Transformer GIC Thermal Response
This spreadsheet (revised November 3, 2017) includes sample formulas for calculating transformer winding and metallic parts hot spot temperatures as described in the NERC white papers Transformer Thermal Impact Assessment White Paper and Screening Criterion for Transformer Thermal Impact Assessment.
It is provided with the following disclaimers:
- Input parameters in this spreadsheet are samples provided for illustration only and not intended to represent any specific transformer.
- Proper parameters corresponding to the studied transformer should be entered, including the full-load oil temperature, time constants for metallic parts and windings, and step-response characteristics for metallic parts and windings. The input parameters cells are shaded gray in the spreadsheet.
- The calculations assume a simplified single-pole transfer function to relate the transformer thermal response to the effective GIC for both metallic parts and windings, in the form of 1/(1 + sT). Higher-order models may provide more accurate temperature modeling.
To use the spreadsheet:
- Create the GIC(t) time series for the transformer(s) of interest. (Another Knowledge Base entry provides an input file for generating a GIC(t) time series for the NERC Benchmark GMD Event.)
- Paste the GIC(t) into the “XfrTimeSeries” spreadsheet. The time values (in seconds) should be in column A. If you produce the GIC(t) with the Benchmark GMD Event Time Series csv input and PowerWorld Simulator’s “Load Time-Varying Input and Calculate Transformer IEffective” option, you may copy the data from the resulting csv output file into columns A through F. Note that the spreadsheet is presently formatted for GIC(t) for THREE transformers (columns D-F, shaded yellow). If columns for additional transformers are needed, they should be inserted to the left of column F. Formulas start in column G. These may be moved, but should not be overwritten. The named range “ResultsIeff” should encompass all of the results in the yellow region.
- Temperature calculations in “XfrTimeSeries” are made for one transformer at a time. The transformer is selected by editing the number in cell B2 (shaded blue) to correspond to the column number of the transformer (beginning with 1 in column D, shaded green).
- Edit the input parameters on the “Parameters” spreadsheet as necessary. The input parameter cells are shaded gray. The parameter values provided in the spreadsheet are for illustration and not represented as accurate for any specific transformer.
- The resulting time series for transformer metallic hot spot temperature and transformer winding hot spot temperature are shown in columns H and J, respectively, of the spreadsheet “XfrTimeSeries” (assuming data for 3 transformers in columns D through F) . They are also graphed on the sheet entitled “TimeSeriesChart”.
February 9, 2015