Percentage Differential Protection Research Articles

Accurate transformer equivalent circuit for percentage differential protection simulation under DC bias

Percentage differential protection (PDP) is one of the main protections of the transformer. The traditional transformer T equivalent circuit is insufficient to simulate the uneven saturation characteristics of the core for PDP under DC bias. Therefore, the transformer π equivalent circuit with three-segment component saturation is proposed for transformer PDP circuit simulation. FEM simulation is carried out to analyze the performance of transformer. The simulation and the experiment on PDP operation and restraint currents are conducted. Compared to the experiment, the errors of operation and restraint currents are significantly reduced using the proposed circuit under DC bias. The circuit simulations of transformer internal and external faults are implemented. The electromagnetic field analysis verifies the limitation of T equivalent circuit for PDP. The proposed method can achieve better performance in both transformer internal and external fault circuit simulation than the traditional method.

High-Frequency-Based Transmission Line Percentage Differential Protection With Traveling Wave Alignment

High-Frequency-Based Transmission Line Percentage Differential Protection With Traveling Wave Alignment

Transformer differential protection scheme based on self‐adaptive biased characteristic curve and considering cross‐country faults

AbstractThe differential protection of transformers sometimes does not have reliable performance facing some faults and events such as saturation of current transformers (CTs) during internal and external faults, inrush currents, and cross‐country faults (CCFs). In this paper, a new transformer differential protection scheme based on the self‐adaptive biased characteristic curve and considering CCFs and various disturbances are used. First, the maximum overlap discrete wavelet transform (MODWT) was used to extract the superior characteristics of sampled differential current of the transformer at different levels. Then, by calculating the duty cycle (D) values of energy coefficients extracted in each periodicity by MATLAB software, a new self‐adaptive biased characteristic curve will be obtained in different operating conditions. Finally, the percentage differential protection operation is adjusted based on the new adaptive characteristic curve zones. Differential current sampling under different operating conditions was performed on a real three‐phase transformer in EMTP software. The simulation results show that the proposed adaptive differential protection scheme can accurately detect various faults and events occurring in the transformer and increase system reliability.

Experimental studies on the rtEthernet-based centralized fault management system for smart grids

The distribution smart grids in future are likely to have looped structures with a variety of new electronic devices to integrate renewable energy. However, tremendous challenges are brought to the fault management system (FMS), particularly the ultra-fast speed of fault localization with data acquisition at many different locations over a large geographical area. In this work, we propose a centralized fault management system (CFMS) with operation resilience based on real-time Ethernet (rtEthernet) protocols for the protection of smart grids. First, we propose a model to estimate the communication cycle time and the mis-synchronization error based on rtEthernet protocols. The model can be used to design CFMS over a large geographical area with a large number of power system devices. Second, we propose to use the instantaneous values of sample points in the percentage differential protection algorithm, instead of the value of root mean square (RMS), so that ultra-fast speed for data sampling and fault localization can be achieved. Third, we have established a comprehensive test-bed for the CFMS by using our large-scale real-time digital system (RTDS) to simulate the power system. Our extensive experimental studies have demonstrated that the proposed CFMS achieves ultra-fast speed within a sub-cycle and protects the smart grids successfully.

Comparative evaluations on operation performances of differential protection criteria using different current expressions

This paper aims at the appropriate applications of two important current differential protection criteria by quantitative analyses. Combining theoretical analysis with simulation tests, the overall performances of two typical percentage differential protection criteria are compared in terms of the operation sensitivity and security. First, with appropriate parameter settings, the comparative sensitivity analysis between the phase‐current‐based criterion and the superimposed‐component‐based criterion is done. Further, the security of these criteria is compared, and some disadvantages of the criterion based on phase current directly are reported. The performance of the criteria during the current transformer (CT) saturation when experiencing heavy external faults are studied, and some valuable findings are reported as well. With the conclusion drawn from this paper, the applications of both criteria can be arranged more reasonably. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Adaptive differential protection of three-phase power transformers based on transient signal analysis

This paper presents a three-phase power transformer percentage differential protection formulation based on transient signal analysis. The proposed formulation uses discrete wavelet transforms (DWT) to extract transitory features of non-stationary signals with fast transition, mapping the signal in time–frequency representation. The proposed formulation was implemented on MATLAB® environment and evaluated through a case study using BPA’S ATP/EMTP software. Comparative test results are presented showing that the proposed formulation is highly reliable, fast, accurate and easy for real-life construction.

An Adaptive Operating Characteristic to Improve the Operation Stability of Percentage Differential Protection

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.

Percentage Differential Protection of Double-circuit Line Using Wavelet Transform

This article presents development of a new percentage differential protection scheme for double-circuit transmission line using wavelet transform (WT). The work presented addresses the problems encountered by conventional distance relays when protecting double-circuit transmission lines sharing the same right of way. By the use of powerful analyzing and decomposing features of WT, a new technique is presented that takes care of the problems faced by pilot independent distance relay. The suggested technique depends on the six line currents of the two parallel lines at each end. The idea of the protection algorithm is based on the percentage of the difference of the two line current of each corresponding phase at each terminal. The measured six line currents at the relay location are decomposed into three levels of decomposition using the db4 mother wavelet. The summation of third level approximation coefficients are used as bias current whereas third level detailed coefficients are used as differential current. The proposed method eliminates many of the problems associated with double-circuit lines, such as high fault resistance, cross-country fault, mutual coupling effects, remote infeed, and avoids the problem of single-end supply. The stability of the relay under varied system configurations and operating conditions is examined. The relay algorithm is tested for various probable fault inception angles and loading conditions and with varying fault resistance between 0–150 ohms. The proposed wavelet based scheme provides encouraging results for different fault and system conditions. Relaying signals under different fault conditions were obtained by simulating the system using PSCAD/EMTDC.

A developmental package of interactive software for illustrating power-system protection principles in educational and industry training programs

This paper describes the philosophy, development and use of a series of microcomputer-based software packages which assist in the analysis and demonstration of some fundamental concepts associated with power system protection and related areas. These easily-used, interactive programs employ extended screen color graphics capabilities to demonstrate fundamentals of steady-state synchronous-machine behavior, instrument transformers, time-overcurrent relay operation, directional relaying, percentage differential protection of a generator, and distance relaying. They include the display of instructions and tutorials, parameter values and numerical results, phasor diagrams, one-line diagrams, circuit diagrams, and device animation as appropriate. The software described is representative of what the authors envision to ultimately form a very comprehensive but expandable set of training modules for the power-system protection area. The modules are applicable to both academic power programs and industry training efforts. >

A stand-along digital protective relay for power transformers

The complete design of a stand-alone prototype digital protective relay for three-phase power transformers is described. The major emphasis is on the detailed description of the hardware and software of the prototype relay. The protection functions implemented include: a percentage differential protection with a second-harmonic restraint for magnetizing inrush and a fifth-harmonic restraint for overexcitation conditions, and a separate protection for high-impedance primary and secondary ground faults. The relay design is tested with the Fourier algorithm, and any other relay algorithm can be used by replacing only one subroutine. The relay hardware consists of a data acquisition board and a digital processing board which is based on the TMS320E15 processor. Sample real-time test cases are discussed. The results show that the relay never misoperated and correctly identified all the faults.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Stand-alone Digital Protective Relay for Power Transformers

The complete design of a stand-alone prototype digital protective relay for three-phase power transformers is described. The major emphasis is on the detailed description of the hardware and software of the prototype relay. The protection functions implemented include: a percentage differential protection with a second-harmonic restraint for magnetizing inrush and a fifth-harmonic restraint for overexcitation conditions, and a separate protection for high-impedance primary and secondary ground faults. The relay design is tested with the Fourier algorithm, and any other relay algorithm can be used by replacing only one subroutine. The relay hardware consists of a data acquisition board and a digital processing board which is based on the TMS320E15 processor. Sample real-time test cases are discussed. The results show that the relay never misoperated and correctly identified all the faults. >