Interphase Short Circuit Research Articles

Active Power Backflow Suppression Strategy of Cascaded PV Solid-State Transformer Under Interphase Short-Circuit Fault Condition

Currently, the grid-tied guidelines all require large and medium-sized photovoltaic (PV) power stations to stay connected to the grid during low-voltage ride through (LVRT). However, three-phase cascaded PV solid-state transformer (SST) has the inherent active power backflow problem during asymmetric voltage sags, causing that H-bridge dc-bus voltages are out of control and that the converter will be disconnected from the grid because of overvoltage fault. The existing control strategy is capable of avoiding active power backflow in theory by injecting appropriate zero-sequence voltage, but the overmodulation range is larger during interphase short-circuit fault, weakening active power backflow suppression effect. For this issue, this article proposes a combined control method of positive–negative-sequence maximum–minimum harmonic zero-sequence voltage injection strategy and adaptive zero-sequence voltage compensation strategy, which can shrink effectively active power backflow range of three-phase cascaded PV SST, increasing its adaptability to different output powers and different grid drop depths, and then improving LVRT capability of the PV power generation system. Finally, a low-voltage and low-power experimental prototype is made to verify the effectiveness and feasibility of the proposed control strategy.

An H8 Current-Source Inverter Using Single-Gate WBG Bidirectional Switches

Due to the high forward voltage drop of reverse-blocking (RB) switches, conventional current-source inverters (CSIs) typically suffer efficiency penalties. Bidirectional (BD) switches, on the other hand, can also block reverse voltages but with less conduction loss than RB switches, making them more attractive candidates for CSI switches. This article discusses the difficulties inherent in implementing BD switches in CSIs, such as dc-link overvoltage, interphase short circuit, more complicated commutation schemes, high body diode conduction loss, and additional gate control signals. To address these issues, a new CSI topology (H8-CSI-BD) is proposed, which is optimized for the use of single-gate wide bandgap (WBG) BD switches. The proposed topology and its modulation scheme guarantee safe operation of CSI, eliminate BD switch’s body diode conduction loss, and achieve significant efficiency improvement. In addition, its requirement for single-gate control signals for its BD switches simplifies control and gate drive circuits noticeably. The advantages of the H8-CSI-BD topology over the other CSIs using either RB or BD switches are confirmed by analysis, simulation, and experimental results.

The results of the production tests of the method for diagnosing the eccentricity of the rotor of an asynchronous electric motor

Ensuring the reliability of electrical equipment in agriculture remains an urgent problem, since rugged operating conditions and aggressive environment hinder its rational use. The high accident incidence rate of asynchronous motors in most cases is invariably caused by the failure of the inter-turn insulation and interphase short circuit or short circuits to the housing. The probability of an emergency situation increases with an increase in the radial clearance in the bearings and, consequently, the occurrence of static eccentricity of the rotor. The developed method for diagnosing the static eccentricity of the rotor of an asynchronous motor is based on the analysis of the rotor speed; the amplitude of the rotor speed change was used as a diagnostic parameter. The paper presents the change in the rotation frequency depending on the difference in the amplitudes, resulted from the study conducted for different values of static eccentricity. The test results have shown that with an increase in the eccentricity of the rotor, the amplitude of the speed fluctuations increases.

Fault location method for interphase short circuit in digital distribution network based on genetic algorithm

Fault location method for interphase short circuit in digital distribution network based on genetic algorithm

Fault location method for interphase short circuit in digital distribution network based on genetic algorithm

Fault location method for interphase short circuit in digital distribution network based on genetic algorithm

Traveling Wave Fault Location Technology in Distribution Network Based on Non-Contact Sensor

In view of the fact that traditional traveling wave sensors need to be directly connected with primary high-voltage equipment, the layout is not flexible, construction is inconvenient, and the traditional ferromagnetic coil traveling wave sensors have problems such as low sensitivity and magnetic saturation. The use of magnetoresistance chip to design non-contact traveling wave sensor is proposed. Theoretical analysis of the magnetoresistance chip is carried out, and the tunnel magnetoresistance chip is selected as the non-contact sensor magnetic sensitive element; the non-contact sensor hardware circuit is designed, the sample is trial-produced, and the experimental test is carried out. The experiment shows that the non-contact sensor can detect a traveling wave signal with a bandwidth of 100kHz∼5MHz, which meets the requirements of traveling wave detection for common fault types in the distribution network. A demonstration project has been built, and operation shows that the non-contact sensor can successfully detect single-phase grounding, interphase short circuit, lightning strikes and other fault types traveling wave signal, sensitivity is higher than traditional traveling wave sensor, positioning error is less than 150m.

Research on robot for repairing broken strands in 500kV High Voltage Live Operation

The 500kV transmission line is an important part of the power transmission network. Due to the complex climate internal stress corrosion, lightning, external damage and other factors, transmission line is prone to crack in the wire, aluminum wire broken and spread phenomenon. It result in the current carrying capacity of transmission wire reduced. The local heating of the broken section is serious and the safety distance between the lines becomes short which affects the safe operation of the line and even causes serious accidents such as interphase short circuit and flash over of the transmission line. Therefore, repair must be carried out and the traditional manual repair method requires climbing the pole and tower and high in the air to eliminate the potential safety risks in time. Working in the strong electromagnetic field environment and most are in the state of power failure, even if the electrical maintenance must wear insulation clothing. There is a large labor intensity, high risk and low efficiency. Use of robots to replace manual operation can effectively reduce labor intensity and risk improve operation efficiency.

Research on External Fault of Salient Pole Synchronous Motor at Rated Load

The pumped storage power station is an inevitable product of the power system structure and power supply demand development to a certain stage, and it is a necessary management tool to ensure the safe and stable operation of the power system. Pumped storage power plants have the ability to improve and balance the load of the power system, which can improve the quality of power supply to the power grid and improve overall economic benefits. With the development of high-tech industries such as informatization and digitization and the improvement of people’s living standards, society has higher and higher requirements for pumped storage power stations. Pumped storage motor is a three-phase salient-pole synchronous motor used in pumped storage power stations. This paper simulates and analyzes the stator voltage, current and electromagnetic torque when single-phase grounding short circuit, inter-phase short circuit, and two-phase grounding short circuit occur in pumped-storage motors, and the law of change is obtained.

Application of Distribution Network Current Differential Protection Based on Ubiquitous Internet of Things in Line Selection and Location of Small Current Grounding System

In order to find the fault point of one-phase grounding in distribution network as soon as possible and prevent instantaneous fault from developing into permanent fault or inter-phase short circuit, Tongxiang Electric Power Company of Jiaxing, Zhejiang Province adopts neutral point flexible grounding system, which solves the difficulty of fault location and avoids the malpractice of frequent tripping of the system. Based on the communication mode of power wireless private network, the feasibility of implementing fast differential protection in distribution network by using improved mutation algorithm is analyzed through MATLAB simulation. Under the influence of overhead line, cable line, the first or the end of line and transition resistance in flexible grounding system, differential protection can effectively reduce the extension of fault range, improved the relay protection level of distribution electric network to meet the reliability requirements of power supply system.

Investigation Into Fault-Tolerant Capability of a Triple Redundant PMA SynRM Drive

Fault tolerant machine drives are being favored in safety critical applications, thus, they are being actively investigated. However, most of the solutions address the winding or switch open circuit only, which is insufficient since intraphase and interphase turn short circuits are more likely in the machine drives as a result of insulation degradation, and the consequences are usually catastrophic. Magnets and capacitor may also fail and cause damage during operation. All these faults should be properly addressed in fault tolerant machine drives for safety critical applications. Hence, a triple redundant, nine-phase (3 × 3 phase) permanent magnet assisted synchronous reluctance machine drive is presented by investigating the fault tolerances against various faults. The different fault behaviors are evaluated and the corresponding fault tolerant capabilities are analyzed. The machine fault tolerance is examined on a 35 kW prototype drive. Both the analysis and experimental tests demonstrate that the machine drive exhibits excellent fault-tolerant capability under most common types of faults, including the intraphase and interphase short circuit, uncontrolled rectification, demagnetization, and dc capacitor fault.

Influence of transition resistance and fault moment on DC system commutation process caused by two‐phase fault of AC system

Commutation failure caused by the fault of AC system at inverter side seriously affects the safety and stability of high-voltage direct current (HVDC) system. Although two-phase fault is a typical asymmetrical fault, the studies on commutation failure caused by two-phase fault are few compared with the studies on commutation failure caused by three-phase fault or single-phase fault. In this study, the features of two-phase fault occurring on commutation bus is analysed theoretically. The analysis shows that the transition resistance will affect the amplitude and phase of the commutation voltage at Y-Y and Y-D1 transformer valve sides. Furthermore, the change regularity of the commutation voltage along with the change of transition resistance is given. Taking interphase short circuit as an example, the influence of different fault moments on commutation process is studied. For the first commutation process before the fault, the possible cases of commutation failure are given for fault moments in one cycle. For the first commutation process after the fault, a calculation method of critical voltage drop is given. Simulation results verify the correctness of the analysis.

Research on Motor Relay Protection of High-Voltage Variable Frequency Motor Drive System

Abstract – This paper regards motor differential protection and single phase grounding protection. Firstly, this paper introduces the traditional principle and setting methods of them, and points out that the traditional relay protection device is no longer applicable under the situation of high-voltage variable frequency motor driver applications. Secondly, according to the feature that variable frequency driver runs between 0 Hz to 50 Hz, the paper analyzes the characteristics of voltage and current waveforms at different frequencies when inter-phase short circuit or single-phase grounding occurs. Based on the analyses above, the paper goes a step further to study the configuration program and setting methods of differential protection and single phase grounding protection in the situation of the high-voltage inverter drive occasions.

Backup Protection for Six-Phase Transformer Based on Six-Sequence Components

The six-phase transmission can improve the power transmission density of the transmission lines effectively, and save line corridor. To save the problem that the sensitivity of the traditional transformer backup protection is low in six-phase transmission system, a backup protection for six-phase transformer was proposed. An over-current protection criterion is proposed for interphase short circuit and opposite zero sequence over-current protection criterion is proposed for ground faults, based on the six-sequence components relationship, and the existence of six-sequence components in different fault types. Theoretical analysis and EMTDC simulation experiments prove that the scheme is feasible.

Study on Dynamic Response of Torsional Vibration of Turbo-Generator Unit Caused by Short Circuit Fault

When short circuit faults happen near power plant or generator terminal, severe transient torque shock will act on the shaft system, which seriously affects the safe and stable operation of the unit. Using the increment transfer matrix method, the dynamic responses of torsional vibrations are calculated in this work. Combined with the complex Morlet wavelet and time-frequency contour map, the time-frequency domain characters of dynamic torque are analyzed. The analyzed results show that the torque value caused by three phase short circuit fault is largest. The order of torque value from high to low is two phase short circuit to ground, two phase interphase short circuit and single phase short circuit. The electric distance between short circuit point and generator is more short, and the torsional vibration is more serious.