Sound Feeder Research Articles

Single‐phase high‐impedance fault protection for low‐resistance grounded distribution network

After a single-phase high-impedance fault (HIF) for low-resistance grounded distribution network (LRGDN) occurs, fault current level is very low and cannot be detected by conventional overcurrent relays. In this study, composite power of each feeder which is composed of complex power and its conjugate is defined, and a HIF protection method based on the composite power of each feeder is presented. For a sound feeder, the phase angle of the composite power is equal to 0, and its amplitude is approximately 0. However, for the faulty feeder, the phase angle of the composite power is π, and its amplitude is much greater than 0. Base on the above significant difference, the protection criterion for HIFs in the LGRDN can be obtained. Theory analysis and simulation results show that the proposed method does not need to check the polarities of the zero-sequence current transformers and is able to remove faulty feeder reliably. Besides, the protection can accurately operate for HIFs in the case of noise interference and unbalanced current. The experimental results based on RTDS also show the efficiency of the proposed method.

Deep-Learning-Based Earth Fault Detection Using Continuous Wavelet Transform and Convolutional Neural Network in Resonant Grounding Distribution Systems

Feature extraction for fault signals is critical and difficult in all kinds of fault detection schemes. A novel simple and effective method of faulty feeder detection in resonant grounding distribution systems based on the continuous wavelet transform (CWT) and convolutional neural network (CNN) is presented in this paper. The time-frequency gray scale images are acquired by applying the CWT to the collected transient zero-sequence current signals of the faulty feeder and sound feeders. The features of the gray scale image will be extracted adaptively by the CNN, which is trained by a large number of gray scale images under various kinds of fault conditions and factors. The features extraction and the faulty feeder detection can be implemented by the trained CNN simultaneously. As a comparison, two faulty feeder detection methods based on artificial feature extraction and traditional machine learning are introduced. A practical resonant grounding distribution system is simulated in power systems computer aided design/electromagnetic transients including DC, the effectiveness and performance of the proposed faulty feeder detection method is compared and verified under different fault circumstances.

Faulty feeder detection by adjusting the compensation degree of arc‐suppression coil for distribution network

A scheme of single-phase-to-ground faulty feeder detection by adjusting the compensation degree of arc-suppression coil (CDASC) for compensated distribution network is presented in this study. The scheme defines transient variation components (TVCs) of feeders, which use the transient signals of zero-sequence current of each feeder and zero-sequence voltage in the bus before the adjustment and those after the adjustment. The TVCs of sound feeders always keep almost 0, while the TVC of faulty feeder changes remarkably before and after adjusting CDASC. On the basis of TVCs, faulty feeder detection can be achieved sensitively and accurately with simple and practicable procedure without sophisticated algorithms. The performance of the scheme validated by digital simulation with various fault conditions of different transition resistances, fault inception angles, white noises and compensation degrees.

Features-clustering-based earth fault detection using singular-value decomposition and fuzzy c-means in resonant grounding distribution systems

The transient zero-sequence current of each feeder in a resonant grounding system is characterized by nonlinearity and nonstationarity when a single-phase-to-ground fault occurs. Because there is a significant difference between the fault transient zero-sequence current waveforms of the fault feeder and the sound feeders, a new fault feeder detection method is presented, based on a time-frequency matrix (TFM) and polarity distribution matrix (PDM) singular values clustering algorithm. By applying a Hilbert-Huang transform band-pass filter and waveform transformation to the transient zero-sequence current waveform of each feeder, the TFM and PDM can be constructed, which are decomposed by singular-value decomposition (SVD). Moreover, the normalized singular values of the TFM and PDM are merged together and are used to form the amplitude-polarity feature matrix (APFM). Thus, the feature quantities including the amplitude and polarity information of each fault transient zero-sequence current waveform are obtained. Then, fuzzy c-means clustering is applied to the APFM so as to detect the fault feeder by dividing the fault feeder and sound feeders into two categories without a certain threshold setting. Simulations were carried out via PACAD/EMTDC® and a physical system under various kinds of fault conditions and factors including asynchronous sample, two-point-grounding fault, and arc fault. Simulated results show that the proposed method has the characteristics of high accuracy and reliability in earth fault feeder detection.

Faulty Feeder Detection of Single Phase-Earth Fault Using Grey Relation Degree in Resonant Grounding System

It is difficult to detect the faulty feeder if single phase-earth faults occur in a resonant grounding system, mainly due to its very low-current fault. Since the similarity of transient zero-sequence current waveforms between faulty feeder and sound feeder is lower than that between two sound feeders, this paper presents a protection scheme for faulty feeder detection based on the grey relation degree that can characterize the similarity among curves. Slope relation degree, one kind of grey relation degree, is chosen to characterize the similarity of transient zero-sequence current waveforms between one feeder and other feeders, and the slope relation matrix that represents the relationship among all feeders can be established. The protection criterion established by using the slope relation matrix can be applied to detect the faulty feeder of single phase-earth faults. It is noted that the proposed method is applicable to the system where at least three or more feeders are presented. Electromagnetic Transients Program (EMTP) simulation results and adaptability analysis have confirmed the effectiveness and reliability of the proposed scheme.

Mal-operation risk assessment for the feeder overcurrent protection in large-scale clustering wind farms

Abstract Conventionally, the Doubly-fed Induction Generator (DFIG) has no impacts on the arrangement and the setting of the feeder overcurrent protection in the large-scale, concentrated wind farm, since the DFIG has long been regarded as a normal load under the fault conditions. As a result, existing overcurrent protection equipped on a sound feeder may mal-operate when a fault occurs on adjacent feeders, if the DFIG feeding current on the corresponding sound feeder is high enough. To prevent this, further investigation is thereby undertaken in this paper. The characteristics of the DFIG feeding current is analyzed under various fault conditions in the first place. Secondly, the feeder overcurrent protection is set according to currently-applied principles, based on which the corresponding mal-operation zone and the mal-operation risk are calculated under different system operation conditions. It can be deduced from the results that a reasonable DFIG crowbar resistance value and an optimized wind farm arrangement can be of positive effect to limit the mal-operation risk. Directional element must be configured for the existing protection if above countermeasures are not available and the mal-operation risk still exists.

Zero-sequence compensated admittance based faulty feeder selection algorithm used for distribution network with neutral grounding through Peterson-coil

For faulty feeder selection problem in case of single-phase grounding fault in distribution network with neutral point un-effectively grounded, a novel per-unit zero-sequence compensated admittance based faulty feeder selection algorithm was proposed. By introducing the compensated admittance, the difference of zero sequence admittance between the faulty feeder and the sound feeders was amplified, which could be utilized as a technically practical judging criterion. In order to eliminate the discrimination dead zone, the ratio of compensated admittance with respect to the susceptance of the feeder itself is adopted as supplement criterion. Together with the admittance angle criterion, a reliable comprehensive criterion for identifying single-phase grounding fault feeder in neutral point non-effectively grounded system is formed. A series of simulation test results indicate that, the algorithm proposed is independent of the network structure and parameters, the fault condition or the fault resistance, thus improving the success rate of fault feeder selection significantly.

Shunt Petersen-Coil with Resistor for Single Phase Fault Detection in Resonant Grounded Power Distribution Systems

The failure current in resonant grounder power distribution system is small, so it is difficult to detect the fault feeder. This passage presents the equivalent circuit of resonant grounded system, and discusses the difference of electrical characteristics between faulty feeder and sound feeders by using shunt resistors. To reduce the influence of shunt resistors on the system and improve the detection sensitivity, it presents the method of shunting multi-level resistors, and it proves the sensitivity and reliability of this method by EMTP simulation.

변압기 권선을 이용한 자속구속형 초전도 전류제한기의 전류제한 및 전압강하 보상 특성

The superconducting fault current limiter (SFCL) can quickly limit the fault current shortly after the short circuit occurs and recover the superconducting state after the fault removes and plays a role in compensating the voltage sag of the sound feeder adjacent to the fault feeder as well as the fault current limiting operation of the fault feeder. Especially, the flux-lock type SFCL with an isolated transformer, which consists of two parallel connected coils on an iron core and the isolated transformer connected in series with one of two coils, has different voltage sag compensating and current limiting characteristics due to the winding direction and the inductance ratio of two coils. The current limiting and the voltage sag compensating characteristics of a SFCL using a transformer winding were analyzed. Through the analysis on the short-circuit tests results considering the winding direction of two coils, the SFCL designed with the additive polarity winding has shown the higher limited fault current than the SFCL designed with the subtractive polarity winding. It could be confirmed that the higher fault current limitation of the SFCL could be contributed to the higher load voltage sag compensation.

Faulty Feeder Detection and Fault Self-Extinguishing by Adaptive Petersen Coil Control

The characteristic of the single-phase earth fault in the Peterse coil grounded distribution network is discussed in this paper. It is disclosed that only the derivative of the zero-sequence current of the faulty feeder changes with the controllable inductance of the Petersen coil, while the derivative of the zero-sequence current of the sound feeder is kept invariable. Therefore, a novel faulty feeder selection criterion is proposed. A variety of simulation tests is carried out. The exactness and sensitivity of the proposed scheme are verified by simulation test results.

A selective single-phase-to-ground fault protection for neutral un-effectively grounded systems

Single-phase-to-ground faults are the most frequent faults likely to occur in power distribution networks. As for a neutral un-effectively grounded system (NUGS), the low fault current is very common in the case of occurrence of a single-phase earth fault, leading to hard identification of the faulty feeder. In conventional way, this target can be possibly achieved by the comparison of the polarities, magnitudes, or the phase angles of the zero-sequence currents of all feeders connected to the same busbar. However, it becomes a difficult task to implement this functionality into the protection of feeder. In this paper, a novel single-phase-to-ground fault protection for NUGS is put forward. Different from conventional centralized-comparison protection, this protection can detect single-phase-to-ground fault on the feeder individually, and can be realized on FTU (Feeder Terminal Unit). It is based on the measurement of the zero-sequence voltage and zero-sequence current. The tripping strategy follows the characteristic of the modified inverse-time delay curve. By means of analyzing the characteristics of the zero-sequence transient currents, it is disclosed that the magnitude of the zero-sequence current of the faulty feeder should be greater than that of any sound feeder. Then a composite compensated voltage is formed based on the zero-sequence voltage and zero-sequence current to evaluate a revising factor for every feeder respectively. Using this revising factor to modify the identical standard inverse-time delay curve adopted by all the feeder zero-sequence overvoltage protections, the tripping time of the zero-sequence overvoltage protections of all feeders will differ from each other. In this case, the selectivity of the protection can be guaranteed. This proposed algorithm is validated with the EMTP simulation tests.

병렬연결된 두 코일의 자기결합을 이용한 초전도 전류제한기의 전류제한 및 전압강하 보상 특성 분석

The superconducting fault current limiter (SFCL) plays a role in compensating the voltage sag of the sound feeder adjacent to the fault feeder as well as the fault current limiting operation of the fault feeder. Especially, the SFCL using magnetic coupling of two coils with parallel connection has different voltage sag compensating and current limiting characteristics due to the winding direction and the inductance ratio of two coils. In this paper, the current limiting and the voltage sag compensating characteristics of a SFCL using magnetic coupling of parallel connected two coils were analyzed. Through the analysis on the experimental results considering the winding direction of two coils, the SFCL designed with the additive polarity winding was shown to have the higher limited fault current than the SFCL designed with the subtractive polarity winding. In addition, it could be confirmed that the higher fault current limitation of the SFCL could be contributed to the higher load voltage sag compensation.

A Modified Selective Ground Relay for Ungrounded Distribution Systems

Selective ground relays (SGRs) are useful fur distinguishing a faulted feeder from the sound feeders in ungrounded systems. However, they sometimes mis-operate due to human or device errors. Particularly, the reversed polarity of zero-sequence current transducers (ZCTs) is the most frequent cause of mis-operation. This paper presents a modified SGR for reducing the probability of mis-operations caused by the reversed polarity of ZCTs. The modification is achieved by introducing an adaptive time delay, which depends on the magnitude of the zero-sequence current and the phase angle deviation from the reference. The modified SGR was successfully demonstrated on a sample ungrounded system without mis-operation.