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Journal ArticleDOI

Self-adaptive transformer differential protection

25 Mar 2013-Iet Generation Transmission & Distribution (The Institution of Engineering and Technology)-Vol. 7, Iss: 1, pp 61-68
TL;DR: In this paper, a novel adaptive protection criterion is proposed, which can self-regulate the parameters of percentage differential characteristic (e.g., pickup current, restraint coefficient and restraint current at the knee point of the slope characteristic) on the basis of operating conditions of power transformers.
Abstract: Setting the pickup current and slope of differential relays of power transformer protection is a well-known compromise. It has been the focus of study to improve both the security and sensitivity of transformer differential protection recently. However, it is difficult to achieve a high degree of security and sensitivity at the same time by conventional percentage restraint differential criteria based on a fixed predetermined characteristic curve. Therefore a novel adaptive protection criterion is proposed in this study, which can self-regulate the parameters of percentage differential characteristic (e.g. pickup current, restraint coefficient and restraint current at the knee point of the slope characteristic) on the basis of operating conditions of power transformers. The test results show that the proposed scheme provides a high operating sensitivity on internal faults, while retaining higher security on all external faults. Furthermore, because of self-regulation of the setting values of relays, it is more convenient for engineers in the field who only need to give the upper and lower limits but not the exact value of the settings of protective relay.
Citations
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Journal ArticleDOI
TL;DR: A new approach to protection that promises to eliminate the majority of the problems that lead to misoperations is presented and demonstrated in the laboratory and its application to a substation coordinated protection system capable of detecting and dealing with hidden failures is described.
Abstract: The introduction of the microprocessor-based numerical relay in the 1980s resulted in multifunctional, multidimensional, communications-enabled complex protection systems for zone and system protection. The increasing capabilities of this technology created new unintended challenges: 1) complexity has increased and selecting coordinated settings is a challenge leading to occasional miscoordination; 2) protection functions still rely on a small number of measurements (typically three voltages and three currents) limiting the ability of protection functions to dependably identify the type of fault conditions; and 3) present approaches are incapable of dealing with hidden failures in the protection system. Statistically, 10% of protection operations are misoperations. This paper presents a new approach to protection that promises to eliminate the majority of the problems that lead to misoperations. The approach is described, demonstrated in the laboratory, compared to traditional protection functions and its application to a substation coordinated protection system capable of detecting and dealing with hidden failures is described. This paper also discusses the planned field testing of the approach.

102 citations


Cites background from "Self-adaptive transformer different..."

  • ...In recent years, adaptive differential relays have been studied [6]–[7]....

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Journal ArticleDOI
TL;DR: A new algorithm for discrimination between internal faults and inrush current conditions in power transformers is presented and is used to identify inrush and internal fault currents in power transformer.
Abstract: In this study, a new algorithm for discrimination between internal faults and inrush current conditions in power transformers is presented. First, the proposed algorithm removes the pre-fault conditions of the fault currents. Then, those currents are processed using the discrete wavelet transform to obtain the wavelet matrix. The correlation matrix is computed from wavelet matrix to know the eigenvalues associated with each frequency scale and to reduce the analysed information. This algorithm, which the authors are going to call wavelet correlation modes, is used to identify inrush and internal fault currents in power transformer. To validate the proposed algorithm, simulations are carried out in power systems computer-aided design software, and the obtained signals are analysed in order to evaluate its performance and sensitivity.

39 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a review of the most important techniques and a critical comparison between them and present new alternatives, such as frequency response analysis, an offline application technique.
Abstract: Faults diagnosis in power transformers has been traditionally based on the insulation resistance measurement, polarisation index, analysis of dissolved gasses in oil, dissipation/power factor measurement, and partial discharges within many other alternatives. Originally, all these techniques presented an offline implementation, that is, with the transformer out of service. Currently, some of them, such as partial discharges measurement or gas analysis (gas chromatography), are carried out online in those cases in which the importance of a machine justifies it. These techniques have been recently complemented with new alternatives, such as frequency response analysis, an offline application technique. At the same time, in recent years, development of online diagnostic strategies has been carried out only based in monitoring of electrical variables. These techniques have the advantage of being economical in relation to traditional ones. Its development are incipient and with high growth potential. This study presents a review of the most important techniques and a critical comparison between them.

31 citations

Journal ArticleDOI
TL;DR: In this paper, a histogram of the normalized rotated current (NRC) frequency distribution was proposed to detect external faults with different degrees of CT saturation, internal faults, and transferring faults.
Abstract: Current transformer (CT) saturation can cause the maloperation of transformer differential protection under external faults. To avoid this problem, a method based on the histogram of the normalized rotated current (NRC) is proposed. NRC is obtained by a symmetric waveform transformation of a part differential current. An index based on the histogram is defined to evaluate the NRC frequency distribution. The external faults with different degrees of CT saturation, internal faults, and transferring faults can be clearly distinguished by the proposed method. Moreover, the detection time is invariably less than a half cycle after the obvious increase of the differential current. Simulation results validated the proposed method.

24 citations

Journal ArticleDOI
TL;DR: In this paper, an effective approach is proposed to improve the differential and restricted earth fault (this paper) protections sensitivity of industrial transformers, which not only realises the fault current limitation function, but preserves sensitivity of the protections.
Abstract: 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.

22 citations

References
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Journal ArticleDOI
TL;DR: It is suggested that maximum value from adaptive relaying will result from integration with existing or planned substation control and data acquisition functions and interfacing with the central energy management system (EMS).
Abstract: Concepts for adaptive protective relaying of transmission lines are presented. These include changes in online relay settings, relay characteristics, or logic in response to power system or environmental changes, or as a result of operating experience. Such changes as line-out or generator-out contingencies, which affect fault current distributions and degrade the system's security level, initiate adaptive protection system responses. Adaptive relaying is shown to be capable of improving relaying reliability and power system security and of achieving better utilization of transmission facilities. Most of the concepts require a hierarchical computer system, involving front-line parallel processors, a substation host, and remote central processors, all linked by channels that transmit data or relaying changes prior to or after a disturbance. It is suggested that maximum value from adaptive relaying will result from integration with existing or planned substation control and data acquisition functions and interfacing with the central energy management system (EMS). Emphasis is placed on use of interim hardware approaches to allow evolutionary development. >

211 citations

Journal ArticleDOI
TL;DR: A method of symmetrical component analysis for the detection of current-transformer saturation in a numerical current differential feeder protection relay shows significant improvement in sensitivity on internal faults while still maintaining a high level of stability on external faults and nonfault events.
Abstract: 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.

87 citations

Journal ArticleDOI
TL;DR: Based on the comprehensive analyses of the existing current differential protection criterion, a new type of adaptive restraint coefficient-based criterion is put forward in line with a variety of fault conditions in this paper.
Abstract: Based on the comprehensive analyses of the existing current differential protection criterion, a new type of adaptive restraint coefficient-based criterion is put forward in line with a variety of fault conditions. The restraint coefficient of this criterion can be adaptively adjusted according to the operation and fault conditions of the system. In this case, this criterion can guarantee the stability of the protection during external faults. Taking into account the increasing applications of current differential protection in the extremely high voltage or even ultra-high voltage transmission systems, the work performed in this paper is provided with better performance in the case of external faults and various high-resistance internal faults than the existing criterion. Hence, it is promising to apply the current differential protection for 750-kV and above transmission lines. Using Electromagnetic Transients Program software, a simulation model based on 750-kV transmission lines in the Northwest China power grid is established to validate the proposed scheme. All of the real data are provided by the utility of the Northwest China power grid and China Northwest Electric Power Design Institute. The simulation results show that the proposed scheme has satisfactory operation performance.

44 citations

Journal ArticleDOI
C. A. Mathews1
TL;DR: In this article, a transformer is energized and there is an inrush of magnetizing current, which flows in only one winding of the transformer, producing a differential current which tends to operate conventional percentage differential relays.
Abstract: POWER TRANSFORMERS usually are protected against damage due to internal faults by percentage differential relays, which compare currents on opposite sides of the transformer. However, when a transformer is energized, there is often an inrush of magnetizing current, which flows in only one winding of the transformer, producing a differential current which tends to operate conventional percentage differential relays. Special means, therefore, are necessary to prevent transformer relays from operating falsely on magnetizing inrush currents.

41 citations

Journal Article
TL;DR: The concept of adaptive relaying, which allows computer relays to monitor themselves and to report their condition to a central location, and various applications, including load effect, cold load pickup, end-of-line protection, transformer protection, and automatic reclosing are explained.
Abstract: The concept of adaptive relaying is explained. The reasons for choosing adaptive relaying are examined, and various applications are described. These include load effect, cold load pickup, end-of-line protection, transformer protection, and automatic reclosing. The tradeoff between dependability and security of protection is discussed. The ability of computer relays to monitor themselves and to report their condition to a central location is also discussed. >

40 citations