IEEE Std C37.20.1 pdf free download

IEEE Std C37.20.1 pdf free download.Metal-Enclosed Low- Voltage (1000 Vac and below, 3200 Vdc and below) Power Circuit Breaker Switchgear.
For the U0SCS of this document, the following terms and definitions apply. The IEEE Sianciarcis Dictionari’ Online should be consulted for terms not defined in this clause.
Note that the definitions of terms contained in this standard, or in other standards referred to in this standard, are not intended to embrace all legitimate meanings of the terms. They are applicable only to the subject treated in this standard.
auxiliary compartment: That portion of the switchgcar assembly that is assigned to the housing of auxiliary equipment, such as voltage transformers, control power transformers, or other miscellaneous devices.
circuit breaker compartment: That portion of a switchgear assembly that contains one low-voltage power circuit breaker and the associated primary conductors and secondary control connection devices, and may include current transformers.
design tests: Tests made by the manufacturer to determine the adequacy of the design of a particular type, style, or model of equipment or its component parts to mccl its assigned ratings and to operate satisfactorily under normal service conditions or under special conditions if specified, and may be used to demonstrate compliance with applicable standards of the industry.
NOTE Design tests are sometimes called type tests.
field tests: Tests made after the switchgear assembly has been installed at its place of utilization. mechanism-operated cell switch: See: mechanism-operated contact.
mechanism-operated contact (NIOC): A circuit breaker mechanism-operated auxiliary switch which is mounted in the stationary housing and is operated by linkage which cooperates with the circuit breaker mechanism. Sin: mechanism-operated cell switch.
The rated short-circuit withstand current determines the minimum bus bracing which is required of the design. The bus bracing may be able to withstand higher values than the stated rating. When adding or upgrading circuit breakers, consult the manufacturer about the capabilities of the bus bracing.
For LV ac and LV dc switchgear assemblies with no fused circuit breakers, the rated short-circuit withstand current is the short-circuit current rating of the circuit breaker with the lowest short-circuit current rating in the assembly.
For LV ac switchgear assemblies with all fused circuit breakers, the rated short-circuit withstand current is the short-circuit current rating of the fused circuit breakers with the lowest short-circuit rating used in the assembly.
For LV ac switchgear assemblies with both fused and unfused circuit breakers, the rated short-circuit withstand current is the short-circuit current rating of the unfused circuit breaker with the lowest short- circuit current rating in the assembly.
The rated short-circuit withstand current, which is expressed in rms symmetrical amperes, times 2.3 (for unfused circuit breaker assemblies) or times 2.16 (for fused circuit breaker assemblies), equals the peak current tir which the assembly shall be qualified by the short-circuit current withstand tests of 6.2.5. The short-circuit withstand current can also be expressed in rms asymmetrical amperes by multiplying times 1 .33 or 1 .247 for unfused and fused circuit breaker assemblies, respectively. The rrns asymmetrical current values for low-voltage switchgear assemblies are similar in concept to the rms asymmetrical momentary current ratings for medium-voltage switchgear assemblies, except that larger multipliers are required for medium-voltage switchgear assemblies for the higher X/R ratings. The short-circuit withstand current has also sometimes been called bus bracing, but continued use of this term is discouraged. If bus bracing is used, the specifier should state whether the current is in rms symmetrical or rms asymmetrical amperes. Refer to the multiplying factors fur the curve MNI in IEEE Std C37.26 fur multipliers to convert from rms symmetrical amperes to rms asymmetrical amperes at a specific power factor or X!R ratio.IEEE Std C37.20.1 pdf download.