Protection of power transformer using multi criteria decision-making

Power transformers are protected by different relays that operate independently. Malfunction of each relay has a major role in reducing the reliability of the protection system. In order to mitigate the main drawbacks of the power transformer relays, an overall protection scheme is presented in this paper. This scheme proposes a novel multi criterion algorithm using decision-making based on fuzzy logic. In this paper the outputs of restricted earth fault relay and a directional check unit, are combined with the output of the differential protection relay. Therefore, problems that are pertaining to independent operation of each relay have been mitigated and the relays cover protection blind spots of each other. The improved power transformer protection (IPTP) scheme enhances the sensitivity and reliability of the power transformer protection. Extensive simulations are used to measure the effectiveness and merit of the proposed IPTP relay. The above efforts result in a multi criteria approach for protection of power transformers.     

Inrush current estimation and hot-swapping for safe parallel battery pack

ABSTRACT

Batteries used in electric vehicles and microgrid applications use battery modules connected in series to satisfy the voltage required for each system, and battery modules are connected in parallel to increase capacity. In this parallel connected system, in order to disconnect and reconnect a specific battery module or to reconnect a new battery module, the battery module to be newly connected should have a small state of charge (SOC) difference from the existing battery modules. In particular, when a new battery is to be connected under a load current, there is a problem that excessive inrush current may occur in a specific battery module due to the load current distributed to each module and the current due to the SOC difference. Therefore, in this paper, we propose a method of estimating the inrush current through an equivalent electrical modelling analysis for the case where a battery module is newly added in a system in which the battery modules are connected in parallel. In addition, the power management algorithm for the battery pack system with inrush current estimation is presented. The proposed method is validated through simulations and experiments of a battery pack system in which 10 battery modules of 710V and 120Ah are connected in parallel.     

A fault analysis of DC electric arc furnaces with SVC harmonic filters in a mini-mill plant

This paper proposes the most feasible solution to overcome the failure of the 2nd harmonic filter in the static VAR compensator (SVC) which operates with the DC electric arc furnace (EAF) at Gwangyang Steel Mill in Korea. In order to investigate the causes of this failure, various measurements were carried out on the DC EAF and the main transformer at the PCC (point of common connection). It was concluded that the two causes for the failure are; the inrush current in the main transformer, and the parallel resonance between the system impedance and the harmonic filter. Three solutions to suppress the transformer inrush current and another three solutions to avoid the parallel resonance are suggested. The feasibility of these solutions was verified through the computer simulation with PSCAD/EMTDC. The most feasible solution to avoid further failures of the 2nd harmonic filter was selected, based on the estimated result for the six optional solutions in the point of performance and cost.     

温度、电压、谐波、涌流等对电容器寿命的影响

对温度、电压、谐波、涌流等影响电力电容器实际使用寿命的因素作了分析,提出了相应的解决办法。     

基于Pscad/Emtdc电网合环仿真的研究

本文以抚州金巢变电站10kV配电网合环为例,基于电磁暂态仿真软件PSCAD/EMTDC准确地搭建了系统仿真模型,以解决配电网合环操作过程中可能出现的涌流现象引起保护误动作。提出在合环点两侧相位差较小时候合环,或者通过调整变压器分接头以减小合环点两端母线电压差,从而减小合环电流。     

Application of Park's power components to the differential protection of three-phase transformers

This paper presents a new scheme for power transformers differential protection, in which the concept of the Park's instantaneous differential powers is introduced. The proposed method is able to detect winding insulation failures and to distinguish them from magnetizing inrush current transients. Experimental and simulation results are presented and discussed.     

ANN-Based Protection Scheme for Power Transformer

The implementation of a pattern recognizer for power system diagnosis can provide great advancement in the protection field. The work reported in this paper demonstrates the use of an Artificial Neural Network (ANN) as a pattern classifier for differential relay operation in the protection scheme for power transformer protection. The proposed relay takes care of maloperation due to inrush current, overexcitation, and ensures operation during internal fault. The off-line experimental result presented in this paper shows that a FeedForward Neural Network (FFNN) can be considered as an attractive alternative method to make the discrimination among normal, magnetizing inrush, overexcitation, and internal fault currents in a digital relay implementation. Results showing the performance of the protection scheme indicate that it is fast and reliable.     

用相关函数原理识别变压器励磁涌流和短路电流的新方法

变压器采用纵联差动保护时,如何正确识别励磁涌流和内部故障时的短路电流是关键问题。文章将变压器励磁涌流和各种内部故障电流均看作随机信号,应用数字信号处理中的相关函数原理对采样数据进行分析,计算采样数据的自相关函数,并与正弦电流形成的标准自相关函数进行相似比较运算,利用相似系数大小区分短路电流和励磁涌流。理论分析和动模试验结果验证了该方案的可行性。     

基于变压器模型的新型变压器保护原理的研究

针对变压器电流保护多年来一直存在的区分励磁涌流和内部故障电流的难题，该文阐述了基于变压器模型的新型变压器保护方案的基本原理，推导出了基于该原理的两绕组和三绕组变压器的动作方程，提出了变压器保护方案。该方案不受励磁涌流的影响，并且避开了变压器难以得到的内部参数。仿真试验结果表明该方案能够可靠、迅速的切除变压器内部故障。