Abstracts 2015

By: Zarko Djekic – Ausgrid, Australia 

High impedance (HiZ) differential schemes have been used for busbar protection over many decades. Traditionally, performance of Hiz schemes has been good and utilities faced very few issues related to security and dependability of the scheme. Early schemes had been implemented using high (usually nonlinear) impedance voltage relays. Over time, the voltage relays had been replaced with electromechanical (EM) instantaneous overcurrent relays and resistors. More recently, EM relays have been replaced with solid state and numerical overcurrent relays. At the same time requirements for smaller CT have been growing due to switchgear size reduction. General understanding is that scheme performance is expected to remain satisfactory as long as few original design “rules of thumb” are met.

This paper describes modelling of high impedance differential scheme and testing results. High impedance scheme CTs have been modelled and simulation results verified by high current primary tests. Relay model has been verified and results compared to operations of several EM and numerical relays. Results were presented, and discussed. It was found that performance (speed of operation) of high impedance schemes using numerical relays can be poor under certain conditions even if all “rules of thumb” were followed. This is result of different characteristics of the new numerical current relays compared to the old voltage relays. The paper presents some recommendations for “rules” associated with the CT requirements and modifications to the scheme to improve speed of operation.

By: Alexander Apostolov – PAC World, USA

The increased availability of non-conventional current and voltage sensors and stand-alone merging units from different suppliers, together with the integration of redundant communications interfaces based on the PRP and HSR create an environment for the wide spread development and implementation of digital substations.

The paper describes the concepts and principles of a digital substation:

• definition of digital substations
• components of digital substations
• architectures of digital substations

The second part of the paper describes the functional hierarchy of the digital substation and how the individual functions are implemented using different IEC 61850 services.

The last part of the paper discusses the benefits of the digital substation:

• cost savings
• efficient construction
• efficient installation
• efficient commissioning
• efficient maintenance

By: Ian Young – Schneider Electric, Australia

This paper looks at the practical use of GOOSE for protection applications. GOOSE itself brings many benefits which can be utilised for various protection signals, however, isolation and testing are critical considerations which are often seen as deficiencies in edition 1 of the IEC61850 standard. A key driver for edition 2  was to overcome these limitations. This paper looks at various isolation and test methods used for edition 1 and compares them to using edition 2.

A major drawback of edition 1 was the inability to use online simulation. This limitation was not obvious and care is needed to ensure simulated or test messages are not used on a live system. This paper looks at the new simulation modes available in edition 2 which greatly improves this situation. The edition 2 simulation mode is quite powerful and this paper also looks at how this functionality can be used in a practical application.

One of the stated objectives of edition 2 is to create solutions that can incorporate edition 1 relays. This paper also looks at the practicality of doing this.

By: Terry Foxcroft – Snowy Hydro, Australia  

Line protection systems were replaced between Transgrid’s Upper Tumut Switching Station and Snowy Hydro’s Tumut 1 and Tumut 2 Power Stations.

A risk of a downed conductor before synchronising the line at the switching station was identified, and a protection system designed to detect this failure.Traditional systems would not detect this unique event until a significant quantity of fault current was reached with a possible bush fire.

The predicted event occurred less than a year after the protection was installed, and was correctly cleared with no extra plant or environmental damage.

This paper examines the thought processes required to see the need, the need and implementation of the protection, and the resulting fault and protection operation.

By: John Ainsworth – Ausgrid, Australia

The Electrical Protection of power systems is an essential and critical function. The level of dependability and security required is the highest of any of the secondary circuit functions used in substations. This paper is a statement of the key functional principles and requirements  underlying the concepts and design of protections systems and schemes. The requirements are stated in a way which is independent of the technology used, so as to avoid restricting the development of new technology or applications. This approach is in the spirit of IEC 61850 in providing  base rules and a framework for developing solutions without restricting the development of new solutions and improved functionality. The content includes key objectives of protection, basic principles applying to any scheme, all of the components involved (not just the relays), primary and back-up principles ( Remote BU and Local BU) and their implications. It deals with the requirements of secondary isolations of individual schemes required to permit safe work on a scheme while the remainder of the substation is in service, and with the requirements for simulated functional proving of protection schemes, again in a live substation. Segregation principles are also covered.

By: Alexander Apostolov – PAC World, USA

The power system automation community is going through a period of transition from the world of hard wired systems and proprietary configuration and analysis tools into the world of distributed IEC 61850 communications based systems and object oriented standards based engineering and analysis tools. This requires the development of a new set of skills in order to help the specialists from our industry understand and use the new technology.

The main goal of this paper is to introduce the Extensible Markup Language (XML) and the Unified Modeling Language (UML) to the protection and control community and focus on the UML diagrams and XML files used in the IEC 61850 standard and in some IEEE standards related to protection and control in order to help the readers understand the diagrams and files included in or defined by the different standards.

The first half of the paper presents the Extensible Markup Language (XML) and the Unified Modeling Language (UML). It describes some of the key types of UML diagrams defined for the description of static structures of complex systems and the dynamic behavior between the different objects in the system, as well as the structure and components of an XML files. The second part of the paper discusses the use of UML diagrams and XML files in the definition of the standard.

Examples of the use of UML diagrams in IEC 61850 and in the description of the principles of operation of control commands are given later in the paper.

Examples of the use of XML in the IEEE C37.239: IEEE Standard for Common Format for Event Data Exchange (COMFEDE) standard are presented at the end of the paper.

By: Usman Mahmood – Energy Australia NSW, Sy Bui – Aurecon Group, Australia

Reliability, Efficiency and Safety are the key objectives of any modern power system and can be achieved by implementing fully automated systems. The IEC61850 standard has revolutionized the automation process by standardising system specifications, configuration language, naming convention, communication protocol, and conformance testing. Use of IEC61850 compliant devices can simplify engineering design process, increase flexibility and reduce engineering costs. In order to operate and maintain IEC61850 based systems, plant engineers must acquire knowledge about communication protocols, computer network, classes, and objects etc.

In New South Wales (NSW), the protection systems for large turbo-generators (660MW units and above) and associated generator transformers have reached the end of their operating life. Most NSW generating companies have already embarked on a program of replacing these generator and generator transformer protection systems. The new protection systems used IEC61850 compliant protection relays with an optical, peer to peer communication messaging system known as “GOOSE”. Being a protection retrofitting project to existing generating units, there were a number of difficult choices and design consideration in selecting the levels of IEC61850 implementation to these new protection systems. This paper looks at the extent of IEC61850 implementation in these retrofitted generator and generator transformer protection systems in NSW. It also provides a discussion on the impacts of the IEC61850 system on the operation and maintenance of these protection systems and possible future improvements.

By:  Greg Finlayson & Mitchell Eadie – Schneider Electric, Australia

This paper discusses methods of analysing waveform recordings from numerical relays to diagnose power system events and confirm relay operations. Comtrade format recordings often only capture the physical analogue and digital signals wired to the relay, while internal protection functions will use algorithms to manipulate these signals before determining a trip condition.

With a basic understanding of the relay algorithms the operating quantity can be derived from the recording and compared to an operating characteristic to verify settings and confirm relay operations. Examples presented include analysis of harmonic content of inrush waveforms, trip locus of differential and impedance based characteristics, high impedance based protection trips and fault finding installation and application issues.

By: Graeme Heggie – Electranet, Australia  

Over national holiday breaks low loads and high proportional wind generation can combine and result in fault levels on the network dropping to unexpected values. In the event of a system fault this could adversely affect the operation of protection schemes. If protection schemes do not detect faults the effects of system events will become more widespread leading to unnecessary extensive damage to assets and power supply disruption.

Using examples for protection of lines and transformers the paper should inform how low fault levels may affect scheme operation.

Looking at the operation of single phase tripping schemes, this paper will analyse how the schemes work to clear a fault and the importance of ensuring tripping at all ends of the protected feeder with particular emphasis on Wind Farm fault supplying capability and protection scheme sensitivity looking at various differential, distance and distance signal-aided line protection schemes. For transformer protection we look at how basic relay settings are modified by zero sequence filtering and ratio compensation leading to differing sensitivity.

By: Terry Foxcroft – Snowy Hydro, Australia      

Protection systems deal with two different types of faults, ones we expect and faults that are unique and had not been considered.

This paper describes black swan events, and how we as protection people should make our system black swan tolerant.

It looks at several events, not all within the power industry, and describes how different thinking may have prevented incidents from occurring. It describes the affect of outliers on fault analysis and black swan recognition.

By: Martin van der Linde – NOJA Power, Australia

Utilities operating in Australia face many adversaries with regards to power distribution; challenges which would drive most international counterparts to alternative markets. Australian utilities are a much more resilient group, and with modern developments in pole mounted switchgear, the obstacles faced are not quite as insurmountable as they used to be.

Australian utilities possess among the longest feeders in the world, and long feeder lines exacerbate the issues presented with power quality and bushfire risk, but with recent developments in capabilities of automatic circuit reclosers (ACRs), it is possible to alleviate this headache. Further updates to recloser control capabilities have caused the advent of remote ACR power quality monitoring, and this new capability has opened the door for greater reliability on long feeders as more accurate, local and relevant power quality data can be gathered. All of this information can be remotely interrogated, retrieved and then manipulated to grant utilities unprecedented resources to improve their reliability of supply. Additionally, new capabilities to control and manipulate reclosing sequences remotely without having to edit settings along with simple self-diagnosing communications systems to ensure reliable network reporting and awareness, it is possible to reduce and manage the bushfire risk.

This paper outlines the recent developments in bushfire mitigation strategies through the use of pole mounted ACRs, specifically the NOJA Power RC10 system. Additionally, the application use of remote Power Quality data gathering using the NOJA Power RC10 system is discussed. Recent developments in the capability of data capture from this recloser system allows for a greater understanding of network performance to be formed. This information can be used to improve network performance and financial bottom line for utilities by optimisation of their currently installed resources.

By: Zahra Bayat – Yarra Trams, Australia

A suitable protection system is required for every reliable and secure power supply. Isolating the fault current in minimum time is the most important part of DC protection in traction system. Also, providing the appropriate discrimination between load and fault current on the protection functions is resulting to decrease noises tripping on protection system. This paper will describe the concepts of DC protection system on the following items:

• Single Line Diagram of D.C traction system
• Scheme of protection functions on transformer/rectifier circuit
• Traction feeder protection schemes
• Principal impact of load analysis scheme on the tram network

In addition, it will describe some of DC power system limitations and implications such as:

• Problems of single end fed electrical section specially on long distance feeding point condition
• The effects of different type of vehicles and their starting current
• Pantograph voltage limitations
• Underground cable screen Fault
• Overhead conductor limits

By: J. Blumschein, C. Dzienis, Y. Yelgin – Siemens AG, Germany

Smart grids of the future will have new challenging requirements for the protection elements regarding selectivity and dependability. The load flow will be increasing, the magnitude and direction of load flow may be changing frequently and even the network topology will be more complex than today. This paper presents a new design of distance protection which perfectly fits to the requirements of the smart grid of the future.

The impedance measurement is based on the calculation of the load compensated fault reactance X and from line resistance separated fault resistance. This method is applied for phase to ground as well as phase to phase faults. Separation of the fault resistance improves the accuracy of the impedance calculation. The method reduces the negative influence of fault resistance during high load flow and minimizes the risk of wrong pickup during high load condition.

Once a fault is detected it is very important to select the faulted loop to calculate the impedance to the fault. For complicated faults in the complex network of a smart grid this can be a challenging task with a certain risk of non-selective fault clearance.

In the past the loop selection was done by a so called decision tree, in which several criteria were applied sequentially to find the faulted loop. Thereby, only the result from one criterion selects the faulted loop.

The new approach is different. Several criteria based on magnitudes of voltages and currents, changes in voltages and currents, symmetrical components or impedances are applied in parallel. The results of each single criterion are weighted and combined to get a final result for the selection of the faulted loop. With this principle the efficiency of the loop selection has been optimized to different network topologies by changing the weights of each criterion.

The same principle is applied to the directional element. Multiple criteria based on actual voltages, memorized voltages, symmetrical components or delta quantities are applied in parallel. The final result is obtained as a weighted combination of the result of each single criterion.

By: Leonardo Torelli – CSE Uniserve, Australia / Ilia Voloh – GE Energy, Canada / Zhihan Xu – GE Energy, Canada

Modern communication networks have dramatically increased the implementation of the line differential scheme as one or both primary protection for transmission lines. The transmission network is usually meshed which also provides fault current contribution from both ends of the line. Considering the ongoing need to reduce CAPEX investment, it is expected that the supply to specific loads, for instance mining in rural zones of Australia, the transmission network could be expanded radially with single or double circuit applications. In a radial system, in the event of fault, fault current contribution is drawn mainly from the source side. This scenario could potentially create issues to the operation of supervisory elements of the line differential relay at the remote end. This paper reviews this specific application with particular attention to solutions which balance the need for security, speed and dependability of the line differential protection scheme.

By: Maty Ghezelayagh – TasNetworks, Australia / Chris Simmons – Hydro Tasmania, Australia

This paper describes the design, installation and commissioning of new numerical protection and control and intertripping schemes at an EHV substation. The substation supplies a critical and large industrial plant (paper mill). The connection consists of two radial 110kV transmission lines connecting four 25 MVA, 110/6.6 kV transformers two of which are dual wound. Each transmission line is directly connected to a transformer. The 6.6 kV sides of transformers are connected to different busbars via circuit breakers. For a fault on the 110 kV lines or the transformers the remote end 110 kV Circuit Breaker and appropriate 6.6 kV circuit breakers must open.

This arrangement required complex intertripping schemes between protection devices of the transformers within the substation and between the protection of the local substation and remote substations.

The secondary work at the local and remote EHV substation included installing new 110 kV transmission line protection scheme consisting of Main ‘A’ and Main ‘B’ new numerical relays for each line. This included removal of existing inter-tripping schemes.

The secondary work at the local and remote EHV substation included installing new 110 kV transmission line protection scheme consisting of Main ‘A’ and Main ‘B’ new numerical relays for each line. This included removal of existing inter-tripping schemes.

The project necessitated an innovative design, settings and logic programming to be implemented on new relays. Existing secondary infrastructure including copper cables and intra substation fibres of the single old protection scheme were utilised for the now duplicated transmission line protection. This involved the following:

• Removal of the existing multi- intertripping schemes and reconfiguration using new numerical protection scheme with appropriate setting and logic programming.
• Utilizing fibre optic cable and digital transceivers/receivers for provision of trip/close circuits.
• Implementing a reliable design and settings based on sound standard policy/philosophy
• Installing, testing and commissioning the new protection and intertripping schemes with minimum plant outages due to load critically.

Finally the paper discusses that how the implementation of the project involved innovative solutions so that new primary equipment and secondary copper cabling was not required while providing high system reliability and security.

By: Maty Ghezelayagh – TasNetworks, Australia

Conventional calculation of loadability limits of distance relays for different characteristics such as Mho and Lenz is based on determining the minimum permissible load impedance which is equivalent to maximum load current in order it does not encroach to the last forward zone reach of distance relay with a safety factor. In this paper it is shown that this philosophy which is still used in some utilities for calculation of relay load limit (RLL) is not applicable to modern numerical relays due to utilizing of the following elements for EHV transmission lines:

• load encroachment element (LE)
• Power swing blocking(PSB)

The functionality of LE is to block the relay under normal loading condition as long as the load impedance is within the LE characteristic. Its characteristic consists of a circle cut by straight lines which represent load angle. The radius of circle represents the magnitude of minimum load impedance. Bearing in mind that LE respond only to balance positive current, it is shown that LE characteristic does not need to grade with any forward zones as long as the maximum load angle is less than the line angle with sufficient margin.

The main objective of PSB is to block the operation of phase distance elements for stable swing. Its characteristic consists of two blinders or circles, one inner and one outer. The inner blinder/circle should encompass the outermost zone of phase distance protection that has been selected for blocking. The outer blinder/circle should be set so that the closest minimum load impedance locus to be outside the outer blinder/circle characteristic for all loading conditions.

In this paper it is shown that the loadability limit of distance relays of numerical relays should be calculated based on outer blinder/circle characteristic of PSB rather than conventional method of last forward zone, otherwise the functionality of PSB will be ineffective and relay may trip on stable swings. With this concept mathematical equations for calculation of RLL are developed for two cases, one with blinder and the other one with circular characteristic for PSB.

In addition to impedance relays, methodology for calculation of RLL for current differential and overcurrent protection of new numerical relays are given.

Finally, the results of analysis of system disturbances which have occurred under normal system loading conditions due to wrong relay’s settings, design errors, relay failures and human errors during testing are discussed. It will be shown how these disturbances could have been prevented if correct design philosophy and test procedures had been implemented.

By: Georgios Konstantinou, Guishi Allen Wang, Baburaj Karanayil and Vassilios G. Agelidis – Australian Energy Research Institute (AERI) & School of Electrical Engineering and Telecommunications, Australia

The complexity of a modern power system makes testing and verification of protection settings invaluable but ever-more complicated and challenging. Real time digital simulation provides an efficient and cost-effective way of testing the performance of a protection relay under all possible faults and transient system conditions (e.g. power swings, out-of-step etc…) using accurate network model and parameters. More importantly, the hardware-in-the-loop (HIL) configuration of the relay with the real-time digital simulator (RTDS), provides a means of observing the effects of a relay or breaker operation on the whole power system in a dynamic manner and in real-time. Additional functionalities include scenario playback, interaction between the equipment under test (EuT) and other relays, breakers and power system equipment and interoperability – IEC 61850 compatibility testing. The end result is a verified, fine-tuned and optimal set of protection settings. The RTDS available at UNSW Australia (Fig. 1) is a unique piece of infrastructure for the country and the largest of its kind in research institutions globally. It is capable of modelling up to 1620 single phase nodes of a power system and simultaneously test up to four separate relays. This paper will introduce the RTDS equipment, its configuration and present some possible cases of protection system testing. Its aim is to demonstrate the capabilities of the system and its value for Australian utilities and practicing protection engineers.

By: Wing Chan, Si-Dieu Tran, Sameep Gharti Chhetri – Power and Water Corporation, Australia

The Darwin region’s power supply is linked to the major generating plant at Channel Island via a pair of parallel 132kV transmission lines. The existing protection system is in service since 1986 and has experienced a few blackouts and near-miss power disturbances. It consists of redundant distance protection with communication assisted reverse blocking scheme to accelerate the Zone 2 tripping in order to improve system stability.

The protection system for this double circuit line is scheduled for replacement by modern microprocessor based relays and new communication equipment. This paper describes the review of the proposed protection upgrade considering the combined impacts of the influencing factors on distance protection including:

• mutual coupling
• fault impedance
• load flow
• source impedance ratio
• single pole tripping and auto reclose
• current reversal

The new protection scheme is then selected based on the N-1 criteria and lessons learned from past experience. Actual major system disturbance records are converted into COMTRADE format and used to verify the new protection scheme before they are put into service.

By: Fred Steinhauser – OMICRON electronics, Austria

In the past, the application of communication aided protection schemes was limited because of the limited availability, high cost and decent performance of communication channels. Even if protection for important lines was communication aided, extensions added to the system and their related protection were often not included in such schemes. But exactly the complexity added by such extensions and new challenges to protect these modified systems made the application of protection communication even more desirable.

A system that grew from a two terminal line to a three terminal configuration and that was later again extended by two additional feeders serves as an example for the considerations. The protection on the two main buses is from the solid state generation, while the protection for the third (newer) leg is already numerical. None of these relays has built-in communication features, the protection communication for the transfer tripping scheme of the initial system was established by external communication devices that could just transfer a few bits point-to-point.

On the other hand, a migration strategy was in place that shall lead a way from the existing SDH/PDH network, that could be utilized anyway only by the most important applications, to an MPLS network that serves a wide range of applications. Now available layer 2 paths through the MPLS infrastructure allow even to exchange IEC 61850 GOOSE messages directly between devices in different substations. With GOOSE to binary I/O converters attached to the protection relays, a protection scheme including all important feeders could be set up with decent effort.

Of course, such a distributed protection scheme with complex functional dependencies needs to be thoroughly tested. The same communication infrastructure that transports the protection information can be as well used to connect and control test and measurement equipment. The distributed protection system is best tested and the events are best measured by a test system and a measurement system which are both time synchronized and distributed as well. Besides the assessment of the protection’s ability to detect faults in the electrical power system, the performance of the communication is measured as well.

Applying state-of-the-art technologies for the protection system and the test and measurement equipment delivers an efficient and performant solution.