Lighting and Switching Coordination in Substations

Question: Discuss about theLighting and Switching Coordination in Substations. Answer: Introduction Insulation coordination is a sure way of protecting the substation power system by coordinating switching. One of the biggest safety risks in substation is the occasional lightning being experienced in most parts of the country. An S/S that is not properly designed against this natural phenomenon would often experience dangerous power surges. Therefore, the process of designing the power switching coordination systems in a substation is a critical undertaking that would ensure overall safety of the equipment and operators. The various equipments in the substation must be protected against these dangerous power surges that mostly frequent the system. Normally the lightning would strike and last for about 0.25 seconds. Although this could be a very short time but the damage caused afterwards can be transmitted to the entire system. Notably, surge protection can never be a 100% in any given power system where large voltages are generated. Most systems would work by confining the damage to a designated section in the system. Properly designed systems with proper switching coordination would mostly guarantee an automatic protection system. So how does the lightning affect the system? When it strikes the system, there is normally dramatic escalation of the voltage level. Consequently, the current wave propagation also escalates to levels that the system can not withstand. In such situations, system breakdown results preceded by melting of the conductors and arcing hence the system become dangerously unsafe to the human operators. Therefore, it is often desired to design more effective and efficient surge protection systems that would guarantee safety even when it strikes unexpectedly. Surge protection systems are often integrated into the overall power network so as to carry out the function of regulating power surges. It is common to analyze their characteristics so that they can be designed to smoothly operate within the safe limits. Therefore, firstly, it is imper ative to study the lightning strokes and how switching coordination could be used to protect the substation system against overvoltage and power surges. Literature Review Many researchers have greatly attempted to uncover different methods that could be used for surge protection. The following paragraphs outline some of the tremendous contributions by various researchers in this area: Elahi, H et al (1989) Although this is an old paper, it is still very relevant to assist in the analysis of the modern power network systems. The author mainly explored the purpose of performing insulation coordination in hvdc converter stations. He opines that insulation is mainly done to achieve the following purpose: -The maximum steady state, temporary and transient voltage levels could be determined hence exposing the equipment requirement voltage levels -The protective devices, commonly used such as the surge arresters could have their characteristics analyzed hence establishing the extent of surge protection and ultimately their durability. The paper also proposed a procedure for surge protection where gapless metal oxide arresters could be used for insulation protection .According to the author, this method is cost-effective and performs better than other designs. Das Kanabar (2015) This paper proposed a dynamic tool for grid power control. The authors admit that the modern power system has become more dynamic and complex hence there is need to protect the grid power using a more sophisticated protection system. They proposed a centralized substation protection control system. He attributes that the evolution of relays has occurred since the 1960s where electromechanical relays were the common types. Later, solid state relays dominated the field but the most modern systems have microprocessor based relays that are more superior in functionality than the solid state relays. They operate using logic and often described as intelligent. Therefore, modern technologies around the surge protection system normally are constituted of the hardware platforms onto which the software configurations can be built. The linkage between the two elements is via a sophisticated communications channel with supported protocols such as the MMS, GOOSE and synchrophasor (Das Kanabar, 2 015). The authors also opine that the element of control in such protection system is often complex and a system architectural implementation such as SCADA normally offer better monitoring and control. Every tiny but critical portion of the system could be monitored by this system hence providing real-time data to the operators for necessary action to be taken. However, the author agrees that more work need to done to improve the performance of such a system and even they go further to recommend various architectural designs of the system. Fulchiron, D (1995) This author attempted to explain exactly what happens to the substation power network when lightning strikes. During stormy weather, lightning are usually common and sometimes they can unexpectedly strike the substation power network. Mostly their polarity is negative to the substation and they dangerously damage the entire system by escalating the voltage levels in the network. Consequently, the current flowing in the network also surges to levels that cause breakdown of the conductors hence system breaks down completely. According to Fulchiron (1995) the voltage surge is given by the formula: U = Zc i/2 where Zc = is line zero characteristics impedance and I is the injected current into the system. The surged voltage value is normally in the range of million volts, a level that no system can withstand hence arcing is normally experienced before the network can shut down completely. Pacificorp (2010) It establishes various protection schemes that could be used against the lightning. Notably, the arresters combined with the breaker protection are often viewed as better option. The transformer is being rated as the most critical part of the substation hence they are often protected on both sides by the breakers with the arresters connected on both sides as well such that when it strikes, the system goes offline automatically hence preventing damage that may occur in the absence of these surge protection systems. It is also being proposed that substations with capacities of 138kV and below be protected by shielding, and use of lightening arresters. Furthermore, breaker protection could be used for capacities between 69kV and 139kV. Hypothesis Hence the hypothesis that would guide the research-to-be-done include: Centralized protection provides better switching coordination than decentralized system Challenges The major challenges that are likely to be faced include: The lack of standardized methods and techniques for surge protection and network insulation making it difficult to characterize the networks The information about substation insulation is still at infantile stage hence expectedly data on the existing systems may not be sufficient for the research work Seemingly the research work in this area has stalled; hardly do we have the designers seriously considering this risk (natural phenomenon) to the power network system Conclusion The work of providing a near perfect insulation system in power network system is still in progress. Certainly, more research work is still expected especially in discovering methods and techniques that could be used to temporarily switch off the system during lightening strikes but almost go online automatically. The existing ones operate in such a manner that ones they go offline, it will require a human operator to bring it back to operation. Besides, reportedly, some of the existing systems have been jamming severally during operation. Therefore, the future work will certainly focus on delivering solutions that are more reliable; although it should be noted that 100% efficiency can never be guaranteed. Reference Fulchiron, D. (1995).Overvoltages and insulation coordination in MV and HV. Available at: https://www.studiecd.dk/cahiers_techniques/Overvoltages_and_insulation_coordination_in_MV_and_HV.pdf Das, R Kanabar, M. (2015).Centralized Substation Protection and Control. Available at: https://www.pes-psrc.org/Reports/IEEE_PES_PSRC_WG%20K15_Report_CPC_Dec_2015.pdf Elahi, H et al. (1989). Insulation Coordination Process for HVDC Converter Stations: Preliminary and Final Designs. Available at: https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=4310601 Arrester works.(2010). Insulation Coordination FAQ. Available at: https://www.arresterworks.com/services/insulation_studies.php Pacificorp. (2010). Lightning and Other Overvoltage Protection. Available at: https://www.rockymountainpower.net/content/dam/pacific_power/doc/Contractors_Suppliers/Power_Quality_Standards/1B_7.pdf