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Customer Success Story

Gerdau Steel

SVC for flicker mitigation from a steel plant

Gerdau AmeriSteel Manitoba (GAM) located in Selkirk Manitoba Canada, operates two electric arc furnaces. One furnace (eccentric bottom tapped, EBT) is used for the melting of scrap steel and the other, a ladle furnace, for subsequent processing of the molten steel. In 2007, a Static Var Compensator (SVC), replacing an old synchronous condenser, was commissioned adjacent to the melt shop for reduction of network disturbances and for power factor correction.

Electric arc furnaces (EAFs) in general, represent troublesome loads on the feeding three-phase power supply, which is usually the public grid. During operation, an EAF when used for melting scrap such as GAM’s EBT causes the following on the interconnected grid:
− Voltage fluctuations and flicker;
− Negative-phase sequence components in currents and voltages;
− Harmonics.

An SVC is an efficient means of mitigating the above mentioned threats to power quality in the plant as well as in the feeding grid. The outcome is a winning situation for all stakeholders:
− Compliance with the power quality standards specified by the grid company.
− Other consumers connected to the common grid are spared the nuisance of disturbances emanating from the steel plant.
− The steel manufacturer can operate the steel plant without infringing on operational agreements with the grid company.

The following are the tasks of the SVC:
− To parry the rapidly fluctuating consumption of reactive power of the furnace(s).
− Maintain a stable power factor at the Point of Common Connection (PCC), independent of the reactive power fluctuations from the furnace loads.
− Reduce flicker at the PCC to acceptable levels.
− Filter the harmonics generated by the furnace(s).
− Stabilize the system voltage at the load bus.
− Mitigate the voltage unbalance generated by the furnace(s)

Main data  
System   SVC 
Commissioning year   2007
Bus voltage   13.8 kV
 SVC rating   0-80 Mvar capacitive
 Harmonic filters    2nd harmonic / 27 Mvar
3rd harmonic / 26 Mvar
4th harmonic / 27 Mvar
 Control scheme    Phasewise, open loop susceptance regulator, plus a three phase closed loop susceptance regulator
 Thyristor valve    PCT equipped, water cooled, with indirect light firing.