancing reliability and reducing maintenance needs.

The standard is essential to ensure these systems perform correctly under all conditions, supporting nuclear safety through robust design, rigorous functional requirements, and clear verification and validation processes.

Key Topics

• Scope and System Design: Specifies the performance and functional characteristics of low voltage static uninterruptible power supply systems in nuclear power plants. The standard addresses supply system divisions, system boundaries, and graded approaches aligned with the defence-in-depth safety principle.

• Functional Requirements: Details performance expectations for static UPS systems, batteries, chargers, inverters, bypass switches, and converters for voltage stabilization. It mandates protection against power transients and disturbances to safeguard connected equipment from voltage fluctuations on AC distribution systems.

• Load and Distribution Management: Outlines requirements for the design of distribution systems including load allocation, earthing, and management of loads with different safety classifications, ensuring stable and interference-free supply.

• Monitoring, Protection, and Maintenance: Emphasizes continuous monitoring, electrical protection methods, equipment qualification, ageing management, and testing regimes to guarantee long-term reliability and operational readiness of SUPS in nuclear plants.

• Safety Emphasis: Applies a graded verification and validation approach, addressing not only safety-critical equipment but all connected systems to maintain high levels of reliability in nuclear power operations.

• Battery Protection under Abnormal Conditions: Specifies that when batteries are connected in parallel, isolation devices must be employed to prevent failures from spreading across divisions, enhancing system resilience.

Applications

IEC 61225:2019 is indispensable for:

• Nuclear Power Plant Operators and Engineers: Designing and maintaining static uninterruptible power supply systems that reliably support instrumentation, control, and other electrical loads critical for safe plant operation.

• Suppliers and Manufacturers: Developing UPS equipment compliant with rigorous nuclear industry standards to ensure safety, reliability, and immunity to electrical disturbances.

• Regulatory Authorities and Auditors: Establishing benchmarks for evaluating the performance and safety of power supply systems in nuclear facilities.

• Maintenance and Testing Personnel: Implementing procedures for inspection, qualification, and ageing management to extend the life and efficacy of power supply infrastructure.

The standard supports maintaining continuous operation of vital systems during power fluctuations, outages, or abnormal conditions, thereby contributing to nuclear safety and operational stability.

Related Standards

• IEC 61508 - Functional Safety of Electrical/Electronic/Programmable Electronic Safety-related Systems: Addresses overall safety lifecycle requirements which complement UPS system safety as in IEC 61225.

• IEC 62040-1 - Uninterruptible Power Systems (UPS) - General and Safety Requirements: Provides basic safety requirements applicable to static UPS systems outside nuclear-specific contexts.

• IEC 60880 - Nuclear Power Plants - Instrumentation and Control Systems Important to Safety - Software Aspects: Relevant for software components interfacing with SUPS devices.

• IEEE 446 (Red Book) - Recommended Practices for Emergency and Standby Power Systems for Industrial and Commercial Applications: Offers best practice guidelines on uninterruptible power supply systems that may cross-reference IEC requirements.

These related standards complement IEC 61225:2019 by addressing broader safety, software, and emergency power system practices relevant to nuclear facility power management.

Keywords: IEC 61225, static uninterruptible power supply, SUPS, nuclear power plants, uninterruptible DC power supply, uninterruptible AC power supply, nuclear instrumentation, power system requirements, defense-in-depth, battery protection, electrical power systems, nuclear safety.