Proposed Protection Principle Research Articles

A high speed and sensitive protection for distribution network with DGs using ferrite rings as line boundary

AbstractThere exist problems of hard coordination and threshold setting as well as low sensitivity in overcurrent relay due to the bidirectional and small fault current when distributed generators are integrated into the distribution network. This paper introduces ferrite rings (FRs) to act as boundaries of distribution feeders, and a peak time of voltage traveling wave‐based protection is proposed. The characteristics of FRs are analyzed and their feasibility as line boundary is validated. The fault characteristics of internal and external faults are analyzed when FRs are installed at both ends of the protected feeder. The results show that the peak time of the voltage travelling wave of the internal fault is far smaller than that of the external faults. According to the difference, the fault detection method and the protection scheme are proposed. Simulations in PSCAD and experiment validate that the proposed protection principle can reliably distinguish between internal and external faults. Besides, the proposed protection scheme has higher sensitivity compared to ROCOV‐based protection.

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).

A Faulty Pole Detection Method for the VSC-HVDC System Based on the Aperiodic Component Energy

Compared with a cable line, an overhead line is vulnerable to failures. When a fault occurs on a VSC-HVDC overhead line, the DC current increases sharply, thus threatening the operation safety of the VSC-HVDC system. Also, the fault current can cause irreversible damage to the power device. Therefore, it is necessary to define a principle for fast and reliable identification of faulty poles. Taking a single-pole fault as a research object, this paper analyzes the equivalent circuit of a VSC-HVDC system's fault and derives the fault current expression considering both under- and over-damping of the system. In both considered cases, the fault current contains a significant aperiodic component. The discrete wavelet packet is used to extract the aperiodic component of the fault current, and a protection principle based on the aperiodic component energy is proposed. The VSC-HVDC system model is constructed on the PSCAD/EMTDC and RTDS. The results of a large number of simulations and experiments show that the proposed protection principle can identify a faulty pole in 2 ms. In addition, the proposed principle can be used to respond to remote faults under high transition resistance and noise interference.

A novel MMC bridge arm protection based on sum current of upper and lower bridge arms

In flexible direct current transmission system, due to the nonlinear operation of the converter, the bridge arm current contains other components besides the power frequency component when a fault occurs at the outlet of DC line, which may lead to the calculated power frequency current amplitude greater than the setting value, and the existing bridge arm overcurrent protection will misoperate. In order to solve the problem, a novel converter bridge arm protection based on the sum current of upper and lower bridge arms is proposed. Firstly, the equivalent circuit of high voltage direct current system based on modular multilevel converter (MMC-HVDC) before blocking the insulated gate bipolar transistors (IGBTs) is established in the case of a bipolar short-circuit occurs at the outlet of DC line, the bridge arm current is deduced, and the influence factors and variation characteristics of each component in bridge arm current are studied. Secondly, the misoperation reasons of the existing overcurrent protection of converter bridge arms are analyzed. Finally, a novel MMC bridge arm protection based on the sum current of upper and lower bridge arms is proposed, and its action characteristics of the internal and external faults of the bridge arm are analyzed. To overcome the problem that the proposed protection cannot reflect the upper and lower bridge arms short-circuit, a supplementary criterion is proposed to identify this fault by measuring whether the upper bridge arm current and the lower bridge arm current are mainly power frequency components. The sum current protection and the supplementary criterion can reflect various faults in bridge arms, including the short-circuit between two bridge arms which can not be reflected by the existing bridge arm overcurrent protection, and they will not misoperate in the case of a fault occurs in DC line. The simulation results verifies the effectiveness of the proposed protection principle.

Single-Ended Fast Protection for Transient Power of Multi-Terminal Flexible and Direct Power Grids Containing Renewable Energy

With the proposal of the carbon peak goal, a multi-terminal flexible DC grid containing various renewable energy becomes the one of main ways of renewable energy power transmission. Thus, it is increasingly important to improve its transmission reliability and stability. This paper proposes a single-ended protection principle based on the analysis method of transient power change for the “mesh structure” ring-shaped flexible direct current (DC) grid. Based on the propagation characteristics of voltage, current, and anti-traveling waves during fault periods, the transient power variation coefficient based on SOD transformation is introduced to distinguish the internal and external faults. Besides, simulation based on the PSCAD/EMTDC platform within the Zhangbei four-port network verifies the effectiveness of the proposed protection principle under various fault conditions. Meanwhile, the protection criterion is designed according to the difference in the change coefficient of the transient power SOD within and outside the fault time zone. Moreover, the setting value of the start of protection is obtained by analyzing the simulation results, thus a set of fast and reliable single-ended protections for the same-side short-time transient power window of an enhanced flexible straight power grid is developed via combining it with the starting criterion of a sudden voltage change.

Research on single-ended protection principle of LCC-VSC three-terminal DC transmission line

The line-commutated converter-voltage source converter (LCC-VSC) three-terminal DC transmission system is one of the effective means for large-scale new energy transmission and consumption, and a fast and reliable protection scheme is the key to its reliable operation. However, the LCC-VSC DC system has characteristics such as LCC converter and VSC converter control strategies, fault response, and uneven boundary elements, which makes it difficult to directly apply the existing protection principles. To the above problems, this paper first proposed a single-ended protection principle based on line attenuation characteristics. The protection principle uses the ratio of the high and low-frequency signals of the line mode voltage to express the line attenuation characteristics and uses this ratio to identify internal and external faults. A model of the LCC-VSC three-terminal transmission system is established to verify the feasibility and effectiveness of the proposed protection scheme. The simulation results show that the proposed protection principle can accurately identify internal faults and external faults and has a strong ability to withstand fault resistance and noise interference.

New Principle of Pilot Protection Based on Kendall’s Rank Correlation Coefficient

Affected by the control strategy after MMC failure, the fault current on the converter side of the AC line interconnected with the MMC is significantly different from the fault characteristics of the traditional power supply in amplitude and phase. The new fault current characteristics lead to the inapplicability of the traditional longitudinal current phase differential protection. In order to solve the problem of the applicability of relay protection, a new principle of longitudinal protection based on Kendall’s rank correlation coefficient is proposed. After the AC line fails, the Kendall grade correlation coefficient of the calculated current on both sides is calculated to distinguish the internal and external faults. Simulations are carried out on the RTDS platform, and the results show that the proposed protection principle can reliably distinguish between internal and external faults and has the ability to withstand transition resistance under various control reference values.

A Design of Integrated Protection Principle for Box-type Substation

Box-type substation plays a very important role in distribution network. The protection of traditional box-type substation needs to be equipped with multiple equipment, and there is often a lack of selectivity between protections of low-voltage side and low-voltage outgoing lines of transformer. In order to solve these problems, an integrated protection principle of box-type substation is proposed, which uses relay protection to replace the traditional protection form. An adaptive fault component overcurrent protection is proposed to improve the sensitivity of protection, and an operation time selection criterion is put forward to ensure selectivity and clear fault quickly in some cases. Finally, the performance of proposed protection principle is verified by PSCAD simulation.

Active Injection for Single-Ended Protection in DC Grid Using Hybrid MMC

To identify the fault area more accurately and improve the reliability and sensitivity of the traditional protection principle on DC lines, an active injection for single-ended protection in the DC grid is proposed. Considering the influence of fault impedance, the effect of frequency-dependent parameters, numerical differential error, and the strength of DC boundary, high controllability of hybrid modular multilevel converter is utilized to inject sinusoidal signals with different frequencies into the line at DC terminal of each converter. Then the single-ended fault identification equation is constructed to preliminarily identify the fault area. According to the amplitude difference of the injection signals in different fault areas, the fault areas of the DC grid can be further distinguished. Simulation results verify the effectiveness of the proposed protection principle, improved reliability and sensitivity of protection, and full length protection of line without DC boundary.

A New Protection Principle of Hybrid Bipolar HVDC Line Based on Voltage Fault Component Rate of Change

At present, hybrid HVDC transmission has become a research hotspot. In this paper, the fault-added state characteristics of the hybrid bipolar HVDC transmission system with different faults on the DC transmission line are analyzed by connecting small inductors on both sides of the HVDC transmission line. A single-ended quantity protection method using voltage transient components is obtained. By analyzing the rate of change of voltage fault component, the transient energy component is used to calculate the instantaneous energy magnitude of the transient voltage component to distinguish the fault in the region. The energy function is constructed by the transient voltage of the positive and negative rectifiers to fault selection. The simulation results verify the correctness of the proposed protection principle and can achieve fault pole selection.

A Novel Pilot Protection Principle Based on Modulus Traveling-Wave Currents for Voltage-Sourced Converter Based High Voltage Direct Current (VSC-HVDC) Transmission Lines

Protection for transmission lines is one of crucial problems that urgently to be solved in constructing the future high-voltage and large-capacity voltage-sourced converter based high voltage direct current (VSC-HVDC) systems. In order to prevent the DC line fault from deteriorating further due to the failure of main protection, a novel pilot protection principle for VSC-HVDC transmission lines is proposed in this paper. The proposed protection principle is based on characteristics of modulus traveling-wave (TW) currents. Firstly, the protection starting-up criterion is constructed by using the absolute value of the 1-mode TW current gradient. Secondly, the fault section identification is realized by comparing the polarities of wavelet transform modulus maxima (WTMM) of 1-mode initial TW currents acquired from both terminals of the DC line. Then, the selection of fault line is actualized according to the polarity of WTMM of local 0-mode initial reverse TW current. A four-terminal VSC-based DC grid electromagnetic transient model based on the actual engineering parameters is built to assess the performance of the proposed pilot protection principle. Simulation results for different cases prove that the proposed pilot protection principle is excellent in reliability, selectivity, and robustness. Moreover, the data synchronization is not required seriously. Therefore, the proposed novel pilot protection principle can be used as a relatively perfect backup protection for VSC-HVDC transmission lines.

A New HVDC Transmission Lines Protection Using Special Frequency Component from One-terminal Current

In this paper by analyzing the topological structure made of smoothing reactor and DC-filter of HVDC transmission systems, we found that the structure of the filter is different when internal or external fault occurs. Furthermore the difference of the structure can result in the difference of the current. According to the difference of the current, a new rapid protection principle for HVDC transmission lines only using current signal from one-end is proposed. Simulation results and the verification results with field data show that the proposed protection principle can identify internal or external fault and it can identify the fault pole. It can operate rapidly, reliably, with high sensitivity and selectivity in different fault conditions.

Single‐end time‐domain transient electrical signals based protection principle and its efficient setting calculation method for LCC‐HVDC lines

In view of the facts that existing line commutated converter based high voltage direct current (LCC-HVDC) line protection cannot realise satisfactory selectivity, speed, sensitivity, reliability and practicability simultaneously, and that the work of setting calculation for line protection is very onerous and time-consuming due to extremely large amounts of electromagnetic transient simulations, a novel single-end time-domain transient electrical signals based protection principle incorporating all these satisfactory features and its efficient setting calculation method are proposed. For the proposed protection principle, the DC line current change criterion is employed as a directional element, which can identify faults in the positive direction of line protection, while the rate of voltage change criterion is used as a boundary element, through which the opposite internal and external faults can be distinguished. Moreover, an efficient setting calculation method is proposed based on a so-called ‘setting calculation preparation quantity’ concept, through which the setting calculation values can be determined efficiently based on only several simulations by systematically analysing the impact of various operating conditions on the post-fault transient electrical signals of LCC-HVDC systems. Finally, the simulation result based on a ±800 kV ultra-HVDC practical model verifies the validity of the proposed protection principle and its efficient setting calculation method.

Implementation and Application of Practical Traveling-Wave-Based Directional Protection in UHV Transmission Lines

Traveling-wave-based protection is becoming attractive in ultra-high-voltage (UHV) transmission systems due to the requirement for high-speed protection. However, the poor transfer characteristics of coupling capacitor voltage transformers (CCVTs) for high-frequency voltage have strictly limited its application. A novel traveling-wave-based protection scheme considering the characteristics of CCVTs and current transformers is proposed in this paper. The dyadic wavelet transform is used to extract the polarities of voltage and current traveling waves for fault direction identification. A prototype is further developed for practical applications. Extensive laboratory tests are performed to assess the performance of the developed scheme. The prototype has been applied to the 750-kV substations in China and an external fault was recorded during the operation period, validating the effectiveness and reliability of the proposed protection principle.

A novel whole-line quick-action protection principle for HVDC transmission lines using one-end voltage

A novel rapid protection principle for HVDC transmission lines only using voltage signal from one-end is proposed in this paper in order to solve the problems of traditional protection principle using one-end data of HVDC, such as poor reliability and insufficient sensitivity. By analyzing the transmission characteristic of the electric network, which is made of reactor and DC-filter of HVDC transmission systems, it is clear that when internal and external fault occurs, the measured voltage is obviously different for some special frequency-band signals. For the difference, internal and external fault can be distinguished. Compared with the traditional protection methods, the protection principle is simple and has absolute selective and a general setting principle, the sample frequency is lower, and it is easy to be implemented. It can substitute the traveling-wave-based method for primary protection with more practicability in project. Simulation results show that the proposed protection principle can identify the fault occurring in the DC line or beyond the DC line and it can identify the fault pole. Moreover, it can operate rapidly, reliably, with high sensitivity and selectivity, under different fault conditions.