scope:

Foreword

Following reports of circuit breaker failures in applications where very fast TRVs were determined to be the cause, and after thorough analysis of TRV data gathered from all parts of the world, this guide was suggested by the IEEE Switchgear Committee's Task Force on Transient Recovery Voltages. The task force suggested that another class of definite purpose circuit breakers was needed for fast TRV applications. Circuit breakers designated as definite purpose for fast transient recovery voltage rise times applications would be subjected to special fast TRV parameters during both Test Duty 2 (30% of rated short-circuit current) and Test Duty 1 (7% of rated short-circuit current) trials, to demonstrate the capability to interrupt circuits characterized by fast inherent TRVs. A few words of clarification are in order:

• No fast T₂ values or tests are proposed for fault currents greater than 30% of rated short-circuit current.

• The proposed fast T₂ values were chosen to meet 90% of the known fast TRV circuits, but even these fast values do not meet the requirements of all fast TRV applications.

• A circuit breaker that would meet the requirements for definite purpose for fast TRV rise times applications may or may not also meet the requirements for definite purpose circuit breakers for capacitor switching.

It is the purpose of this guide to communicate the suggested values to those in the industry who are interested and who would be in a position to offer comments and suggestions for further revisions.

Table 1B contains values for circuit breakers designed and tested to the circuit breaker ratings contained in ANSI C37.06-2000, Table 1. These circuit breaker ratings have a rated voltage range factor (K) equal to 1.0.

Tables 2B and 3B contain values for circuit breaker ratings contained in ANSI C37.06-2000, Tables 2 and 3.

This guide was initially approved as a "trial-use" guide in 1997. Experience with the trial-use document since then has been favorable, and the document is now approved for more general use as a guide. Only minor editorial revisions have been made to the guide, plus suitable revisions to the text of this "Foreword."  

Scope

This guide is issued as a supplement to C37.06 for high-voltage circuit breaker applications where the transient recovery voltages (TRV) rise to the crest value much more rapidly than those specified in ANSI C37.06:

Table 1, Preferred ratings for indoor circuit breakers with voltage range factor K=1.0;

Table 2, Preferred ratings for outdoor circuit breakers 72.5 kV and below; or

Table 3, Preferred ratings for outdoor circuit breakers rated 123 kV and above. 2