scholarly journals Short circuit fire risk assessment in investigating and examining fires caused by emergency modes in overhead transmission lines

2022 ◽  
Vol 6 (4) ◽  
pp. 363-368
Author(s):  
Yu. S. Kozlova
Keyword(s):  
Transmission Lines ◽  
Fire Hazard ◽  
Short Circuit ◽  
Electric Power System ◽  
Ignition Source ◽  
Electrical Network ◽  
Fuel Load ◽  
Overhead Transmission Lines ◽  
Protection Devices ◽  
Short Circuits

Emergency modes (short circuits) in electric power system and equipment are the main technical cause of fires. However, it is not always possible to prove the involvement of a particular operating mode in a fire. The fire hazard can be due to three components: a fuel load, an oxidizer and an ignition source. Since overhead transmission lines are used in an open space, they are oxidized. The presence of a fuel load is confirmed by a fire. The source of ignition should be identified. The aim of the study is to develop an algorithm for assessing the fire hazard for short circuits in overhead transmission lines with 1000 V. The study was conducted using scientific analysis, physical experiment and simulation. The ignition source is due to the appearance of an energy source with parameters sufficient to ignite a fuel load. The probability of ignition in overhead line wires depends on the probability of occurrence of the short circuit itself  ( Qi (v1) ) , the probability of failure of protection devices  ( Qi (v2) ), and the probability that the electric current value in the event of a fault is in the range of fire hazard values (Qi(z)). The values of the first two components are determined on the basis of statistical data, taking into account the theory of reliability. The third component is based on the experiment results. The experimental studies made it possible to establish the ranges of fire hazard values for uninsulated aluminum wires of various cross-sections, thereby providing the possibility of calculating ( Qi (z). Using the data obtained and information about the nature of changes in short-circuit currents and performance characteristics of protection devices, depending on the line length, an algorithm for assessing the fire hazard for a short circuit was developed. The results make it possible to assess the fire hazard for short circuits in various sections of the electrical network, made by overhead transmission lines, and to establish the involvement of sparks generated by short circuits in a fire

scholarly journals An Optimized Coordination Strategy between Line Main Protection and Hybrid DC Breakers for VSC-Based DC Grids Using Overhead Transmission Lines

Energies ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1462 ◽  
Author(s):  
Zheng ◽  
Jia ◽  
Gong ◽  
Zhang ◽  
Pei
Keyword(s):  
Transmission Lines ◽  
Power Transmission ◽  
Short Circuit ◽  
Power Grids ◽  
Fault Line ◽  
Long Distance ◽  
Coordination Strategy ◽  
Overhead Transmission Lines ◽  
Depth Analysis ◽  
Dc Breaker

Compared with alternating current (AC) power grids, the voltage-sourced converter (VSC)-based direct current (DC) grid is a system characterized by “low damping”, as a result, once there is a short-circuit fault on the DC transmission line, the fault current will rise more sharply and the influence range will be much wider within the same time scale. Moreover the phenomenon that a local fault causes a whole power grid outage is more likely to occur. Overhead transmission lines (OHLs) have been regarded as the mainstream form of power transmission in future high-voltage, large-capacity and long-distance VSC-based DC grids. However, the application of overhead transmission lines will inevitably lead to a great increase in the probability of DC line failure. Therefore, research on how to isolate the DC fault line quickly is of great significance. Based on the technology route for fault line isolation using DC breakers, on the basis of in-depth analysis of traditional coordination strategy, an optimized coordination strategy between line main protection and a hybrid DC breaker for VSC-based DC grids using overhead transmission lines is proposed in this paper, which takes the start-up output signal of line main protection as the pre-operation instruction of the corresponding hybrid DC breaker. As a result, the risks of blockage of the modular multilevel converter (MMC) closer to the fault position and of damage to power electronic devices in main equipment can be reduced effectively. Finally, the proposed coordination strategy was verified and analyzed through simulation.

Short circuits currents comparison of 6 (10) kV and 20 kV.

2020 ◽  
Vol 14 (1) ◽  
pp. 21-26
Author(s):  
S. SKRYPNYK ◽  
◽  
A. SHEINA ◽  
Keyword(s):  
Power System ◽  
Transmission Line ◽  
Transmission Lines ◽  
Power Supply ◽  
Short Circuit ◽  
Electric Arc ◽  
Electrical System ◽  
Three Phase ◽  
Short Circuits ◽  
Short Circuit Currents

Most failures in electrical installations are caused by short circuits (short circuits), which occur as a result of a failure in the electrical strength of the insulation of the conductive parts. A short circuit is an electrical connection of two points of an electric circuit with different values of potential, which is not provided by the design of the device, which interferes with its normal operation. Short circuits may result from a failure of the insulation of the current-carrying elements or the mechanical contact of the non- insulated elements. Also called a short circuit is a condition where the load resistance is less than the internal resistance of the power source. The reasons for such violations are various: aging of insulation, breakages of wires of overhead transmission lines, mechanical damages of isolation of cable lines at ground works, lightning strikes in the transmission line and others. Most often, short-circuits occur through transient resistance, such as through the resistance of an electric arc that occurs at the point of damage to the insulation. Sometimes there are metallic short circuits in which the resistance of the electric arc is very small. The study of short circuits in the power grid is a major step in the design of modern electrical networks. The research is conducted using computer software, first by modeling the system and then simulating errors. A malfunction usually leads to an increase in the current flowing in the lines, and failure to provide reliable protection can result in damage to the power unit. Thus, short-circuit calculations are the primary consideration when designing, upgrading, or expanding a power system. The three-phase short circuit is the least likely. However, in many cases, the three-phase short circuit is associated with the most severe consequences, as it causes the highest power imbalances on the shafts of the generators. The study of transients begins with the mode of three-phase closure due to its relative simplicity in comparison with other types of asymmetry. In most cases, the analysis and calculation of the transient regime of the electrical system involves the preparation of a calculated scheme of substitution, in which the parameters of its elements are determined in named or relative units. The electrical substitution circuitry is used to further study the transients in the power system. The definition of electrical and electromagnetic quantities in relative units is widely used in the theory of electric machines. This is because it significantly simplifies the theoretical calculations and gives the results a generalized view in the practical calculations of currents and residual voltages at the short circuit. By the relative value of any value is understood as its relation to another value of the same name, taken as the base. So, before presenting any quantities in relative units, we need to choose the basic units. In the electrical system with increased voltages, the overall load capacity of the network increases, which in turn makes it possible to supply high-quality electrical energy over a greater distance. In the process of comparing the type of transmission lines, it should be noted that the advantages of the cable transmission line. According to the results of the calculation of short-circuit currents, it can be concluded that in networks with a larger line cross-section and a higher voltage, the short-circuit currents are larger. Thus, during the transition of the electric networks to the higher voltage class of 20 kV, the currents of the KZ increased by 43% compared to the 6 kV electric network. This analysis shows that the importance of reliable power supply in the power supply system for high voltage classes must be high and have equipment to prevent emergencies. In the future, it is planned to develop a systematic calculation of short-circuit currents for a number of transmission lines and to conduct mathematical modeling in the system of applications for the study of transient processes at short circuits.

Grounding Connections

2018 ◽  
pp. 84-123
Keyword(s):  
Transmission Lines ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Power Sources ◽  
Grounding Resistance ◽  
Overhead Transmission Lines ◽  
Ground Fault ◽  
Multiple Power

This chapter sheds light on the following: TT system (earthed neutral), automatic disconnection for TT system, TN system (exposed conductive parts connected to the neutral), TN-C system, TN-S system- TN-C-S system, IT system (isolated or impedance-earthed neutral), IT system (impedance-earthed neutral), grounding transformer connection and design, grounding of industrial and commercial generators, Zigzag grounding transformer earthed systems (solid grounding, resistance grounding, reactance grounding, resonant grounding (ground-fault neutralizer), location of system grounding points selection and grounding locations specified by the NEC and multiple power sources. The chapter contains also the different methods used in determining the levels of short circuit current. It contains also details about the grounding through resistances for transformers and generators and reactances for overhead transmission lines.

Investigation of dependences of selectivity of devices of protection against the value of short circuit currents in electrical networks up to 1000 V

2021 ◽  
pp. 98-100
Author(s):  
I. Radko ◽  
◽  
V. Nalivayko ◽  
O. Okushko ◽  
I. Bolbot ◽  
...  
Keyword(s):  
Single Phase ◽  
Modular Design ◽  
Short Circuit ◽  
Electrical Network ◽  
Electrical Networks ◽  
Circuit Breakers ◽  
New Energy ◽  
Short Circuits ◽  
Pole Scheme ◽  
Short Circuit Currents

According to PUE-2017, each group line must be protected against short circuits. Instant disconnection (cut-off) of the line in the event of short circuits provides an electromagnetic release of the circuit breaker. Reliable tripping is possible if the current of a single-phase short circuit is greater than the instantaneous tripping current. Today on the market are widely available circuit breakers with characteristics "B", "C" and "D", which are characterized by different multiplicities of the cut-off current of the electromagnetic release. Some European companies produce circuit breakers with other characteristics, which greatly expands the possibilities protection of electrical equipment. The difficulty in organizing the selectivity of protection is that the circuit breakers of modular design when switching off short circuits are characterized by the same switching time (not more than 0.05 s). The purpose of the research is to find ways to organize the selectivity of protection in electrical networks with voltage up to 1000 V using reliable values of short-circuit currents. In networks with a voltage of up to 1000 V, the current of a single-phase short circuit can be calculated fairly accurately if the exact values of all sections of the electrical network are known. In practice, it is not always possible to obtain reliable data on the numerical characteristics of the 0.4 kV network to which a new energy facility is connected. Therefore, it is proposed to consider part of the network as an active quadrupole, the characteristics of which are obtained by measurements at the point of connection. For further calculations it is necessary to know the voltage at the clamps of the four-pole scheme and the internal impedance. Based on the theory of four-pole scheme, you can get the original data for calculations without calculating the internal parameters of four-poles scheme. Thus, it is proposed to use a hybrid method for estimating the magnitude of probable short-circuit currents in electrical networks up to 1000 V when designing new energy facilities. Credible values of short-circuit currents will allow to organize selective protection of electric networks.

On the Problem of Selecting and Replacing Current Transformers for Relay Protection Devices

2020 ◽  
Vol 63 (6) ◽  
pp. 72-82
Author(s):  
Stanislav Kuzhekov ◽  
◽  
Andrey Degtyarev ◽  
Nikolay Doni ◽  
Aleksey Shurupov ◽  
...  
Keyword(s):  
Power Systems ◽  
High Speed ◽  
Short Circuit ◽  
Relay Protection ◽  
Electric Power Systems ◽  
Current Transformers ◽  
Magnetic Cores ◽  
Protection Devices ◽  
Short Circuits ◽  
The Stability

In connection with cases of incorrect operation of high-speed relay protection devices (RPD) in case of short circuits outside their range, the issue of replacing current transformers (CT) of class P with more ad-vanced current converters is relevant. The article shows that the decision to replace existing class P CTs with CTs with a non-magnetic gap should be made taking into account the probability of saturation of the magnetic cores of the latter in a transient short-circuit mode, as well as an increase in their dimensions compared to class P CTs. The issue of using optoelectronic current converters should be resolved after the latter are put into mass production, taking into account the difficulty of integrating the latter with the RPDs implemented using an Electromechanical base. In many cases, the correct functioning of high-speed RPDs without replacing existing CTs of class P can provide the following measures: the use of algorithms that increase the stability of the oper-ation of high-speed RPDs when the CT is saturated; taking into account in the calculations of the settings the rectangular characteristic of the CT magnetization in transient modes and the permissible deceleration of pro-tections under the condition of the dynamic stability of electric power systems; refusal to use CT connection groups (physical sum of currents, delta and star).

scholarly journals The Short-Circuit Protections in Hybrid Systems with Low-Power Synchronous Generators

Energies ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 160
Author(s):  
Bartosz Rozegnał ◽  
Paweł Albrechtowicz ◽  
Dominik Mamcarz ◽  
Natalia Radwan-Pragłowska ◽  
Artur Cebula
Keyword(s):  
Single Phase ◽  
Low Voltage ◽  
Short Circuit ◽  
Circuit Breaker ◽  
Synchronous Generator ◽  
Synchronous Generators ◽  
Electrical Systems ◽  
Protection Devices ◽  
Short Circuits ◽  
Damage Type

Single-phase short-circuits are most often faults in electrical systems. The analysis of this damage type is taken for backup power supply systems, from small power synchronous generators. For these hybrid installations, there is a need for standard protection devices, such as fuses or miniature circuit breaker (MCB) analysis. Experimental research mentioned that a typical protective apparatus in low-voltage installations, working correctly during supplying from the grid, does not guarantee fast off-switching, while short-circuits occur during supplication from the backup generator set. The analysis of single-phase short-circuits is executed both for current waveform character (including sub-transient and transient states) and the carried energy, to show the problems with the fuses and MCB usage, to protect circuits in installations fed in a hybrid way (from the grid and synchronous generator set).

The UHVDC Transmission Line Lightning Disturbance Identification Based on the Morphology

2014 ◽  
Vol 1008-1009 ◽  
pp. 603-609
Author(s):  
Rui Rui Cao ◽  
Ju Rui Yang
Keyword(s):  
Transmission Lines ◽  
Short Circuit ◽  
Low Frequency ◽  
Transient State ◽  
Spectral Energy ◽  
Complex Signal ◽  
Main Criterion ◽  
Lightning Stroke ◽  
Multi Scale ◽  
Overhead Transmission Lines

Research and identify overhead transmission lines’ transient characteristic which was caused by lightning stroke is significant to develop the protection and improving its reliability based on transient state. A complex signal can be resolved into several parts which have respective physical meanings by mathematical morphology’s multi-scale decomposition and this can reveal the local features of waves. Therefore, the transient current of ±800 kV UHVDC transmission lines, caused by the non-fault lightning stroke, fault lightning stroke and other line short circuit, can be decomposed by the multi-scale morphology decomposition to extract the spectral energy from the high and the low frequency bands, and the ratio of those two spectrum energy forms main criterion to realize the identification between lightening disturbance and the fault states. According to the ratio of the maximum of the current’s amplitudes of decomposition waveform of the first head of current’s second scale and sixth scale, to further distinguish the lightning stroke fault from the line short circuit. Extensive simulations show that the approach is correct and effective.

scholarly journals Effect of Distributed Photovoltaic Generation on Short-Circuit Currents and Fault Detection in Distribution Networks: A Practical Case Study

2021 ◽  
Vol 11 (1) ◽  
pp. 405
Author(s):  
Daniel Alcala-Gonzalez ◽  
Eva Maria García del Toro ◽  
María Isabel Más-López ◽  
Santiago Pindado
Keyword(s):  
Renewable Energy ◽  
Radial Distribution ◽  
Short Circuit ◽  
Renewable Energy Sources ◽  
Distribution Network ◽  
Distribution Networks ◽  
Energy Sources ◽  
Protection Devices ◽  
Short Circuits ◽  
Short Circuit Currents

The increase in the installation of renewable energy sources in electrical systems has changed the power distribution networks, and a new scenario regarding protection devices has arisen. Distributed generation (DG) might produce artificial delays regarding the performance of protection devices when acting as a result of short-circuits. In this study, the preliminary research results carried out to analyze the effect of renewable energy sources (photovoltaic, wind generation, etc.) on the protection devices of a power grid are described. In order to study this problem in a well-defined scenario, a quite simple distribution network (similar to the ones present in rural areas) was selected. The distribution network was divided into three protection zones so that each of them had DG. In the Institute of Electrical and Electronic Engineers (IEEE) system 13 bus test feeder, the short-circuits with different levels of penetration were performed from 1 MVA to 3 MVA (that represent 25%, 50%, and 75% of the total load in the network). In the simulations carried out, it was observed that the installation of DG in this distribution network produced significant changes in the short-circuit currents, and the inadequate performance of the protection devices and the delay in their operating times (with differences of up to 180% in relation to the case without DG). The latter, that is, the impacts of photovoltaic DG on the reactions of protection devices in a radial distribution network, is the most relevant outcome of this work. These are the first results obtained from a research collaboration framework established by staff from ETSI Civil and the IDR/UPM Institute, to analyze the effect of renewable energy sources (as DG) on the protection devices of a radial distribution network.

Adaptive restart scheme based on active injection current ratio for half-bridge MMC-HVDC with overhead transmission lines

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Jingru Zhang ◽  
Baina He ◽  
Renzhuo Jiang ◽  
Xingmin He ◽  
Yanchen Dong ◽  
...  
Keyword(s):  
Transmission Lines ◽  
Short Circuit ◽  
Stable Operation ◽  
Multilevel Converter ◽  
Dc System ◽  
Critical Segment ◽  
Protection Devices ◽  
Suppression Strategy ◽  
Auxiliary Module ◽  
Action Decision

Abstract Modular multilevel converter for high voltage DC system has great potential as the key role in global energy interconnection. Adaptive reclosing or restarting after suffering from short-circuit faults is a critical segment to realize safe and stable operation. An adaptive restart scheme for the half-bridge sub-module transmission system is proposed, which is based on the active current injection of the auxiliary fault discriminate module. Combined with the engineering experience, the transient characteristics of the line current during the fault restart stage are analyzed. The ratio of the current peaks at both ends of the fault point is used as the criterion. Moreover, the restart current suppression strategy is introduced into the adaptive restart scheme. It provides a decision-making basis for discriminate the property of the fault and improves the success rate of fault restart. The simulation results show that after the external auxiliary module is introduced into the adaptive restart stage, the restart current does not exceed the rated value. Finally, The permanent fault and the transient fault can be successfully distinguished, providing a reliable guarantee for the subsequent action decision of the protection devices.

Sign in / Sign up

Export Citation Format

Share Document