The Substations of the Future-Emerging Trends in Substation Development - Report Example

The Substations of the Future-Emerging Trends in Substation Development Abstract This paper discusses the future developments in the design of substations. It explains the new improvements and technologies that are required for future substations. Substations will be made by retrofitting the existing ones through a replacement of legacy equipment with new technology, designing new ones using shelf technologies or green filed design. The substation of the future will be more reliable, of a lower cost and more secure. It will also have re-configurability, interoperability, controllability and flexibility. Future substation will have multiplex sensors and multifunctional IEDs among other elements. The interaction of the primary and secondary equipment in the substation is very important. The paper discusses the general techniques for substation design, criteria for primary and secondary equipment, the design approach for meeting these criteria, technology for conventional substations and the new technology. The techniques for designing primary and secondary equipment for future substations are also discussed. Finally the retrofit design is explained before the conclusion. The future substation will definitely be one that overcomes the shortcomings of conventional substations. Future Substation Developments Introduction A substation is one of the parts of the system where electricity is generated, transmitted and distributed and where transformers change high voltage to low voltage or vice versa. The substation also connects different elements of the power system such as loads, transformers, transmission lines and generators. To make the connecting elements more flexible, circuit breakers serve the purpose of high power switches. Electric power moves through many substations between the consumers and generating plants. The voltage may change through many steps. Substations exist in different types which include distribution substations, switching substation, transmission substation and collector substation among others. A substation is used for general functions such as transformation of voltage, acting as a connection point for lines of transmission, monitoring points for the control center, switchyard for configuration of networks, protecting apparatus and power lines and communication with the control center and other substations. The future holds a lot for substation design and development. In the future, the world will need substations that are highly reliable, have huge economical benefits, are simple, show intelligence, can allow for modularization and whose environmental impact is low. Pressure from the above requirements and the available developments in technology will bring about the concept of a future substation that would be better than the one for today. The design of a future substation will require that engineers understand how the primary and secondary equipment within the station interact. They will also need to understand how primary system parameters transform to secondary quantities used in intelligent electronic devices (IEDs) as well as the presence of new sensor designs that do not present many of the problems existing in conventional instrument transformers. In future, substations will rely on modular approach of the design of the primary system of the substation. It will also be based on the multifunctional IEDs that provide functions such as protection, measurements, recording and control. The integration of these functions into the automation systems of the substation is also of significance. There is a restructuring in electricity markets which will make them more competitive and able to facilitate heavy transfers of power over large geographical areas. This essay will discuss in detail the emerging trends in substation development. Figure 1; IEDs (http://www.pserc.wisc.edu) General Technique of Designing a Substation For there to be the exploitation of all the economical and technical potential of substation development, more focus has gone into the study of how substations can make it possible for the network to have more intelligence. This type of development is called “smart grid”. Engineers agree that the substation of the future should have improvements in security, reliability, re-configurability, flexibility, inter-operability, controllability, maintainability, lower cost and friendliness to the environment (Kezunovic, Fellow, IEEE, Yufan Chenyan, Ghavami, 2010, p. 1175). However, substation designers emphasize on cost, environmental impact, reliability and operational flexibility. Primary Equipment Criteria The examination will focus on primary equipment in each design that share criteria such as cost, environmental impact, reliability, footprint and safety. Reliability has to do with the mode of control of power transfer, high efficiency, high situational awareness, improved carrying capacity and redundancy improvement. Safety deals with limitation of touch and step potential, risk of explosion or fire, surveillance and use of seismically qualified equipment to keep away intruders and unauthorized users Kezunovic et al 2010, p. 1176). To take care of the environmental impact, the equipment must produce low noise emissions, use water recycling, have limited electric and electromagnetic fields and be above the level of the ground. They should show flexibility in that they should be of a plug and play design, be easy to operate, have low maintenance levels with an integrated compact design. The foot print should be compact and small while the costs are kept low and with a life cycle whose cost is also minimized (Atanackovic, McGillis, & Galiana, 1998, 1173). Secondary Equipment Criteria The criteria for primary and secondary equipment are similar in certain aspects. The secondary design equipment focuses on reliability, interoperability, controllability, re-configurability and economic benefits. For purposes of reliability, secondary equipment should be compact and integrated. Secondary functions must have a lot of communication which is conducted through fiber optics, wireless apparatus and coaxial cables. Protection devices must be present as systems that can work without depending on each other (Brandstrom & Lord, 2009, p. 55). Secondary equipment should also have inter-operability which means that IED implementation must allow for continuous communication in the secondary system and interfacing which networks the management system. Secondary equipment should also have controllability. Better manual, local and automatic functions helps to achieve high speed response within normal time. Re-configurability is required for secondary equipment. Future changes, retrofits and upgrades are simple are doable with little effort and time. Finally, secondary equipment must have economic benefits. The design of green field substation must consider energy market participation, the maximization of profit the reduction of risk in the operation of the system (McDonald 2012, p. 117). Design approach to meet the criteria The substation of the future requires one to consider several scenarios. There exist 3 substation types that can be considered. The first type would require the existing substations to be retrofitted through the replacement of legacy equipment with new technologies without causing a disruption on the continuity of service. The second type is the implementation of a new substation design using new technologies. The last type would be envisioning the green-field substation design with totally new techniques, apparatus and protocol, considering energy market, maximization of profits and system price and operation (Kezunovic 2010, p. 78). Conventions Substations There is a big change in the electric power industry and substation design is also showing changes. The orthodox Air Insulated Substation (AIS) design makes use of so many disconnectors so as to allow room for repair and maintenance with very little interruption. The occupied AIS area is huge and the demand for maintenance of the open air devices is high especially where environmental conditions are severe. A part from the switch gear its parts and subsystems are open to aging and wear in the course of exploitation which leads to higher events of faults (Borlase 2012, p. 113). New substations should be more compact and somehow protected from the impacts of the environment. Existing designs of substations have their sensing and signal processing operates on the basis of individual sensors that are put on the switchyard and wired to the control house. The control house has the control, protection and monitoring devices that make use of those signals for making decisions. This concept does not facilitate data integration and the processing of signals in the substation. The IEC 61850 substation automation standard has a higher integration degree, high flexibility levels and a shorter time for construction and commissioning (Mladen et al 2010, p. 89). Functional integration levels and communication flexibility have important advantages in reading costs. This integration has an effect not just on substation design but also on other components like monitoring, control and protection by making it possible for hardwired faces to be replaced with communication links. The new design for primary equipment must be compact, friendly to the environment and allow for reduced cost maintenance and operations. The new secondary side is designed based on IEC 61850 standards and must make use of multifunctional IEDs and synchronized technology for sampling. The issue of cyber security must be emphasized because of the increase in the vulnerability of protection, control and automation systems by use of Ethernet communications between substations and between devices (Werle et al 2000, p. 257). Substation designs in the future will require current and new standards and technologies and other methodologies that differ from existing designs. The designs of the new substations will need to have the costs reduced while the same technical performance or improvement in performance is maintained with no increase in costs or very little if any. Upgrading existing substations and building new ones in urban areas will bring about increased gas insulated substations all over the world. Bearing in mind the fact that many more substations will be built in places with extreme climatic conditions, secondary and primary equipment should have the ability to operate in harsh weather conditions (Lusby 1993, p. 6). When the IEC 61850 standard was published as a new international standard for communication in substations, it became a very significant step in defining “copper-less” substations for the future and will greatly impact on future designs of substations. Available and New Technology New technology available for use in substations includes synchronized sampling based on GPS, optical sensors, multifunctional IEDs and different communication media. i) Synchronized sampling The Global Positioning System of satellites is normally very useful in the utility industry for provision of reference time signal which is then received in every substation via a GPS receiver. Purpose signals may be used for two purposes. The first purpose is the synchronization of the sampling clock during data acquisition system input in IEDs. The second purpose is time-stamping of the data obtained by IEDs (Atanackovic et al 1998, p. 1177). ii) Optical voltage and current sensors The most important purpose for optical sensors is the wide frequency bandwidth, increased accuracy and the wide dynamic range. In addition, the new sensors allow for the implementation of monitoring and control with two critical application features. A single sensor could have various IED purposes. It may also serve a big number of IEDs through the process bus. iii) Communication Media When dealing with intra and inter-communications media, substations of the modern era have different options. These include high speed coaxial cable serial bus, microwave radio, Fiber optic cables and spread spectrum wireless radio. There are two options for optical fiber use which include multi mode and single mode. The single mode can have a single stream of laser generated light for purposes of communication over long distances (Xie et al 2002, p. 860). On the other hand, multi mode has many streams of light generated through LED and used for communication over short distances. There are many benefits of optical fibers. They can be used for long distance communication, have smaller size, are of greater capacity, are light in weight and have electromagnetic isolation. The new substation design has a hybrid system that has the fiber optic cables integrated with the concept of high speed bus. iv) Multifunctional IEDs Multifunctional IEDs have more functions in just a few devices and this result in simple designs that have lesser wiring. IEDs are important because they allow for communication via computer networks and working with multiple applications and a lot of information can be availed in a remote manner. For the grid monitoring and control system used in the modern day, there should be IEDs enabled with GPS which apart from its most important function it can perform clear acquisition of data for purposes of extensive monitoring (McDonald, 2012, p. 134). Future technology includes: Multiplex sensors In the instrumentation of electric power grids, the FFPI is beneficial over ordinary sensing technologies because it provides immunity to electromagnetic interference, low possibility of damage from lighting, no grounding problems that may affect sensors when there are high electrical voltages and currents (Atanackovic, et al. 1993, p. 1173). Multiplex sensors can locate electronic equipment for sensor monitoring and processing of signals at long distances from the sensor elements. It has a bigger variety to measurements and has the ability of multiplexing several sensors to different types over one optical fiber lead connection. Its sensing elements have a small size and weight. Multiplex sensors also provide the potential for a lower life cycle cost for the instrumentation of the power grid. Multiplexing allows for light to be supplied to multiple sensors using one optical source. One can use a dingle light detector to change the optical signal from many sensors and also use a single electric signal processor to work out measures and values for several sensors. Multiplexing lowers the cost for every sensor. Its application is important for the instrumentation of substations in a cost effective manner (Lusby 1993, p. 78). This happens where there is need to remotely monitor many points. The alarm processing approach for the future would have 2 modules, one placed at the substation and the other at the system level. A structure with two levels is made to utilize the huge amount of data in the substation automation system (SAS) level. Local processing in substation computers is done and its results are relayed to help in the energy management system level alarm processor. The figure below shows the general software structure to show the explained concept. Figure 2; Software structure (http://www.pserc.wisc.edu) There are many benefits arising from this design. The SAS level alarm processor makes use of measurement data that can only be found in the substation and therefore it can identify the type of disturbance in the substation. The EMS-level alarm processor heavily depends on the outcome of SAS level alarm processor. Since a lot of the analysis has been carried out independently at the substation, the efficiency of the EMS-level alarm processor is high. Because of the 2-level structure of the future alarm processor, it is possible to accomplish more complex analysis functions in good time. Dispatchers react to more distilled and valuable information including the proposed actions to be undertaken (McDonald, 2012, p. 141). Design of Primary Equipment i) High Temperature Superconductors Substation HTS cable, HTS FCL and SMES are available on commercial basis but are still limited in their installations. It is possible to have a distributed superconducting substation. A superconducting substation has the HTS transformer as its major transformer, conducting is done with the HTS cable, fault current limiting is done through Superconducting Fault Current Limiter (SFCL) while the SMEs is used for controlling voltage stability and problems with power quality. Future substations will need to have a single cryogenic refrigeration system for provision of liquid helium for all the HTS devices. It is more economic this way than having a single cryogenic refrigerator for each of the HTS devices. A superconducting substation satisfies the green field substation requirement such as high efficiency, flexibility, lower emission of CO2, safety, aesthetic view and reliability (Brandstrom & Lord, 2009, p. 67). ii) Solid State Transformer A solid state transformer steps up and steps down voltage just the same way a conventional iron core transformer does. The future transformer will not be bulky in size, require to be maintained regularly, and have issues of power quality. It will be possible to have a high frequency converter which is the central part of the solid state transformer because of the availability of materials made form Silicon Carbide. The SST has a smaller size and weight because it makes use of the high frequency converter as shown in the figure below. Figure 3; High frequency conversion (http://www.pserc.wisc.edu) Because of the presence of semiconductors in the operation, when it stops to operate the high frequency transformer can’t allow any power through it. The High Frequency transformer therefore acts as a circuit breaker as well (Brandstrom & Lord, 2009, p. 87). Future substations will not need to have a circuit breaker before and after the transformer, something that is common in traditional designs. The substation area is also smaller because the SST has a smaller size and has no circuit breakers. The solid transformer has a higher level of controllability in its transformation of AC voltage. The harmonious distortion and phase balancing are regulated within the system because there is power conversion through one HF converter. Each of the sides of the SST can work in a synchronous manner and therefore it can perform the same functions as a transformer with variable frequency or a back to back HVD. The wave forms on each SST side can either be alternating or direct current. Therefore, a direct current converter system provides battery interfaces for storage of energy and connection to solar cells or fuel cells (Kezunovic 2010, p. 88). This can be seen as a future form of HVDC terminal with the transformer integrated into it, more so when renewable energy is among the major sources of energy. The solid state transformer that has silicon carbide material in it is more advantageous than the present transformer in matters of size and operation. SST that has a high frequency converter many has high potential as an alternative to an ordinary HVDC station. It is the advantage of dynamism in performance, lower filtering requirement and need for rigid space. Silicon Carbide technology is expected to a critical part in advancing power electronics in systems of distribution and transmission. Power electronics devices with high voltage will come with high frequency, will be less complex, with a smaller size and lower costs. This will be a big challenge to conventional alternating current devices (Kezunovic 2010, p. 90). Design of Secondary equipment i) Fiber-optic multiplexed sensors and control networks It is possible to multiplex data from many sensors on digital communication then the data is used at the substation with a number of processing units. Current developments in substation automation integration standards are making it possible to have interconnection among IEDs from different traders found in today’s substations into a single system. In order to bring signals inside the control room is will require that a multiplexed sensor network be used. Obvious feature extractors for signal processing that can serve many applications within the substation is located at the place of conversion from analogue to digital. The integration provides flexibility that defines new applications that can be given to the substation layout. The Fabry-Perot interferometer which is otherwise known as Fabry –Perot etalon has 2 mirrors for reflectance R1 and R2 which have a length cavity L between them. It serves as a sensor for multiplexing analogue measurements (Brandstrom & Lord, 2009, p. 76). Figure 4; FFPI sensors in a multiplexing arrangement (http://www.pserc.wisc.edu) This new paradigm of distribution processing shows a major shift from the existing centralized model where all output sensors are directed to the central location for purposes of decision making and decision making and this saves computing power and transmission bandwidth. Retrofit Design This approach tries to retrofit the already existing substations. The most important thing in retrofitting is to consider legacy equipment and to disrupt service continuity the least. Substations can be retrofitted by replacement of substations with the use of new technologies or carrying out an expansion on the already available substations through the use of new technology (Xie, Manimaran, Vittal, Phadke, & Centeno, 2002, p. 860). i) Dry-type transformer The common transformer in many substations is made of an iron core and windings insulated with paper or oil. New technology has created the dry type transformer which is oil free. It is better than the conventional one because it has benefits in terms of performance and the environment (Borlase, 2012, 78). Figure 5; Insulation structure of a conventional and dry transformer (http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=5563267&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F5559272%2F5563238%2F05563267.pdf%3Farnumber%3D5563267) The dry transformer is of a smaller size than the conventional one. It has smaller transportation units and it and it has a freedom of design that makes dimensioning easy so that requirements are met. In the dry type, there are two different fan systems for maintaining normal temperature conditions inside the transformer. This differs from the conventional type. If one fan stops functioning, the remaining fan can maintain the temperature of the transformer at normal levels (Borlase, 2012, 78). ii) Flexible AC Transmission Systems (FACTS) ‘FACTS’ is made up of equipment based on power electronics to increase the stability and the ability of the network to transfer power (Werle, Wasserberg, Borsi, & Gockenbach, 2000, p. 43). FACTS technology steps up the power and increases the transmission lines capacity by controlling parameter lines. ‘FACTS’ does not substitute mechanical switches but it combines with other controllers to stretch out the carrying power of lines to get near its limits. Improving the technology of power semi-conductors and the reduced cost of FACTS controllers increases the chances on using the FACTS technology on a bigger scale. FACTS technology may become a common thing in future substations (Hingorani & Gyugyi, 2001, p. 67). iii) Use of fiberglass in substations Fiberglass is important because it is cost effective, resistant to rot and corrosion, long lasting, durable and strong and is easily installed. On special applications it needs an additional veil to increase its protective capabilities such as retardation of flames, resistance to heat, UV protection and resistance to corrosion. The material is good for corrosive outdoor areas. Fiberglass can be substituted with steel, or concrete or wood on constructions. There are high chances that fiberglass material will begin occupying a very important place in the design of future substations. They can be used as alternatives in the place of steel and wood in the design of substation equipment. They make it possible to save in the long term and to reduce costs and the trouble of repairs. Fiberglass applications like trench cover, pole, and shelter and oil containment are good for retrofitting conventional substations. Kezunovic 2010, p. 168). iv) Switchyard monitoring devices Sensors are used for measuring primary equipment signals in substations including circuit breakers, transformers and power lines among others. Original analog sensors with copper wires will no longer be in use and their place will be taken by optical fiber based sensors for purposes of metering and monitoring. Optical fiber voltage and current sensors have the advantage of not having saturation, lower size and weight, high accuracy, friendliness to the environment, safety, wider dynamic range, low maintenance and high band width (Kezunovic, Yufan, Guo, & Ghavami, 2010, p. 77). a) Temperature sensors Some substations especially the old ones lack this technology. Instead of using analog apparatus with copper wires, their place may be taken up by optical apparatus with fiber based sensors for temperature measuring. Products such as SIEMENS SIRIUS 3RS2 and 3RS1 for monitoring temperatures in liquid, gas and solids are compatible with the existing analog apparatus. They can also have many functions taking place in one device. SIRIUS 3RS1 and 3RS2 have relays for monitoring temperature, air conditioning, heating and ventilation systems that are reliable just like motors and all of them have 3 sensors working in a simultaneous manner (Mladen, Chenyan, Yufan & Mohsen, 2010). Therefore, the analysis equipment that has digital displays is applicable to a wide range of temperature and on various sensor types. b) Pressure sensors Many substations do not have these sensors and most of those that exist today are analog. The place of analog substations will be taken by substations with optical sensors such as ABB S261. The S261 sensors are used together with 261 compact transmitters which allow measurements of a gauge, absolute or level pressure. Different remote seal types exist and this makes it possible to have optimum design (Brandstrom & Lord, 2009, p. 90). c) Vibration sensors New optical technology like vibration sensor switch, the VBS01 Series makes it possible to monitor the vibration of circuit breakers in an optical manner. d) Fiber optic cables Large substations have a cable length of about 200,000 feet. Copper wiring is heavy and this is a source of interference. Some old substations have these wires destroyed by rodents. Currently, there are many challenges in the electrical substation which affect secure and reliable communications (Kezunovic & Taylor, 2004, p. 32). The challenges are among others, extreme high temperatures, high voltages, faults such as high currents, electromagnetic interfaces and electrostatic discharges. To be able to counter such challenges and to create secure, reliable, economical and safe communication substation upgrading should be done using fiber optic cables that interconnect all protection, monitoring and control parts (Lusby, 1993, p. 67). In addition, there is no other power from outside needed for fiber optic transceivers made to function in the tough substation environment. Substation performance can be affected by the performance, reliability and weight of the wiring. The technology has other benefits such as higher speed, low costs, increased resistance to electromagnetic interference and longer distance of information transmission. Before copper wires are replaced with fiber optic cables, consideration must be placed on cost and technical aspects. It is hard top install fiber optics because they need expert human resources. Fiber is also sensitive to twisting. One must consider all these factors when examining the available retrofit options (McDonald, 2012, p. 45). Figure 6; Switchyard monitoring devices (http://www.pserc.wisc.edu) New Substation Design The new substation design will include among other technologies, the gas insulated substation design. Gas Insulated Substation (GIS) design The gas insulated switch gear provides higher flexibility and reliability when compared to other solutions. Because the design is that where gas is enclosed, GIS provides the best solution for substations located underground and indoors. GIS technology greatly helps to reduce the occupied area in hybrid and outdoor substations. GIS configurations are applicable on bus bar arrangement. This includes the single bus bar, the double bus bar, double bus bar with double circuit breaker, single bus bar with transfer bus, ring bus bar and half circuit breaker scheme (Brandstrom & Lord, 2009, P. 56). Conclusion In conclusion, this essay has discussed the future trends in the development of substations. The future holds a lot for substation design and development. In the future, the world will need substations that are highly reliable, have huge economical benefits, are simple, show intelligence, can allow for modularization and whose environmental impact is low. The design of a future substation will require that engineers understand how the primary and secondary equipment within the station interact. They will also need to understand how primary system parameters transform to secondary quantities used in intelligent electronic devices (IEDs) as well as the presence of new sensor designs that do not present many of the problems existing in conventional instrument transformers. Developments in substation design include retrofitting existing substations, implementation of new substation designs and the green filed design. Future substations will need to overcome many or all of the shortcomings of the current substations. This will require the integration of new technology into the design. Such changes will require the inclusion of multifunctional IEDs and multiplex sensors just to mention a few. There are many other discoveries and developments in terms of technology that will be used in constructing substations and it is expected that the substations of the future will be far much effective, efficient and friendly to the environment than those existing today. Bibliography Atanackovic, D., McGillis, D.T. & Galiana, F.D., 1998. “The application of multi-criteria analysis to substation design”, IEEE Trans. Power Systems, vol. 13, issue 3, pp: 1172-1178. Borlase, S. 2012. Smart Grids: Infrastructure, Technology, and Solutions. CRC Press, 2012. Brandstrom, F., Lord, W. 2009. “The future substation –reflection about design”, 20th International Conference on Electricity Distribution, Prague. Hingorani and L. Gyugyi, 2001. Understanding FACTS, concepts and technology of flexible AC transmission systems. Dehli: Standard Publishers Distributors. Print. Kezunovic, M. & Taylor, H. 2004. “New Solutions for Substation Sensing, Signal Processing and Decision Making”, Hawaii International Conference on System Sciences HICSS-37, Waikoloa Vilage, Hawaii. Kezunovic, M. Yufan G.,Guo, C. & Ghavami, M. 2010. “The 21st Century Substation Design: Vision of the Future”, IREP 2010, the Bulk Power System Dynamics and Control – VIII, August 1-6, Buzios, Rio de Janeiro, Brazil Kezunovic, M., Fellow, IEEE, Yufan G., Chenyan G., Ghavami, M. 2010. The 21st century substation design: Vision of the Future. Texas A&M University College Station, Texas, USA. Lusby, J.R. 1993. “Fundamental Concepts in Substation Design”, Rural Electric Power Conference. Papers Presented at the 37th Annual Conference, pp: D2/1 – D225. McDonald, J.D. 2012. Electric Power Substations Engineers, Third Edition. CRC Press, 2012. Mladen K., Chenyan G., Yufan G., Mohsen G., 2010. “New concept and solution for monitoring and control system for the 21st century substation,” Accepted by POWERCON 2010, Smart Substations and Equipment, October 24-28, Hangzhou, China. Werle, V. Wasserberg, H. Borsi, and E. Gockenbach, 2000. “A new protection and monitoring system for dry type transformers based on innovative sensor technologies,” pp. 255–258. Xie, Z., Manimaran, G., Vittal, V., Phadke, A.G., Centeno, V., 2002. “An information architecture for future power systems and its reliability analysis”, IEEE Trans. Power Systems, vol. 17, issue 3, pp: 857-863, 2002. Read More