IEEE Std C37.20.7-2017 pdf download – IEEE Guide for Testing Switchgear Rated Up to 52 kV for Internal Arcing Faults.
4. Ratings 4.1 General An IEEE guide cannot mandate or defne equipment ratings. This guide is intended to establish a level of performance for the equipment under specifc conditions. Although these conditions are not an equipment rating, they are the basis of the equipment evaluation described in this guide and are listed in the ratings clause for convenience. 4.2 Accessibility type A distinction is made between two levels of accessibility to switchgear assemblies. These levels correspond directly to the burn indicator placement given in 5.5.2. Type 1—Switchgear with arc-resistant designs or features at the freely accessible front of the equipment only. Type 2—Switchgear with arc-resistant designs or features at the freely accessible exterior (front, back, and sides) of the equipment only. The accessibility shall be designated by selecting the Type (either Type 1 or Type 2) and by adding the appropriate suffx to designate the specifc performance features tested. For the basic test described in this guide, a suffx of “A” is used, i.e., Type 1A or Type 2A, to identify the basic rating. Additional performance features and the suffxes that designate them are found in Annex C.
4.3 Internal arcing short-circuit current The internal arcing short-circuit current is the current level to be used as the prospective current value for testing. The preferred value of the internal arcing short-circuit current is the rated short-time current of the equipment. For equipment that does not have a rated short-time current, the preferred value for the internal arcing short-circuit current shall be the rated short-circuit current. Where fuses or current-limiting circuit breakers are intended to provide current-limiting protection for the equipment, it shall be noted that a protective device is required for this rating by a mark on the nameplate (see 6.3). Notwithstanding the aforementioned, the vertical section containing the current-limiting device shall be subject to the internal arcing short-circuit current testing procedure on the incoming terminals of the protective device to determine the maximum internal arcing short-circuit current for the vertical section with no protection. An additional test shall be made on the vertical section downstream from the protective device to determine the maximum internal arcing short-circuit current for the vertical section when the current-limiting device is not operating in its current- limiting range. The maximum internal arcing short-circuit current rating tested without the current-limiting device installed shall be noted on the nameplate (see 6.3).