• Configured three phase EAF electrical model using power
70
Reactor Primary Power (MW)
supply equipment parameters. • VM2 indicates EAF tap 15 utilized for main melting. Utilized tap 15 measurements taken over several heats in October. • Model used to calculate power curves at reactor primary for various melting conditions. • VM2 measurements overlaid to check accuracy of model for various melting conditions. • Chart shows that model accuracy is good. • Can use model to calculate every electrical variable of interest on a per-phase or three-phase basis for various melting conditions, tap combinations and transmission voltage conditions.
High Stability
80
60 50 40
Rough Melting
30 20
EAF Tap 15, Reactor Tap 2 10 0
0
10
20
30
40
50
60
70
80
90
Secondary Current (KA)
Bryant Solutions bryantsolutions.biz
RWI, Arc Power and Operating Region
RWI 0.9
Arc Power 0.8
Available Operating Region
• Available operating region of AC EAF is always constrained (per-tap). • Lower bound constrained by stability metrics, RWI, arc length, arc power, heat stage, etc. • Upper bound usually constrained by arc power and/or transformer/cable loading. • EAF Tap 15 operating region indicated for mid-melt conditions. • Lower bound (conservatively) selected based on Sin(Φ) (stability metric). • Upper bound selected based on EAF transformer and reactor loading limitations. • Chart indicates that maximum RWI is achievable during early/ main melting.
1.0
Normalized RWI and Arc Power
• Refractory Wear Index (RWI) - Metric developed by Schwabe to quantify radiative heat of arc. Proportional to product of Arc Power and Arc Length. • Absolute value of RWI not so important. Location of peak of RWI curve is of interest. • Calculated and normalized RWI and Arc Power curves for EAF tap 15 and medium stability conditions. • Scrap is melted by radiative heat from the arcs. • Early/Main melting is the most efficient phase of melting. The arcs are completely surrounded by scrap. • Should maximize radiative arc energy (RWI) during early/main melting.
0.6
0.5
0.4
0.3
0.1
0
0
10
20
30
40
50
60
70
80
90
Secondary Current (KA)
Bryant Solutions bryantsolutions.biz
Dynamic/Adaptive Control • VM2 data indicates that adaptive control features of SmartArc are being utilized throughout the heat. • Use of adaptive control only recommended during refine (if at all) in order to adjust arc length for varying slag height. • Do not recommend use of dynamic tap changing based on stability. • SmartArc implementation of adaptive control utilizes stability and heat stage classification in an attempt to maximize input power as measured from the EAF transformer primary or secondary. • Implicitly assumes increasing power as measured from EAF primary/secondary results in increased operational efficiency. Not necessarily correct. • SmartArc adaptive control frequently misconfigured resulting in degraded performance. • Does not calculate or use RWI or Arc Power.
Bryant Solutions bryantsolutions.biz
Dynamic/Adaptive Control 80
Reactor Primary 70
Arc 60
Do Not Operate In This Region
50
Power (MW)
• Power curve scatter charts indicate that operating point is occasionally on the wrong side of the curve. • Results in less power at higher current, increased energy and electrode consumption. • Recall that RWI and arc power peaks occur at lower current level than reactor primary peak. Never want to be to the right of the Arc Power peak. • Unclear which tap configurations this is occurring on. VM2 interface not cooperating. • Potential causes: - Misconfigured adaptive control. - Misconfigured impedance control combined with transmission voltage sag.
40
30
20
10
0
0
10
20
30
40
50
60
70
80
90
Secondary Current (KA)
Do Not Operate Here
Bryant Solutions bryantsolutions.biz
Recommendations • Develop new power profile to trial. • Maximize RWI during main melting. • Disable adaptive control during main melting. • Ensure all operating points are below arc power peak. • Ensure impedance regulation features are configured properly. • May require multiple profiles for various scrap conditions and/or operational requirements. • Ensure operating point drift is not occurring due to transmission voltage sag. • Investigate per-phase RWI balance. • Investigate use of EAF taps 16 through 18. • Investigate DigitArc gains during early melt period.
