Wang Zengping

A novel adaptive scheme of discrimination between internal faults and inrush currents of transformer using mathematical morphology

This paper addresses a new relaying scheme for identifying the inrush current and short circuit current caused by internal fault on the basis of sudden changes detection using novel morphological gradient (NMG), transient current signals are then extracted by use of morphological opening and closing transform. Based on different characteristics of transient signals between the short circuit current and the inrush current, the transformer protection method is proposed. This method can avoid the symmetrical inrush current and saturation of current transformer (CTs). The results of Electrical Power Dynamic Laboratory (EPDL) indicate that the proposed technique can also deal with the sampled data contaminated with various kinds of noises and DC components and is stable during internal faults with external shunt capacitance in a long EHV transmission line

Research on optimization of recloser placement of DG-enhanced distribution networks

An optimization method is proposed to identify the optimum recloser placement to improve system reliability for distribution networks with distributed generators (DG). DG may reduce the number of interruptions and/or durations for customers residing within their protection zones, thus increasing the reliability of service. A composite reliability index is defined as the objective function in the optimization procedure. Then, the zone-network method is introduced for reliability evaluation. An improved genetic algorithm that named multiple-population genetic algorithm (MPGA) is used to search for the optimum solutions. Using the MPGA, the optimization can be solved with mutli-population, and the influence of improper genetic parameters can be greatly decreased and premature convergence can be overcome effectively. Simulation work is carried out based on a 69-segment 8-lateral distribution feeder with distributed generation to validate the effectiveness of the proposed method.

Single-ended transient positional protection of transmission lines using mathematical morphology

This paper presents a novel single-ended transient positional protection (SCTPP) scheme developed using the combined scheme with multi-filter units of mathematical morphology (MFUMM) and multi-resolution morphological gradient (MMG). Multi-filter units can effectively and gradually suppress a variety of random and pulsed noises existing in fault-generated transient signals which can be detected by using multi-resolution morphological gradient. The fault can be located accurately according to relative traveling times and polarities of transient signals. A typical 500-kV extremely high voltage (EHV) transmission system has been simulated by PSCAD/EMTDC to evaluate the scheme. The simulation results show that this scheme is capable of locating accurately under various types of faults occurring at different positions on power lines. Meanwhile, it should be indicated that this algorithm has less computational complexity than multi-resolution wavelet transform, which makes it possible to put into practice

A Novel Adaptive Algorithm to Identify Inrush Using Mathematical Morphology

A novel scheme based on mathematical morphology to distinguish the inrush current from the internal fault current in power transformers is proposed, which is derived from high non-linearity in exciting cores of transformers. Transient current signals are extracted by use of the novel morphological gradient and morphological opening and closing transform, meanwhile various kinds of additive white noises are effectively suppressed by adaptive filtering. Based on different characteristics of transients between the short circuit current and the inrush current, the transformer criterion is developed. The proposed technique is immune to CT saturation. A total of 120 Electrical Power Dynamic Laboratory (EPDL) simulation cases are used to test the performance of the technique. This method has stability during the symmetrical inrush current and can be implemented in real time with very high accuracy. The results of different EPDL testing systems verify the feasibility and practicability of the proposed scheme

A Transmission Line Unit Protection Technique Based Combination Modulus by Using Mathematical Morphology

This paper presents a concept of combination modulus (CM) to solve the problem that the transient-based protection techniques may fail to detect faults under certain conditions. The CM features are analyzed and discussed in detail. A novel transmission line unit protection scheme is proposed by comparing transient current CM polarity. The mathematical morphology (MM) technique is used to extract the polarity features from fault-generated current wave signals propagating along transmission lines during a post-fault period. The simulation results of the ATP/EMTP software show that the reliability of the protection scheme proposed has been considerably improved.

Study on the Influence of TCSC on Fault Component Distance Protection

Based on the characteristics of TCSC, the influence of TCSC on fault component distance protection is analyzed. With the new setting resistance to be ZZd-jXC, the action of fault component distance protection on the line equipped with TCSC is presented. It is concluded that the fault component distance protection will not act incorrectly, but the range of protection will be reduced, especially when the TCSC is bypassed

Research on the influence of TCSC to EHV transmission line protection

Thyristor controlled series capacitor (TCSC) used in power transmission line can increase the transportability and the stability of system, and decrease the system loss significantly. At the same time, TCSC brings many serious problems to transmission lines fault location and protective relaying. This paper analyzes the influence of TCSC to EHV transmission line protection, especially to the high-frequency directional protection. It can be obtained from the analyzing that the addition of TCSC to EHV transmission line would make the high-frequency directional protection unwanted operation or failure to operate. In order to solute the problems TCSC caused, this paper presents a novel transient protection scheme based on wavelet transform (WT). The simulation tests have proved that the analyzing and solution of the appearance of TCSC in EHV transmission line are correct.

A New Technique to Identify Internal Faults and Inrush Currents Using Morphological Gradient with Adaptive Filtering

This paper presents a novel technique for distinguishing between transformer inrush currents and internal fault currents. On the basis of basic morphological transforms and their combined modes, transient current signals can be extracted meanwhile a variety of noises can be greatly suppressed by use of the novel morphological gradient (NMG) with adaptive weighting. Based on different characteristics of energy spectrum analysis of extracted transients between the short circuit current and the inrush current, the transformer protection criterion is proposed. This method can avoid the symmetrical inrush current and the operating time of the scheme is less than one power frequency cycle with very high accuracy. The results of dynamic simulation verify the feasibility of the proposed method.

A new principle of discrimination between inrush current and internal fault current of transformer based on self-correction function

When differential protective relays are applied to transformer protection, how to identify the magnetizing inrush current and short circuit current caused by internal fault is the key problem. Here, regarding the inrush current and short circuit current as the random signal, the sampled data are analyzed by correlation function principle in the digital signal processing (DSP) and the self-correlation function of the sampled data is calculated. Through the similar comparison operation conducted by standard self-correlation function (SSCF) formed with sinusoidal current the short circuit current and the inrush current can be distinguished by the magnitude of similarity coefficient. The results in electrical power dynamic laboratory (EPDL) verify the feasibility of the proposed method

A Novel Inductance Calculation Method in Power Transformer Model Based on Magnetic Circuit

For the problems in the inductance calculation of transformer simulation model, this paper presents a calculation method with transformer magnetic circuit. This method calculates the mutual inductance and leakage inductance respectively. When calculating the leakage inductance, the effect of vertical leakage flux and horizontal leakage flux have been considered, which makes the calculating result are more correct. In order to prove the validity of this method, the data of simulation test and dynamic analog test have been compared. The results have proved that the method of magnetic circuit calculation is accurate.