Line Protection Research Articles

Single-ended protection method for hybrid HVDC transmission line based on transient voltage characteristic frequency band

Hybrid high-voltage direct current (HVDC) transmission has the characteristic of long transmission distance, complex corridor environment, and rapid fault evolution of direct current (DC) lines. As high fault current can easily cause irreversible damage to power devices, rapid and reliable line protection and isolation are necessary to improve the security and reliability of hybrid HVDC transmission system. To address such requirement, this paper proposes a single-ended protection method based on transient voltage frequency band characteristics. First, the frequency characteristics of the smoothing reactor, DC filter, and DC line are analyzed, and the characteristic frequency band is defined. A fault criterion is then constructed based on the voltage characteristic frequency band energy, and faulty pole selection is performed according to the fault voltage characteristic frequency band energy ratio. The proposed protection method is verified by simulation, and the results show that it can rapidly and reliably identify internal and external faults, accurately select faulty poles without data communication synchronization, and has good fault-resistance and anti-interference performance.

Roadmap to modernization of line protection in active distribution systems

The nature of distribution systems is changing from passive to active networks due to the integration of Distributed Energy Resources, especially Inverter-Based Distributed Generation (IBDG). This change presents challenges for existing fuse-based unidirectional protection schemes, as active networks experience bidirectional flow of power and small fault current contribution from IBDGs. Such fault behavior can impact the protection scheme’s sensitivity and selectivity, compromising the reliability of active distribution networks and leading to customer outages due to improper fault isolation. The problem is exacerbated in networks that allow the islanded mode of operation. Upgrading the entire protection system to microprocessor-based relays is expensive. Instead, this work proposes a planning strategy to optimally upgrade protective devices. The proposed framework is able to incorporate IBDG integration plans, distribution system reliability targets, protection requirements, and economic viability throughout the planning horizon. The obtained strategy determines the optimal number, location, and deployment time of protective devices in consideration of network characteristics. The developed optimization model is formulated as a Mixed-Integer Linear Programming problem. The results verify the proposed framework’s ability to economically upgrade the protection scheme while enhancing the reliability of the active distribution network with IBDGs.

A novel pilot differential protection for HVDC transmission line based on the differential voltage

The HVDC transmission system has played an important role in modern power system. In traditional HVDC transmission line protection, the differential protection is invulnerable to high fault resistance, but its time delay is too long due to the distributed capacitance current. In order to solve this problem, a novel pilot differential protection is proposed in this paper. The compensating voltage on the setting point on the line can be calculated by using the voltage and current at two terminals of the line, separately. The difference value of the compensating voltages calculated by the voltage and current at rectifier side terminal and the inverter side terminal are defined as the differential voltage in this paper. When external fault occurs, the compensating voltage on the setting point calculated by the rectifier side terminal and inverter side terminal should be almost the same, so the differential voltage should be relatively small. However, when internal fault occurs, the compensating voltage on the setting point calculated by the two terminals are different, so the differential voltage should be relatively large. The analysis proves that the differential voltage can be used to identify the fault. A ±800 kV UHVDC system is modeled for simulation in PSCAD/EMTDC, and the correctness and effectiveness of the proposed protection method is verified.

An Improved Method of Traveling Wave Protection for DC Lines Based on the Compensation of Line-Mode Fault Voltage

The protection of high voltage direct current (HVDC) transmission line is the key to development of the HVDC transmission technology. To deal with the problem that the traditional traveling wave protection (TWP) has low sensitivity under high resistance faults, an improved TWP scheme based on the compensation of the line-mode component of fault voltage (LMCFV) is proposed. The expressions of the LMCFV of HVDC system at different fault locations are derived. Conclusions can be drawn that the LMCFV and fault resistance are linear when the DC line fault occurs, whereas the linear state will be broken for the external fault. Based on this, the LMCFV for the metal fault occurring at the DC line midpoint is used as the reference value to compensate for the faults in other cases of the HVDC systems. The protection scheme constructed based on the compensatory LMCFV and compensation coefficient can accurately identify fault of the DC line. Finally, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\pm }$</tex-math></inline-formula> 800 kV model of HVDC systems is built in PSCAD to verify the protection performance. The effect of fault resistance can be eliminated by compensatory LMCFV, and the DC line fault can be quickly and reliably identified by the simulation results.

Experimental Study on the Transient Electric Shock Characteristics Between Metal Sheds and the Human Body Near Ultrahigh Voltage Alternating Current Transmission Lines

With the development of ultrahigh voltage (UHV) transmission lines in China, line corridors are becoming increasingly limited, and the lines pass closer to inhabited areas and the occurrence probability of induced electric shocks are increased. The research on transient electric shock and human sensory is essential due to the displeasure and complaints of people on electric shock. In this article, a real-size metal shed was established near a 1000-kV UHV alternating current (ac) transmission line, and the induced voltage and transient current characteristics were studied when the human body was in contact with the shed. Then, the amplitude and pulsewidth of the transient electric shock current were investigated, and the associations between discharge energy and sensation were established. The research found that transient electric shock is the most serious when the grounded human body contacts the insulated shed, and the imparted electric shock energy reaches 25 mJ. When the body and the shed are grounded, there is no electric shock sensation. When the insulated human body is in contact with the insulated shed, the electric shock sensation is intermediate, and women's perceptions of pain are more intense. The results provide references to transient electric shock protection for power transmission lines.

Distance Protection for Lines Connecting Converter Interfaced Renewable Power Plants: Adaptive to Grid-end Structural Changes

Typical fault current characteristics of converter interfaced renewable power plants have significant impact on the reliability of traditional line distance protection. Large degrees of system non-homogeneity introduce substantial error in the apparent impedance calculation. In this paper, an adaptive distance relaying method for lines connected to converter-interfaced renewable power plants is proposed. A range of fault current phase angles is identified using the local and remote equivalent source impedances, which are calculated using only local measurements. Corresponding to the lower and upper bound of the identified range of fault current phase angle, two apparent impedances are calculated based on priority to dependability and security of protection operation. The trip decision is made based on the weighted sum of the first and second apparent impedances. Tuning of the dependability and security weightage factors based on the calculated remote grid-end source impedance, ensures adaptability and reliability of operation, even after structural changes in the grid. The proposed method is verified using IEEE 39 bus system and validated using field data. Comparative assessment with practically proven distance and modified distance protection method for lines connected with renewables is also provided.

Transition and Issues of Substation Protection Relay Systems for Power Distribution

In June 2023, the Protection Relay System Technical Committee planned a special issue labeled as “Protection Relay System Technology in Power Distribution Stations”. Protection relay systems play a vital role in the stable operation of power systems. In recent years, they have also been responsible for solving various problems in power systems, such as the realization of mass introduction of renewable energy, expansion of the operational capacity of power distribution facilities, and rationalization of facility configuration. The following topics were gathered and discussed as a result of the call for this special issue.: (1) Proposals for distribution line protection methods (short circuit protection, ground fault protection), (2) Case studies using IEDs (IEC 61850), N-1 inter trip scheme, bus bar protection relays, and comprehensive retrofits, (3) Optimizing accident recovery during distribution line accidents, (4) Voltage adjustment methods using storage battery capacity operation, (5) Bank Recorder and switchboard configuration when dealing with reverse power flow. A total of 10 papers were submitted. This commentary touches on the contents of the technical reports as an aid to understanding these papers. It also outlines the history of distribution substation protection relays and the latest technology in distribution substation protection relay systems.

A Non-unit transient travelling wave protection scheme for multi-terminal HVDC system

The rapid and accurate dc line protection scheme is of great value in isolating dc line faults and improving the reliability of multi-terminal HVDC systems. Nowadays, the traveling wave (TW) protection is widely used as the primary protection in HVDC transmission systems. However, the traditional TW protection has the problems of poor resistance to high impedance faults and the setting value depends on simulation. For the hybrid three-terminal LCC/MMC HVDC system, this paper provides a fast non-unit protection scheme. Firstly, the time-domain expressions of the backward line-mode voltage TW after different line faults occur are derived respectively. Based on the expressions, a non-unit protection scheme depending on the difference value of the line-mode backward TW is proposed. Finally, the scheme is verified by simulation. The method only needs single-ended data to realize the rapid dc line protection without converter station communication which has a clear theoretical calculation method in setting values and a strong robustness to high-resistance fault.

Single-end traveling wave protection method in flexible DC transmission line based on dominant frequency attenuation characteristics

The conventional traveling wave protection (TWP) for flexible DC transmission lines suffer from low-sensitivity problem in far-end high-impedance faults. Also, they are lack of theoretical basis in threshold setting. In this paper, the initial traveling wave is analysed considering the frequency attenuation law and discrepancy between internal and external faults. Then, the frequency domain expressions of the initial traveling wave are analysed deeply. By enhancing the influence of high-frequency components in energy calculation reasonably, the initial traveling wave dominant frequency (ITWDF) is constructed, which can reflect the fault location and the attenuation characteristics of the boundary. The expressions of the ITWDF show that the ITWDF decreases with the increasing fault distance, and the ITWDF is significantly different between the internal faults and the external faults. On this basis, a single-ended TWP method based on the attenuation characteristics of the ITWDF is proposed. The method is immune to the fault impedance, and the expressions of the ITWDF provide a theoretical basis for protection threshold setting as well. The simulation results show that the proposed method can fast and correctly identify line faults, even with 1000 Ω fault impedance. The ITWDF can reflect the fault location effectively, and the threshold setting is simple. Moreover, the proposed method is high-adaptability in different network topologies.

PROTECTION OF ELECTRICAL TRANSMISSION LINES WITH SOURCES OF DISTRIBUTED GENERATION

The article examines the parameters of remote protections with a time delay dependent on the resistance of the short-circuit loop for distribution lines with redundancy and sources of distributed generation (DRG), taking into account the peculiarities of the parameters of these lines and their modes of operation and operating conditions. Obtained characteristics of protection devices, which are recommended when setting up remote protection of such lines with a voltage of 6...20 kV. The advantages of using a remote protection connection scheme for interphase voltages and phase current differences, as well as the use of separate protection against double earth faults, and in their absence - connection schemes for line voltages and phase currents, are justified. The reliability of the remote protection of full resistance should be evaluated by the value of the maximum length of the arc, which is determined at a given coefficient of sensitivity of the remote protection by the voltage drop at the place of installation of the protection in the event of a short circuit.

Pilot protection of lines emanating from DFIG-based wind farms during balanced faults

Wind farms (WFs) are increasingly connected to high-voltage (HV) grids, for which pilot protection—including differential protection and directional comparison blocking pilot protection (DCBPP)—is normally deployed as the primary relaying scheme. Despite extensive research into differential protection, the possible effects of WFs on DCBPP have not been studied to date. This paper unveils a serious defect associated with DCBPP that utilizes the superimposed component-based directional element (SCBDE) as the supervisory element. It is shown that for HV lines emanating from doubly fed induction generators (DFIGs)-based WFs, the positive-sequence SCBDE may provide misleading indications of fault directions during balanced faults, consequently causing the malfunction of DCBPP when faults are located inside protected lines. To secure the protection of lines during such problematic conditions, this paper also proposes a novel pilot protection scheme by applying the dynamic time warping (DTW) algorithm. The main idea behind the proposed scheme is to differentiate internal faults from external faults directly depending on the dissimilarity degree of current sampling sequences at two ends. Taking advantage of the distinctive waveshape properties of DFIG fault currents under crowbarred states, the proposed scheme can operate for internal faults at a high speed. In the meantime, the monotonicity and continuity attributes of the DTW algorithm enable the proposed scheme to be independent of a strictly identical sampling frequency and exhibit strong tolerance against synchronization errors and data packet loss. A thorough performance evaluation under various balanced faulty conditions corroborates the efficacy of the proposed scheme.

A Protection Scheme for DC Distribution Line based on the Fault Current Limiting Control of DAB Converter

In the DC distribution network, the ability of the converters to withstand overcurrent is very poor. When a fault occurs in the DC line, the converter protection and line protection cannot be easily coordinated, making it difficult to ensure selective fault removal. This paper investigates protection for the DC distribution line connected with the DAB converter. First, a fault current limiting scheme for the DAB converter using phase shifting and constant current control is proposed. Then a protection scheme for the DC distribution line based on the similarity of the fault currents flowing on both sides of the line is proposed. The effectiveness of the fault current limiting control scheme and the protection scheme is verified in PSCAD/EMTDC simulation.

Non-unit traveling wave protection for flexible HVDC lines based on the ratio of the waveform fitting residual

Non-unit traveling wave protection for flexible HVDC lines based on the ratio of the waveform fitting residual

Negative sequence current accumulation difference based wind farm collection line protection for MMC-HVDC system

During the fault of the wind power collection line of the MMC-HVDC system, the amplitude of the fault current may be limited due to the control of the converter, which leads to the severe limitation of traditional protection. In this paper, based on the difference of negative sequence current accumulation, a new protection scheme for wind farm collection lines is proposed. First, the negative sequence current equivalent circuit of the wind farm collection line is constructed. Then, the distribution characteristics of negative sequence current at different fault locations are identified. On this base, a novel protection scheme based on transient negative sequence current accumulation difference using interconnected blocking signals is proposed. The RTDS simulation results show that the protection scheme can accurately identify faults of different types and locations.

A single‐ended protection method for flexible DC distribution grid

AbstractConsidering that no current limiting inductances (CLIs) are installed at the end of the DC line in the flexible DC distribution grid, the protections relying on line boundary are no longer applicable. To overcome this problem, the paper proposes a single‐ended protection method independent of line boundary. Firstly, the Peterson equivalent circuit is applied to analyze the amplitude‐time ratio of initial voltage travelling wave (ARIVTW) under internal and external faults. Secondly, the fault direction criterion based on the fault component current and the fault type criterion based on the pole voltage are built. Subsequently, the fault identification criterion is constructed by using the ARIVTW, and the corresponding protection method is formed. Finally, the flexible DC distribution grid is built in PSCAD to verify the proposed method. The simulation results show that the method is robust to fault resistance and noise. Besides, the method realizes the protection of the whole line, which has good selectivity and engineering applicability.

ELECTRICITY TRANSMISSION AND ENVIRONMENT: EFFECT OF WIND LOADS ON LIGHTNING SHIELDING PERFORMANCE OF OVERHEAD POWER LINES

In this paper the estimation of wind load effect on the lightning shielding performance of overhead power lines was performed. According to electro-geometrical model any phase conductor has horizontal exposure width where this conductor is not protected against lightning by the overhead ground wire. A typical double circuit 220 kV lattice power transmission line tower was considered. Obtained results demonstrate that in the presence of thundercloud in windy conditions unprotected distance of phase conductor may increase due to deflections of phase conductors. Geometric locations of the conductor attachment points on the suspension insulator string and the lower point of the conductor sagging were calculated in the range of wind pressure from 0 to 800 Pa. This allowed to determine the exposure width values of a 220 kV overhead power line upper phase conductor in the same range of wind pressure values. The results show that for a minimum lightning current of 3 kA, the unprotected distance increases by 4.323 times from 4.167 m to 18.013 m when the wind pressure increases from 0 to 800 Pa (from 0 to 36.140 m/s). For a minimum lightning current of 5 kA, the unprotected distance increases by 7.735 times from 2.825 m to 21.851 m when wind pressure and wind speed vary in the same range. Although the transmission line is reliably protected against lightning strikes with currents greater than 16 kA at wind pressure of up to 200 Pa (18.070 m/s), when the wind pressure increases from 300 Pa to 800 Pa (from 22.131 m/s to 36.140 m/s), the unprotected area increases from 4.752 m to 26.204 m. In Summary, the results show that the influence of wind load must be taken into account in the tasks of calculating lightning protection of overhead power lines. Further efforts should be focused on studying the lightning shielding performance of overhead power lines of higher voltage classes.

A non-unit transmission line protection scheme for MMC-HVDC grids based on a novel distance criterion

Ultra-fast, selective, and reliable protection is significant for MMC-HVDC grids. The methods utilizing the characteristics of fault current limiting reactor (FCLR) are unsatisfactory to detect high resistance faults. In this paper, a novel distance criterion is proposed to form the non-unit protection scheme. The line-zero-mode fault equivalent circuit is built to analyze the characteristics of fault traveling waves at the inductive terminal considering the influence of MMC and the refraction and reflection at the fault point. A multi-resolution morphological gradient algorithm (MMGA) is employed to extract the geometric features of the fault traveling waves. The magnitude of the first modulus maxima of the line-mode fault voltage after MMGA constitutes the start-up criterion. The estimated velocity and the change direction of the line-mode components are adopted to identify if the fault happens in-region. The 4-terminal ±500 kV MMC-HVDC grid built in PSCAD/EMTDC demonstrates that the proposed scheme can accurately identify various faults. The sensitivity analysis shows that the proposed scheme is almost immune to the size of FCLR, the equivalent parameters of MMC, the noise environment, and the DCCB breaking process. The proposed scheme has low requirements for sampling frequency and can be utilized to identify the temporary fault.

A protection method for LCC-VSC hybrid HVDC system based on boundary transient power direction

In a line-commuted converter–voltage source converter (LCC-VSC) system, in the hybrid multi-terminal high-voltage direct-current (HVDC) sending end, a line-commuted converter (LCC) converter is used, while the receiving end uses a full-half hybrid modular multi-level converter (MMC), with a fault self-clearing capability. The DC line faults can be self-cleared within 1–2 ms. Therefore, there is an inevitable problem of short availability of faulty information since only 1-ms complete fault data are available to identify faults. Thus, it is necessary to develop a fast and reliable protection scheme for an LCC-VSC system. To address this need, this paper proposes a DC line protection method based on the boundary transient power direction. First, the characteristics of boundary transient power direction of the internal and external faults are analyzed. For an internal fault, the boundary transient power direction is positive, whereas for an external fault, this direction is negative. Therefore, this paper uses the sum of the boundary transient power directions to structure internal- and external-fault identification elements and a pole detection element. The proposed method is validated by real-time digital simulations using Kun-Liu-Long LCC-VSC three-terminal hybrid HVDC–RTDS test system. Numerous tests have demonstrated that the proposed protection method is effective in detecting different fault types under various fault distances, fault transition resistance values, and signal-to-noise ratios in the period of 1 ms. Compared with the existing methods, the proposed protection principle has a better performance in withstanding fault transition resistance (600 Ω) and noise interference (10 dB).

Shunt faults detection and classification in electrical power transmission line systems based on artificial neural networks

PurposeThis study aims to focus on an adaptive method for fault detection and classification of fault types that trigger in three-phase transmission lines using artificial neural networks (ANNs). The proposed scheme can detect and classify several types of faults, including line-to-ground, line-to-line, double-line-to-ground, triple-line and triple-line-to-ground faults.Design/methodology/approachThe fundamental components of three-phase current and voltage were used as inputs in the ANNs. An analysis of the impact of variations in the fault resistance, fault type and fault inception time was conducted to evaluate the ANNs performance. The survey compares the performance of the multi-layer perceptron neural network (MLPNN) and Elman recurrent neural network trained with the backpropagation learning technique to improve each of the three phases of the fault detection and classification process. A detailed analysis validates the choice of the ANNs architecture based on the variation in the number of hidden neurons in each step.FindingsThe mean square error, root mean square error, mean absolute error and linear regression are measured to improve the efficiency of the ANN models for both fault detection and classification. The results indicate that the MLPNN can detect and classify faults with a satisfactory performance.Originality/valueThe smart adaptive scheme is fast and accurate for fault detection and classification in a single circuit transmission line when faced with different conditions and can be useful for transmission line protection schemes.

Single-ended DC line protection scheme based on first peak time of current-limiting reactor voltage

Fast and sensitive DC line protection is an important guarantee for the security of the flexible DC grid. However, the reliability and sensitivity of the DC line protection are greatly affected by the high fault resistance. To overcome this problem, this paper proposes a novel single-ended line protection scheme for multi-terminal flexible DC grid. Firstly, the propagation characteristics of traveling wave after the internal and external faults are analyzed. Furthermore, a single-ended protection criterion based on the first peak time of current-limiting reactor transient voltage is proposed to distinguish the internal and forward external faults, which is independent of simulation. Then, based on the change characteristics of fault component current, a fault direction criterion and fault pole identification criterion are constructed to identify the backward fault and fault pole, respectively. Finally, extensive simulations and experiments show that the proposed protection scheme can identify the fault quickly and sensitively even for the internal remote-end fault with high fault resistance.