IEEE Std C37.06.1-2017 pdf download – IEEE Recommended Practice for Preferred Ratings for High-Voltage (>1000 volts) AC Circuit Breakers Designated Defnite Purpose for Fast Transient Recovery Voltage Rise Times.
3. Definitions For the purposes of this document, the following terms and definitions apply. The IEEE Standards Dictionary Online should be consulted for terms not defined in this clause. 6 For service conditions, definitions, interpretation of ratings, tests, and qualifying terms, see IEEE Std C37.04, IEEE Std C37.09 [B3], and IEEE Std C37.011 [B4]. R10 series: A series of preferred numbers 1.0–1.25–1.6–2.0–2.5–3.15–4.0–5.0–6.3–8.0 and their products by powers of 10 as defined in IEC 60059. For example: 10–12.5–16–20–25–31.5–40–50–63. The designations of the series begin with “R” and the series are called “Renard Series”. transformer-limited fault (TLF): A fault fed by or limited by a transformer directly connected to the interrupting device without transmission lines or cables connected in parallel with the transformer. transformer-limited fault breaking current: The highest fault current that the circuit breaker is capable of breaking in a circuit having a power-frequency recovery voltage corresponding to the rated maximum voltage of the circuit breaker and having a TRV parameters better than or equal to the rated values assigned.
4. Rated TLF breaking currents for circuit breakers The transformer-limited fault current is not simply a percentage of short circuit current (I sc ) of circuit breaker; however it does depend on the transformer short-circuit power. It is unreasonable to require it to be in all cases a TLF current equal to 30% of the rated short-circuit current as previously thought. Hence a rated TLF current rating is introduced in Table 1. This way the current specified would correspond to the actual need (Annex B) in service instead of a fixed percentage (10% or 30%) of the rated short-circuit current that is in many cases far from the real need.
5. Transformer limited fault TRV The rate of rise of transient recovery voltage (TRV) is influenced by the transformer capacitance and capacitance between the transformer and the circuit breaker. A high-frequency TRV condition may occur when there is a fault with a short-circuit current fed by a transformer without any appreciable capacitance between the transformer and the circuit breaker. In usual cases TLF is covered by terminal fault test duties T10 and T30. However, in some cases of TLF the rate-of-rise of recovery voltage (RRRV) exceeds the values specified in the standards for terminal faults. This is due to the fact that the surge capacitance of transformers is relatively small (e.g., 3000−6000 pF for 550 kV and 800 kV applications). 7 The corresponding natural frequency of the transformer results in a TRV having a rate-of-rise that is two or three times the value for a terminal fault. TLF currents vary in a wide range and they depend on the short- circuit power of the transformer.