Harmonic Problem due to Saturable Devices in Steel Re-Rolling Plant – A Case Study

This paper investigates the causes of harmonic norms violations in the medium scale (less than 2 MW load) re-rolling industry paying for the penalty. The major drive motor in this industry draws the heavy current with deep in the voltage at the terminal of the motor when steel bars are re-rolled with steps passes. To overcome the problem of voltage deep, the taps of the distribution transformer supplying these loads are selected on higher side. This situation leads to the over excitation of the transformer during the light load condition (between the passes) of the re-rolling operation resulting the operation of transformer in nonlinear zone. During this operation the harmonics due to saturation are generated and injected into the distribution systems and are the cause for damages to the capacitor banks. This problem is analyzed by mathematical modeling of the load condition with the transformer. The site investigation is carried out using power analyzer Megger-PA-9 plus V604 and supported by the simulation in PSCAD/EMTDC. This investigation leads to suggesting the remedial measures which is implemented to accommodate the harmonics inconformity with IEEE-519 standard.