Power Transformer No-Load Loss Prediction with FEM Modeling and Building Factor Optimization

Estimation of power transformer no-load loss is a critical issue in the design of distribution transformers. Any deviation in estimation of the core losses during the design stage can lead to a financial penalty for the transformer manufacturer. In this paper an effective and novel method is proposed to determine all components of the iron core losses applying a combination of the empirical and numerical techniques. In this method at the first stage all computable components of the core losses are calculated, using Finite Element Method (FEM) modeling and analysis of the transformer iron core. This method takes into account magnetic sheets anisotropy, joint losses and stacking holes. Next, a Quadratic Programming (QP) optimization technique is employed to estimate the incomputable components of the core losses. This method provides a chance for improvement of the core loss estimation over the time when more measured data become available. The optimization process handles the singular deviations caused by different manufacturing machineries and labor during the transformer manufacturing and overhaul process. Therefore, application of this method enables different companies to obtain different results for the same designs and materials employed, using their historical data. Effectiveness of this method is verified by inspection of 54 full size distribution transformer measurement data.

Robust subsynchronous interaction damping controller for DFIG-based wind farms

This paper proposes a robust controller to improve power system stability and mitigate subsynchronous interaction(SSI)between doubly-fed induction generator(DFIG)-based wind farms and series compensated transmission lines.A robust stability analysis is first carried out to show the impact of uncertainties on the SSI phenomenon.The uncertainties are mainly due to the changes in the power system impedance(e.g.,transmission line outages)and the variations of wind farm operating conditions.Then,using theμ-synthesis technique,a robust SSI damping controller is designed and augmented to the DFIG control system to effectively damp the SSI oscillations.The output signals of the supplementary controller are dynamically limited to avoid saturating the converters and to provide DFIG with the desired fault-ride-through(FRT)operation during power system faults.The proposed controller is designed for a realistic test system with multiple series capacitor compensated lines.The frequency of the unstable SSI mode varies over a wide range due to the changes in power system topologies and wind farm operating conditions.The performance of the proposed controller is verified through electromagnetic transient(EMT)simulations using a detailed wind farm model.Simulation results also confirm the grid compliant operation of the DFIG.