PRM Engineering
Project Risk Management
+55 11 97169,5160
Short Circuit, Selectivity and Incident Arc Study
OBJECTIVE
We are a family owned and operated business.
We present in a succinct way the procedure adopted in the elaboration of studies of short-circuit, selectivity and incident energy of electric arc of Electric Power Systems. The assessment of the supportability or interruption capacity of the system components from the connection with the concessionaire system to the panel bars, the settings of the relay settings and other protection devices and the definition of the protective clothing against the thermal effects of the electric arcs to be used in interventions on energized equipment.
We are a family owned and operated business.
Incident Energy Calculations based on International Standards NFPA-70E (Standard for Electrical Safety Requirements for Employee in Workplaces) and IEEE Std 1584 (Guide for Performing Arc-Flash Hazard Calculations), which are the best technical references regarding arc risk that are applied in a complementary way to NR 10.
REQUIRED DATA TO EVALUATE THE RISK OF ELECTRIC ARC
We are a family owned and operated business.
Survey of the Single Line Diagram, types of protective equipment and grounding systems;
Elaboration of the Short Circuit and Selectivity Study;
Obtain the characteristics of the different types of equipment, mainly if they are certified as “Resistant to the Internal Arc“; Evaluation of the possibility of resources that reduce the probability of arc or that reduce short-circuit currents and operating times - EPCs;
Proceed with the calculation of incident energy for different operating and maneuver situations.
Determine the approach limit for free areas, restricted areas and identification.
Determination of PPE and appropriate electrical clothing;
Update the procedures with the new PPE and clothing in order to minimize risks and provide guidance on safety practices.
SOFTWARE
SKM - Power Tools for Windows (PTW) programs are preferably used for the elaboration of studies of electrical power systems, as it is a common and standard tool in many companies that hire this type of engineering service. However, other programs such as EDSA, ETAP, etc. can be used at the request of the client.
METHODOLOGY OF WORK
The works to be developed are developed in three stages:
First stage: Field Survey;
Second stage: Modeling and data processing;
Third stage: Preparation of reports.
First Stage: FIELD SURVEY
The necessary information for the preparation of the studies is collected from the documents available in the archives of the Plant and in the verification of equipment in the field, such as machine panels, bus safes, general medium and low voltage panels and secondary panels. They are briefly summarized, but are not limited to data from:
Contribution of the concessionaire's short-circuit current, which feeds the Plant;
Characteristics of electrical cables;
Characteristics of current and potential transformers;
Bus short-circuit capacity;
Protection devices composed of fuses or circuit breakers installed in panels or in the safes of the buses that supply the machines;
Ability to interrupt circuit breakers and motor starters;
Electric motor plate data;
Transformer board data;
Generator plate data;
Protection relays and checking the current settings;
Second Stage: DATA MODELING AND PROCESSING
Elaboration or updating of Unifilar Diagrams
System modeling
Calculation of three-phase, phase-to-ground, phase-to-phase and phase-to-ground short-circuit currents
The purpose of the short circuit study is to ensure that all electrical equipment can withstand or interrupt the electrical energy that may exist during various short circuit conditions. In the study, the short-circuit currents are calculated and compared with the equipment withstand currents or with the rated interrupting capacities.
Equipment that does not support or is capable of interrupting the presumed short-circuit current at its terminals is undersized and must be replaced.
Protection coordination study
The purpose of the protection coordination study is to ensure that the devices are selected and adjusted in order to have selectivity between devices (relay, fuse or circuit breaker), providing maximum protection for the equipment and minimizing the incident energy by reducing the interruption time. .
The objective is to actuate the device closest to the fault, minimizing the impact on the entire electrical system.
Elaboration of the Electric Arc study
The purpose of the Arc Flash study is to calculate the incident energy in the event of a short circuit while working or operating an exposed part of energized equipment. The arc flash study uses the short-circuit current, the interruption time of the upstream protection device, the arc distance and other data to calculate the incident energy. The study then uses the calculated incident energy to determine the arc protection zone and the appropriate PPE's to perform services with energized equipment. The purpose, therefore, of the Arc Flash study and the use of appropriate PPE's is to minimize damage to people exposed to electric arc and maximize the likelihood of survival.
Generation and Installation of Electric Arc Warning Labels
