Short Circuit Studies

Why have a short circuit study done?

Short-circuit studies are done to determine the magnitude of the prospective currents flowing throughout the power system at various time intervals after a fault occurs. The magnitude of the currents flowing through the power system after a fault varies with time until they reach a steady-state condition. This behaviour is due to system characteristics and dynamics. During this time, the protective system is called on to detect, interrupt, and isolate these faults. The duty imposed on this equipment is dependent upon the magnitude of the current, which is dependent on the time from fault inception. This is done for various types of faults (three phase, phase-to-phase, double-phase-to-ground, and phase-to-ground) at different locations throughout the system. The information is used to select fuses, breakers, and switchgear ratings in addition to setting protective relays.

The short circuit data is used to determine the bolted three-phase short circuit current, which is in turn used to calculate the arcing fault current. The short circuit analysis is required for proper sizing of circuit breakers and/or fuses. Normal system operating method, alternate operation, and operations that could result in maximum fault conditions is thoroughly evaluated.

Compliance:

The short-circuit study is performed by Arc Flash Advisors in accordance with the recommended practices and procedures set forth in ANSI/IEEE 399 and the step-by-step procedures outlined in the short circuit calculation chapters of IEEE 141 and ANSI/IEEE 242, following the recommendations of NETA.

Study Report:

Following the recommendations of NETA, the results of the short-circuit study will be summarized in a final report containing the following items:

•Basis, description, purpose, and scope of the study.
•Tabulations of the data used to model the system components and a corresponding one line diagram.
•Descriptions of the scenarios evaluated and identification of the scenario used to evaluate equipment short-circuit ratings.
•Tabulations of equipment short-circuit ratings versus available fault duties. The tabulation shall identify percentage of rated short circuit and clearly note equipment with insufficient ratings.
•Conclusions and recommendations.

What benefits would I receive from having a Study performed?
A Short Circuit Study will show you the probable and possible values of fault currents within the system and show you what impact short circuits and failures would have on your fuses, circuit breakers, and your facility’s operation. More specifically:

•Increased facility reliability
•Increased equipment protection
•Increased operating efficiency
•Help prevent downtime
•Prevent damage by identifying underrated equipment
•Prevent damage by identifying overloaded equipment