Some aspects of the calculation of short circuits in mine distribution networks. The calculation of the effective values of the short-circuit currents is carried out in order to determine the minimum

2020 ◽  
Vol 14 (1) ◽  
pp. 66-69
Author(s):  
V. KALINICHENKO ◽  
◽  
I. PRIDATKO ◽  
Keyword(s):  
Short Circuit ◽  
Distribution Networks ◽  
Two Phase ◽  
Cable Network ◽  
Transformer Substation ◽  
Three Phase ◽  
Short Circuits ◽  
Artificial Introduction ◽  
Short Circuit Currents ◽  
Circuit Power

The calculation of the effective values of the short-circuit currents is carried out in order to determine the minimum value of the current of the two- phase short-circuit required to select the settings of the means of protection, as well as the maximum value of the current of the three-phase short-circuit required to test the switching equipment for the ability to switch off. In most studies, the calculation of short-circuit currents is carried out only taking into account the total resistance of the transformer substation and the cable network. They also take into account the maximum short-circuit power (100MVA) due to the use of high-voltage explosion-proof switchgear type KRUV-6 without taking into account the influence of the external network. An external network, in turn, may limit the short-circuit power below 100MVA. The calculation of the short-circuit power of the external system with regard to the network parameters was considered. The actual magnitude of this capacity differs from that accepted in the known calculations and is below these values due to the natural or artificial introduction of reactor reactance and causes an error of 10-40%. Remote short-circuits of the distribution network reduce the short-circuit power of the input terminals of the step-down transformers, and therefore the influence of the external network on the short-circuit currents in the district networks increases. This approach will allow the determination of short-circuit currents in the mine distribution networks with higher accuracy. This will reduce the risk of accidents in an explosive mining environment.

scholarly journals DETERMINING A TYPE OF A DAMAGE IN THE CURRENT PROTECTION OF POWER LINES OF 6–35 KV

2017 ◽  
Vol 60 (6) ◽  
pp. 497-504 ◽  
Author(s):  
F. A. Romaniuk ◽  
E. V. Buloichik ◽  
O. A. Huryanchyk ◽  
M. A. Shevaldin
Keyword(s):  
Dynamic Properties ◽  
Short Circuit ◽  
Distribution Networks ◽  
Two Phase ◽  
Worst Case ◽  
Reliable Determination ◽  
Three Phase ◽  
Short Circuits ◽  
Current Unbalance

The methods to identify types of phase-to-phase short circuits that can be used to improve technical excellence by speed-current line protection of distribution networks of 6–35 kV are considered. As a result of the assessment of the appropriateness of their application in current protection, the choice was made in favor of the method based on the control of the relative current unbalance. The influence of contact resistances and load currents of various levels on the magnitude and character of the change of relative unbalance taking into account the errors of measuring transformers of current has been studied with the aid of the method of numerical experiment. It is demonstrated that in a lot of cases of arch short circuits in the loaded power line and in idle mode, the control only asymmetry is insufficient for reliable determination of the type of damage. A better algorithm has been proposed for determining phase-to-phase short circuit based on the control and the analysis of the two relative unbalance currents determined by the current values of the differences of the phase currents of the line. Its serviceability was evaluated. It was found out that in all the modes being considered, the proposed method – when boundary conditions are properly chosen – makes it possible to fix three-phase and two-phase short circuit on the protected line, and in the area of remote redundancy. The dynamic properties of the proposed method are investigated for different modes of the line. It is established that in the worst case, the determining of the damage is provided during the time not exceeding 25 ms.

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.

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.

Ensuring Electrical Safety of a Mountain Quarry by Choosing Selective Relay Protection in the Electrical Networks with the Voltage above 1 kV

2021 ◽  
pp. 31-37
Author(s):  
R.V. Klyuev ◽  
◽  
V.I. Golik ◽  
I.I. Bosikov ◽  
O.A. Gavrina ◽  
...  
Keyword(s):  
Short Circuit ◽  
Relay Protection ◽  
Sensitivity Coefficient ◽  
Electrical Safety ◽  
Electrical Networks ◽  
Cable Network ◽  
Urgent Task ◽  
Short Circuits ◽  
Maximum Current Protection ◽  
Short Circuit Currents

An important and urgent task is the calculation and choice of selective relay protection, which allows to ensure safe conduct of work in the conditions of mountain quarries. In the work, on the example of mountain quarry, the calculations were carried out for ensuring electrical safety of the consumers in case of emergency modes occurrence due to the appearance of short-circuit currents. At the same time, short-circuit currents in a 6 kV network, maximum current protection and current cut-off were determined, a selectivity map of protection operation was drawn up. Calculations show that with the correct protection settings, the required sensitivity coefficient is ensured in case of the short circuits at any point in the network. The selectivity map of relay protection is drawn up for a normal scheme, in which sectional switches are off at all the voltage levels. The inclusion of these switches does not affect the choice of the protection operation current, and only increases the sensitivity coefficient of the current protection and earth-fault protection. When arranging power supply schemes for the consumers, it is recommended: not to connect more than two consumers of EKG-4.6 or PKTP-400/6 type to the feeder supplying EKG-8; do not connect more than four consumers of EKG-4.6 or PKTP-400/6 type to a separate feeder; 6 kV quarry network and the boiler should be powered from different busbar sections of KRU-2 complete switchgear; it is advisable to have a cable network length of at least 5–6 km from one section of 6 kV KRU-2 busbars, which will increase the reliability of protection against single-phase earth-faults.

Two-Phase Short Circuit in the Power Grid Powered by a Transformer with a Y/Δ-11 Winding Connection

2020 ◽  
pp. 25-30
Author(s):  
Aleksandr S. Serebryakov ◽  
Vladimir L. Osokin ◽  
Sergey A. Kapustkin
Keyword(s):  
High Speed ◽  
Short Circuit ◽  
Relay Protection ◽  
Electric Circuit ◽  
Operational Reliability ◽  
Research Purpose ◽  
Industrial Complex ◽  
Two Phase ◽  
Short Circuit Currents ◽  
Secondary Winding

The article describes main provisions and relations for calculating short-circuit currents and phase currents in a three-phase traction transformer with a star-triangle-11 connection of windings, which feeds two single-phase loads in AC traction networks with a nominal voltage of 25 kilovolts. These transformers provide power to the enterprises of the agro-industrial complex located along the railway line. (Research purpose) The research purpose is in substantiating theoretical equations for digital intelligent relay protection in two-phase short circuits. (Materials and methods) It was found that since the sum of instantaneous currents in each phase is zero, each phase of the transformer works independently. We found that this significantly simplifies the task of analyzing processes with a two-phase short circuit. In this case, the problem of calculating short-circuit currents in the traction network can be simplified by reducing it to the calculation of an ordinary electric circuit with three unknown currents. (Results and discussion) The article describes equations for calculating short-circuit resistances for one phase of the transformer when connecting the secondary winding as a star or a triangle. The currents in the phases of the transformer winding at short circuit for the star-triangle-11 and star-star-with-ground schemes are compared. It was found that when calculating short-circuit currents, there is no need to convert the secondary winding of the traction transformer from a triangle to a star. (Conclusions) It was found that the results of the research can be used in the transition of relay protection systems from electromagnetic relays to modern high-speed digital devices, which will increase the operational reliability of power supply systems for traction and non-traction power consumers.

scholarly journals Complex Electronic Protection for Low-voltage Three-phase Induction Motors

2020 ◽  
Vol 11 ◽  
pp. 11-17
Author(s):  
Gabriel Nicolae Popa ◽  
Corina Maria Diniș
Keyword(s):  
Induction Motors ◽  
Low Voltage ◽  
Short Circuit ◽  
Electronic Devices ◽  
General Purpose ◽  
Two Phase ◽  
Dc Voltage ◽  
Electric Drives ◽  
Normal Limits ◽  
Three Phase

Low-voltage three-phase induction motors are most often used in industrial electric drives. Electric motors must be protected by electric and/or electronic devices against: short-circuit, overloads, asymmetrical currents, two-phase voltage operation, under-voltage, and over-temperature. To design the electronic protection currents, voltages and temperature must be measured to determine whether they fall within normal limits. The electronic protection was design into low capacity PLC. The paper presents the designs and analysis of complex electronic protection for general purpose low-voltage three-phase induction motors. The electronic protection has Hall transducers and conversion electronic devices for AC currents to DC voltages, AC voltages to DC voltage, temperature to DC voltage, a low capacity PLC, switches, motor’s power contactors, and signalling lamps has been developed. Experiments with complex electronic protection, for different faults are presented. The proposed protection has the advantages of incorporating all usual protections future for the low-voltage three-phase induction motors.

ENGINEERING ANALYSIS OF THE THREE-PHASE SHORT CIRCUIT MODE IN THE 10 KV ELECTRIC NETWORK TAKING INTO ACCOUNT THE INFLUENCE OF LOAD CURRENTS

2021 ◽  
pp. 74-83
Author(s):  
YURI D. VOLCHKOV ◽  
Keyword(s):  
Remote Monitoring ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Load Current ◽  
Electric Network ◽  
Operating Modes ◽  
Three Phase ◽  
Feed Network ◽  
Short Circuits ◽  
Switching Devices

Abstract. The load current aff ects the value of the short-circuit current in the electric network and, consequently, the voltage value. In some cases, this infl uence must be taken into account for the correct choice of switching devices, remote monitoring the operating modes of electric networks, and determining the modes. It is possible to disconnect loads connected through magnetic starters and contactors. Failure to consider the infl uence of the load current can lead to an incorrect interpretation of the identifi ed grid operating modes during remote monitoring and, as a result, incorrect dispatcher’s decisions. In addition, it is also insuffi cient to specify the choice of switching devices in the 10 kV feed network. The article describes a method for analyzing the three-phase short circuit mode in a 10 kV feed network, taking into account the infl uence of load currents. The method is exemplifi ed by the case of an actual electric network – the 10 kV ring feed network containing reclosers and receiving power from diff erent sections of lowvoltage buses of the “Kulikovskaya” 110/35/10 kV substation, belonging to the Branch of PJSC «DGC of Center”-“Orelenergo.” For this network, the values of the three-phase short-circuit currents at points with diff erent distances from the substation buses have been determined. The authors have fi guredout the values of the load currents and their shares in the total short-circuit current. The voltage values at different points of the network in the case of short circuits have also been determined. The research proves that the effect of the load current on the total short-circuit current should be taken into account for the case of remote short circuits.

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