1. Interharmonic Levels at a DC Arc Furnace Installation Erich W. Gunther Electrotek Concepts, Inc.

2. Load and Supply Characteristics DC Arc Furnace Contract demand of 100 MW 345 kV PCC, 7811 MVA SC SVC on 34.5 kV Bus –2nd, 3rd, 5th, 7th, 12th (HP) filters

3. Load Current Statistics

4. Load Current Waveforms Light LoadHeavy Load

5. Arc Furnace Generated Waveform Distortion Difficult to classify and separate phenomena –Attributes of both transient and steady state phenomena –Waveform distortion characteristics change rapidly –Observed interharmonic levels may be due to actual interharmonic injection, a side effect due to the changing load, or both Use appropriate analysis method based on expected impact to system –Harmonic, Interharmonic, Transient, Flicker, Unbalance

6. Interharmonic Impacts Makes filter design more difficult Adverse impact on control systems Can excite low frequency oscillations in mechanical systems Communications interference Light flicker

7. IEC Measurement Method

8. 12 Cycle Snapshot 250.0A 0.0A -250.0A 298KV 0.0V -298KV 10.00 ms/div0.00ns200.00ms Snapshot WaveformModel 9010/9020 8V/8I 04/26/98 01:35:14.00 AM Three Phase Wye Ia

9. Spectrum of Snapshot

10. Interharmonic Metrics Total Interharmonic Distortion (TID) –RSS of IEC based interharmonic components –Normalized by fundamental for voltages –Normalized by peak demand for currents –IEC statistical approach used - report 95% CP Individual Interharmonic Interval Levels

11. Results for Currents

12. More Current Results

13. Results for Voltages

14. More Voltage Data

16. Conclusions IEC measurement methods are relatively easy to apply - similar level of effort as for harmonic measurements Measured levels are low –Difficult to measure accurately (A/D resolution) –Statistical techniques required (many samples) Low levels can cause observable impacts More work on relating impacts to measured levels required