1. Harmonic blocking differential protection, which is widely used to protect converter transformers in HVDC systems, may fail to operate during internal faults of the converter transformer.
2. Simulation results showed that an internal phase-to-ground fault on the DC side induced a heavy DC component in the fault current that caused half-cycle saturation of the transformer.
3. This half-cycle saturation resulted in a significant increase in the second harmonic content of the differential current, triggering incorrect blocking of the differential protection despite a genuine internal fault.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
1. Ground Fault Protection (GFP) devices are used to protect electrical installations from fire risks by quickly detecting insulation faults.
2. GFP devices operate by measuring residual fault currents, which involves monitoring the vector sum of all live conductor currents and tripping the circuit if it exceeds the device's threshold.
3. Standards like IEC 60 364 and the National Electrical Code (NEC) require the use of GFP or Residual Current Devices (RCD) depending on the earthing system, with the NEC specifying very low sensitivity GFP devices for North American TN-S systems to address fire risks from potential high fault currents.
The Continuity of power supply that is reliability of power supply is highly essential for the
development of the country. The electric power is distributed to the consumers through electrical network.
The study involves the analysis of various obstacles for reliable power supply, interruption in electric
power distribution due to defects in relays and circuit. Cost benefit by the prevention and reliability in
power supply.
Transient recovery voltage is a high frequency voltage that appears across circuit breaker contacts immediately after the electrical arc is extinguished due to the contacts being close together. This transient recovery voltage tries to restrike the arc and causes high dielectric stress between the contacts, which can lead to arc restrike if the stress is too low.
This document discusses inrush current in power transformers. It provides calculations and typical values for inrush current parameters such as peak value, wave shape, energy parameter, and maximum di/dt. It also examines the effect of transformer design parameters like the number of phases, winding connection, size, core material, geometry, design induction, and joint type on inrush current values. General equations are presented for calculating inrush current waveform based on factors like applied voltage, impedance, energization angle, and core material properties.
Transient Recovery Voltage(TRV) in Interruption of Small Inductive Currents b...Ali Sepehri
Transient Recovery Voltage(TRV) in Interruption of Small Inductive Currents by Circuit Breakers.
Article 5(01.10.2018) direct link: https://lnkd.in/gXe3Qbr
1) Voltage sags and interruptions are usually caused by faults on the power system and switching events to isolate faults. They are characterized by reductions in RMS voltage outside normal operating ranges.
2) A voltage sag is a short-term reduction in voltage lasting 0.5 to 30 cycles. A momentary interruption causes a complete loss of voltage for 2 to 5 seconds. Sustained interruptions last over 1 minute.
3) Utilities face more complaints about power quality due to sensitive electronic loads in customers' facilities. Sags and interruptions can cause processes and equipment to malfunction or restart, costing industries productivity.
Out of phase current switching in High Voltage Circuit BreakersAli Sepehri
Out-of-phase switching occurs when two power systems or a generator and power system are connected with a phase angle difference between their voltages. This causes out-of-phase currents that a circuit breaker must interrupt. The transient recovery voltage (TRV) under out-of-phase conditions has a very high peak but moderate rate of rise and current. Examples where out-of-phase switching may occur include accidentally connecting a generator at the wrong phase angle or two power systems losing synchronization due to a fault. Proper protection, synchronization, and circuit breaker design are needed to safely handle out-of-phase switching conditions.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
1. Ground Fault Protection (GFP) devices are used to protect electrical installations from fire risks by quickly detecting insulation faults.
2. GFP devices operate by measuring residual fault currents, which involves monitoring the vector sum of all live conductor currents and tripping the circuit if it exceeds the device's threshold.
3. Standards like IEC 60 364 and the National Electrical Code (NEC) require the use of GFP or Residual Current Devices (RCD) depending on the earthing system, with the NEC specifying very low sensitivity GFP devices for North American TN-S systems to address fire risks from potential high fault currents.
The Continuity of power supply that is reliability of power supply is highly essential for the
development of the country. The electric power is distributed to the consumers through electrical network.
The study involves the analysis of various obstacles for reliable power supply, interruption in electric
power distribution due to defects in relays and circuit. Cost benefit by the prevention and reliability in
power supply.
Transient recovery voltage is a high frequency voltage that appears across circuit breaker contacts immediately after the electrical arc is extinguished due to the contacts being close together. This transient recovery voltage tries to restrike the arc and causes high dielectric stress between the contacts, which can lead to arc restrike if the stress is too low.
This document discusses inrush current in power transformers. It provides calculations and typical values for inrush current parameters such as peak value, wave shape, energy parameter, and maximum di/dt. It also examines the effect of transformer design parameters like the number of phases, winding connection, size, core material, geometry, design induction, and joint type on inrush current values. General equations are presented for calculating inrush current waveform based on factors like applied voltage, impedance, energization angle, and core material properties.
Transient Recovery Voltage(TRV) in Interruption of Small Inductive Currents b...Ali Sepehri
Transient Recovery Voltage(TRV) in Interruption of Small Inductive Currents by Circuit Breakers.
Article 5(01.10.2018) direct link: https://lnkd.in/gXe3Qbr
1) Voltage sags and interruptions are usually caused by faults on the power system and switching events to isolate faults. They are characterized by reductions in RMS voltage outside normal operating ranges.
2) A voltage sag is a short-term reduction in voltage lasting 0.5 to 30 cycles. A momentary interruption causes a complete loss of voltage for 2 to 5 seconds. Sustained interruptions last over 1 minute.
3) Utilities face more complaints about power quality due to sensitive electronic loads in customers' facilities. Sags and interruptions can cause processes and equipment to malfunction or restart, costing industries productivity.
Out of phase current switching in High Voltage Circuit BreakersAli Sepehri
Out-of-phase switching occurs when two power systems or a generator and power system are connected with a phase angle difference between their voltages. This causes out-of-phase currents that a circuit breaker must interrupt. The transient recovery voltage (TRV) under out-of-phase conditions has a very high peak but moderate rate of rise and current. Examples where out-of-phase switching may occur include accidentally connecting a generator at the wrong phase angle or two power systems losing synchronization due to a fault. Proper protection, synchronization, and circuit breaker design are needed to safely handle out-of-phase switching conditions.
Protection of transmission lines (distance)Rohini Haridas
This gives idea about necessity of protection of transmission line and protection based on time grading as well as on current grading. Also includes three step distance protection of transmission line
Voltage Escalation in Shunt Reactor Switching in Circuit BreakersAli Sepehri
Voltage Escalation in Shunt Reactor
Switching in Circuit Breakers
Article direct link: https://www.linkedin.com/pulse/voltage-escalation-shunt-reactor-switching-circuit-breakers-sepehri/
Inrush current reduction in three phase power transformer by using prefluxing...IAEME Publication
This document discusses reducing inrush current in power transformers. It begins by introducing transformers and explaining that inrush current can be up to 10 times the nominal current and cause issues. One method to reduce inrush current is point-on-wave switching, which controls energization based on residual flux. However, measuring residual flux is difficult. The paper proposes a prefluxing technique which sets the initial flux in the transformer before energization using controlled switching. It models a 300MVA, 11/400kV transformer in MATLAB and compares inrush current reduction using point-on-wave switching and prefluxing. The aim is to minimize the peak inrush current and reach steady state current faster.
This document discusses power system protection schemes, including:
- Zones of protection with protective relays coordinated between zones
- Attributes of reliable, selective, and fast relaying
- Fault clearing times of relays and circuit breakers
- Protection of system components like feeders, transmission lines, transformers, generators
It provides examples of overcurrent protection design using time-graded and current-graded discrimination. Directional relays, differential protection, and power line carrier communication are also summarized.
The document discusses voltage sags and interruptions. It covers sources of sags and interruptions such as faults in the distribution system. Methods to estimate voltage sag performance and mitigate sags are described, including reducing faults, improving fault clearing time, modifying the supply system, and using voltage stabilizers. Active series compensators and static transfer switches are discussed as technologies to improve power quality during sags. Ferroresonant transformers can handle most sag conditions by maintaining nearly constant output voltage.
This document discusses transformer inrush current and its impact on differential relays. Transformer inrush occurs when the flux in the transformer core needs to be established, causing a large magnetizing current to flow. This inrush current appears as a differential current that can cause misoperation of transformer differential relays. The document examines characteristics of inrush current like the switching point, remnant flux, system impedance, and transformer design. It also discusses various harmonic-based methods for restraining differential relays during inrush like percentage of total harmonic, percentage of 2nd harmonic, and adaptive 2nd harmonic methods. The considerations for applying these methods include reliability, security, and speed of operation.
Protection of lines
Overcurrent Protection schemes
PSM, TMS
Numerical examples
Carrier current and three-zone distance relay using impedance relays
Protection of bus bars by using Differential protection
Edwin Newsletter on transformer failures on 13 October 2015Edwin Low
The document discusses transformer failures and their investigation. It provides details on transformer types, components, and typical tests conducted during failure analysis. Two specific failure cases are described:
1) A dry transformer in a wind turbine failed during commissioning due to a manufacturing defect - a conductive winding turn was displaced and overlapped another turn, causing arcing during energization.
2) An oil-filled transformer failed due to inadequate mechanical strength holding the winding turns. An external fault caused electromechanical forces, displacing windings and exposing conductors between turns, leading to arcing at multiple points. The root cause was a manufacturing defect in the winding assembly.
Transients can cause slow degradation, erratic operation, or catastrophic failure in electrical parts, insulation dielectrics, and electrical contacts used in switches and relays. The possible occurrence of transients must be considered in the overall electronic design. Required circuit performance and reliability must be assured both during and after the transient
This document provides an overview of transformer asset management (TAM). It discusses that TAM focuses on reliability, risk management, and optimizing lifecycle costs for power transformers. A key part of TAM is developing a Transformer Asset Management Plan (TAMP) that qualitatively assesses transformer condition, risks of extended use, and an effective inventory strategy. Condition monitoring and testing are important to assess transformer health and aging. Asset management tools help calculate expected lifetime based on loading and usage. Procuring spare transformers requires evaluating repair costs, load demands, and risks to minimize outages and losses.
This document discusses improving the low voltage ride-through (LVRT) capability of doubly fed induction generator (DFIG)-based wind turbines using a dynamic voltage restorer (DVR). During faults, voltage dips can cause overcurrent and overvoltage in the DFIG rotor circuit if not compensated. The DVR is proposed to inject compensating voltage and prevent rapid changes in the stator voltage, allowing the rotor side converter to operate normally. Both symmetrical and asymmetrical voltage dips are investigated. Simulations using PSCAD/EMTDC verify the DVR approach improves the DFIG's LVRT capability with benefits of independent phase voltage compensation, lower volume, weight and cost compared to other solutions.
Transformer Diagnostics | Sweep Frequency Response AnalysisHamedPasha1
Proper commissioning and periodic testing of high voltage equipment is vital to the longevity of your valuable assets. Research shows that improper commissioning along with “set-and-forget” mentality has been the leading causes of premature failures.
Sweep frequency response analysis (SFRA) is one of the most powerful diagnostic tools for assessing mechanical damage to a transformer winding. Analysis of the results, which are in the form of frequency response traces can, however, be daunting to new users.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
The document describes the simulation and design of a differential relay. It discusses various types of differential protection including current, biased, and voltage balance differential relays. It also covers the application of differential protection for an alternator, including the operating principles under normal, external fault, and internal fault conditions. Biased differential protection is described as a method to prevent operation during external faults that could cause CT saturation. The project involves simulating a differential relay using Multisim software and implementing the design in hardware.
protection of transmission lines[distance relay protection scheme]moiz89
The document discusses various aspects of transmission line protection including classification of transmission lines, types of faults, protection schemes, requirements of distance protection, over current protection, phase comparison protection, and distance protection schemes. It also covers autoreclose philosophy, power swings, fuse failure function, and other protection functions.
This document analyzes very fast transient overvoltages (VFTOs) in transformers in 400kV gas insulated substations (GIS) using wavelet transforms. It presents a model of a three-phase, two-winding transformer designed in MATLAB Simulink to simulate VFTOs generated by circuit breaker operations under open and closing conditions. Wavelet transform analysis is applied to the results to investigate suppression of overvoltage magnitudes and resonant frequency amplitudes. The analysis shows the proposed technique provides high accuracy in mitigating VFTOs using wavelet transforms.
SWICTH GEAR AND PROTECTION (2170906)
DISTANCE RELAY
• There are mainly Three types of distance relay
1) Impedance Relay
2) Reactance Relay
3) Mho Relay
The document discusses the theory of circuit interruption in power systems. It begins by introducing circuit breakers, which can manually or automatically open a circuit under normal or fault conditions. When contacts within a circuit breaker open under a fault, an arc is produced that must be extinguished to interrupt current flow. There are two main methods for extinguishing arcs: the high resistance method, which lengthens and cools the arc to increase its resistance over time; and the low resistance or current zero method, used for AC circuits, which maintains a low resistance arc until current reaches zero to naturally extinguish the arc.
1. A fuse element melts when current exceeds its rating, opening the circuit.
2. Fuses are rated based on their current and time-current characteristics to provide coordinated protection across a system.
3. Proper fuse selection and coordination is necessary to clear faults while preventing unnecessary operations and minimizing stress on system components.
This document summarizes a research paper that proposes a microcontroller-based system to monitor and protect electric distribution transformers. The system would detect faults like single line-ground faults, line-to-line faults, double line-ground faults, overvoltage, and undervoltage. It would send fault alerts via GSM network to a control station. A user interface using MATLAB would display the distribution system status. The aim is to minimize equipment damage from faults and improve power distribution monitoring and management. Key components include step-down transformers, a microcontroller, GSM module, and bridge rectifier.
Protection of transmission lines (distance)Rohini Haridas
This gives idea about necessity of protection of transmission line and protection based on time grading as well as on current grading. Also includes three step distance protection of transmission line
Voltage Escalation in Shunt Reactor Switching in Circuit BreakersAli Sepehri
Voltage Escalation in Shunt Reactor
Switching in Circuit Breakers
Article direct link: https://www.linkedin.com/pulse/voltage-escalation-shunt-reactor-switching-circuit-breakers-sepehri/
Inrush current reduction in three phase power transformer by using prefluxing...IAEME Publication
This document discusses reducing inrush current in power transformers. It begins by introducing transformers and explaining that inrush current can be up to 10 times the nominal current and cause issues. One method to reduce inrush current is point-on-wave switching, which controls energization based on residual flux. However, measuring residual flux is difficult. The paper proposes a prefluxing technique which sets the initial flux in the transformer before energization using controlled switching. It models a 300MVA, 11/400kV transformer in MATLAB and compares inrush current reduction using point-on-wave switching and prefluxing. The aim is to minimize the peak inrush current and reach steady state current faster.
This document discusses power system protection schemes, including:
- Zones of protection with protective relays coordinated between zones
- Attributes of reliable, selective, and fast relaying
- Fault clearing times of relays and circuit breakers
- Protection of system components like feeders, transmission lines, transformers, generators
It provides examples of overcurrent protection design using time-graded and current-graded discrimination. Directional relays, differential protection, and power line carrier communication are also summarized.
The document discusses voltage sags and interruptions. It covers sources of sags and interruptions such as faults in the distribution system. Methods to estimate voltage sag performance and mitigate sags are described, including reducing faults, improving fault clearing time, modifying the supply system, and using voltage stabilizers. Active series compensators and static transfer switches are discussed as technologies to improve power quality during sags. Ferroresonant transformers can handle most sag conditions by maintaining nearly constant output voltage.
This document discusses transformer inrush current and its impact on differential relays. Transformer inrush occurs when the flux in the transformer core needs to be established, causing a large magnetizing current to flow. This inrush current appears as a differential current that can cause misoperation of transformer differential relays. The document examines characteristics of inrush current like the switching point, remnant flux, system impedance, and transformer design. It also discusses various harmonic-based methods for restraining differential relays during inrush like percentage of total harmonic, percentage of 2nd harmonic, and adaptive 2nd harmonic methods. The considerations for applying these methods include reliability, security, and speed of operation.
Protection of lines
Overcurrent Protection schemes
PSM, TMS
Numerical examples
Carrier current and three-zone distance relay using impedance relays
Protection of bus bars by using Differential protection
Edwin Newsletter on transformer failures on 13 October 2015Edwin Low
The document discusses transformer failures and their investigation. It provides details on transformer types, components, and typical tests conducted during failure analysis. Two specific failure cases are described:
1) A dry transformer in a wind turbine failed during commissioning due to a manufacturing defect - a conductive winding turn was displaced and overlapped another turn, causing arcing during energization.
2) An oil-filled transformer failed due to inadequate mechanical strength holding the winding turns. An external fault caused electromechanical forces, displacing windings and exposing conductors between turns, leading to arcing at multiple points. The root cause was a manufacturing defect in the winding assembly.
Transients can cause slow degradation, erratic operation, or catastrophic failure in electrical parts, insulation dielectrics, and electrical contacts used in switches and relays. The possible occurrence of transients must be considered in the overall electronic design. Required circuit performance and reliability must be assured both during and after the transient
This document provides an overview of transformer asset management (TAM). It discusses that TAM focuses on reliability, risk management, and optimizing lifecycle costs for power transformers. A key part of TAM is developing a Transformer Asset Management Plan (TAMP) that qualitatively assesses transformer condition, risks of extended use, and an effective inventory strategy. Condition monitoring and testing are important to assess transformer health and aging. Asset management tools help calculate expected lifetime based on loading and usage. Procuring spare transformers requires evaluating repair costs, load demands, and risks to minimize outages and losses.
This document discusses improving the low voltage ride-through (LVRT) capability of doubly fed induction generator (DFIG)-based wind turbines using a dynamic voltage restorer (DVR). During faults, voltage dips can cause overcurrent and overvoltage in the DFIG rotor circuit if not compensated. The DVR is proposed to inject compensating voltage and prevent rapid changes in the stator voltage, allowing the rotor side converter to operate normally. Both symmetrical and asymmetrical voltage dips are investigated. Simulations using PSCAD/EMTDC verify the DVR approach improves the DFIG's LVRT capability with benefits of independent phase voltage compensation, lower volume, weight and cost compared to other solutions.
Transformer Diagnostics | Sweep Frequency Response AnalysisHamedPasha1
Proper commissioning and periodic testing of high voltage equipment is vital to the longevity of your valuable assets. Research shows that improper commissioning along with “set-and-forget” mentality has been the leading causes of premature failures.
Sweep frequency response analysis (SFRA) is one of the most powerful diagnostic tools for assessing mechanical damage to a transformer winding. Analysis of the results, which are in the form of frequency response traces can, however, be daunting to new users.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
The document describes the simulation and design of a differential relay. It discusses various types of differential protection including current, biased, and voltage balance differential relays. It also covers the application of differential protection for an alternator, including the operating principles under normal, external fault, and internal fault conditions. Biased differential protection is described as a method to prevent operation during external faults that could cause CT saturation. The project involves simulating a differential relay using Multisim software and implementing the design in hardware.
protection of transmission lines[distance relay protection scheme]moiz89
The document discusses various aspects of transmission line protection including classification of transmission lines, types of faults, protection schemes, requirements of distance protection, over current protection, phase comparison protection, and distance protection schemes. It also covers autoreclose philosophy, power swings, fuse failure function, and other protection functions.
This document analyzes very fast transient overvoltages (VFTOs) in transformers in 400kV gas insulated substations (GIS) using wavelet transforms. It presents a model of a three-phase, two-winding transformer designed in MATLAB Simulink to simulate VFTOs generated by circuit breaker operations under open and closing conditions. Wavelet transform analysis is applied to the results to investigate suppression of overvoltage magnitudes and resonant frequency amplitudes. The analysis shows the proposed technique provides high accuracy in mitigating VFTOs using wavelet transforms.
SWICTH GEAR AND PROTECTION (2170906)
DISTANCE RELAY
• There are mainly Three types of distance relay
1) Impedance Relay
2) Reactance Relay
3) Mho Relay
The document discusses the theory of circuit interruption in power systems. It begins by introducing circuit breakers, which can manually or automatically open a circuit under normal or fault conditions. When contacts within a circuit breaker open under a fault, an arc is produced that must be extinguished to interrupt current flow. There are two main methods for extinguishing arcs: the high resistance method, which lengthens and cools the arc to increase its resistance over time; and the low resistance or current zero method, used for AC circuits, which maintains a low resistance arc until current reaches zero to naturally extinguish the arc.
1. A fuse element melts when current exceeds its rating, opening the circuit.
2. Fuses are rated based on their current and time-current characteristics to provide coordinated protection across a system.
3. Proper fuse selection and coordination is necessary to clear faults while preventing unnecessary operations and minimizing stress on system components.
This document summarizes a research paper that proposes a microcontroller-based system to monitor and protect electric distribution transformers. The system would detect faults like single line-ground faults, line-to-line faults, double line-ground faults, overvoltage, and undervoltage. It would send fault alerts via GSM network to a control station. A user interface using MATLAB would display the distribution system status. The aim is to minimize equipment damage from faults and improve power distribution monitoring and management. Key components include step-down transformers, a microcontroller, GSM module, and bridge rectifier.
1) The document describes the performance of a quadrilateral relay for protection of extra high voltage transmission lines during faults with high resistance.
2) A PSCAD/EMTDC model of a 300km transmission line is developed and a quadrilateral relay scheme with two zones is designed and tested under different fault conditions.
3) Simulation results show that the quadrilateral relay can accurately detect faults located in zones 1 and 2 and is well-suited for providing flexible protection during high resistance faults on EHV transmission lines.
The document discusses the design of a microcontroller-based system for parameter measurement and protection of electrical transformers using power line communication. It aims to monitor transformer parameters like voltage, current, temperature and protect against overcurrent and overvoltage faults. The system uses current and voltage sensors connected to a microcontroller to measure parameters. If a fault is detected, the microcontroller sends a trip signal to a relay to disconnect the transformer. It is intended to provide improved reliability compared to traditional electromechanical protection techniques.
Review on Different Techniques for Differential Protection of Power TransformerIRJET Journal
This document reviews different techniques for differential protection of power transformers. It begins with an introduction to the importance of protecting expensive power transformers from internal faults. It then summarizes several existing techniques for digital relaying, including signal processing methods, model-based techniques, and artificial neural networks. The remainder of the document discusses specific techniques in more detail, including methods using current and voltage ratios, wavelet transforms, second central moment analysis, convolutional neural networks, and wavelet energy entropy. Each technique is evaluated based on its ability to quickly and reliably distinguish between internal faults and transient events like inrush currents. The reviewed methods generally demonstrate improved performance over traditional techniques in differentiating fault types and avoiding maloperation.
Differential Protection of Power Transformer in Substationijtsrd
Protection scheme required for the protection of power system components against abnormal conditions such as faults etc., and that essentially consists of protective relaying and circuit breaker. Protective relay senses the fault and determines the location of fault. Then, protective relay sends the tripping command to the circuit breaker. Therefore, proper care should be taken in designing and selecting an appropriate relay which is reliable, efficient and fast in operation. The voltage transformer and current transformer continuously measure the voltage and current of an electrical system and are responsible to give feedback signals to the relays to enable then to detect abnormal conditions. This paper describes differential protection for power transformer, especially the rating of purposed system is 100 MVA, 230 kV 33 kV at substation. Thida Win | Hnin Nandar Maung | Ye Min Hein "Differential Protection of Power Transformer in Substation" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-5 , August 2019, URL: https://www.ijtsrd.com/papers/ijtsrd27995.pdfPaper URL: https://www.ijtsrd.com/engineering/electrical-engineering/27995/differential-protection-of-power-transformer-in-substation/thida-win
transformerdesignandprotection-130408132534-phpapp02.pptThien Phan Bản
The document discusses transformer protection principles and methods. It describes various types of faults that can occur in transformers like ground faults, phase-to-phase faults, and interturn faults. It then covers mechanical protections like Buchholz relays, sudden pressure relays, pressure relief valves, and temperature indicators. Electrical protections discussed include biased differential relays, restricted earth fault relays, and overfluxing protection relays with inverse-time characteristics to match transformer thermal withstand capabilities.
This document discusses protection of power electronic converters (PECs) in dense power systems. It begins with defining PECs and describing their fault response characteristics and grid code requirements. It then discusses both the positive and negative impacts of widespread PEC integration on power system protection. Potential protection solutions are presented, such as using energy storage to contribute fault current or controlling the PEC's fault behavior. The document concludes that as PEC proliferation increases, protection coordination may experience challenges that require investigation of mitigation solutions.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Circuit breakers are mechanical switching devices that can make, carry, and break electrical currents under normal and abnormal circuit conditions such as short circuits. They contain two contacts - a fixed contact and a moving contact. The moving contact opens and closes the circuit using stored energy from a spring or compressed air. Circuit breakers also contain closing and tripping coils that activate the stored energy mechanism to open or close the circuit. There are different types of circuit breakers including low, medium, and high voltage varieties as well as air, oil, vacuum, and SF6 models. Proper selection depends on factors like voltage, current rating, frequency, and interrupting capacity.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Research Inventy : International Journal of Engineering and Scienceresearchinventy
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
1) The document describes the simulation of a differential relay for transformer protection using MATLAB/Simulink. A differential relay operates by comparing the current flowing into and out of a transformer and tripping the circuit breaker if there is a difference, indicating an internal fault.
2) The simulation models a power system including a transformer protected by a differential relay. Current transformers measure the primary and secondary currents which are compared in the relay.
3) Under normal operation the currents match and the relay does not trip, but internal faults create a difference that causes the relay to send a trip signal to the circuit breakers to isolate the fault. The simulation tests the relay under different fault conditions.
The document discusses protection of alternators from various faults. It describes 7 types of faults that alternators require protection from: (1) failure of prime mover, (2) failure of field, (3) overcurrent, (4) overspeed, (5) overvoltage, (6) stator winding faults, and (7) unbalanced loading. It then provides details on differential protection and the Merz-Price circulating current scheme, which is commonly used to protect against stator winding faults. It also discusses limitations of this scheme and modified schemes for protection in other situations.
Concept and Viability of High Temperature Superconductor Fault Current Limite...IOSR Journals
This document discusses the concept and viability of using a high temperature superconductor fault current limiter (HTSFCL) for power system protection. It begins with an introduction to the increasing fault current levels in power systems due to rising loads. It then reviews previous fault current limiting methods and outlines the ideal characteristics of a fault current limiter. The document focuses on modeling and simulating an HTSFCL using MATLAB. The HTSFCL design incorporates superconducting and stainless steel layers. Simulation results show the HTSFCL's ability to limit fault currents within a cycle by transitioning from a superconducting to resistive state as temperature rises during a fault.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
1. The document discusses power quality issues in smart grids, including various types of disturbances like voltage sags, transients, and harmonics. It defines several harmonic indices used to measure power quality.
2. Key power quality issues with smart grids are discussed, such as sustained interruptions, voltage regulation challenges, and harmonics from distributed generation sources. Operating conflicts from utility protection requirements, reclosing, interference with relaying, and other issues are also summarized.
3. Various power quality problems that can arise from interactions between distributed generation systems and the grid are described at a high level, including issues related to fault clearing, reclosing, voltage regulation, harmonics, islanding, ferroresonance, and sh
Bus bars are the nerve center of a power system where various circuits are connected. Differential protection is suitable for bus bars since terminals are near each other, allowing comparison of current entering and leaving via CTs. Any difference signals an internal fault and causes the relay coil to trip circuit breakers on both sides, isolating the bus. CT ratios for bus differential schemes equal the maximum feeder current divided by 1 or 5 amps. External faults may cause maloperation if a CT saturates, but a stabilizing resistance can restrain the relay. Dot convention defines the direction of current flow in CT secondaries. Only class PS CTs should be used to avoid undesired difference currents. Differential protection is important to protect bus bars
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Unwanted blocking of diffrential protection during converter transformer internal faults
1.
53
Summary
High-Voltage Direct Current (HVDC) technology
transports bulk electrical power over long distances
efficiently and economically, and also allows the
interconnectionofasynchronouspowergrids.InaHVDC
converter station, a converter transformer provides the
appropriate voltage for converter commutation and also
ensures galvanic isolation between the AC system and
the DC link. The provision of adequate protection for a
converter transformer is crucial; it must limit the damage
to the transformer and adjacent plant when an internal
short-circuit fault occurs.
Differential protection is widely applied to converter
transformers, owing to its simple operating principle,
high sensitivity on internal faults, and excellent security
on external faults. Nevertheless, a challenge is to prevent
mal-operation during transformer energization (i.e.
magnetizing inrush). Numerous techniques have been
used to discriminate between inrush conditions and
internal faults, but harmonic blocking is the simplest
and the most widely used solution. Harmonic blocking
assumes the second harmonic component dominates
the inrush current, but is an insignificant component of
the internal fault current. However, this approach is less
effective in modern transformers that use cores made by
low-loss amorphous materials; these materials produce
lower harmonics in the inrush currents. The challenges
are even more complex for a converter transformer,
which operates in a complicated environment affected by
AC and DC stresses.This suggests significant second and
fifth harmonic components can occur in the internal fault
current, and the fault current may behave like an inrush
current. As a result, a harmonic blocking element may
wronglyinhibittheoperationofthedifferentialprotection,
and the converter transformer may be subjected to fault
currents for an extended period, leading to severe damage
or even the rupture of the transformer tank.
Differential protection must detect all possible short-
circuit faults within a converter transformer, but few
studies have considered how harmonic blocking
performs when an internal fault occurs in a converter
transformer. This paper investigates whether harmonic
blocking is suitable for identifying inrush conditions in a
convertertransformer.Toachievethis,theCIGREHVDC
benchmark test system available in PSCAD/EMTDC
is utilized, and an appropriate differential protection
scheme is designed for the converter transformers.
Asymmetrical internal faults are simulated to assess
the operating behaviour of the differential protection
with harmonic blocking. The test results demonstrate
the differential protection is unable to initiate a trip
signal when an internal phase to ground fault is applied
on the DC side of a converter transformer. The fault
analysis implies the fault current contains a heavy DC
component which flows towards the fault point via
the windings of the converter transformer. This heavy
DC component induces a DC bias flux, which leads to
significant converter transformer half-cycle saturation,
and results in an increase in the second harmonic in
the differential current. As a result, the ratio of second
harmonic to fundamental in the differential current is
beyond the pre-set blocking threshold, restraining the
differential protection. The results analysed in this paper
demonstrate a harmonic blocking inrush identification
approach may adversely block the operation of the
Unwanted blocking of differential
protection during converter transformer
internal faults
Y. ZHAO*, P. CROSSLEY
The University of Manchester United Kingdom
KEYWORDS
HVDC, converter transformer, differential protection, half-cycle saturation, harmonic blocking
* yucong.zhao@postgrad.manchester.ac.uk
2.
54
the negative sequence components in the AC system
could introduce second harmonics into the thyristor
valves due to the interaction between the AC and DC
systems, causing unnecessary blocking of differential
protection. More tests, however, need to be conducted to
further verify these points. Paper [6] analysed the failure
of differential protection operation during converter
transformer internal faults. It was demonstrated that the
waveform of the differential current was high in the first
halfcycle of the fault current, but small in the next half-
cycle; this characteristic was similar to an inrush current
and consequently, the additional harmonics caused the
differential protection to be wrongly blocked. However,
the explanation about this result was based on the wave-
shape characteristics of the differential current, and the
reason for this unusual characteristic and the increase in
harmonics remain uncertain.
This paper thoroughly investigates the reasons
differential protection may fail to trip during a converter
transformer internal fault. To achieve this, the CIGRE
HVDC benchmark test system was simulated, and an
appropriate differential protection was applied to the
converter transformers. Multiple types of internal faults
were used to assess the dependability of differential
protection with harmonic blocking. Fault analysis
demonstrates an internal asymmetrical fault on the DC
side of the converter transformer results in a heavy DC
component that dominates the fault current and flows
to the fault point through the windings of the converter
transformer. This causes the converter transformer to
experience significant half-cycle saturation, which
results in the generation of excessive second harmonic
components. Eventually, the ratio of second harmonic
to fundamental in the differential current goes beyond
the blocking threshold, and this wrongly activates the
harmonic blocking.
2. Operating behaviour of
differential protection with
harmonic blocking during
converter transformer internal
faults
2.1. Modelling
To thoroughly demonstrate the operating behaviour of
differential protection during an internal fault on a
converter transformer.
1. Introduction
High-Voltage Direct Current (HVDC) is an effective
technique for delivering bulk electrical power over long
distances and for interconnecting asynchronous grids.
In a HVDC system, a converter transformer isolates the
AC grid from the DC link, and provides the appropriate
commutation voltages required by the valves. To limit
the damage to a converter transformer during short
circuits, differential protection is usually employed as
themainprotectionschemeowingtoitssimpleoperating
principle, high sensitivity on internal faults, and good
security against mal-operation on external faults and
non-fault events [1].
Nevertheless, conventional differential protection
encounters a critical challenge, i.e. distinguishing
between magnetizing inrush and internal faults.
Numerous methods have been proposed to prevent
differential protection mal-operation in the event of
transformer energization, and the most widely applied
approach is harmonic blocking. This approach assumes
the second harmonic component dominates an inrush
current but is significantly lower in a fault current.
Although the effectiveness of harmonic blocking has
beenconfirmedinmanyapplications,thisapproachhasa
limitation; it can be difficult to determine an appropriate
blocking threshold which can be guaranteed to not affect
the operating performance during an internal fault. This
is because the second harmonic component seen in the
internal fault current, may in some cases be as high as
that observed in an inrush current, and as a result, the
operationofdifferentialprotectionwouldbedesensitized
or delayed [2],[3].
Time-delayed fault clearance is unacceptable for
converter transformers, but few studies have considered
the operating behaviour of harmonic blocking during
converter transformer internal faults. Paper [4]
considered the harmonics produced by converters might
lead to the harmonic blocking element misjudging
the current caused by an internal fault to be an inrush
current, which means the operation of the differential
relay would be wrongly blocked. Paper [5] suggested,
in the case of converter transformer internal faults,
3.
55
where and arethephasecurrentsobtainedfromthe
protectionCTsattheACandDCsidesofT1respectively.
The operating characteristics of the protection were set
in accordance with conventional criteria, i.e. the tripping
threshold was 0.3 p.u., the breakpoint was 2 p.u., the
lower slope 1 was 30%, and the high slope 2 was 60%.
According to the surveys conducted by CIGRE WG
C2/B4.28 [9], the majority of transformer failures were
related to connections and terminals, because these
components are usually subjected to the superimposed
AC and DC stresses. In this regard, different types of
fault, single-phase to ground, phase-to-phase to ground,
and three-phase faults were applied on the terminal at
the DC side of T1 respectively, and each fault lasted for
0.5seconds.Thefollowingsubsectionsdescribeselected
results, where the differential protection failed to operate
on an internal fault.
2.3. Scenario 1: Single-phase to ground fault
Initially, a single-phase to ground (A-G) fault occurred
on the DC side T1 terminal at t = 1.005 s. The response
of differential protection is demonstrated in Fig. 2. In
this figure, Diff denotes the waveform of differential
current;Funddenotesthemagnitudeofthefundamental
component of differential current; and 2nd Ratio
denotes the ratio of second harmonic to fundamental
components in the differential current. The grey shaded
region shows when the harmonic blocking element was
activated.
As illustrated by the A-Diff in Fig. 2, the asymmetrical
A-G fault leads to an increase in differential current,
and the corresponding magnitude (A-Fund) is beyond
the operating threshold. In the meantime, the content
of the second harmonic in the A-phase differential
current increases, and the harmonic blocking element
is activated for a very short time (less than 10 ms).
This is caused by the sudden transient onset of the fault
which produces second harmonics in the differential
current, and this will occur for all faults [10]. The
A-2nd Ratio in Fig. 2 demonstrates a brief gap between
the shaded areas, suggesting the harmonic blocking
element is deactivated for 2 ms. In practice, the
differential protection is unable to operate during this
differential protection with harmonic blocking during
converter transformer internal faults, the CIGRE HVDC
benchmark test system available in PSCAD/EMTDC was
utilised, see Fig. 1. This is a standard reference model for
the study of an HVDC system in terms of control strategy
and recovery performance. This system is a monopolar
HVDC link designed to operate at 500 kV and 1000 MW.
The AC/DC converters are represented by two six-pulse
thyristor-based valves in series connection (i.e. forming
12-pulse converters) and are installed at both the rectifier
andinvertersides.Ineachconverterstation,twoconverter
transformers with winding connections of grounded
and provide a 30° phase shift to achieve the 12-pulse
rectification. More information about the primary system
can be found in [7] and [8].
In this paper, the protection of the converter transformer
T1 installed on the rectifier side is primarily studied.
The default parameters of T1 in this benchmark system
are 603.73 MVA and 345/213.4557 kV. The positive
sequence leakage reactance and copper loss are 0.18 p.u.
and 0.02 p.u. respectively, and the air-gap reactance is
0.2 p.u.; the knee point is 1.25 p.u. and the magnetizing
current is 1%. The protection currents are measured
from the CTs installed on both sides of the converter
transformer T1. To simplify the investigation, the
protection CTs are over-dimensioned, i.e. they do not
saturate during transient conditions. Therefore, the turns
ratio of the CTs on the AC and DC sides are 1500/5 and
2000/5 respectively, and each is connected to a burden
2.2. Transient study
In this study, the converter transformer T1 was
implemented with conventional percentage differential
protection with harmonic blocking. The differential
current and the bias current were derived using the
following equations:
(1)
(2)
Fig. 1. Single-line diagram of CIGRE benchmark HVDC system
4.
56
differential relay should initiate a trip signal. However,
the second harmonic ratios, A-2nd Ratio and B-2nd Ratio,
in the A and B phase differential currents are greater
than 15% for the entire duration of the fault occurrence.
Consequently, the differential protection is incorrectly
blocked, and this fault cannot be cleared in a reasonable
time.
3. Fault analysis
The previous two examples demonstrate incorrect
blocking of differential protection during converter
transformer internal faults. However, to determine
exactly why the protection failed to operate, Scenario 1
is now thoroughly analysed.
As illustrated in the A-Diff in Fig. 2, the waveform of
differential current sharply increases after the fault
initiation and then decreases demonstrating spikes.
This waveshape characteristic suggests the converter
time, i.e. differential protection cannot reliably detect
this internal fault and trip the T1 circuit breaker.
ThisA-Gfaultalsoresultsinasecondharmonicincrement
in the B-phase differential current. As illustrated by the
B-2nd Ratio in Fig. 2, the ratio of second harmonic to
fundamental is beyond the inhibiting threshold for the
entire transient period. Therefore, if the cross-blocking
function of the relay is activated, this A-G fault would
not be cleared within an appropriate time, as the relay is
incorrectly blocked by the harmonic blocking associated
with the B-phase differential element.
2.4. Scenario 2: Two-phase to ground fault
In this scenario, a double-phase to ground (A-B-G)
fault occurred on the DC side of T1 at t = 1.00 s. Fig.
3 describes the response of the differential protection
during this transient condition. It can be seen the
magnitudeofthedifferentialcurrents,A-DiffandB-Diff,
are above the tripping threshold, and consequently, the
Fig. 2. Failure to trip of differential protection duringA-G internal fault
5.
57
D61) of the valve group G1 are grounded, as shown in
Fig. 5. After the fault occurs, the DC currents on the
transmission line significantly decreases; the control
system at the rectifier side then provides fast response
to this current reduction and reduces the firing angle
from the nominal level ( ) to the minimum
limit ( ) to maintain the current level, as shown
in Fig. 6. This suggests the firing pulse is persistently
initiated to trigger the thyristors, i.e. the lower-arm
thyristors of G1 and the thyristors of G2 are capable of
conducting and commutating during the fault condition.
Consequently, after the fault occurs, DC currents are
converted by the valve group G2 and then delivered by
the lower-arm thyristors of G1. Because of the potential
difference between the fault point and the converter
ground electrode, these DC currents then return to the
ground electrode of G2 via the ground. As a result, a
new loop for DC currents is formed, i.e. valve group G2
– lowerarm of G1 – windings of converter transformer
transformerishalf-cyclesaturatedduringthefaultperiod.
Normally, the asymmetrical saturation of a transformer
is due to the superimposed AC flux and DC bias flux,
where the latter results from the DC components in
the fault current. To determine the DC components
experienced by T1 during the transient period, the Fast
Fourier Transform (FFT) module is used to extract the
DC components in the terminal currents of T1 and they
are displayed in Fig. 4. Note the reference direction of
theterminalcurrentistowardsthetransformer;hencethe
negative magnitude denotes the DC components flow
out of T1. Fig. 5 illustrates, during the transient period,
the flow path of these DC components produced by the
thyristors, based on the bridge-conducting sequence.
Note that the commutation overlap period is neglected.
The A-G fault on the DC side ofT1 can be treated as
a short-circuit across the valves [6],[11], i.e. the anode
of the upper-arm thyristors (D11, D31, and ) and
the cathode of the lower-arm thyristors (D21, D41, and
Fig. 3. Failure to trip of differential protection duringA-B-G internal fault
6.
58
in Fig. 5 (a)); the DC components in D61 and D21 flow
through the “short” by passing through the a-b and c-a
windings of the converter transformer T1 respectively
(see the red and yellow arrows in Fig. 5 (b) and (c));
afterwards, these DC components are superimposed on
the faulted phase currents and flow through the “short”.
The DC components displayed in the lower plot of Fig.
4 confirms this phenomenon, i.e. they flow into the
convertertransformerT1viathephaseBandCterminals
and out of T1 via the phaseA terminal.
– ground fault point – the ground – ground electrode of
G2.
Hence, during the transient period, the lower-arm
thyristors of G1 experience a “threephase short-circuit”,
and the fault currents deviate from the zero axis as they
contain significant DC offsets [12],[13]. Based on the
newly formed DC current loop, the fault currents flow
through the “short”. Hence the DC component in D41
flows into the faulted phase directly (see the pink arrow
Fig. 4. DC components in the terminal currents of T1
Fig. 5. Path loop of DC components experienced by T1
Fig. 6. Firing angle of the rectifier
7.
59
4. Conclusion
The operating behaviour of differential protection with
harmonic blocking in the event of converter transformer
internal faults was evaluated in this paper. A differential
protection scheme was designed and implemented on
the converter transformer used in the CIGRE HVDC
benchmark test system. The investigation shows that
differential protection is unnecessarily blocked when
an internal asymmetrical fault occurs on the DC side
of the converter transformer. Based on fault analysis,
it was demonstrated the DC components dominate the
fault current and they flow to the fault point via the
windings of the converter transformer. As a result, the
converter transformer is significantly saturated, due to
the additional DC bias flux, and this produces second
harmonics in the differential current. Consequently,
the ratio of second harmonic to fundamental in the
differential current exceeds the pre-set blocking
threshold, and the differential protection is incorrectly
blocked. The presented results demonstrate a harmonic
blocking based inrush identification method may
adversely affect the operation of differential protection
during converter transformer internal faults.
5. Bibliography
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Teodorescu, Design, Control and Application of Modular
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Chichester, UK: John Wiley & Sons, Ltd, 2016.
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When the converter transformer T1 experiences these
DC components, it initially remains in the linear region
of its hysteresis loop, and a portion of the DC currents
are transiently induced on the AC side of the converter
transformer, as shown in the upper plot of Fig. 4. These
DC components generate DC excitation voltages across
the winding and the core. Because flux linkage is the
integraloftheexcitationvoltagebytime,thefluxlinkage
oftheconvertertransformercorerampsupaftert=1.005
s, as indicated by Fig. 7. When the flux increases, the
magnetic operating point of the core is gradually shifted
up, above the knee point, and the core enters saturation.
This suggests the non-linear inductance of the core
significantly reduces and eventually can be considered
as zero. Therefore, the voltage drop across the winding
falls to zero and the induced DC components in the
primary windings diminish. Ultimately, the converter
transformer enters into a severe half-cycle saturated
condition because of the DC components in the fault
current. Spikes are presented in the differential current,
and evenorder harmonics are produced; as a result,
the ratio of second harmonic to fundamental in the
differential current is beyond the inhibiting threshold
which leads to the incorrect blocking of the differential
protection.
The primary reason differential protection fails to trip
during converter transformer internal faults is half-
cycle saturation of the transformer core. This saturation
stems from the significant DC components in the
asymmetrical fault current. As a result, high levels of
the second harmonic component are measured by the
differential protection and this causes the activation of
a second harmonic blocking element. The likelihood of
unnecessary blocking is higher when the cross-blocking
functionisactivated.Consequently,aharmonicblocking
based inrush identification method is not suitable for
differential protection applied to converter transformers,
i.e. it is unable to differentiate inrush conditions from
internal faults.
Fig. 7 Converter transformer’s flux linkage increment due to extra DC bias flux
8.
60
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[12] J. Cheng and Z. Xu, “Analysis of AC Faults in Converter
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