PC37.112/D2, Jul 2017 is a technical document for overcurrent relay time characteristic equations, supporting engineering work in power and energy systems. It addresses the mathematical relationships used to define how a relay responds as current rises above a set threshold, which is important for protection coordination and consistent relay behavior. For utilities, industrial facilities, and protection engineers, this standard helps provide a common basis for evaluating performance and specifying time-current characteristics.

PC37.112/D2, Jul 2017 overview

This standard focuses on the equations used to describe overcurrent relay timing, a core part of protective relaying in electrical systems. PC37.112/D2, Jul 2017 is relevant where time-current coordination must be defined clearly for design, testing, or procurement. In practice, it supports a shared technical language for comparing relay characteristics and understanding how a device should operate under fault or overload conditions within power system protection schemes.

Typical use cases

PC37.112/D2, Jul 2017 may be used when specifying or reviewing overcurrent protection for distribution feeders, industrial switchgear, motor protection arrangements, and other power system circuits. It is also useful in coordination studies, relay setting development, and documentation for equipment that must respond predictably to abnormal current levels. Engineers and system integrators can use it to align relay behavior with required operating times and to support consistent application across similar installations.

Why this standard matters

Accurate time characteristic equations are essential for protection design, because small differences in relay timing can affect selectivity, equipment stress, and fault clearing performance. PC37.112/D2, Jul 2017 helps reduce ambiguity when comparing relay behavior or checking compliance with expected operating characteristics. That makes it valuable for specification review, testing, and procurement where predictable overcurrent response is needed. Using a common reference also supports safer and more consistent protection coordination across connected systems.

• Overcurrent relay time equations
• Protection coordination reference
• Power system fault response
• Relay setting and evaluation
• Engineering and testing support