A Pragmatic Guide to Modelling, Control and Optimization of AC EAFs

Transcription

1 A Pragmatic Guide to Modelling, Control and Optimization of AC EAFs Billy W Bryant Jr - SimOpTech February 27, 2017 Revision 1.0 Contents 1 Introduction Background And Goals Notational Conventions Disclaimer License Safety 12 3 Background AC Voltage, Current And Power Phase Sequence And EAF Phase Rotation Complex Impedance RMS Values Of Periodic Functions Phasor Representation Of Voltage And Current Complex Power Overview Of Power System Equipment Circuit Breakers Transformers Secondary Delta Closure High Current Cables EAF Arms

2 CONTENTS Pitch Circle Diameter Series Reactors VAR Compensation Per-Unit Analysis Measurement Instrument Transformers Potential/Voltage Transformers Voltage Transformer Arrangements Current Transformers Rogowski Coils Energy Metering Impact Of Harmonics Power Quality Metering EAF Control Metering EAF Grounding, Grounds And Measurement References EAF Secondary Voltage Measurement EAF Secondary Current Measurement EAF Secondary Impedance Measurement KPI Measurement EAF Power System Modeling And Analysis Impedance Representation Of EAF Power System Components Transmission System Step-Down Transformer(s) VAR Compensation Series Reactance EAF Transformer Secondary Impedance Arc EAF Equivalent Circuits Single Phase Approximations Three Phase Model EAF Time Variance Simulation Control Arc Parameters billybryant.net 2

3 CONTENTS Arc Stability Metrics RWI Arc Length Maximum Arc Power Phases Of Melting Bore-In Early Melt Late Melt Refine Power Profiles: Level 2 Control Power Profile Development How Many Profiles? Profile Modification Frequency Visual Modeling of Control Power Curves Circle Diagrams Voltage Stability Phase Balance And Control Mode Phase Coupling And Control Mode Phase Balance PI Control Gains: Level 1 Control Typical Control Features Variable Gain PI Control Over-Current And NCC Control Adaptive Control Which Regulation System Is Best? Optimization Prerequisites Voltage Constrained EAFs Series Reactance Assessment Finding Influential Parameters Selection Of Set-Points Electrode Consumption Operational Trials Examples Low Hanging Fruit Maximum RWI billybryant.net 3

4 LIST OF FIGURES Reactance Assessment Reactance Assessment Quick Wins Power Quality Voltage Stability Power Factor Voltage Flicker Mitigation Flicker Approximations Harmonics List of Figures 1 Instantaneous Power, Voltage And Current Positive Phase Sequence Phasor Diagram Electrode Tightening Proper EAF Phase Rotation Voltage And Current With 45 Degree Delay Impedance Angle Sin Magnitude And RMS Equivalent Voltage And Current Phasors With 45 Degree Delay Complex Power Triangle IEEE VAR Sign Conventions Preferred External Delta Closure Pitch Circle Diameter Series Reactor Equivalent Circuit High To Medium Voltage Parallel Step-Down Transformers Multiple Base ECD VT Open Delta Connection Standard Secondary Voltage Measurement Circuit Actual VT Measurement Circuit Heat Vs Charge KWH Per Ton Transformer Equivalent Model Arc Reactance Model Comparison EAF Single Phase ECD billybryant.net 4

5 LIST OF FIGURES 24 EAF Three Phase ECD Arc Power Vs Heat Stage RWI Vs Heat Stage Arc Length Vs Heat Stage Arc Power Vs Arc Resistance Arc Power Vs Magnitude Of Secondary Impedance Control Variables Vs Arc Power Completed Single Phase Example Secondary Impedance Components Comparison Of Stability Metrics B k = Comparison Of Stability Metrics B k = Power Factor Vs Location Time Variance Of Power Factor RWI vs Arc Power Arc vs Secondary Power Curves Primary Power Factor And Arc Power Operating Point Diagram Schwabe Chart Circle Diagram Voltage Stability Three Phase Secondary Equivalent Circuit Three Phase Secondary Equivalent Circuit Three Phase Dynamic Response Standard Regulator Control Algorithm Variable Gain Proportional Configuration Measured Mast Speeds Adaptive Control Of Current Regulation Impedance Error Deadband Range Deadband Response Short Circuit Current Flow Voltage Flicker SVC Voltage Stability Contribution SVC Addition And Contribution Harmonic Filter Equivalent Circuit billybryant.net 5

6 LIST OF TABLES List of Tables 1 Notational Conventions And Units IEEE VAR Sign Conventions Transformer Weight By Form Standard X/R Ratios Burden Calculation Example IT Accuracy Example IEEE C57.13 VT Accuracy Classes IEEE C57.13 VT Standard Burdens IEC VT Accuracy Classes IEEE C57.13 Metering CT Accuracy Classes IEEE C57.13 Metering CT Burden Designations IEC Metering CT Accuracy Classes Arc Stability Metric Comparison Non-Approximated Arc Stability Metrics Comparison Example Power Profile EAF Secondary Control Parameter Comparison billybryant.net 6