Phase-to-ground fault is the most probable fault type in power systems, which is generally limited through neutral grounding resistor. The grounding resistor may have negative impacts on the system such as decrease in...
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Phase-to-ground fault is the most probable fault type in power systems, which is generally limited through neutral grounding resistor. The grounding resistor may have negative impacts on the system such as decrease in sensitivity of the differentialprotection. Fault current limiter (FCL) is a suitable alternative for the grounding resistor. However, the input signals of differentialprotections may be adversely affected by the FCL, resulting mal-operation of this protection. In this study, effects of FCL installed in neutral line of power transformers on the relevant differential protection algorithms are analysed. Performance of some well-known differential protection algorithms for discrimination between internal fault and magnetising inrush currents in presence of the neutral FCL is evaluated in detail. Then, a supplementary method based on the least error squares technique is proposed to rectify the deformed portion of the current waveform due to presence of the FCL. The reconstructed signal is considered as a proper input for the discrimination algorithms. Various simulations and experiments are carried out to validate the performance of the suggested technique. The results indicate the consistency of the suggested technique for different power systems, operating conditions, and real applications.
This paper presents a novel algorithm for power transformer differentialprotection based on wavelet transform (WT) and introduces new indices to distinguish internal faults from normal operating conditions and the oc...
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This paper presents a novel algorithm for power transformer differentialprotection based on wavelet transform (WT) and introduces new indices to distinguish internal faults from normal operating conditions and the occurrence of the inrush current. The proposed setting-less algorithm has no limits on the structure, dimension, capacity, and core type of the transformer. For this purpose, six indices based on fault detection functions extracted from WT transform are presented. Then, weighting factors for the indices by using the least squares method are calculated. In order to validate the proposed method, the approach has been evaluated on four transformers with 2 kVA, 10 kVA, 400 kVA, and 125 MVA. The success rate of fault detection in 10 kVA, and 125 MVA transformers was 100% and in 2 kVA and 400 kVA transformers was 93.33% and 94.44%, respectively. Also, the proposed algorithm has a remarkable capability in fast fault detection to protect the power transformer.
This study describes a new differential protection algorithm for power transformers, which is not affected by transient conditions. The proposed algorithm uses the statistical second central moment, statistical varian...
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This study describes a new differential protection algorithm for power transformers, which is not affected by transient conditions. The proposed algorithm uses the statistical second central moment, statistical variance, to characterise the signal waveform. The goal is to obtain the variance from each differential current after a pre-processing filter stage and to compare it with a threshold. The event will be identified as an internal fault, or otherwise as an inrush current. The algorithm was implemented in MATLAB, and a broad array of cases was carried out using the electromagnetic transient software PSCAD. All results show the algorithm successfully differentiated inrush from the internal fault conditions in over 2000 cases.
This study presents a novel differential protection algorithm (DPA) for power transformer using chirplet transform (ChT). The proposed method combines the features of biased restraint characteristic (BRC) of the conve...
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This study presents a novel differential protection algorithm (DPA) for power transformer using chirplet transform (ChT). The proposed method combines the features of biased restraint characteristic (BRC) of the conventional differential relay and out-turn of ChT in a two-stage algorithm. In the first stage, the BRC plane is divided into three zones: namely, high-set (HS), non-trip and vulnerable zones. The tripping decisions are carried out in the first two zones based on differential and biased current. However, if the operating condition of the power transformer falls in the vulnerable zone, then there is an ambiguity in discriminating internal fault, inrush current and current transformer saturation cases. Therefore, in the second stage, ChT is applied to differential current signal to obtain an energy distribution on the time-frequency plane with respect to time, frequency and chirp rate. Then, using the mean and standard deviation of the normalised energy, power transformer operating conditions are classified. Also, most of the DPAs available in the literature are system dependent. However, the proposed novel DPA can be effectively used for any system. The proposed scheme is validated for two power transformer systems using PSCAD to simulate various operating conditions and MATLAB to implement the algorithm.
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