편단 CT 포화 고장 발생시 양단 전류 순시치를 이용한 전류차동계전기의 내·외부 고장위치 판별방안

An electric power system is often faced with disturbance problems. The 150 kV transmission line from GI Ngimbang to GI Babat 1 experienced several disturbances due to a single-phase short circuit to the ground. The approach to determining the value of the impedance is by considering the value of the capacitance using the Phi Nominal Method with the center of the capacitance value located at the ends of the line which is divided equally in size. The main protection system used on the transmission line is the Distance relay, but the Distance relay is still not reliable and responsive. So with these shortcomings, it can be overcome by using a Line Current Differential transmission line protection system, it is proven that the Differential Line Current performance can work well. The research was conducted to analyze the performance of the Line Current Differential protection relay on the 150 kV Ngimbang-Babat 1 transmission line by calculating the impedance and capacitance values. The calculation is simulated in modeling the system against short circuit faults in determining the protection relay settings. From the results of the study, it was found that the accuracy of the Line Current Differential setting value can work by providing a disturbance signal to the power breaker (PMT) to perform tripping when a disturbance occurs in an area that is secured by a protection relay (internal fault), while the protection relay cannot work when an external disturbance occurs. secured area protection relay(external fault).

The design, evaluation and implementation of a busbar current differential protection relay that operates in conjunction with a current transformer (CT) saturation detection algorithm is described. The detection algorithm detects the start and end of each saturation period based on the third-difference function of the current. A blocking signal is activated during saturation and for one cycle after it ends. For internal faults that cause CT saturation, the relay operates before activation of the blocking signal and consequently, a trip signal is issued. For external faults that cause saturation, the blocking signal arrives first and the trip signal remains inactive. The technique does not delay the operating time of the delay. Test results indicate that the relay can discriminate between internal and external faults even when a CT is severely saturated due to the effect of remanent flux. The relay is implemented in a protection scheme based on a digital signal processor. The new relay achieves a high level of stability on external faults and a major improvement in sensitivity for internal faults.

A method of symmetrical component analysis for the detection of current-transformer (CT) saturation in a numerical current differential feeder protection relay is presented in this paper. The performance of the differential relay is investigated for various faults on a typical Electro-Magnetic Transients Program/Alternative Transients Program (EMTP/ATP) simulated transmission feeder. The simulator includes the effects of CT saturation. A comparison between simulation and tests conducted on an analog model testbench are also evaluated. The results show a high degree of similarity and illustrate the effect that CT saturation imposes on the sensitivity and stability of the protection scheme. An algorithm is presented that shows significant improvement in sensitivity on internal faults while still maintaining a high level of stability on external faults and nonfault events.

Conventional second harmonic current restriction approach is an adopted method which has been implemented to transformer differential protection schemes. Because of unreliable nature of this approach in discrimination between inrush current, internal faults and external faults and due to the saturation of current transformers, we present new features of the differential protection scheme. This helps to determine the feasibility and applicability of the proposed approach in differential protective scheme for power transformer. The Current Transformer Saturation (CTS) phenomenon issue and its revelation is one of the most significant problems in power system protection particularly in the differential protection. In this paper, the saturation phenomenon and its effects on the differential protection are analyzed. Prevalent algorithms in digital signal processing which are implemented in power system cannot correctly recognize this phenomenon. Mal-operation of differential protection relay takes place when saturation in CT is appeared. This paper presents a Third-Difference Algorithm (TDA) for CTS recognition. In order to make comparison between the presented approach and prevalent digital protective algorithm, an identical case study is simulated. Simulation results also show that the TDA is both satisfactory and consistent with expectation. Keywords: Current transformer, Saturation phenomenon, Third-difference Algorithm, Internal and external faults.

The busbar protection relays typically implements low impedance percentage differential principle using dual slope characteristics. These relays may sometimes misoperate in response to the CT saturation during close-in external faults, and the subsidence current present after clearing external faults. A primary reason for such misoperations is the fact that the traditional percentage differential principle relies exclusively on current magnitudes rather than directionality for tripping decisions. This paper evaluates the performance of an enhanced bus differential relay which uses different principles that distinguish between external and internal faults so as to enhance the security of differential protection. Extensive testing has been carried out to evaluate the effectiveness of the new principles in enhancing the security for external faults.

This paper presents an improved current differential protective principle. Marti model of the transmission line is applied in this principle, which place emphasis on solving frequency-dependent line parameters. The operating current expressions for an internal fault are also deduced in frequency domain. Finally, simulating comparison have been carried out between the proposed protective principle and Bergeron model based protection for Chinese 1000kV UHVAC test demonstration project. Simulation results show that this improved principle has high reliability for both internal and external faults. The 1000kV UHVAC transmission lines which are being constructed in China, in hybrid with HVDC links, will form the backbone of the future Chinese grid to cope with the requirement of increased power transmission over longer distances. It is important for relay protection to secure normal operation of UHV grid. The split-phase current differential protection is first applied owing to its rapidity and absolute selection. But due to the negative impact of large distributed capacitive currents, the reliability and sensitivity of traditional current differential relay decay seriously (1). Therefore, some scientists proposed the novel protective principles, which can not be affected by capacitive current (2), (3), (4). Reference (2) put forward a principle of pilot differential protection based on Bergeron model. It describes that currents at both sides of a line could be calculated by means of Bergeron model formula firstly, and then compared with the measured currents at the same side. This comparative result is just operating current in this protective scheme. Here the calculated currents and the measured currents at the same side are taken for comparison, by contrast in a traditional current differential relay a current value at one side is subtracted from that at the opposite side. The advantage lies in the Bergeron model-based principle is independent on the capacitive current, and it is unnecessary to calculate the compensating current. It must be noted that a transmission line is assumed to have constant parameters in the Bergeron model. However it has long been recognized that line parameters vary with frequency in actual electromagnetic transient process. Therefore if Bergeron model formulas are used, there exits calculating errors which would cause the accuracy and sensibility of relays reduce obviously. In order to solve this problem, an improved current differential protective principle is presented in this paper. The principle applied Marti model of the transmission line, which is based on traveling wave propagation. The frequency-dependent characteristics of line parameters are taken into account. By using of this approach, we will get a more accurate result. In addition, a new criterion adapting to this principle are presented. Finally, by making use of EMTPE and MATLAB software, the improved current differential protective principle, and the protection based on Bergeron model are both simulated on the first 1000kV UHVAC transmission line in China, also called as the 1000kV UHVAC test demonstration project. Simulating comparison shows that this improved principle is correct and reliable.

Enhancing grid protection: The crucial role of resistive-type superconducting fault current limiters in transmission line current differential relays

Adaptive additional current-based line differential protection in the presence of converter- interfaced sources with four quadrant operation capability

The usage of the high-harmonic restraint is one of the most common ways to ensure the non-operation of the power transformer differential protection when a magnetizing current inrush occurs. The application of this method allows not only to lower the minimum operating current of the protection, which increases its sensitivity to the developing inter-winding faults, but also provides inaction of the protection when unbalance currents increase during a transient caused by an external fault. However, there is no accurate information in the literature on possible ranges of variation of content of higher harmonics in the differential current in the cases when external or internal faults occur. This complicates the calculation of settings of protective relays, ensuring their most effective functioning. In this paper authors analyze the content of the higher harmonics in the differential current in the cases of external and internal faults, taking into account the saturation of the measuring current transformers in order to determine the range of variation of the higher harmonics under these conditions. It is shown that in all cases the ranges of variation of higher harmonics overlap which makes it difficult to create an effective differential protection that recognizes emergency and normal operation conditions operation only by harmonic analysis of the operating signal

Busbar protection is an essential component in power system design, protecting the most important system node for network stability and security. When faults occurs on busbar itself, it takes much time to isolate the bus from source which may cause much damage in the bus system. Faults in power system are classified as internal and external faults. Faults within the zone are termed as internal faults whereas, the faults outside the Zone are called as external faults. Ideally, a relay looking after the protection of a zone should operate only for internal faults. It should restrain from operating for external faults or through faults. In this paper the busbar protection using differential protection scheme has been investigated for internal and external faults. An algorithm has been developed to improve the selectivity of the relay and the same has been tested in IEEE9 bus system for internal and external faults. Separation of De-noised signal from fault signal is made using wavelet transform so that the nature of fault occurs on the system can be identified. In this study Daubechies 4 at level 3 is used to separate original signal and de-noised signal. The entire simulation has been done using MATLAB R2017a.

There is a smoothing reactor and DC filter between the inverter and the direct current line to form a boundary in the HVDC transmission system. Since this boundary presents the stop-band characteristic to the high frequency transient voltage signals, the high-frequency transient voltage signal caused by external faults through boundary will be attenuated and the signals caused by internal faults will be unchanged. A new algorithm based on mathematical morphology is presented for fast discrimination between internal fault and external fault. The method is based on the principle that the waveform caused by internal fault contains much wave peak and wave trough and the waveform caused by external fault changes slightly.

The paper presents a methodology on how to discriminate: internal and external faults; for a transmission line protected by differential protection scheme, during the presence of charging current. Transmission line with high voltage levels (400-765kV) peculiarly has this disadvantage. Various plots for a Distributed Transmission line Model with Source at both the ends” with internal and external faults were plotted and analyzed. Through the comparison of current samples at zero crossings for remote end and local end buses, after that implementation of proposed DSA (Difference Squared and Averaged) theory, were able to distinguish whether the fault is internal or external. The techniques better compared to conventional techniques since threshold taken under consideration; obtained through experimentation on various system models for varying degree of parameters via certified thresholding method. And the uniqueness lies with the fact that it provides a provision to distinguish transient disturbances from internal fault.

Modern microprocessor based relays used for busbar and transformer protection, typically implement a low impedance percentage differential principle using dual slope characteristics. These relays may sometimes misoperate in response to the CT saturation during close-in external faults, and the subsidence current present after clearing external faults. A primary reason for such misoperations is the fact that the traditional percentage differential principle relies exclusively on current magnitudes rather than directionality for tripping decisions. This paper describes two novel principles that distinguish between external and internal faults so as to enhance the security of differential protection; directional phase angle comparison and rate-of-change of differential current. The paper also discusses mathematical models used for each principle and their interaction during operation as well as their interaction with the traditional dual slope method. In addition, the paper compares the performance of a protective device using the traditional dual slope method vs. one with the new principles. Test cases are presented to illustrate the effectiveness of the new principles in enhancing the security for external faults.

In this study, a hyperbolic S-transform-based method is proposed to discriminate most important transient fault currents of transformers. First, the proposed method discriminates external faults from other disturbances. Then, the S-transform is applied to differential currents. An index is suggested by using absolute deviations of the S-matrix of differential currents to discriminate internal incipient faults in addition to inrush currents and internal faults. The relay issues an alarm signal in the case of the incipient fault but restrains during the magnetising inrush current. If an internal fault is recognised, the relay will issue a trip signal. To study the robustness of the suggested method, a program is developed in the MATLAB environment. The inputs of this program are differential current signals, derived from a system modelled by EMTP software. In order to simulate the internal incipient fault along with internal turn to turn and turn to earth faults, the transformer is modelled as 8×8 RL matrices, derived by using subroutine BCTRAN in EMTP. Also, differential currents are contaminated by noise and it is shown that the suggested method is not affected by noise and it can discriminate incipient faults, inrush currents, internal faults and external faults.

A new differential protection scheme based on Synchro-squeezing transform applied to AC Micro-Grid