DC Protection Research Articles

Research on detection and protection technology of DC residual current

Abstract To realize that the residual current device can accurately and quickly detect the fault when the fluctuating DC residual current occurs in the system and improve the system’s safety, a DC residual current detection and protection method based on VMD was proposed. Particle Swarm Optimization (PSO) was used to optimize the penalty factor and the number of decomposition layers of VMD. The minimum envelope entropy of the residual current signal is used as the fitness function to obtain the optimal combination. The criterion of fault occurrence is established based on the optimal modal component mutation characteristic of the residual current decomposed by VMD. Experiments show that this method can identify faults quickly and effectively when pulsating DC residual current is generated in the system.

Energy dissipation methods and protection device synergy strategies for offshore wind power receiving end surplus power

Abstract Firstly, a theoretical analysis of the fault ride-through scheme is carried out based on the land-side AC faults in the offshore wind power delivery system. According to the topological structure of the DC energy consumption device, the working mode and switching of the DC energy consumption device are analyzed and studied. Secondly, the DC protection action of offshore wind power flexible and direct transmission systems was studied, and the switching strategy of energy-consuming devices was determined. Then the impact of the switching of the energy-consuming device on the DC protection function was studied, focusing on the synergy between the DC overvoltage protection and the switching judgment voltage of the energy-consuming device. Finally, based on a typical offshore wind power flexing project, a system model is built in PSCAD/EMTDC to verify the effectiveness of the proposed synergy strategy.

Fault Detection and VSC-HVDC Network Dynamics Analysis for the Faults in Its Host AC Networks

High-voltage direct current (HVDC) transmission is preferred over high-voltage alternating current (HVAC) for long power lines for asynchronous power grid interconnection and high-level renewable energy integration. The control and protection functions associated with HVDC systems help with fast and secure clearance of faults. The control and protection challenges in the embedded HVDC network are of great concern for the stable and secure operation of an HVDC network. The DC fault current may reach an extremely high level in a rather short period because of the low impedance in a DC system, which is dangerous for converters, and disturbances in the AC network directly influence the performance of the HVDC system. Sometimes, faults on the AC side may lead to disconnection or failure of the DC link, causing reliability problems as well as huge economic losses. AC and DC protection solutions are being developed for HVDC systems to enhance their sustainability and reliability. As such, AC and DC faults should be detected and cleared at a faster rate. Therefore, in this article, the feasibility of the synchro-squeezed transform (SST) is analyzed for detection purposes. For more accurate and faster detection, the signal is first decomposed using the empirical mode decomposition (EMD) technique, and then the SST is applied. A discrete Teager energy (DTE) spectrum is obtained with the processed signal, which works as the detection index. The algorithm shows low sampling frequency requirements, with higher efficiency and reliability for the purpose. PSCAD/EMTDC version 4.6 software and MATLAB 2022a software is used for the modeling and simulation.

DC protection in modern HVDC networks: VSC-HVDC and MTDC systems

Considering the importance that HVDC systems are expected to have in the future of power networks, this paper aims to provide a wide overview of the protection against DC faults. In particular, it analyzes the detection and location techniques that have been proposed to date, focusing on the approaches that are set to be applied in modern HVDC networks, which comprise VSC-HVDC and MTDC systems.

DC protection coordination for multi‐terminal HB‐MMC‐based HVDC grids

AbstractFast progress of High Voltage Direct Current (HVDC) technology has been considerable over the past decades. Emerging Modular Multilevel Converter (MMC) provides power systems with promising solutions to integrate large‐scale renewable energy sources, as well as multiple asynchronous power grids. Consequently, implementation of a multi‐terminal HVDC transmission system has been easier using MMC converters. However, protection of multi‐terminal MMC‐based HVDC grids under DC fault conditions is a challenge for the industry. This study sheds light on concept of system‐level DC protection coordination for multi‐terminal HVDC grids. Although, there are different protection methods for HVDC transmission systems including multi‐terminal ones, there are no well‐defined protection coordination strategies for transmission links protection and belonging HVDC converters under DC fault conditions. The proposed protection coordination prevents unnecessary tripping of MMCs in the multi‐area HVDC grids and supports the system with minimum effect on healthy parts. For the first time, different HVDC Converter Tripping (HCT) profiles are presented based on a fully selective protection strategy and their characteristics are discussed comprehensively. Simulation results demonstrate the effectiveness of the proposed strategy for multi‐terminal MMC‐based HVDC grids. The proposed coordination can be applied to DC grid code requirements of meshed HVDC grids in the future.

DC line fault discrimination based on maximum information coefficient

In DC networks, conventional line differential protection has the disadvantages of low reliability, weak resistance to transition resistance, and vulnerable to harmonic interference. In this paper, a fault identification method based on maximal information coefficient (MIC) is proposed for non-high resistance faults in the DC side of a flexible DC distribution network containing a modular multilevel converter (MMC) with single pole grounding DC protection inside and outside segments. The failure prediction is performed based on the reciprocal information at two sides of the line current. At the same time, for single-pole grounded high-resistance faults, the MIC is compared using the zero moduli of the current at two sides of the line for the recognition of high-resistance faults. The MMC-based flexible DC transmission network model is built and validated in the PSCAD/EMTDC platform. The results show that the method can identify faults protection inside and outside segments on the DC line area quickly and reliably. It also has the ability to resist harmonic interference and has an endurance of resistance for single-pole faults on the DC side; meanwhile, for high-resistance faults, it can also be detected accurately.

Voltage Stability Assessment of a Campus DC Microgrid Implemented in Korea as a Blockchain-Based Power Transaction Testbed

Recently, the generalization of P2P (peer-to-peer) technology with enhanced security due to blockchain technology and the expansion of renewable energy-based distributed energy resources have led to blockchain technology being applied in power transactions, thus giving the potential to become a new platform for DC microgrid operation. Meanwhile, the voltage of a DC microgrid represents the balance of energy supply and demand and also serves as a stability index. The balance is represented as a steady state; the stability is represented during and after events. This paper examines the stability of the DC microgrid built on a university campus in Korea and, in particular, the blockchain technology-based power transactions performed in the DC microgrid. The test is based on the pre-planned transaction schedule applied in the DC microgrid. The transaction schedule has used day-ahead and real-time bidding data. Although many technologies are included in the project, this paper focuses on the voltage stability of the DC microgrid. In addition, the DC protection is applied and evaluated. To consider general DC protection, the DC breaker was simplified with several IGBTs, diodes, capacitors, and arrestors and was designed to interrupt the fault current within five milliseconds. The stability was evaluated using a PSCAD/EMTDCTM.

Optical Investigation of a Spark Gap for DC Protection around Current Zero

The applied experimental setup consists of a pair of fixed electrodes forming a short gap in air. The electrodes are connected with a thyristor forming a parallel current path. Once the thought flashover ignited arc has burnt a given time in the range of several hundreds of microseconds, the thyristor will be fired causing a commutation of the current in the semiconductor path. Hence, the current through the electrode gap will be reduced. The extinguishment of the arc permits the creation of a current zero in the gap. The focus of the experimental work is set to the analysis of the arc plasma during the DC phase and its distinction in the current extinction phase (current zero). High speed camera observation and optical emission spectroscopy are carried out and combined with the electrical measurements.

Test Method of Secure and Controllable FPGA Chip Used in Flexible DC Transmission Control and Protection System

Flexible DC transmission control and protection system is a high-performance distributed computing system, which has the characteristics of high-speed data acquisition and fast processing, and uses a large number of high-performance FPGA (Field Programmable Logic Array) chips. FPGA has the characteristics of high integration and complex manufacturing process, and its security and controllability is faced with many challenges. The reliability of FPGA is an important standard to measure its performance, so reliability test fault screening is very important to ensure its normal operation. Although the automatic test equipment (ATE) can test the fault of FPGA, it is not convenient for field testing due to the price, test environment and other factors. In this paper, a design scheme of built-in self-test (BIST) for fault detection and fault diagnosis is proposed, which can detect faults of look-up table (LUT) and interconnection resources (wires and programmable switches). At the same time, considering the effect of rising temperature on fault probability, a controlled self-heating element (SHE) is constructed by using the internal resources of FPGA to provide the required temperature for BIST testing. Finally, an integrated layout scheme of BIST and SHE is proposed. An experiment of self-heating of FPGA chip is completed by TSINGHUA PGL22G, which verifies the correctness and feasibility of the theory.

Analysis of an accident of abnormal increase in pole bus differential current caused by DC line faults

This paper analyzes an accident of abnormal increase of pole bus differential current and pole differential current of a converter station caused by line fault of a ±800 kV extra high-voltage direct current transmission project. After a lightning strike caused a short circuit and grounding of the DC line, the sudden voltage change protection of the DC line was triggered and the DC full voltage restart was successful. The pole bus differential current and pole differential current of the converter station have reached the protection set but have not reached the protection delay set; therefore, the differential protection has not acted. This paper first introduces the configuration principles of pole differential protection, pole bus differential protection, and line voltage sudden change protection for extra-high voltage converter stations. Second, the operation of the DC protection under this fault was analyzed in detail, and the reasons for the occurrence of pole bus differential current and pole differential current were also analyzed in this paper. Then, the range of equipment that caused the abnormal increase in differential current was identified. Finally, the lightning strike model was built on the real-time digital system, and the fault was simulated and replicated. It was determined that the abnormal increase in differential current was caused by the discharge of the pole bus surge arrester caused by the second lightning strike on the DC line.

Implementation of Control Standardization Based on HCM5000G DC Control and Protection Platform

This paper introduces the whole construction of the control standardization simulation system based on the HCM5000G DC control and protection platform, which can meet the requirements of engineering design and various control performance indexes by adopting the standardization design of the self-control and localization platform. In this paper, the construction principle of the standardized control system and the optimization strategy of the control structure are discussed in detail, and the engineering simulation model is realized by using the real-time digital simulation system with the layered and distributed standardized interface design, which provides an important reference for the future large-scale application of the control and protection of DC Engineering.

A novel pilot protection method for UHVDC transmission lines based on U-I characteristics

As one of the principal protections of UHVDC transmission lines, pilot protection requires strict synchronization and small data flow by exchanging the current on both terminals under the limitation of DC protection action rapidity. To solve this problem, this paper finds that the DC voltage and current on both terminals of the line have different plane distribution characteristics when faults occur internally and externally in the system area, and then advances a novel pilot protection method for UHVDC transmission lines based on U-I characteristics. By setting up the U-I plane with DC voltage and current as variables, analyzing the dynamic trajectory of the real-time captured U-I plane, constructing protection criteria based on the U-I plane on the rectifier side and inverter side separately, and finally converting the judgment results into state information. Both terminals of the line identify the fault location by exchanging the longitudinal comparison of state information. This protection project only utilizes the instant tracks of voltage and current in the rectifier side and inverter side at the time of fault to judge. The principle is simple and can quickly locate faults. The state messages of the two terminals are not modified by the data asynchrony on both terminals. This protection method is convenient for setting, has high sensitivity, and can quickly identify interior and exterior faults. The results are testified by theoretical analysis and simulation verification.

A CURRENT RETENTION BASED PROTECTION ALGORITHM FOR DC MICROGRIDS

Microgrids have been identified as a step towards goals of global green energy generation as they offer attractive options of renewable resource inclusion in decentralized energy networks, thus providing incentive towards meeting a booming energy demand sustainably. They are however impaired by the characteristic nature of Distributed Renewable Energy Resources (DRERs). While DRERs and microgrids offer the advantage of sustainable energy generation and autonomous operation with respect to the traditional grid, their intermittency and unconventional characteristics due to deviation from the traditional power grid structures causes trepidation while opting for them. A cause of concern while employing microgrids in daily use is the peril to personnel and equipment during the occurrence of a fault. To mitigate severe loss of life and property, it is important to develop and design protection algorithms for microgrids. While there is a comparatively large pool of knowledge on AC microgrid protection, DC microgrid protection is challenging and is being focused on by researchers around the world. The unorthodox nature of these networks cause conventional protection algorithms to be unsuitable and make the protection of these microgrids tasking. The work in this paper aims to contribute to efforts in the protection of hybrid microgrids. While the work in this paper is limited to the DC side of the grid, the proposed algorithm is able to detect and identify the location of various types of DC faults. The algorithm is verified on a secondary radial hybrid microgrid and is further compared with existing DC protection algorithms on various performance parameters.

Multisegmented Intelligent Solution for MT-HVDC Grid Protection

Fault detection continues to be a relevant and ongoing topic in multiterminal High Voltage Direct Current (MT-HVDC) grid protection. In MT-HVDC grids, however, high DC-fault currents result from a failure of a complex protective threshold in traditional protection schemes, making Voltage Source Converter (VSC) vulnerable to such potent transient currents. In this innovative single-ended DC protection scheme, multiple time window segments are used to consider the effects of the transient period across limiting inductors at each end of the link. Multiple segments of 0–0.8, 0.8–1.5, and 1.5–3.0 ms reduce relay failure and improve the sensitivity to high fault impedance while requiring minimal computational effort. It employs feature extraction tools such as Stationary Wavelet Transform and Random Search (RS)-based Artificial Neural Networks (ANNs) for detecting transmission line faults within DC networks. Its goal is to improve the accuracy and reliability of protective relays as a result of various fault events. Simulations showed that the proposed algorithms could effectively identify any input data segment and detect DC transmission faults up to 500 ohms. Accuracy for the first segment is 100% for fault impedance up to 200 ohms, whereas the second and third segments show 100% accuracy for high impedance faults up to 400 ohms. In addition, they maintain 100% stability even under external disturbances.

Wavelet multiscale principal components and traveling waves enabled machine learning technique for protection of MT-HVDC systems

The interconnection of renewable energy sources to conventional power grids is widely recognized and promoted by the deployment of high voltage direct current (HVDC) technology. One of the biggest challenges associated with the HVDC systems is the rapid rate of rising DC fault currents, resulting in the immediate collapse of the converter stations. Conventional schemes of AC protection and low-speed DC protection are not worthy and mature because of the abrupt rising characteristics of DC currents. Therefore, protection techniques are being developed for reliable bulk power transfer and interconnection of unsynchronized grids via DC links. Timely identification, classification, and determination of location are the most fundamental characteristics of any protection scheme. This research paper proposes a machine learning-based protection method that establishes a rapid and reliable solution addressing the drawbacks of existing protection schemes. A multi-terminal high voltage direct current (MT-HVDC) test system is designed in Matlab/Simulink. Pole-to-ground and pole-to-pole faults are applied at different fault locations to assess the validity of the proposed algorithm. For this, DC voltages and currents are measured and analyzed. Power spectral analysis of traveling waves and Wavelet multiscale principal components analysis are employed for the extraction of featured data to classify and locate the DC faults. This reduced dimensional featured data is utilized for training and testing the support vector machine learning algorithm to analyze the accuracy of the proposed protection technique. Simulation results confirm the accuracy of rapid identification, classification, and location of DC faults.

Interdependencies in HVDC grid protection: Impact of converter parameters and controls on DC fault‐ride‐through capabilities and protection system design

AbstractFor future multi‐terminal HVDC networks, protection systems based on DC circuit breakers (DCCBs) are envisioned to limit the loss of power transmission towards AC grid(s). Yet, HVDC protection system design is considered a major challenge—especially in a multi‐vendor setup. In particular, protection systems shall enable HVDC converters to ride through DC faults without protective blocking. Several studies have performed sensitivity analyses to determine the DCCB properties and current‐limiting inductor properties that are required to enable converter fault‐ride‐through (FRT), but the HVDC converters themselves have been simplified and kept identical. However, in a multi‐vendor setup, the exact converter design is not known at the time of DC protection planning. Therefore, this paper investigates the impact of different converter properties on the DC‐FRT behaviour, and reveals implications on HVDC protection design. Firstly, analytical approaches are proposed to mathematically derive potential impact factors on the converters’ FRT characteristics, also considering different converter control architectures. Secondly, a comprehensive EMT study demonstrates a significant impact of the converter parameters on the FRT behaviour. Analytical approaches and EMT results are compared with regard to limitations and applicability, such that the paper's findings can support the development of functional requirements for multi‐vendor multi‐terminal HVDC networks.

Transformation of conventional transformers for enhanced DC mitigation in AC power networks with advanced grid support

The flow of quasi-DC or DC in AC networks may trigger half-cycle saturation of electrical grid transformers that could lead to their internal heating or grid collapse. Apart from the requirement of DC mitigation measures, the conversion of conventional power grid into an intricate network demands the need for power equipment with dynamic control capability. The transformers provide the most strategic point in the grid for the introduction of DC protection and grid-support features. This paper proposes a fractionally rated power-electronics module coupled to neutral and ground terminals of conventional transformers that delivers efficient power network protection against quasi-DC or DC flow with different advanced grid-support features injected on the transformer primary. The proposed concept is validated on an experimental hardware prototype employing power hardware-in-the-loop (P-HIL) configuration of Typhoon HIL-402 and compared with the simulation results in this paper. Also, a transformer and associated module protection approach employing a hybrid bypass switch has been suggested and experimentally validated in this work. The experimental results validate the capability of the module to counter DC injection, perform harmonics mitigation, voltage control or unbalance compensation, impedance matching and power flow control at the same injection point.

Research on intelligent storage system for DC control and protection system card based on FERET and RFID

In view of the current state grid company’s board card spare parts are in a state of extensive management, no hierarchical and classified management, and problems such as affecting the performance indicators and circulation of the DC control and protection system boards. In this paper, a special intelligent storage system for DC control and protection system based on face recognition technology (FERET) and radio frequency identification technology (RFID) is studied. Firstly, analyzing the technical principle of the intelligent storage system. Secondly, the warehouse in/out management module based on FERET and the automatic card warehouse in/out module based on RFID are designed. Then, the structural framework and workflow of the intelligent warehousing system are established. Finally, a special intelligent storage system for DC control and protection system card is designed, which has the characteristics of leading technology, stable performance, reliable quality, simplicity, and practicality.

A hybrid circuit breaker with fault current limiter circuit in a VSC-HVDC application

A conventional hybrid circuit breaker (HCB) is used to protect a voltage source converter-based high voltage direct current transmission system (VSC-HVDC) from a short circuit fault. With the increased converter capacity, the DC protection equipment also requires a regular upgrade. This paper adopts a novel type of HCB with a fault current limiter circuit (FCLC), and focuses on the responses of voltage and current during DC faults, which are associated with parameter selection. PSCAD/EMTDC based simulation of a three-terminal VSC-HVDC system confirms the effectiveness and value of HCB with FCLC, by using an equivalent circuit modelling approach. Laboratory experimental tests validate the simulation results. The peak fault current is reduced according to the current limiting inductor (CLI) increase, and can be isolated more quickly. By adopting parallel metal oxide arrester (MOA) with the main branch of HCB, voltage stresses across the breaker components decrease during transient and continuous operation, and less energy needs to be dissipated by the MOA. The remnant current for all cases is transmitted to power dissipating resistor (PDR) in the final stage, and the fault current is reduced to the lowest possible value. When the current from the main branch is transferred to the FCLC branch, transient voltage spikes occur, while smaller PDR is required to absorb current in the final stage.

Abnormal handling mechanism and improvement measures of optical DC current transformer in smart grid environment.

An optical DC current transformer anomaly handling mechanism is proposed to address the problem that the conventional DC current transformer anomaly handling mechanism cannot compensate for the defect of capacitor anomaly blocking. First, the implementation principle, modulation loop, demodulation method and its anomaly warning mechanism of the sine-wave modulated all-fibre-optic current transformer (FOCT) are investigated, and the effects of light source intensity and modulation voltage on current decoding are explained. The modulation loop is then simulated and modelled and a FOCT anomaly handling mechanism is proposed based on the Bessel function with real-time dynamic current compensation for small changes in modulation depth. Finally, an integrated dynamic test system for DC current transformers and DC protection is designed, and the actual system operation and fault model is established using the RTDS simulation system. The experiments demonstrate that the proposed FOCT anomaly handling and improvement measures can effectively improve the transient performance of FOCT, and at the same time provide a complete set of testing means for the engineering application and later upgrade and replacement of FOCT.