IEC 61225-2005 pdf – Nuclear power plants – Instrumentation and control systems important to safety – Requirements for electrical supplies.
1 Scope This International Standard specifies the performance and the functional characteristics of the electrical supply systems required for the instrumentation and control (I&C) systems important to safety of a nuclear power plant. Guidance is also given on the possible use of these supplies for other I&C systems. These supplies should be fed from primary sources of suitable redundancy and reliability, so that the safety and functional objectives of the I&C system can be adequately achieved. This standard defines the methods of application of IAEA Safety Guide NS-G-1 .3. The specific design requirements for the components of the I&C power supply system are covered by IEC standards and standards listed in the references and are otherwise outside the scope of this standard. The scope of the I&C power supply system covered by this standard does not apply to supplies to certain equipment within an I&C system, which may need specific and special quality or reliability of power supplies, such as closer tolerances of frequency or voltage or of interruption time for loss of supply shorter than the period required by the normal tolerances of IEC standards relevant to power plants. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60038:2002, IEC standard voltages IEC 601 46-2:1 999, Semiconductor converters – Part 2: Self-commutated semiconductor converters including direct d.c. converters IEC 60686:1 980, Stabilized power supplies, a.c. output IEC 60709, Nuclear power plants – Instrumentation and control systems important to safety – Separation IEC 60780:1 998, Nuclear power plants – Electrical equipment of the safety system – Qualification
3 Definitions For the purposes of this document, the following definitions apply. Other terms not defined below are defined in IAEA Safety Guide NS-G-1 .3. 3.1 item important to safety item that is part of a safety group and/or whose malfunction or failure could lead to radiation exposure of the site personnel or members of the public [Derived from IAEA Safety Guide NS-G-1 .3] 3.2 safety system system important to safety, provided to ensure the safe shutdown of the reactor or residual heat removal from the core, or to limit the consequences of anticipated operational occurrences and design basis accidents [IAEA Safety Guide NS-G-1 .3] 3.3 safety-related I&C system I&C system important to safety which is not part of a safety system [IAEA Safety Guide NS-G-1 .3] 3.4 safety system support features collection of equipment that provides services such as cooling, lubrication and energy supply required by the protection system and the safety actuation systems [IAEA Safety Guide NS-G-1 .3]
4 System requirements 4.1 Function and description I&C electrical supplies generally consist of the following non-interruptible systems (see Figures 2 and 3): – a d.c. power system with battery-chargers and batteries, supplying d.c. loads and inverters; – an a.c. power system with back-up batteries and inverters, supplying a.c. loads. The d.c. power system shall supply the d.c. loads, including input to the inverters, control, monitoring, protection, switching and auxiliary power, during normal operation, anticipated operational occurrences, and accident conditions. If loads important to safety require continuous power, a suitable non-interruptible power system shall be provided to supply such loads in accordance with Clause 6. If a supply important to safety is needed, then its functions shall be classified according to IEC 61 226. Its design and implementation shall be according to that standard and its references, to provide assurance of sufficient integrity of supply. Subclause 8.4 provides the constraints on connecting I&C loads important to safety and I&C loads not important to safety. Functions and general requirements of I&C systems including their power supplies should be provided in accordance with IEC 61 51 3. 4.2 System divisions The d.c. power system and the non-interruptible a.c. power system shall be divided into redundant and independent divisions in accordance with Clause 5 of this standard. Each division of the d.c. power system shall consist of at least a battery supply, a battery charger and a distribution system (Figure 2). Each division of the non-interruptible a.c. power system shall consist of at least a supply from a d.c. power system, a d.c.-a.c. inverter, and a distribution system. Another a.c. back-up power supply and an automatic switchover device should also be provided (Figures 3 and 4).