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CIGRÉ B5 COLLOQUIUM CALGARY 2005. Special Report for Preferential Subject 1 Transformer Protection, Monitoring and Control Special Reporter: Simon Chano* Canada. 15 September 2005 Calgary, Canada. SUMMARY. 20 papers submitted by authors from 15 different countries.

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Special Report for Preferential Subject 1 Transformer Protection, Monitoring and Control Special Reporter: Simon Chano*


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    1. CIGRÉ B5 COLLOQUIUM CALGARY 2005 Special Report for Preferential Subject 1Transformer Protection, Monitoring and ControlSpecial Reporter: Simon Chano*Canada 15 September 2005 Calgary, Canada

    2. SUMMARY • 20 papers submitted by authors from 15 different countries. • Interesting overview of transformer protection enhancements attained by modern numerical relays. • To facilitate the discussion, papers were classified in four subject groups

    3. SUMMARY • Thermal protection & Life Management • Effect of transformer inrush currents on protection functions • Application of multifunction digital transformer protection • Future trends.

    4. KEY WORDS Multifunction Transformer Protection, Enhanced Thermal Protection, Transformer Life Management, Sensitive Inrush Current Detections, Transformer Protection Backup Functions, IEC 61850

    5. INTRODUCTION In recent years, the electric power industry has gone through deregulation and restructuring . Reductions in system expansion along with growing operating stresses from increased load and added bulk power transactions have raised many thermal protection issues and monitoring

    6. Power transformer protective relays perform a vital role in minimizing equipment damage. Advanced numerical technology is offering the possibility to protect power transformers with new protection principles based on higher sensitivity detection algorithms and due to their monitoring capabilities, transformer relays are offering tools for better maintenance scheduling and life management. New methods of detecting inrush or over-excitation currents are increasingly being reported from different papers.

    7. Thermal Protection & Life Management (six papers) • Paper 101: Need for Enhanced Thermal Protection of Power Transformers (Australia) • Paper 103: Life Cycle Management of Power Transformers Using Transformer Protection Relay (Canada / USA) • Paper 107: Recent Trends in Transformer Protection Technology in Japan (Japan) • Paper 112: Considerations on Transformer/ Autotransformer Overload Protection by Thermal Image Modeling (Romania) • Paper 114: Transformer Thermal Simulation (Austria / UK) • Paper 118: Transformer maintenance Interval Management (USA)

    8. Thermal Protection & Life ManagementPaper 101: Need for Enhanced Thermal Protection of Power Transformers (Australia) • Paper 101 describes a simple means of transformer thermal protection based on current measurements from the high and low voltage transformer windings only. • The scheme is based on an implemented user definable logic in accordance to NEMMCO defined thermal protection limits. • Ongoing program to install the discussed new thermal protection schemes which include all MVA sizes and voltage levels.

    9. Thermal Protection & Life ManagementPaper 103: Life Cycle Management of Transformers Using Transformer Protection Relay (Canada / USA) • Paper 103gives an overview of the loss of life of transformers as a result loading. • Hot Spot temperatures of transformers are monitored by available advanced state-of-the-art technologies for monitoring and metering overheating conditions • Assess conditions of transformer insulation and therefore, new maintenance practices to manage the life of transformers are implemented in an available features of an adaptive Protection Relay (TPRO) • Integrated management functions to mitigate the risk of overloading and extend the useful service life of transformers.

    10. Thermal Protection & Life ManagementPaper 107: Recent Trends in Transformer Protection Technology in Japan (Japan) • Paper 107 discusses a temperature prediction scheme where the actual and predicted transformer temperature are calculated using the heat increase formula for the transformer and compare the results with the transformer maximum permissible temperature. • UHV transformer protection, enhanced numerical applications with optical transmission schemes for further cost reduction and improved performance.

    11. Thermal Protection & Life ManagementPaper 112: Considerations on Transformer/ Autotransformer Overload Protection by Thermal Image Modeling (Romania) • Paper 112 discusses a temperature prediction scheme and focuses on overload aspects of transformers by means of thermal image functions. • Acceptable solutions using parameterization methods could be envisioned for protection functions that do not take into consideration the temperature of the cooling medium.

    12. Thermal Protection & Life ManagementPaper 114: Transformer Thermal Simulation (Austria / UK) • Paper 114 presents a thermal model incorporating the following features: • Heat generation, heat transfer and heat storage, oil and the moisture flow. • Thermal data (hotspot, hotoil), • representation of losses, depending on the actual load and, tap changer position, • representation of critical temperatures (hotspots), taking into account ambient temperature and cooling condition, • discusses a temperature prediction scheme and focuses on overload aspects of transformers by means of thermal image functions.

    13. Thermal Protection & Life ManagementPaper 118: Transformer maintenance Interval Management (USA) • Paper 118 discusses a comprehensive transformer management plan by continuously monitoring the factors that cause transformer damage. • Examples are provided on continuous monitoring and recording thermal loading to notify maintenance personnel of problems with fans or pumps. • Other monitoring functions to optimize maintenance practices: comparing measured top-oil temperatures with calculated top-oil temperature. • Through-fault monitoring and the combination of through-fault, temperature, and other factors to optimize maintenance practices.

    14. BRAIN-STORMING QUESTIONS RELATED TOTRANSFORMER THERMAL PROTECTION AND LIFE MANAGEMENT • Different papers discuss different philosophies and different approaches to achieve a desired thermal protection scheme. For each scheme: • Efficiency? • Advantages? • Disadvantages? • Reliability and Security issues ?

    15. EFFECT OF TRANSFORMER INRUSH AND OVEREXCITATION CURRENTS ON PROTECTION FUNCTIONS- SIX PAPERS • Six papers discussed the effect of inrush and over-excitation currents on transformer protection. The following are some key words to this topic. • New restraining algorithms • Different approaches for blocking with DC component and fifth harmonic. • New algorithms to desensitize the relay rather than block its operation when a certain fifth harmonic content is exceeded. • Wave shape recognition techniques

    16. EFFECT OF TRANSFORMER INRUSH AND OVEREXCITATION CURRENTS ON PROTECTION FUNCTIONS(six papers) • PAPER 102: Impact of Transformer Inrush Currents on Sensitive Protection Functions (Canada) • PAPER 104: A Novel Digital Protection Method for Power Transformers Based on Intermission Angle Principle (China). • Paper 108: Transformer Protection Relay Based on the Increment of the Flux Linkages (Korea / UK) • Paper 111: Transformers Digital Differential Protection with Criterion Values Recording Functions (Poland) • Paper 115: Application and Commissioning of Multifunction Digital Transformer Relays (USA) • Paper 119: Power Transformer Protection Improvements with Numerical Relays (USA)

    17. PAPER 102: Impact of Transformer Inrush Currents on Sensitive Protection Functions (Canada) • This paper reviews the impact of transformer inrush currents on five protection functions: (i) main differential function of the transformer, (ii) restricted earth fault protection, (iii) stator differential protection for generators and (iv) sensitive ground directional overcurrent functions used for line and feeder protection, and (v) distance protection. • This paper concludes that harmonic inhibit is a crude solution to the problem due to dc saturation • New sophisticated algorithms address the issue in modern relays

    18. PAPER 104: A Novel Digital Protection Method for Power Transformers Based on Intermission Angle Principle (China). • The paper describes a new approach based on wavelet transform, which can distinguish between inrush current and internal fault current of a transformer without the effect of CT saturation. • Advantages: Distinguish between inrush current and internal fault current without effect of CT saturation and, • Lower hardware request and exact prediction make this criterion easy to be applied in practice.

    19. Paper 108: Transformer Protection Relay Based on the Increment of the Flux Linkages (Korea / UK) • This paper proposes a transformer protection using the Relay Increment of Flux Linkage (RIFL) • Discriminates between internal winding faults and magnetic inrush • Algorithm is faster when compared to conventional relay with harmonic blocking.

    20. Paper 111: Transformers Digital Differential Protection with Criterion Values Recording Functions (Poland) • Digital differential protection systems with the criterion values recording function in order to decrease the number of undesirable operations using: • simplification of the differential protection criterion settings available for the operating personnel, • shifting the responsibility of setting the most difficult parameters to designers, • Using the criterion values recordings for optimization of the differential protection settings, • accepting the criterion values recordings as documentary evidences confirming the accomplishment of the differential protection routine tests and the conjunctive type test of the protection systems.

    21. Paper 115: Application and Commissioning of Multifunction Digital Transformer Relays (USA) • New algorithm using multiple harmonics and cross-phase inrush restraint to enhance security on transformer energizing as well as overexcitation harmonic restraint to desensitize tripping rather than blocking. • “Built-in” commissioning tools such as phase angle metering and functional summary screens to assist the commissioning engineer and eliminate common commissioning errors.

    22. Paper 119: Power Transformer Protection Improvements with Numerical Relays (USA) • Algorithms to ensure security for external faults, inrush, and overexcitation conditions and provides dependability for internal faults. • Approach combines harmonic restraint and blocking methods with a wave shape recognition technique. • Even harmonics of the differential current provide restraint, while the fifth harmonic and d.c. component block relay operation. • Using DC offset blocking ensures security for inrush conditions with very low total harmonic distortion.

    23. BRAIN-STORMING QUESTIONS RELATED TOEFFECT OF TRANSFORMER INRUSH AND OVEREXCITATION CURRENTS ON PROTECTION FUNCTIONS • Different papers discuss different philosophies and different techniques regarding inrush and overexcitation currents. • What would be the future practice for selecting one harmonic restraint algorithm instead of another? • What are the issues to look for if duplicate protection devices from different manufacturers use different restraining and blocking principles? • What are the requirements, if any, in selecting one algorithm principle from another algorithm? • Reliability and security issues ?

    24. APPLICATION OF MULTIFUNCTION DIGITAL TRANSFORMER PROTECTIONSeven papers • Seven different papers discussed advancements in transformer protection using integrated multifunction protection, control and metering capabilities. • Key Words: • Multifunction Transformer Protection Survey, Self monitoring, disturbance recording , Backup Functions, Etc…

    25. APPLICATION OF MULTIFUNCTION DIGITAL TRANSFORMER PROTECTION • Paper 105: Transformer Protection and Monitoring with Multifunction Relays Survey of German Practice (Germany) • Paper 106: Practical Solutions to Protecting Extra Large Split-Phase Autotransformers (Canada / Spain / South Korea) • Paper 109: Advanced Voltage Control for Paralleling Transformers and Networks (Malaysia) • Paper 110: Application of Distance Function as Back-up Protection for Grid Transformer in TNB 500/275/132kV System (Malaysia) • Paper 113: Sensitive Turn-to-Turn Fault Protection for Power Transformers (Sweden / Croatia) • Paper 119: Power Transformer Protection Improvements with Numerical Relays (USA) • Paper 120: A Case Study Evaluation of the Causes for the Premature Failure of transformers on the ESKOM Transmission Network (South Africa)

    26. Paper 105: Transformer Protection and Monitoring with Multifunction Relays Survey of German Practice (Germany) • German survey for protection, monitoring and commissioning. • Self monitoring, disturbance recording and the flexible logic rated high. • All other measuring functions rated low • The transformer monitoring is only applied here and there. “Wait and see” attitude. The classic monitoring techniques are applied instead, whereby the gas analysis is dominant.

    27. Paper 105: Transformer Protection and Monitoring with Multifunction Relays Survey of German Practice (Germany) • Weighting of the characteristics of multi-functional numerical transformer differential protection relays (scaling: 0 not important and 5 very important; bolded lines: average value, grey areas: variations)

    28. Paper 106: Practical Solutions to Protecting Extra Large Split-Phase Autotransformers (Canada / Spain / South Korea) • Dedicated protection to cover winding, ground, bank, unit and tertiary faults. • The protection uses numerous multi-function microprocessor-based relays. • Extended supervision to avoid false operations that would impact power system operation and stability. • Multiple principles and zones for redundancy with trip supervision to monitor relay failures, wiring problems, CT failure situations, etc.

    29. Paper 109: Advanced Voltage Control for Paralleling Transformers and Networks (Malaysia) • Advanced voltage control relay using reactive circulating current to overcome problems regarding paralleling transformers of different impedance; paralleling transformers with different tap position and to overcome high circulating current conditions when networks are operated in parallel.

    30. Paper 110: Application of Distance Function as Back-up Protection for Grid Transformer in TNB 500/275/132kV System (Malaysia) • Overcurrent backup is not adequate to satisfy overall fault clearance requirements for the 500/275/132kV system, and hence distance function was recommended in place of the overcurrent relay. • Best strategy for settings application and selection of relevant functions (e.g., self-supervision, monitoring and disturbance recording) within the distance protection to effectively activate the required backup functions.

    31. Paper 113: Sensitive Turn-to-Turn Fault Protection for Power Transformers (Sweden / Croatia) • Advanced numerical new differential protection principle, which has much higher sensitivity than traditional transformer differential protection for low-level internal faults. • Winding turn-to-turn faults based on negative sequence symmetrical components of currents ( 1% short-circuited turns) . • Operates when power transformer is loaded.

    32. Paper 116: Advanced Transformer Paralleling-Making Control Method Choices (USA) • The control method choices discussed in this paper include: master / follower method, negative reactance method, power factor method, circulating current method, and VAR balancing method. • This paper investigates commonly used methods for controlling paralleled LTC transformer taps and compares and evaluates those methods for different system applications.

    33. Paper 120: A Case Study Evaluation of the Causes for the Premature Failure of transformers on the ESKOM Transmission Network (South Africa) • This paper discusses the influence of external fault environment on the premature failure of ageing transformers. • The paper indicates inadequacy of protection relays and mentions various options as part of a list of recommendations that are being researched by ESKOM in order to mitigate the problems in distribution networks.

    34. BRAIN STORMING QUESTIONS ON THE APPLICATION OF MULTIFUNCTION DIGITAL TRANSFORMER PROTECTION • While all are showing interest in multifunction protection and predictive methods of maintenance by monitoring and self-supervision tools, Survey indicated a conservative approach from users. This raises the following questions: • What are the issues that are refraining protection engineers from using the additional available protection functions? • Is it related to additional relay setting complexity issues? • Is it related to additional testing and normalizing procedures that require additional verification time? • Would more utilities use the various protection functions in the relay if built-in commissioning tools are made available in the relays?

    35. Paper 117: IEC 61850 Based Object Models of Multifunctional Transformer Protection IEDS (USA) • This paper describes the functional hierarchy of transformer protection IEDs and how it is modeled based on the object hierarchy of the IEC 61850 standard. • Logical nodes, data objects and data attributes are used for the modeling. Two basic models are described in detail: • Single Logical Device based model • Multiple Logical Devices based model • An approach that allows the functional grouping of logical nodes based on the principles of IEC 61850 is presented.

    36. PREFERENTIAL SUBJECT - 1 Special Reporter Summary Simon Chano (CA)

    37. PS-1 Question 1Thermal Protection & Life Management • How can one interpret the efficiency of a protection scheme when no ambient temperature or oil temperature sensor measurements are available as inputs? • Brazil: • Widely applied in Brazilian interconnection transformers since the mid seventies, regardless of thermal considerations • A conservative procedure to minimize loss of useful lifetime • Currents above 150 % of rated value lead to trip in 20 s • Currents above 200 % of rated value lead to trip according to a time dependent curve matched to the transformer capability characteristic • Conceived to perform preventive load shedding • Performance evaluation has been done under the load conservation viewpoint – an objective criterion.

    38. PS-1 Question 1Thermal Protection & Life Management • How can one interpret the efficiency of a protection scheme when no ambient temperature or oil temperature sensor measurements are available as inputs? • Canada: What ambient temperature does NEMMCO assume when calculating the transformer capability before shedding load?

    39. PS-1 Question 1Thermal Protection & Life Management • How can one interpret the efficiency of a protection scheme when no ambient temperature or oil temperature sensor measurements are available as inputs? • Japan: the temperature sensor is only used for primary equipment monitoring system. The transformer overload protection relay operates by current only. • The overload protection method involves a multi-step control scheme based on overcurrent relays and power relays, and a temperature prediction scheme.

    40. PS-1 Question 2Thermal Protection & Life Management • What is the practice which is most commonly applied for thermal protection of power transformers? • Japan:Overcurrent measures only using multi-step control scheme ( most commonly used scheme ). • Temperature prediction scheme: Heat increase formula for the transformer, to compare the results with the transformer’s maximum permissible temperature. Thus the control can be performed while considering the predicted time at which the temperature reaches the maximum permissible level. • Germany: Thermal protection replica according the thermal differential equation 1. order is used in Germany

    41. PS-1 Question 2Thermal Protection & Life Management • What is the practice which is most commonly applied for thermal protection of power transformers? • Sweden:The winding temperature measuring is the most important and used overload protection at present • The performance of the current based thermal protection needs to be improved (comparable with the winding temperature measuring)E.g. considering the ambient temperature etc • Improved current based thermal overload protection can be the most important overload protection in the future • Condition monitoring for estimation of the lifetime and the need of maintenance • The available extensive condition information is an important benefit compared to the information available from the winding temperature • measuring Condition monitoring not used • Difficulties to find reliable criteria for the estimation of lifetime and maintenance

    42. PS-1 Question 3Thermal Protection & Life Management • What are the advantages and disadvantages of the approaches discussed in Question 2? • Sweden: • Winding temperature measuring. Current compensated top oil temperature • Most important thermal protectionUsed for transformers > 10-15 MVA • Most used overload protection • Insufficient informationOften not sent to the operation center • Current based thermal overload protection • Used when it is included in numerical transformer protectionor for small transformers • Insufficient performance and will not replace the winding temperature measuring • Valuable information is sent to the operation center

    43. PS-1 Question 3Thermal Protection & Life Management • What are the advantages and disadvantages of the approaches discussed in Question 2? • Japan: Overcurrent scheme • Advantage: Easy setting • Disadvantage: Leading to excessive load shedding • Japan: Temperature prediction scheme • Advantage: Appropriate load shedding, • Disadvantage: Complicated setting due to: complex transformer temperature increase formula- setting dependent on individual transformer characteristics -Difficult to verify relay characteristics coordinate with transformer overload characteristics

    44. PS-1 Question 3Thermal Protection & Life Management • What are the advantages and disadvantages of the approaches discussed in Question 2? • Germany: • Disadvantage: A transformer is a complex protective object. Life time management and condition based monitoring needs more information. • On-line Monitoring Concept for Power Transformers • Advantage: Important Parameters to provide an Early Warning System and Life Management Support by means of On-line monitoring

    45. PS-1 Question 4Thermal Protection & Life Management • What thermal protection considerations do users take into account for transformers with reduced capacity on some taps? • Do some utilities require individual winding thermal monitors for such transformers? Have other solutions been identified that address this issue? • USA: IED based 61850 devices feasable. • Sweden: Complex but could be done

    46. PS-1 Question 5Thermal Protection & Life Management • Is there any statistical data, or other documentation, available to illustrate how often modern thermal protection is being used? • Japan: • Chubu installs thermal protection according to the following rules: • 1- When an important overload is expected due to the loss of one of the paralleled banks. • 2- When an important overload is expected due to the loss of one of the bus-bars. • 3 - When an important overload is expected due to the loss of one of the neighbouring power units. • 4- When overload is not allowed due to the age of the transformers. • There are 218 thermal protections applied in Chubu Electric Power Co. now. 134 thermal protections are numerical types. The transformer thermal protection is a standard equipment in 275kV transformer regardless of the rules above mentioned.

    47. PS-1 Question 5Thermal Protection & Life Management • Is there any statistical data, or other documentation, available to illustrate how often modern thermal protection is being used? • Japan:

    48. PS-1 Question 6Thermal Protection & Life Management • What are the issues/obstacles delaying or preventing the implementation of additional control and monitoring functions? • Sweden: Protection engineer and operation engineers are not “integrated” the same way IEDs are. Operation personnel need to be trained and require more information to maximize use of modern relays. • In May 2005 a new 220/400 kV transformer was installed with all monitoring values sent direct to our NC • USA:IMPORTANT ISSUES TO BE ADDRESSED BETWEEN DIFFERENT TRANSFORMER AND PROTECTION EXPERTS • BELGIUM: DICONNECT 51 TRIP AND SEND TEMPERATURE AND CURRENT READINGS TO OPERATOR

    49. PS-1 Question 6Thermal Protection & Life Management • What are the experiences of users who have already used them? • SAUDI ARABIA: High rate of transformer failure • New project to monitor transformer thermal temperature. • Are there additional issues that need to be considered to encourage use additional features in a multi-function protection device? • If so, should they be elaborated in guides or standards? • What is the practice and experience of other utilities regarding the application of integrated protection and non-protection functions in transformer relays? • Besides the survey results offered in paper 105, which functions of integrated transformer relays are mostly used and offer the best value to the users?

    50. PS-1 Question 6Thermal Protection & Life Management • What would the issues that are delaying or preventing the implementation of these control and monitoring functions? • Brazil: Lack of commands or weak economic signals to motivate the Transmission Operators to equip their old transformers with these recent technologies or to motivate them to stress their new transformers to a limit that could not be handled by traditional functions and conservative settings • Protection, Scada and Equipment Management teams are not close enough (from a technical perspective) to have clearly defined responsibilities in this matter • The initiative of Cigre B5/BR Committee to organize a local joint Seminar, gathering the B5, C2 and A1 people, on the matter of Protection, Control and Monitoring of power transformers .