IEC TR 60909-1:2002

Overview

IEC TR 60909-1:2002 is a Technical Report published by the International Electrotechnical Commission (IEC) that supplements the core standard IEC 60909-0. This report addresses the calculation of short-circuit currents in three-phase alternating current (a.c.) systems, focusing on the derivation, application, and rationale of various calculation factors as referenced in IEC 60909-0. The principal aim is to enhance both technical accuracy and simplicity in the short-circuit current calculation process, providing background and clarification on the key factors that influence these calculations in electric power systems.

Key Topics

• Voltage Factor c: Used to account for variations in system voltage at the point of short-circuit, helping to determine maximum and minimum prospective short-circuit currents.
• Impedance Correction Factors (K, K_G, K_T): Applied when calculating short-circuit impedances of generators, power station units (with or without on-load tap changers), and network transformers to achieve more accurate results under varying operational conditions.
• Peak Current Factor κ: Utilized for the calculation of the peak short-circuit current, which is critical for equipment and system protection.
• Decay and Breaking Factors (μ, λ, q): Applied to determine the decay of the a.c. component and the correct value of breaking currents, especially near generators or asynchronous motors.
• Thermal Effect Factors (m, n): Used for Joule integral and thermal equivalent short-circuit current calculations, important for thermal dimensioning of equipment.
• Asynchronous Motor Contribution: Methods for evaluating how asynchronous motors contribute to the initial symmetrical short-circuit current.

Applications

IEC TR 60909-1:2002 delivers essential guidance for a diverse set of users involved in the design, analysis, and operation of three-phase a.c. power systems, particularly in areas such as:

• Power System Design: Aids power system engineers in accurately assessing fault levels, ensuring proper specification of electrical equipment such as circuit breakers, transformers, and switchgear based on realistic and standardized worst-case short-circuit conditions.
• System Analysis and Protection: Enhances the reliability of short-circuit studies, which underpin the development of protection schemes, coordination of protective devices, and system stability assessments.
• Standards Compliance: Supports utilities, consultants, and manufacturers in meeting international requirements and maintaining consistency across different countries and projects.
• Operational Planning: Assists in planning for various system operating scenarios, including changes in topology, load conditions, and equipment upgrades.

The approach based on standardized calculation factors ensures that safety margins are maintained and economic considerations are balanced with reliable operation, even when detailed operational data are not available during the planning phase.

Related Standards

IEC TR 60909-1 is closely related to other standards and technical reports within the IEC 60909 series and IEC framework, including:

• IEC 60909-0: Short-circuit currents in three-phase a.c. systems - Part 0: Calculation of currents (core calculation procedures referenced in IEC TR 60909-1)
• IEC 60038: IEC standard voltages (provides standard voltage reference values)
• IEC/TR 60909-2: Electrical equipment - Data for short-circuit current calculations
• IEC/TR 60909-4: Examples for the calculation of short-circuit currents

These documents collectively provide a robust methodology and practical examples for the accurate and standardized calculation of short-circuit phenomena in power networks, enhancing electrical safety and system integrity globally.