IEC 61660-1:1997

Overview

IEC 61660-1:1997 is an International Electrotechnical Commission (IEC) standard that outlines a method for calculating short-circuit currents in d.c. (direct current) auxiliary installations within power plants and substations. This standard is particularly relevant to d.c. auxiliary systems that may contain key equipment acting as short-circuit current sources, including:

• Three-phase a.c. bridge-connected rectifiers (for 50 Hz operations)
• Stationary lead-acid batteries
• Smoothing capacitors
• D.C. motors with independent excitation

IEC 61660-1 provides a universal, conservative calculation approach designed to yield sufficiently accurate results for engineering applications-particularly for protection, fuse selection, and system design. The document incorporates corrections from February 1999 and March 2000, ensuring its ongoing applicability and accuracy for users.

Key Topics

• Scope and Applicability: The standard is applicable to d.c. auxiliary networks in power plants and substations using specific sources and equipment listed above. It addresses only three-phase a.c. bridge-connected rectifiers for 50 Hz; other types may require additional considerations.
• Calculation Methodology: IEC 61660-1 offers a standardized approach for determining short-circuit currents, focusing on:
  • Maximum short-circuit current: for defining equipment ratings
  • Minimum short-circuit current: as a basis for protection and fuse settings Calculations account for both time-dependent and quasi steady-state short-circuit currents.
• Definitions and Symbols: The standard provides precise definitions for concepts such as short-circuit current, partial short-circuit current, and peak short-circuit current, along with standardized symbols and subscripts used in equations.
• Practical Considerations: Guidance is provided on data acquisition (e.g., testing or measurement in existing systems), required system parameters, and assumptions such as negligible load currents and zero-impedance faults for conservative calculations.

Applications

IEC 61660-1 is widely used in the following areas:

• Design and Engineering of D.C. Systems: Power plant and substation engineers use this standard to size and select electrical devices capable of withstanding prospective short-circuit events, ensuring reliable and safe system operation.
• Protection Coordination: The calculation of minimum and maximum short-circuit currents supports the correct specification of fuses and protection relays, optimizing system selectivity and safety.
• Compliance and Standardization: Utilities, contractors, and manufacturers refer to IEC 61660-1 to align with international best practices, facilitate regulatory compliance, and guarantee interoperability of subsystems.
• System Upgrades and Maintenance: When integrating new equipment or modifying system topology, professionals can quickly reassess short-circuit risks using the methodologies detailed in this standard.

Related Standards

Several IEC standards complement IEC 61660-1 or are referenced within it:

• IEC 61660-2: Calculation of the effects of short-circuit currents in d.c. auxiliary installations (follow-up to Part 1).
• IEC 60038: Standard voltages used in electrical installations.
• IEC 60896-1: General requirements and test methods for stationary lead-acid batteries.
• IEC 60050 (IEV): International Electrotechnical Vocabulary, providing definitions for terminology used.
• IEC 60909: Calculations of short-circuit currents in three-phase a.c. systems (for relevant comparisons).

By following IEC 61660-1, practitioners in power system design and operations can confidently perform d.c. short-circuit calculations, ensuring robust auxiliary power systems in critical energy infrastructure. For more specialized scenarios or equipment, additional guidance from complementary IEC standards may be required.