Transmission network angle stability protection based on synchrophasor data in control centre

Angle stability appears in many forms in transmission network. There are small active power oscillations which do not endanger the normal operations whereas medium and large oscillations have implications on normal operations. These latter kinds of oscillations in some cases develop in out of step condition, which is dangerous disturbance with serious impact on transmission network and generating units. Transmission network operator’s challenges and obligations are to treat in the right manner angle stability issues in their network. Controlling and protecting network needs to be done in efficient way in order to disconnect disturbance quickly and prevent abnormal network operation without exporting disturbance in surrounding networks. Synchrophasor measurements in control centre offer a platform, which responds in a new way on angle stability in transmission network. Those measurements which are collected in phasor data concentrators, which is a part of Wide Area Monitoring will be used for creating out of step protection. This is the first step to extended system to Wide Area Monitoring Protecting And Control (WAMPAC). Paper gives progress of such project in Croatian Transmission Network Operator (HOPS). Firstly, there will be stated motives for development of new out of step protection based on synchrophasor measurements. Some feasibility aspect elaborated with emphasis on communications latency. Furthermore, designed Matlab model for transmission network and protection with small portions of simulations results and analyses presented in paper reveal potential of proposed solutions. This new protection is based on using voltage angles values from phasor data stream in phasor data concentrator

Special protection scheme for operation of central Zagreb transmission system

The paper presents a Special Protection Scheme solution for the central Zagreb transmission system. The Central Zagreb transmission system is characterized by a highly meshed network with combined overhead and cable sections and a special operation of the 110 kV cable link between two power plants important for the city’s heat and electricity supply. The Special Protection Scheme is developed using static and dynamic analyses of different network scenarios. Island operation is simulated for a consumption and generation surplus, and an underfrequency load shedding scheme is determined. The Special Protection Scheme architecture is presented with a brief description of the telecommunication infrastructure

Transients Caused by Sequential Circuit Breaker Tripping Issued by Busbar Protection

A study of transients in a high voltage substation 400/110 kV is presented in the paper. An analysis was carried out after a fault on the 110 kV busbar, which caused severe damage in the substation. Investigation was focused on a time frame of several sequential circuit breaker trippings. A first step of the study was collection of data from the primary and secondary system in the substation and the control centre. After numerous analyses of data an attempt was made to construct a precision model, which could be used in the computation. Appropriate models were developed for circuit breakers, voltage (potential) and current metering transformers, power transformers, surge arresters, overhead lines and an equivalent grid. The components of the power system can be modelled for the very particular purpose, which means that a different frequency model should be used and each element in this analysis has a specific frequency response. An attempt was made at very detailed modelling of a power transformer, air blast and SF6 circuit breakers. Computed results of fault currents were compared with measurements captured by the disturbance recorders in the field, mainly in differential numerical relays. Different switching schemes and different tripping sequences of several 110 kV circuit breakers were analysed with a constructed model in the millisecond range. Models of circuit breaker with different types of media, air blast and SF6 gas were used in the cases investigated. Modelling of the circuit breakers’ electrical arc was an important item in all cases in order to take into account the interaction between electrical arc and circuit current during the process of current interruption. The Schwarz/Avdonin equation is applied to model the dynamic behaviour of an electric arc. The fault studied was accompanied by a large short circuit current. For this particular case two types of circuit breaker, air blast and SF 6 were modelled. An important conclusion from those analyses was that sequential tripping of several circuit breakers does not cause superposition of overvoltages, because interruption the current happens when it is passing through the zero. Even the record from the substation and the disturbances recorder proves that each particular circuit breaker was successfully opened. On that basis, focus was put only on the final opening of the breaker and its arc extinction. The conclusion can be drawn that such a substation fault should have no influence on excessive overvoltages that can threaten the insulation of components in the substation

Smart grid substation equipment maintenance management functionality based on control center SCADA data

Classic approach to preventive maintenance of equipment in power system substations was based on periodical maintenance according to regulations and best practices recommended by vendors. SCADA system in HOPS is used primary for real-time monitoring and control of the equipment in substations. Real time data available in SCADA databases contain useful information for substation maintenance optimization based on operational conditions. Malfunctions and failures in the substations are monitored via SCADA system. Analyses of these data can be used to evaluate maintenance strategy and plan the reconstructions and replacement of the equipment. This article presents current maintenance management approach in HOPS, which is the only transmission system operator in Croatia, and possible improvements in efficiency of equipment maintenance using SCADA data. Prerequisite for the analyses of these kinds of data is standardization and unification of information names and structures. HOPS put a lot of effort in standardization of SCADA data during last refurbishment of control centers. Use of SCADA data for analysis drives the need for standardization and vice versa. Examples of statistical analyses of the SCADA data are done on multiple levels. High level analyses is used to provide the global overview of the real time data. It can point to suspicious information that require detailed analyses. The signals that appear often in the list can indicate that there is a problem in the primary equipment, monitoring system or alarm configuration. Low level analyses can be done on target information important for equipment maintenance. In this paper some low level analyses are presented for switching equipment, transformer lifetime, equipment in operation, and tap changer operation. An analysis is made for number of switching operations for breakers and disconnectors in different operational conditions. Preventive maintenance should be done based on number of switching in normal operations and even more often for breakers that are often interrupting fault current. SCADA data can be used for availability of the equipment and duration of failures thus providing valuable information to managers. An analysis on RTU communication availability is shown

Transmission network angle stability protection based on synchrophasor data in control centre

Angle stability appears in many forms in transmission network. There are small active power oscillations which do not endanger the normal operations whereas medium and large oscillations have implications on normal operations. These latter kinds of oscillations in some cases develop in out of step condition, which is dangerous disturbance with serious impact on transmission network and generating units. Transmission network operator’s challenges and obligations are to treat in the right manner angle stability issues in their network. Controlling and protecting network needs to be done in efficient way in order to disconnect disturbance quickly and prevent abnormal network operation without exporting disturbance in surrounding networks. Synchrophasor measurements in control centre offer a platform, which responds in a new way on angle stability in transmission network. Those measurements which are collected in phasor data concentrators, which is a part of Wide Area Monitoring will be used for creating out of step protection. This is the first step to extended system to Wide Area Monitoring Protecting And Control (WAMPAC). Paper gives progress of such project in Croatian Transmission Network Operator (HOPS). Firstly, there will be stated motives for development of new out of step protection based on synchrophasor measurements. Some feasibility aspect elaborated with emphasis on communications latency. Furthermore, designed Matlab model for transmission network and protection with small portions of simulations results and analyses presented in paper reveal potential of proposed solutions. This new protection is based on using voltage angles values from phasor data stream in phasor data concentrator

Advanced and Rapid Tool in Control Room to Determine the Cause and Location of Events in Transmission Network

Operating personnel in control room act on SCADA alarm generated on data from station computer. Using new technologies and advanced technical solutions assistance tool can be designed. This tool provides quick help in busy situations for operator. For this new tool with three types of case studies insight will be given in this paper. Introduction part has short information about numbers of alarms and events in Control centre, and their distribution during one month period. Basic principles for alarm handling in SCADA system is given with all limitations. New tool, Intelligent Alarm Processing system is designed and implemented in control room. It has connection to SCADA system with standard data exchange format CIM/XML and run in real time, with only few seconds delay. This system based on Multilevel Flow Model has root cause analyses implemented for power system. Detail fault location algorithm description with block scheme for this Intelligent Alarm Processing system is part of third chapter. Special attention must be paid for modelling protection data in SCADA system which are sent to this new tool. Demonstration of Intelligent Alarm Processing system operation is reported in fourth chapter. Three characteristic disturbances in transmission network were elaborated. Most complex and challenging disturbances for operator in control room is cascading event. This case study is presented in detail in four sequences through graphical user interface. Second case study is also challenging for operators, heavy winter storm with numerous isolated events. In this case study very effective graphical presentation and alarm list with three types, primary event, consequences and detail list for this events were demonstrated. This list pointed out exactly and clearly what happened in the network. Last case study presents common disturbances which appears on daily basis, where this tool is of great assistance because it points on transmission elements very fast

Performance of WHO Angina Questionnaire in Measuring Burden of Coronary Heart Disease in Human Isolate Populations

Isolated human populations represent good candidates for studying genetic and environmental causes of common complex diseases because of their decreased genetic and environmental diversity. The possibility of inexpensive and reliable detection of disease prevalence in such populations is therefore of considerable importance, as comprehensive routine health data and disease registries are rarely available in these populations. In this study, we validated the performance of the WHO Rose Angina Questionnaire (RQ) in measuring the burden of coronary heart disease (CHD) in 9 settlements in these Croatian Adriatic islands. CHD was defined as myocardial infarction (MI) diagnosed by a specialist in the local general hospital, or angina pectoris (AP) by a local general practitioner (GP). The »true« prevalence of CHD in 1,001 adult persons was 10.5%. The results of the RQ screening based on the first 3, 5 and 6 questions were compared with medical record of CHD. Increasing the number of RQ questions from 3 to 6 resulted in decreasing test sensitivity (from 59.0% to 30.5%) and increasing test specificity (from 86.3% to 93.0%) in the prediction of true CHD status. CHD prevalence was overestimated by 76% when subset of the first 3 questions of RQ was used and by 25% when the first 5 questions were used. However, it was underestimated by 10% when the first 6 questions were used. We conclude that RQ is a useful screening method for measuring burden of CHD in isolate human populations, and that the result based on the first 6 questions is a good approximation of the true CHD prevalence in the population, although it should be considered a slight underestimate

Smart grid substation equipment maintenance management functionality based on control center SCADA data

Classic approach to preventive maintenance of equipment in power system substations was based on periodical maintenance according to regulations and best practices recommended by vendors. SCADA system in HOPS is used primary for real-time monitoring and control of the equipment in substations. Real time data available in SCADA databases contain useful information for substation maintenance optimization based on operational conditions. Malfunctions and failures in the substations are monitored via SCADA system. Analyses of these data can be used to evaluate maintenance strategy and plan the reconstructions and replacement of the equipment. This article presents current maintenance management approach in HOPS, which is the only transmission system operator in Croatia, and possible improvements in efficiency of equipment maintenance using SCADA data. Prerequisite for the analyses of these kinds of data is standardization and unification of information names and structures. HOPS put a lot of effort in standardization of SCADA data during last refurbishment of control centers. Use of SCADA data for analysis drives the need for standardization and vice versa. Examples of statistical analyses of the SCADA data are done on multiple levels. High level analyses is used to provide the global overview of the real time data. It can point to suspicious information that require detailed analyses. The signals that appear often in the list can indicate that there is a problem in the primary equipment, monitoring system or alarm configuration. Low level analyses can be done on target information important for equipment maintenance. In this paper some low level analyses are presented for switching equipment, transformer lifetime, equipment in operation, and tap changer operation. An analysis is made for number of switching operations for breakers and disconnectors in different operational conditions. Preventive maintenance should be done based on number of switching in normal operations and even more often for breakers that are often interrupting fault current. SCADA data can be used for availability of the equipment and duration of failures thus providing valuable information to managers. An analysis on RTU communication availability is shown

Lost in Transition – The Island of Susak (1951–2001)

The isolated population of the Island of Susak was thoroughly studied by a multidisciplinary team of the Croatian Academy of Sciences and Arts in early 1950’s. Recently, a team of scientists revisited the island. This paper describes the main characteristics of the transition process during which a massive exodus occurred with 90% of the island’s population migrating to New Jersey, USA. We summarise the differences in lifestyle, economy, social structure and sense of identity between the historic (1950’s) and contemporary (2001) Susak population. We applied contemporary methods (analysis of microsatellite DNA polymorphisms) to investigate local myths about extreme levels of inbreeding and genetic homogeneity among the Susak islanders. Analysis of short-tandemrepeat (STR) loci showed that Susak displayed characteristics of a small homogeneous breeding isolate. The average heterozygosity was found to be low compared to outbred populations. The signature of a recent severe bottleneck could be detected. Analysis of 8 markers located on Xq13–21 in 71 individuals suggested extensive level of linkage disequilibrium (LD). A migrant study was designed to investigate the effects of large environmental changes (Susak vs. USA) and inbreeding (Susak vs. Croatian general population) on some biologically important quantitative traits, such as blood pressure and serum lipids. The results confirmed the positive correlation between inbreeding level and blood pressure that has been reported in the literature on several occasions. The last remnants of this traditional island community will soon be lost forever

Lost in Transition – The Island of Susak (1951–2001)

The isolated population of the Island of Susak was thoroughly studied by a multidisciplinary team of the Croatian Academy of Sciences and Arts in early 1950’s. Recently, a team of scientists revisited the island. This paper describes the main characteristics of the transition process during which a massive exodus occurred with 90% of the island’s population migrating to New Jersey, USA. We summarise the differences in lifestyle, economy, social structure and sense of identity between the historic (1950’s) and contemporary (2001) Susak population. We applied contemporary methods (analysis of microsatellite DNA polymorphisms) to investigate local myths about extreme levels of inbreeding and genetic homogeneity among the Susak islanders. Analysis of short-tandemrepeat (STR) loci showed that Susak displayed characteristics of a small homogeneous breeding isolate. The average heterozygosity was found to be low compared to outbred populations. The signature of a recent severe bottleneck could be detected. Analysis of 8 markers located on Xq13–21 in 71 individuals suggested extensive level of linkage disequilibrium (LD). A migrant study was designed to investigate the effects of large environmental changes (Susak vs. USA) and inbreeding (Susak vs. Croatian general population) on some biologically important quantitative traits, such as blood pressure and serum lipids. The results confirmed the positive correlation between inbreeding level and blood pressure that has been reported in the literature on several occasions. The last remnants of this traditional island community will soon be lost forever