PROTECTION SYSTEMS IN MODERN ENERGY MANAGEMENT ORGANIZATIONS
Mustafa İŞBECEREN1
Nevzat ONAT2
1Telepro Energy and Electronic Systems San. Trade Ltd. Sti., 34785, Atasehir, Istanbul
2Marmara University, Vocational School of Technical Sciences, 34722, Kadıköy, Istanbul
Summary
In this study, the importance and structural features of conservation models in modern energy management organizations are emphasized. The historical development of protection systems and the concept of reliable and selective wide area protection, which is gaining more and more importance in different management structures brought about by the diversity of production/consumption today, are examined. The equipment that should include protection models that can contribute to the purpose of quality and uninterrupted energy supply has been introduced, and suggestions have been made about the functions they can undertake.
Introduction
Protection in power systems is the structures that include the production, transmission and distribution stages of electrical energy and aim to use the energy as safely as possible from failures or events that endanger any part of the power system. Making power systems 100% safe or 100% reliable creates very high costs. For this reason, it is a must to carry out risk analyzes in order to keep the failure rate and the probability of being affected by failures at acceptable levels.
In the two basic regulations published by EMRA on energy quality, service quality is seen as three basic components: continuity of supply, technical and commercial [1]. In the light of this information, minimizing breakdowns and interruptions and increasing the effectiveness and efficiency of maintenance-repair activities are topics with very important techno-economic benefits.
For this reason, it is of great importance that faults and outages in energy systems are detected quickly, as well as accurately reported and used as source information in studies such as necessary improvement, maintenance-repair, replacement on the system by subjecting the obtained data to various statistical analyzes. According to the reports of the American Chamber of Electrical and Electronics Engineers, an equipment failure report;
1) Type, serial number, manufacturer and other information required for classification of the equipment,
2) Installation date, location of the system, length in case of line,
3) Type of fault (short circuit, incorrect operation, etc.),
4) Cause of failure (lightning, ice load, external impact, aging etc.),
5) Time of failure (out of service and re-commissioning time rather than downtime only), date and meteorological conditions,
6) Should include information such as the type of outage (forced or planned, temporary or permanent). Apart from these parameters, it is useful to add the number of subscribers who are de-energized to the information in case the fault causes an interruption [2].
For this reason, it is of great importance to keep detailed reports about this malfunction, as well as to detect the malfunction by the protection system and take the necessary action.
This study briefly summarizes the measures that can be taken to improve the reliability coefficient in protection systems. It especially emphasizes the importance of effective use of data communication and signal processing technologies. In this study, the equipment used to increase the reliability of the protection systems with the innovations provided by modern technology is emphasized and an example is made about the communication infrastructure of the protection system, which is included in the wide area protection systems that have become increasingly widespread in recent years.
- Protection Systems
In order to reduce the damages caused by fault currents, arc and/or overvoltages caused by short circuit or insulation rupture in any of the components of electrical power systems such as generators, transformers, lines and loads, and to eliminate the effects of a continuous short circuit on the general operation of the network and especially its stability. The faulty element and the mains part must be taken out of operation as quickly as possible. All of the equipment that performs this process is called the protection system [3].
Protection relays are electronic or electromechanical devices designed to limit injuries caused by electrical faults and to protect equipment. These relays are only part of the protection system. The protection system is a large structure that includes all equipment in power systems. It should also measure current/voltage information under normal operating conditions of the power grid. Measurements, signal processing and control mechanisms play a very important role in increasing the efficiency of the relays. Main purpose; is to minimize the damage that will occur as a result of the failure. With the realization of this aim, equipment/equipment replacement needs are reduced in the most general sense, the repair process is shortened and the re-commissioning process is accelerated. Thus, the operating time of peak power plants, which produce at higher costs, is reduced. It also makes a very important contribution to the continuity of system stability [4].
Another way to increase the effectiveness of protection systems is to divide the power system into certain zones. Thus, full security can be ensured by including more than one protection alternative in each section.
Today, power systems are very complex structures in which generation, transmission, distribution and consumption units work together at the same time. Production systems vary in terms of raw materials they use and conversion methods. In addition, the enterprises of these production centers can be state, private sector or multi-partner structures. The diversity and management structures at the point of consumption are much higher. The whole system must be operated together with an interconnected structure.
2.1. History of Protection Systems
The first relays used in the protection systems needed since the early 1900s use completely electromechanical technology. The first relay in the literature was presented in 1902 based on the overcurrent principle. Electromechanical relays not only detect the fault, they also produce the necessary power to open the breakers. Following the overcurrent principle, electromechanical relays operating according to the differential (1905), wayfinding (1909) and distance measurement (1923) principles were developed. All relays produced until the 1940s used electromechanical technology. Especially distance relays are widely used in many protection systems today.
The spread of electronic circuit elements led to the development of static relays after 1940. Since 1960, computers that provide the opportunity to sample and record voltage and current signals have allowed the establishment of digital protection systems. Although microprocessors began to replace computers in the early 1980s, digital computing technology continues to be used. Today, especially very high voltage power lines can be effectively protected with digital distance relays and replace the use of electromechanical relays. Figure 1 shows the historical change of protection relay principles and technology groups [5].
- Modern Energy Management Systems
The relay models, whose brief history is given above, have gained a new dimension with the development of effective protection techniques in very large areas with the artificial intelligence, wavelet transform and time synchronization provided by GPS technology. Although generation, transmission and distribution systems have become much more diverse in terms of both technical and management models, the reliability of protection systems is increasing. Digital technology enables many new techniques to be used in this field. Direction comparison, walking wave algorithms, and other transient analysis-based techniques allow the development of very high-speed protection systems.
Modern energy systems have many components that take into account technical, economic, legal and social factors. These components interact with each other. Figure 2 shows the components of a modern energy management system [6]. Here, one of the subsystems is the protection system in which emergency monitoring, analysis and reporting processes are carried out. With this feature, today’s protection systems become complex systems in which signal processing, data storage and analysis processes are carried out beyond just relay coordination. The structures that emerged with the latest developments in protection systems are briefly explained below.
3.1. Adaptive Protection
Adaptive protection systems are structures based on the installation of a large number of relays to adapt to any situation that may occur in the power system. For example, time-delayed overcurrent relays adjust the operating time according to the magnitude of the fault current, or distance relays take different actions depending on the current direction. It is very difficult to predict some situations that may occur due to the complex structures of today’s interconnected networks. Anticipating all scenarios can sometimes force the protection system to work for any particular system condition that is not optimal. If a relay is required to work for a specified situation, it should be able to adapt its settings to changing system conditions. For this reason, an improvement to be made at every stage of the protection system should include a balance between the concepts of economy-performance, reliability-security, complexity-simplicity, speed-sensitivity (selectivity) [7].
3.2. AI Based Protection Systems
Especially artificial neural networks (ANN) are widely used in protection systems. Their most important advantage is that they can be applied to very complex and special cases when the entire system behavior is required to be known. However, the training and testing process of ANN takes a lot of time, and the correct operation of the network is directly dependent on the size of the data being tested and the adequacy of the test data. ANN applications in protection systems are generally used for distance protection.
3.3. Wavelet Transform Methods
In recent years, wavelet techniques, in which signals are defined and analyzed at different scales, have been developed in a different structure from the classical Fourier Transform techniques. Wavelet transform can be used in many areas such as network fault and location detection, comparison and storage of faulty data, identification and classification of the type of disturbance effect, protection of main equipment in the power system and analysis of the network and system under the disturbance effect.
3.4. Wide Field Protection
Protection systems were developed in the early stages to protect equipment in only three systems. However, microprocessor controlled relays provide both protection and measurement functions at the same time. In addition, these relays can communicate with each other and provide very detailed information to system administrators for protection and control purposes. Relays with these features are called “intelligent electronic devices”. High-speed communication lines allow the relays to update their settings very quickly, either among themselves or via the control center. These technological developments and the time synchronization provided by GPS find wide use in backup protection algorithms. Thus, existing and possible faults for a very large network segment can be detected in advance. By detecting the starting point and direction of the fault, its spread can be prevented. In wide area protection systems, auxiliary equipments that undertake very important tasks are used, apart from relays. The most important of these devices are briefly introduced below.
3.4.1. Annunciators
They perform the function of announcing the fault information coming from the relays in various ways. They are functional devices used in electrical networks as well as in other areas. In the case of a malfunction, the simplest models provide the system operator with malfunction information visually and with a sound warning. Today, these devices also undertake the functions of transmitting fault information in desired detail to RTU devices, operator computers, event recorders and data collection centers with the help of a microprocessor unit and software. There are also types that have their own memory on them. Thanks to this memory, the annunciator also gains an event recorder feature, eliminating additional costs for small-sized systems. Annunciator devices can be produced with different signal input numbers according to the needs. Today, annunciator devices with 4, 8, 12, 16, 24, 32 and 48 inputs are commercially available in the market. There are devices in a very wide price range depending on the manufacturer, additional features and especially the quality elements in their production. Figure 3 shows an alarm annunciator with 16 inputs.
3.4.2. RTU Devices
Remote Access Unit (RTU) devices have become one of the most important elements of today’s distribution center automation systems. This unit acts as a cache memory that collects the information from the announcers and stores them in various formats. It also undertakes the transmission of the incoming data to various units with software authorization according to the nature of it. RTUs are microprocessor controlled devices. Especially in recent years, models that can record data with time synchronization using GPS technology enable monitoring and control of very long distance transformer stations from a single center. This feature provides significant communication flexibility and cost savings in large area protection applications. Reducing the communication standards used in providing data to the SCADA system to a single type as IEC61850, especially in recent years, is an issue that is emphasized all over the world and in our country. This is a very costly investment as it requires all relays and measuring devices in the field to support this protocol. However, with the appropriate design of RTU units, it is possible to make a significant saving by eliminating this requirement. An example RTU model is given in Figure 4 [8].
3.4.3. Event Recorders
This unit is located in the power system control center and records all incoming data with time information. Data in the device can be accessed at various levels with software authorization. As a result of the analysis of the information, very detailed information about the behavior of the power system can be obtained. Event recorders are also included as a unit in some relays today. Depending on the system structure, they may have various physical and technical properties.
3.4.4. Other Equipments
In addition to the equipment listed above, communication lines, modems, service provider (server) systems and software can also be used depending on the structure, dimensions and locations of the network section where the protection system works. In particular, protection panels that will increase the operational safety of the system and facilitate fault tracking, panel PCs that provide control over the panel in addition to operator computers, etc. Many equipments are among the components of today’s protection systems.
- Sample
With the equipment detailed in the previous section, selective and reliable coordination of protection systems for very large network sections can be achieved. The main element in this system is to transmit the information from the measuring devices in the field to the operator and the energy management center in the most accurate and fastest way. An example of a structure where multiple distribution centers can communicate at the same time is given in Figure 5.
This model can create a very flexible and user-friendly working opportunity with the software interfaces used. Panel PCs in distribution centers make it easy to follow the breakdown and process. Since all access points provide data flow in GPS synchronization, an event information can be seen without delay by all remote access points connected to the system. The data provided can be transferred to users at all levels through a wide variety of channels with software authorization. As a result of the statistical analysis of these data, many important information can be obtained such as the number of failures, the points where the failures are concentrated, the reasons for their spread, operator performances in the repair and re-commissioning process and many more. Thus, it becomes possible to prevent malfunctions before they occur, by providing a control integrity over the entire system. With these systems, which can prevent possible energy cuts, very important contributions can be made to the country’s economy.
Result
The most important purpose of modern energy management systems is to provide uninterrupted and high quality electrical energy to consumers. With the equipment and approaches mentioned in this article, protection systems can be transformed into structures where data can be obtained that will make a very important contribution to the realization of this purpose. Classical failure reporting processes are done by the operators filling out the printed forms manually or by computer. This method is prone to errors, involves a long and costly application, most of the time there are disruptions in reporting processes, lack of information, the reports cannot be analyzed quickly, etc. includes significant disadvantages. The sample model presented in the study can eliminate all these negativities and ensure that fault records are simultaneously stored in secure environments independent of operator computers, statistical analyzes are made and shared with users at all levels, including consumers, with software authorization. In this way, very important technical and economic benefits can be achieved by reducing the number and duration of outages due to malfunctions and other planned maintenance and repair activities.
Sources
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[8] www.telepro.com.tr