This example provides an introduction to the analysis of arc furnaces and their influence to the supplying power system. The analysis covers the identification of the injected harmonic currents, the calculation of flicker levels according to IEC-61000-4-15, as well as the use of STATCOM equipment as a means of mitigating the furnace's harmonics and flicker. For this purpose, EMT dynamic models of a generic arc furnace [1] and a STATCOM system [2] are employed.

PowerFactory modules used:

- EMT-Simulation

- Power Quality and Harmonic Analysis

Usage instructions:

- Import and activate the attached project

- Activate study case "SC01 - Arc Furnace". An exemplary high-voltage network is modelled where an arc furnace is installed and connected to it via an MV/HV transformer. This study case analyses the harmonic currents generated by the Arc Furnace.

- Run a dynamic simulation for 20 seconds.

- Observe the Arc Furnace Currents and Power.

- Go to the plot "ArcFurnace Current FFT - MV Phase A", double click on the FFT plot (the plot on the right side), click on "Recalculate" and then Execute. Observe the calculated harmonic currents.

- Activate study case "SC02 - Arc Furnace with Statcom". This study case analyses the harmonic currents generated by the furnace when a Statcom is installed and compensates the variations in current of the furnace. A simplified model of a Statcom is included, where the equipment is represented using an AC-current source connected to the MV side of the MV/HV transformer. A simple compensation controller is installed in the Statcom equipment and modelled via the "STATCOM Controller" DSL model.

- Run a dynamic simulation for 20 seconds.

- Observe the comparison between the currents of the HV transformer in the case without/with Statcom compensation (plot "Comparison_MV_Transformer")

- Go to the plot "Comparison_FFT_MV_PhaseA", double click on the FFT plot (the plot on the right side), click on "Recalculate" and then Execute. Observe the calculated harmonic currents in both cases and the effect of the Statcom on harmonics.

- Go to the plot "STATCOM Compensation" and observe the compensated Arc Furnace currents and the compensation Statcom Currents

- Activate study case "SC03 - Flicker Arc Furnace". This case is configured such that the 1 minute short time flicker coefficient (Pst) and Plt (based on 5 Pst values) can be computed when the arc furnace not compensated.

- Run a dynamic simulation for 305 seconds (it may take a long time to finish the EMT simulation).

- Switch to the "Power Quality and Harmonics" toolbox and click on the "Flickermeter" tool

- The Flickermeter command (ComFlickermeter) is pre-configured to calculate the 1 minute Pst coefficient on the phase A voltage of bus T3 (voltage at HV-side of the main transformer). Execute the calculation and make a not of the Pst and Plt results provided in the output window.

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| IEC-61000-4-15 Flickermeter |
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| Signal: y1 |
| Time Window Time [s]: Pst: |
| 1 [ 5,0001 - 65,0000] 1,4562 |
| 2 [ 65,0001 - 125,0000] 1,4117 |
| 3 [ 125,0001 - 185,0000] 1,4578 |
| 4 [ 185,0001 - 245,0000] 1,3938 |
| 5 [ 245,0001 - 305,0001] 1,4194 |
| Plt: 1,4282 |
|
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- Activate study case "SC04 - Flicker Arc Furnace with Statcom". This case is configured such that the 1 minute short and long term flicker coefficients Pst and Plt (based on 5 Pst values) can be computed for the case when a Statcom compensated furnace is existing.

- Run a dynamic simulation for 305 seconds (it may take a long time to finish the EMT simulation).

- Re-do the Flickermeter calculation and compare the obtained short and long term flicker coefficients Pst and Plt with the ones obtained in the previous study case.

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| IEC-61000-4-15 Flickermeter |
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| Signal: y1 |
| Time Window Time [s]: Pst: |
| 1 [ 5,0001 - 65,0000] 0,7158 |
| 2 [ 65,0001 - 125,0000] 0,6716 |
| 3 [ 125,0001 - 185,0000] 0,6635 |
| 4 [ 185,0001 - 245,0000] 0,6406 |
| 5 [ 245,0001 - 305,0001] 0,6746 |
| Plt: 0,6741 |
|
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For all the above cases, the DSL models "Arc Furnace characteristic" and "Statcom Controller" can be re-parameterised as required. For more information on these models, please refer to [1] and [2].

[1] G. C. Montanari, M. Loggini, A. Cavallini, L. Pitti, D. Zaninelli: “Arc-furnace model for the study of flicker compensation in electrical networks”, IEEE Transactions on Power Delivery, Vol. 9, No. 4, October 1994.

[2] Working Group B4.19 - CIGRE Study Committee B4: “Technical Brochure 237 - Static synchronous compensator  (STATCOM) for arc furnace and flicker compensation”, CIGRE, December 2003.