EN IEC 62855:2021

IEC 62855 provides the electrotechnical engineering guidelines for analysis of AC and DCelectrical power systems in nuclear power plants (NPPs) in order to demonstrate that thepower sources and the distribution systems have the capability for safe operation and shutdown of the NPP, bringing it to a controlled state after an anticipated operational occurrenceor accident conditions and finally reaching a safe state.The analytical studies discussed in this document provide assurance that the design basesare satisfied to meet their functional requirements under the conditions produced by theapplicable design basis events. The studies provide assurance that the electrical powersystem is capable of supporting safety functions during all required plant conditions.NOTE The safety functions are described in IAEA Specific Safety Requirements SSR-2/1 related to the design ofthe nuclear power plants..Analytical studies validate the robustness and adequacy of design margins and demonstratethe capability of electrical power systems to support plant operation for normal, abnormal,degraded and accident conditions.The analyses are used to verify that the electrical power system can withstand minordisturbances and that the consequences of major disturbances or failures do not degrade thecapability of the electrical power systems to support safe shutdown of the plant and maintainthe plant in shutdown condition.The analyses are performed with one or more of• simulation tools (software and hardware) that have been verified and validated,• hand calculations, and• tests.This document provides guidance on the types of analyses required to demonstrate that theplant's auxiliary power system can perform the required safety functions. This document doesnot provide specific details on how the analysis should be conducted.This document does not cover digital controllers (such as controllers for rectifiers, inverters,sequencers and electrical protection devices) used in electrical power systems. IEC 61513gives recommendations that apply to the electronic controls and protective elements of theelectrical power systems.This document does not include environmental conditions (i.e. temperature, humidity, etc.) orexternal events (seismic, flooding, fire, high energy electromagnetic pulse, etc.) that mayimpact equipment sizing or protection requirements. The external events lightning andgeomagnetic storms are included.This document does not cover additional or unique requirements for stand-alone powersystem, such as power supplies for security measures in NPPs. Pertinent clauses of thisdocument may be used as a guideline for such systems.Redundancy in the power system design can increase the availability of electrical power tocritical plant equipment. Performing a probabilistic risk assessment (PRA) is a method ofassessing system availability and optimizing design for high reliability. This document doesnot cover improving the reliability of NPP electrical power systems using statistical or diverseand redundant schemes.Requirements for safeguards of personnel involved with installation, maintenance andoperation of electrical systems and general personal safety are outside the scope of thisdocument. General guidance for lightning protection of equipment is provided in relevantclauses of this document.This document is intended to be used:• for verification of the design of new nuclear power plants,• for demonstrating the adequacy and impact of major modifications of electrical powersystems in operating nuclear power plants, and• where there is a requirement to assess and establish operating limits and constraints forexisting plants.Pertinent parts of this document can be used as guidance for decommissioning stages.