DraftLogic Electrical Versus Traditional Methods
Calculating fault currents for a transformer circuit
Project has 10 dry type transformers feeding panels. System voltage is 347/600 as service entry, transformers are feeding a variety of panel loads at 120/208 volts and one 277/480 volt panel. All panels and transformers are in a plant like building environment so sizes, locations and feeder sizes and lengths are varied.
Panels and transformers are located on the drawings and the designer has been requested to calculate fault levels at the panels downstream of each transformer to ensure that the appropriate breakers are selected for this project. Loads have been assigned to each panel but feeders and transformers have not been sized.
Using traditional methods where a designer is using an on line app to check voltage drop and some form of calculation spreadsheet to assist with the fault level calculations here is an analysis of the tasks and estimated time needed.
Typical workflow using traditional methods
1. Size transformers based on panel loads (loads are known). Estimated time 15 minutes
2. Size 20 feeders from code tables. Estimated time 45 minutes
3. Scale length of each feeder (20 ) on the drawings and check voltage drop based on expected load and selected conductor. Estimated time 40 minutes
4. Change conductor size if needed to satisfy voltage drop tolerance. Estimated time 15 minutes
5. Use fault level spread sheet to calculate fault levels for each component of each feeder, typically this will require calculation of three segments per feeder, the section from the transformer feeder breaker or fuse to the transformer, the transformer let though and finally the last segment from the transformer to the downstream panel. An estimated 70 combined mouse clicks and key strokes per transformer circuit. For 10 such circuits an estimated 700 keystrokes mouse clicks and keystrokes needed (each one an opportunity for error). Estimated time at only 10 seconds average per entry = 116 minutes
6. Collate results and prepare report for review. Estimated time 10 minutes.
Summary; Many steps needed, extensive human input for each step resulting in many opportunities for errors to creep into the process. Estimated total cycle time 241 minutes or 4 hours.
If a change is needed because of load variations the whole or part of the process must be repeated.
Same task using DraftLogic Electrical
Assumes panels were placed on the drawing using DraftLogic Electrical software which will automatically draw the single line and calculate all loads, conductor sizes based on voltage drop settings and will also calculate fault levels automatically at all critical points in the system from MDP to all downstream devices.
1. Select “single line” from report dialogue box and click ‘ok’. Estimated time 30 seconds.
2. Wait for automation to perform all calculations, size feeders and generate fault levels. Estimated time 2 minutes.
Summary; Only two steps needed, that take a couple of minutes to execute all required calculations and prepare a report for review in the form of a completed single line diagram. Estimated total cycle time 5 minutes. Using these tools all power tree objects are dealt with not just transformer circuits, the entire power tree from MDP to all downstream devices are sized, voltage drop is calculated and feeder sizes adjusted, all lengths automatically entered with adjustment factors vertical drops and connections within panels allowed for and fault levels calculated for all objects.
If changes occur, make the adjustments to whatever parameter is altered and re-run the process.
DraftLogic Electrical vastly decreases the time taken to do this task the first time around, taking only a few minutes versus four hours for the traditional method!
Not only does DraftLogic Electrical provide this incredible productivity gain, it also minimizes the opportunity for error. As you can guess from the number of manual actions and calculations being made in the traditional method, it is highly likely that errors will creep in to the manual process.
Lastly, these gains in productivity and accuracy only multiply as the work needs to be done over and over to accommodate for change requests and ‘what if’ design scenarios.
Gerry Stebnicki, President
See our website at www.draftlogic.com