Data Collection

Every analysis requires input data, and there is no difference with arc flash. While for some studies we can be conservative for arc flash analysis, it is better to be reasonably precise. Why? Because the highest short circuit current doesn’t always lead to the highest incident energies. This is especially seen when people tend to underestimate Low Voltage installation arc flash hazard, addressing High Voltage as a real threat where reality is most of the time surprisingly different.  

Key factors 

It is important to be accurate when collecting data, and data needs to be based on up to date documentation to reflect existing installation. Very often there is big discrepancy between what is on the drawings and what is in reality. While some facilities maintain documentation very well, others not always. It is very good practice to verify documentation vs as-build reality. This means site visit for data verification and data collection.  Key reason for such decision are: 

• Lack of expertise on site 
• Lack or limited documentation and related difficulties (system mapping) 
• No available staff for arc flash data collection support 
• Independent engineer opinion vs employee  

What make difference?

Every installation is different and data collection also. It depends on: 

• type of business sector e.g. chemical, oil & gas, industrial, automotive, BESS, PV & WIND, marine 
• system size and voltage range (AC, DC, LV, HV, big or small system)  
• available documentation and drawings 
• local support (skilled electrician, engineers, etc.) 

Who can do data collection? 

Since we are talking about low and medium voltage systems, it is required for such person to be certified or authorised electrician or engineer. Data collection can be an elevated risk process since it requires access to electrical switchgears, cabinets and machines. Very often, some covers need to be removed in order to retrieve the right data. It is good to arrange: 

• introduction meeting with technical team 
• provide general plan and if needed to arrange work permits 
• follow site specific safety rules  

What data needs to be collected? 

It depends on specific facility profile and amount of documentation, however some general list can be made. If documentation is good enough, It is good practice to prepare a list of all (known) necessary information’s needed. What we can expect to identify and collect: 

• System operation modes  (normal mode, generator mode, emergency, etc.) 
• Utility fault data, three-phase and single line-to-ground short circuit power, X/R ratios at the power delivery point 
• Utility feeder(s) protection settings, relay type, CT ratio 
• All available documentation for old equipment (generators, relays, breakers) 
• Single line diagrams copy (if on paper only), even old are useful 
• Switchgear, switchboards data (short circuit withstand rating, nominal current, busbar gap, dimensions) 
• Cable data, type, length, conductor material, amount per phase 
• Generator data current decrement curves as per manufacturer tests, nameplate data  
• Transformer data, transformer type, winding connection, voltage ratio, rated power, short-circuit impedance (nameplate data) 
• Motors data  >37kW nameplate and control system type (VFD, DOL, SS, etc.) 
• Medium voltage protective relays type, manufacturer, settings, and CT ratios. 
• Low voltage circuit breakers data and trip unit type and settings 
• LV and MV fuses size and type 

Specific data for AC and DC system analysis

• type of system grounding (for protection and short circuit study) 
• BESS:  battery energy storage system type, designed power, batteries configuration, physical gaps between “+ and –” electrodes, DC protection type and settings 
• PV: inverter type, short circuit specification, configuration of modules connected, topology, DC protection type and settings 
• WIND: generator data sheet and type, converter data and protection type, system topology and min max wind generators connected 
• DC systems – verify electrode gap (min max), short circuit protective device, system voltage  (model range check), DC source type for short circuit study 
• UPS: configuration and working modes (external by-pass, electronic by-pass), power or battery package, UPS short circuit behaviour (current and voltage)  

Example of data collection summary

Site visit and data collection activities need to be performed according to site safety rules. It also requires a site authorised person to accompany the engineer during data collection and allow access to all necessary equipment, switchgears, and switch rooms. Data should be collected and documented as it serves later as a reference point for any assumptions and comments. Good practice is to transfer all the information’s later back to the customer for further use and upgrades. It can look like this example below.