There are many different techniques for discrimination between inrush current and internal faults. However, due to their inherent limitations, the methods have not reached a practical level yet, and the conventional methods are still widely employed in practice despite of their well-known shortcomings. Current transformer saturation and large inrush currents are the most reported cause of the discrimination algorithms mal-operation. This paper deals with an efficient approach to discriminate internal faults from switching conditions in the power transformers which can solve these problems. The proposed method is based on utilising the feature of the non-saturation zone. The performance of the proposed method is tested using the simulations data besides to data collected from a prototype laboratory three-phase power transformer. Also, the proposed method is evaluated and compared with some well-known discrimination schemes including conventional and some new presented schemes by the same simulation and experimental data sets. The results validate the consistency and accuracy of the proposed method.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-gtd.2016.1086

Efficient method for discrimination between inrush current and internal faults in power transformers based on the non-saturation zone

The phase-to-ground fault is the most probable fault in power systems. Generally, the neutral grounding resistor is utilised to limit the current for this fault. However, this resistor decreases the sensitivity of the differential protection. The fault current limiter (FCL) is an attractive candidate to be used instead of the regular grounding resistor. FCL only operates for high fault currents and has a negligible resistance for normal or low current faults conditions. Therefore, it reduces the high fault currents while not affecting the sensitivity of the differential protection. However, the signals used as inputs of the differential protection may be adversely affected by the FCL and this may lead to wrong operation of this protection. A comprehensive study is required to evaluate the performance of differential protection algorithms in the presence of a FCL in the neutral point. This study analyses the impact of high-temperature resistive superconducting FCLs (SFCLs) existed in the neutral point on transformer inrush current discrimination methods. Some well-known methods for discrimination of an internal fault from inrush current are evaluated in the presence of SFCLs. Furthermore, through extensive simulations, their performance is compared with and without the presence of SFCLs.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-smt.2015.0249

Discrimination between internal fault and magnetising inrush currents of power transformers in the presence of a superconducting fault current limiter applied to the neutral point

Due to increase in penetration of Distributed Generations (DGs) in power systems, fault current level is being increased, which results in some problems in the systems. Fault Current Limiters (FCLs) are attractive devices to tackle these problems for transmission and distribution systems. The utilized FCLs may have considerable impact on the signals used for differential protection of power transformers, which leads to mal-operation of these protections. It seems a comprehensive analysis is necessary for performance evaluation of differential protection algorithms in presence of FCLs. This paper deals with investigation of FCLs impact on power transformers’ differential protection. The performance of some well-known differential protection algorithms for discrimination between internal fault current and magnetizing inrush current with and without presence of FCL are evaluated.

Evaluation of power transformer inrush currents and internal faults discrimination methods in presence of fault current limiter

Various unwanted phenomena that are taken place in the transformer may occasionally mal-operate selected fault classification based protective schemes. Hence, it is necessary to discriminate internal fault from external abnormal conditions for unit protection of power transformer. This study presents a new hierarchical ensemble extreme learning machine (HE-ELM) based classifier technique to identify faults in & out of transformer. The component extreme learning machine (ELM) is structured hierarchically to improve its fault data classification accuracy. The developed algorithm is evaluated by simulating multiple disorders on 100 MVA, 132/220 kV transformer with the help of PSCAD software. DWT is used to extract features from acquired current signals from transformer. The feature vector formed after extraction process is fed to the HE-ELM algorithm for data classification. The fault discrimination accuracy of HE-ELM technique is 99.91%. This shows its effectiveness with respect to other classifier techniques. Moreover, the developed algorithm is successfully tested on hardware prototype in laboratory environment under various inrush and fault conditions using Cortex M4 microcontroller (STM32F407) with maximum identification time of 27 ms. The proposed HE-ELM technique is compared with existing support vector machine, probabilistic neural network and ELM techniques for identical fault data. Results demonstrate that HE-ELM outperforms than existing schemes in cross-domain recognition task.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-smt.2019.0102

Identification of internal fault against external abnormalities in power transformer using hierarchical ensemble extreme learning machine technique

Efficient CNN-XGBoost technique for classification of power transformer internal faults against various abnormal conditions

Differential relays are the main protection for power transformers including transmission and industrial transformers. Protection against internal fault is generally relegated to these relays. The most probable internal fault of the industrial transformer is phase to ground type. To limit the fault current in this condition, a limiter resistor is utilised in the transformer. However, it has considerable impact on sensitivity of the differential and restricted earth fault (REF) protections. In this study, an effective approach is proposed to improve the differential and REF protections sensitivity of the industrial transformers. The proposed technique not only realises the fault current limitation function, but preserves sensitivity of the protections. In this method, a developed fault current limiter is utilised in the transformer neutral instead of the neutral grounding resistor. The performance of the proposed technique is evaluated by some simulations and experiments. The results confirm the high capability of the proposed technique in different conditions.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-gtd.2015.1343

Javad Ghafourifard

Papers

New approach to improve sensitivity of differential and restricted earth fault protections for industrial transformers