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  IEC 60255-151 TCC Curve Library (SVG + CSV)
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DEFINITION
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The IEC 60255-151 TCC Curve Library is a standardized, interoperable collection of
time-current characteristic (TCC) curves for protective relays and devices, published
in both SVG (scalable vector graphics) and CSV (comma-separated values) formats to
support visualization, simulation, and coordination analysis in power system
protection engineering.

OVERVIEW
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IEC 60255-151 is an international standard specifying the format, content, and
exchange requirements for time-current characteristic (TCC) curves used in numerical
and electromechanical protective relays. The TCC Curve Library provides
machine-readable, vendor-agnostic representations of standardized inverse-time,
definite-time, and customized relay characteristics—including IEEE C37.112, IEC
60255-15, and user-defined curves—enabling consistent protection coordination
studies across software platforms. Each curve is defined by discrete (time, current)
coordinate pairs in CSV for computational use (e.g., coordination checking,
selectivity verification), while corresponding SVG files offer human-readable,
scalable graphical renderings with embedded metadata (e.g., relay model, standard
compliance, curve type). The library supports traceability, version control, and
integration into digital twin environments, facilitating automated relay setting
validation, arc-flash analysis, and compliance reporting. By decoupling curve data
from proprietary relay configuration tools, it promotes transparency,
reproducibility, and collaborative protection engineering across utilities,
consultants, and OEMs.

KEY COMPONENTS
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1. SVG curve visualizations with embedded metadata
2. CSV datasets containing normalized (I/Iₙ, t) coordinate pairs
3. Standardized JSON manifest describing curve attributes (e.g., standard reference, curve class, tolerance band)

APPLICATIONS
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  - Protection coordination studies (selectivity verification)
  - Relay setting validation and sensitivity analysis
  - Interoperable protection engineering workflows in digital substations

KEY FORMULAS
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IEC Inverse Time Characteristic: t = k × (I/Iₙ)^(-α)
  -> Calculates operating time t (seconds) for a given fault current I relative to rated pickup current Iₙ; k and α are curve-specific constants defined in IEC 60255-15
IEEE Moderately Inverse (C37.112): t = A / ((I/Iₙ)^p - 1)
  -> Computes operating time t for IEEE moderately inverse curves; A and p are constants (e.g., A=0.18, p=0.02 for CO-8)
Definite-Time Delay: t = tₛₑₜ + tₘᵢₙ
  -> Total operating time t comprising set delay tₛₑₜ plus minimum mechanical/electronic delay tₘᵢₙ

RELATED CONCEPTS
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  - Protection coordination
  - Time-current characteristic (TCC)
  - IEC 61850 substation automation

REFERENCES
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IEC 60255-151:2019 – Measuring relays and protection equipment – Part 151: Functional requirements for time-current characteristics (https://webstore.iec.ch/publication/64149)
IEC TR 61850-90-12:2021 – Communication for power utility automation – Guidance for using IEC 60255-151 TCC data exchange (https://webstore.iec.ch/publication/93149)
IEEE Std C37.112-2018 – IEEE Guide for Application of Thermal Overload Protection for Power Transformers (https://ieeexplore.ieee.org/document/8412529)

TAGS
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protection engineering, TCC, IEC60255, SVG, CSV, power systems