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

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20 papers submitted by authors from 15 different countries.

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Interesting overview of transformer protection enhancements attained by modern numerical relays.

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To facilitate the discussion, papers were classified in four subject groups

SUMMARY

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Thermal protection & Life Management



Effect of transformer inrush currents on protection functions

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Application of multifunction digital transformer protection



Future trends

.

KEY WORDS

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

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

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.

Thermal Protection & Life Management (six papers)

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Paper 101: Need for Enhanced Thermal Protection of Power Transformers (Australia)

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Paper 103: Life Cycle Management of Power Transformers Using Transformer Protection Relay (Canada / USA)

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Paper 107: Recent Trends in Transformer Protection Technology in Japan (Japan)

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Paper 112: Considerations on Transformer/ Autotransformer Overload Protection by Thermal Image Modeling (Romania)

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Paper 114: Transformer Thermal Simulation (Austria / UK)

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Paper 118: Transformer maintenance Interval Management (USA)

Thermal Protection & Life Management

Paper 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.

Thermal Protection & Life Management

Paper 103: Life Cycle Management of Transformers Using Transformer Protection Relay (Canada / USA)

   

Paper 103

gives 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.

Thermal Protection & Life Management

Paper 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.

Thermal Protection & Life Management

Paper 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.

Thermal Protection & Life Management

Paper 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, hot oil), 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.

Thermal Protection & Life Management

Paper 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.

BRAIN-STORMING QUESTIONS RELATED TO TRANSFORMER 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 ?

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

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EFFECT OF TRANSFORMER INRUSH AND OVEREXCITATION CURRENTS ON PROTECTION FUNCTIONS

(six papers)

PAPER 102: Impact of Transformer Inrush Currents on Sensitive Protection Functions (Canada)

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PAPER 104: A Novel Digital Protection Method for Power Transformers Based on Intermission Angle Principle (China).

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Paper 108: Transformer Protection Relay Based on the Increment of the Flux Linkages (Korea / UK)

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Paper 111: Transformers Digital Differential Protection with Criterion Values Recording Functions (Poland)

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Paper 115: Application and Commissioning of Multifunction Digital Transformer Relays (USA)

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Paper 119: Power Transformer Protection Improvements with Numerical Relays (USA)

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

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.

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 wi

th harmonic blocking.

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.

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.

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.

BRAIN-STORMING QUESTIONS RELATED TO EFFECT 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 ?

APPLICATION OF MULTIFUNCTION DIGITAL TRANSFORMER PROTECTION Seven papers

 Seven different papers discussed advancements in transformer protection using integrated multifunction protection, control and metering capabilities.

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Key Words:

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Multifunction Transformer Protection Survey, Self monitoring, disturbance recording Functions, Etc…

,

Backup

APPLICATION OF MULTIFUNCTION DIGITAL TRANSFORMER PROTECTION

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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)

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.

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) Flexible settings of protection functions

0 1 2 3 4 5

Higher sensitivity No external matching transformers Short tripping time for Idiff>> stage (approx. 10 ms) Additional protection function in the differential relay (I>, I 2 t, U>, I 2 >, U/f>, …) Additional measuring functions (U, I, P, f, …) Lower current transformer requirements Detection of CT saturation (at external faults) Integrated fault recording Integrated event recorders Commissioning support (e.g. Diff., Restr. - values, angles) Self - monitoring Integrated free programmable Logic Flexible masking of binary inputs and outputs Remote reading of fault records (via modem) Remote setting of protection General remote access by protection experts

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.

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.

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.

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.

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.

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.

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?

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.

PREFERENTIAL SUBJECT - 1

Special Reporter Summary Simon Chano (CA)

PS-1 Question 1

Thermal 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.

PS-1 Question 1

Thermal 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?

PS-1 Question 1

Thermal 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.

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The overload protection method involves a multi step control scheme based on overcurrent relays and power relays, and a temperature prediction scheme.

PS-1 Question 2

Thermal Protection & Life Management

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What is the practice which is most commonly applied for thermal protection of power transformers?

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Japan: Overcurrent measures only using multi-step control scheme ( most commonly used scheme ).

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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.

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Germany:

Thermal protection replica according the thermal differential equation 1. order is used in Germany

   

PS-1 Question 2

Thermal 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

PS-1 Question 3

Thermal 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 protection Used for transformers > 10-15 MVA



Most used overload protection

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Insufficient information Often not sent to the operation center Current based thermal overload protection



Used when it is included in numerical transformer protection or for small transformers



Insufficient performance and will not replace the winding temperature measuring



Valuable information is sent to the operation center

PS-1 Question 3

Thermal 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

PS-1 Question 3

Thermal 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

PS-1 Question 4

Thermal 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

PS-1 Question 5

Thermal 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.



PS-1 Question 5

Thermal Protection & Life Management



Is there any statistical data, or other documentation, available to illustrate how often modern thermal protection is being used?

 

Japan:

25 20 15 The number of t her mal pr ot ect i on Numerical Analogue 10 5 0 1980 Year 1990 2000

PS-1 Question 6

Thermal 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: OPERATOR DICONNECT 51 TRIP AND SEND TEMPERATURE AND CURRENT READINGS TO

PS-1 Question 6

Thermal 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?

PS-1 Question 6

Thermal 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 .

PS-1 Question 7

Inrush Current Effects on Protection

  

What would be the future practice for selecting one harmonic restraint algorithm instead of another? What issues should users look at when a transformer is protected by duplicate protection devices manufactured by different manufacturers especially when the devices use different restraining and blocking principles? What are the requirements, if any, in selecting one algorithm principle from another algorithm?

Sweden :The paper 105 by Hans-Joachim Herrmann indicates that second harmonic inrush current is no longer the best significant way to detect an inrush. What about higher current values which depend on inrush? Utilities favour security to dependability are careful on the method used.

and this is why we

PS-1 Question 7

Inrush Current Effects on Protection

    

What would be the future practice for selecting one harmonic restraint algorithm instead of another ? What issues should users look at when a transformer is protected by duplicate protection devices manufactured by different manufacturers especially when the devices use different restraining and blocking principles? What are the requirements, if any, in selecting one algorithm principle from another algorithm?

Brazil:Second and fifth harmonics restraining method is mostly used in Brazil - The blocking method is not well accepted.

The Brazilian Grid Code specifies the use of hardware redundancy, but there is no special requirement to use relays from different manufacturers It is very important to know how the relay will perform, but it is not expected that users need to select the algorithm Standards for transformer differential protection could be improved if they established more detailed functional tests

PS-1 Question 7

Inrush Current Effects on Protection

    

What would be the future practice for selecting one harmonic restraint algorithm instead of another? What are the requirements, if any, in selecting one algorithm principle from another algorithm?

Japan:Measures against Inrush Current 2nd harmonic restraint schemes are now widely being used for transformer protection relays in Japan.

As more improved measures against inrush current, sequential schemes of “Phase-segregated detection/ three phase lock” and “Phase-segregated detection/ two-phase AND trip” are being used. “Three-phase-sum detection/ phase segregated lock” that adds another phase 2nd harmonic contents to self-phase value is being used too.

Fear of transformer protection relays operation-delay in internal fault is pointed out. New schemes that give up on 2nd harmonic restraint are being studied and some of schemes have been applied to transformer protection relays.

PS-1 Question 7

Inrush Current Effects on Protection

  

What would be the future practice for selecting one harmonic restraint algorithm instead of another? What issues should users look at when a transformer is protected by duplicate protection devices manufactured by different manufacturers especially when the devices use different restraining and blocking principles?

What are the requirements, if any, in selecting one algorithm principle from another algorithm?



Poland For the conventional CT’s advantage that it makes it possible to restrain the differential protection in case of the the second harmonic algorithm transformer inrush currents has the as well as at the CT’s unsymmetrical saturation.

Sometimes the protection differential current is the result of both these phenomena.

PS-1 Question 7

Inrush Current Effects on Protection

    

What would be the future practice for selecting one harmonic restraint algorithm instead of another? What issues should users look at when a transformer is protected by duplicate protection devices manufactured by different manufacturers especially when the devices use different restraining and blocking principles?

What are the requirements, if any, in selecting one algorithm principle from another algorithm?



Poland: The algorithm based on wavelet transform will be better then the second harmonic for differential protection with the unconventional, electronic CT’s, because it allows to reduce the protection operation time.

The duplicate protection devices that use different restraining and blocking principles would give a possibility to compare the restraining methods. The criterion recorder, described in the paper No111, would allow to optimizing the settings of both these protection devices.

PS-1 Question 7

Inrush Current Effects on Protection

  

What would be the future practice for selecting one harmonic restraint algorithm instead of another? What issues should users look at when a transformer is protected by duplicate protection devices manufactured by different manufacturers especially when the devices use different restraining and blocking principles?

What are the requirements, if any, in selecting one algorithm principle from another algorithm?

 

Germany: Future Practice

The amount of 2nd harmonics is too low in some cases during an inrush. An neural network can be an alternative in the future.



PS-1 Question 7

Inrush Current Effects on Protection

What are the requirements, if any, in selecting one algorithm principle from another algorithm?

  

Sweden: Measured in Phase Currents or in Differential Currents?



2 nd harmonic



4 th harmonic

  

5 th harmonic DC offset Wave shape recognition



etc.

Set block level depends on position where measurement is taken



PS-1 Question 7

Inrush Current Effects on Protection

What are the requirements, if any, in selecting one algorithm principle from another algorithm?

   

Sweden: Security?

Block for all inrush cases Not good practice to put burden on the end user to completely set this logic 15% or 7%?

 

Adaptive 2 nd results harmonic + WaveBlock good Correct and easy to use design is manufacturer responsibility

PS-1 Question 7

Inrush Current Effects on Protection



What are the requirements, if any, in selecting one algorithm principle from another algorithm?



Sweden: Dependability?



Trip for all internal faults



Insure that restraint level will trip in spite of CT saturation



Use of adaptive second harmonic blocking



Paper in IEE DPSP 2001

PS-1 Question 7

Inrush Current Effects on Protection

   

What would be the future practice for selecting one harmonic restraint algorithm instead of another? What issues should users look at when a transformer is protected by duplicate protection devices manufactured by different manufacturers especially when the devices use different restraining and blocking principles?

USA and Germany: Neural networks Sweden: special care for this approach What are the requirements, if any, in selecting one algorithm principle from another algorithm?



Japan: Non-harmonic-restraint schemes



(1) Impedance locus scheme protection) (for distance



(2) Parallel winding current-balance relay scheme (for 1000kV transformer with parallel winding)



(3) Tertiary voltage restraint scheme with lower harmonic) (for network

PS-1 Question 8

Multi-Function Numerical Protection



What is the present practice of utilities when applying multifunction relays for transformers?



Brazil: The present practice is to use differential protection Main 1 and Main 2 (redundancy) and backup by overcurrent, particularly for the secondary of the interconnection transformer. It is common practice to apply voltage restriction or controlled overcurrent protection (ANSI 51V) due to low fault current / weak, weak source and high impedance fauls.

PS-1 Question 8

Multi-Function Numerical Protection

             

What kind of adaptive techniques would add additional value to such devices for utilities? Sweden: On-line OLTC position monitoring available since 1998 Via BCD or mA signal Hundreds of installations Excellent performance record Improved Trafo Diff and Voltage Control functionality Adaptive inrush restraint Adaptive bias calculation for 1 ½ CB stations Available since 1998 Thousands of installations Excellent performance record Improved Trafo Diff operation Paper in WPRC 2003 New Features: Detects all turn-to-turn faults with more than 1% of shorted turns

PS-1 Question 8

Multi-Function Numerical Protection



What is the present practice of utilities when applying multifunction relays for transformers?

     

Japan: 1- Improvement of reliability by continuous monitoring and reduction in the number of relay parts 2-Total cost reduction by function integration 3- Labor saving by use of automatic failure analysis and automatic check 4- Improvement of maintainability by analysis of failure data record 5- Function improvement by software addition

PS-1 Question 8

Multi-Function Numerical Protection



What is the present practice of utilities when applying multifunction relays for transformers?

    

UK:

Main protection – one numeric protection with two protection functions (both unit type). One must be responsive to phase-to phase and phase-to-earth faults, the other must at least be sensitive to earth faults. Solution tends to be overall biased differential protection and restricted earth fault.

Backup protection – HV 2-stage 3 phase overcurrent and highest overcurrent.

LV protection – Residually connected earth fault protection phase overcurrent set to protect against faults, not overload (winding temperature caters for this).

PS-1 Question 8

Multi-Function Numerical Protection

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What is the present practice of utilities when applying multifunction relays for transformers?

Germany:

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Mostly used:

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Self supervision (self monitoring)

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No external matching transformers Integrated fault recording (oscillographic) Integrated event recording (messages) Commissioning support (Idiff, Irestr., angles,…) Integrated free programmable logic (PLC) Flexible masking of binary inputs and outputs

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Less used: Additional measuring functions Additional protection function

Remote setting of protection

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PS-1 Question 8

Multi-Function Numerical Protection

What is the present practice of utilities when applying multifunction relays for transformers?

Romania: Usually the following protection functions are used: 1. Technological protection Buchholz relay main tank and LTC, direct trip, ER in 87T Oil flow relay Pressure relief devices 2. Differential protection 1 Instantaneous differential Percentage restraint differential – second harmonic blocking Thermal overload, without top oil temperature 3. Differential protection 2 Instantaneous differential Percentage restraint differential – second harmonic blocking Thermal overload, without top oil temperature 4. Distance protection HV (220 kV)- 21, 50/51, 67N, ER, DR 5. Distance protection LV (110 kV) - 21, 50/51, 67N, ER, DR

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PS-1 Question 8

Multi-Function Numerical Protection

What is the present practice of utilities when applying multifunction relays for transformers?

Romania: Monitoring applied to transformers – separate device HV&LV voltages and currents HV&LV windings temperature Core temperature Oil temperature Pumps and fans Online DGA HV&LV bushings LTC monitoring

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PS-1 Question 8

Multi-Function Numerical Protection

What kind of adaptive techniques would add additional value to such devices for utilities? What are the issues that are preventing additional available protection functions from being used in practice?

Are they related to additional relay setting complexity issues?

Are they related to additional testing and normalizing procedures that require additional verification time?

Would more utilities use additional protection functions if integral commissioning tools were offered? What is the present practice of utilities when applying multifunction relays for transformers?

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Romania: Why not using additional protection and monitoring functions?

Tradition on clear separation between protection (protection engineer task) and monitoring (manufacturer task) Some functions included in other devices (measurement, CB monitoring) Doubt on proper setting calculations Complexity of additional settings Too many protection functions could decrease security

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PS-1 Question 8

Multi-Function Numerical Protection

What is the present practice of utilities when applying multifunction relays for transformers?

 

Canada: Present Practices of one Canadian utility when multifunction relays are applied for protecting transformers Apply main 1 and main 2 percentage restrained differential protection. Usually the protection zone includes HV and LV busses. If necessary for sensitivity, the HV and LV bus zones could be separately protected.

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When dual differential protections are provided, the sudden gas pressure relay is not connected to trip. The concern is numerous mal-operations due to a variety of problems including earthquakes (see paper No. 107).

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Does Japan have any experience or calculation to support adequacy of differential protection as a replacement for Buchholz protection?

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PS-1 Question 8

Multi-Function Numerical Protection

What is the present practice of utilities when applying multifunction relays for transformers?

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Saudi Arabia: Same protection functions used with conventional relays are now used in the numerical relays. The only different is that instead of having one relay for eac It is time consuming to understand the schemes, setting parameters of the basic protection function in numerical relays with different types and versions, Most of the additional functions have not been applied before in the network complicate the scheme. , and we do not feel the necessity of applying them specially they will

PS-1 Question 9

Multi-Function Numerical Protection

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How can data related to fault and disturbance analysis can be utilized to prevent premature failures?

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Canada: Data related to fault and disturbance analysis for reducing premature failures Paper 120 concludes (No. 6) that the automatic reclosing selections in the network are detrimental in some cases. No information is provided on the number of reclosures. If more than one reclose is used, this could contribute to premature failures.

USA: use adaptive reclosing What are the requirements of numerical transformer relays for quality monitoring?

What are the most desirable functions that have yet to be offered?

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PS-1 Question 10

Future Trends

What is necessary to integrate data from multiple IEDs?

What are the essential formats and communication protocols for performing data integration and analysis?

Japan:

The sampling timing of current instantaneous value is at a 30  electrical angle, or at 15  , 7.5

 , 3.75

 , etc.

  The sampling timing of current instantaneous value is generally based on master/slave synchronization control.

Where there is a functional difference between the master and slave as in the case in the figure, the system might be usually set up so that the master equipment executes control and the slave equipment follow-up control.

The sampling timing of current instantaneous value and the timing of data transmission are synchronized.

instantaneous value data.

That is, data periodicity is ensured. This is critical to the prevention of missing

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PS-1 Question 10

Future Trends

What is necessary to integrate data from multiple IEDs?

USA:

Understanding of the functional hierarchy of the protection and control system Understanding of the functionality of the IEDs Understanding of the performance requirements Understanding of the communication protocols

What are the essential formats and communication protocols for performing data integration and analysis?

Mapping versus self description Client/server versus peer-to-peer Support of the engineering process - the Substation Configuration Language Integration of legacy devices

PREFERENTIAL SUBJECT - 1

Conclusion of Special Reporter for PS1 Subject

CONCLUSION

Thermal Protection & Life Management

Improved current based thermal overload protection can be the most important overload protection in the future……

CONCLUSION

Inrush Current Effects on Protection

Security vs Dependability issues Different philosophies New different techniques are available and many other methods are being studied

CONCLUSION

Multi-Function Numerical Protection

Wait and see game for many users Technology available but hardly used Different philosophies will be applied in the future

CONCLUSION

Future Trends IEC 61850

More application papers are needed Future will make us learn