A summary of the recent extreme weather events and their impacts on electricity, S Küfeoğlu, S Prittinen, M Lehtonen

Tags: electricity, Samuel Prittinen, power system, Electrical Engineering, overhead lines, natural disasters, extreme weather conditions, power interruptions, infrastructure, Storm Gudrun, distribution system, power reliability, interruptions, transmission, extreme weather, network operators, Sweden, power outages, extreme weather events, Sinan K�feolu, electric power, Matti Lehtonen, supply security, nuclear power stations, Protection practices, Matti Lehtonen Abstract, nuclear power plant, electricity law, power transmission, electric power grid, blackouts, electric power lines, transmission lines, distribution lines, electric power system, existing system, supply reliability, Protection of Electrical Infrastructure, power lines, International Conference Electric Power Quality, transmission system, power generation, Energy Network Association, distribution systems, hydro power plants, storm protection, related events, underground cables, thermal power plants, Matti Lehtonen Impacts, Gudrun, Matti Lehtonen TABLE, total cost, Toronto Hydro Corporation, Loss of supply, electricity market, DISTRIBUTION LINE, Swedish authorities, Swedish Armed Forces, Transmission system damages
Content: International Review of Electrical Engineering (I.R.E.E.), Vol. 9, N. 4
ISSN 1827- 6660
July ­ August 2014
A Summary of the Recent Extreme Weather Events and Their Impacts on Electricity
Sinan Kьfeolu, Samuel Prittinen, Matti Lehtonen
Abstract ­ North America and Europe have been benefiting of high level of electric power reliability thanks to their robust transmission and distribution systems. Nonetheless, due to the increasing number of extreme weather events, such as; hurricanes, floods and winter storms, there have been many large scale black outs during the last decade. As the societies get more and more dependent to the continuous electric power, the consequences of power interruptions get bigger. This paper summarizes the impacts of some major extreme weather events on the electricity and focuses on the Storm Gudrun of 2005 in Sweden. Protection practices of the electric power infrastructure against natural hazards are presented. Moreover, the changes in the Swedish electricity law regulating the customer compensation scheme due to experiences of Gudrun are briefed. Copyright © 2014 Praise Worthy Prize S.r.l. - All rights reserved. Keywords: Reliability, Disaster, Hurricane, Storm, Electricity, Compensation
I. Introduction The continuity of electric power supply is a crucial matter for the societies. Along with the developments in information technologies many daily life activities and services such as transportation, banking, health services and communications have become more dependent on electricity. Under normal working conditions, sustaining a high level of supply reliability is already a challenge for the electric power society. This challenge increases in many folds when there are abnormal conditions that will result in interruptions in the operations of power system. Some natural disasters caused by extreme weather conditions like hurricanes, winter storms, floods, thunder storms and etc. are worth investigation in terms of their impacts on the electric power infrastructure and resulting economic outcomes. The power system planning is a delicate matter for the authorities. The majority of attention is given to the supply demand balance and hence the future electric power generation capacity is the primary concern for all countries. However, the concepts of supply security and power system reliability mean more than estimating the future electricity consumption. The security of power transmission and distribution is the core part of providing continuous electric power. The developed countries have sound, well ­ planned and well ­ operated power systems. This meant high level of supply reliability for the consumers in these countries. Nevertheless, the experiences during the last decade clearly showed that the electric power system in the European and North American countries is not as reliable as it was thought. The abnormal events, such as extreme weather conditions threaten the supply security.
The increasing number of extreme events, and their vast impacts on the societies and on the economies arouse questions about the power system infrastructure of the developed countries. As it was seen in many occasions, the authorities start to act only after a severe disaster to harden the infrastructure. This is done via policy changes which aim to push the utilities to take action and invest more on the transmission and distribution systems. This paper studies the impacts of several extreme weather events and presents brief information about some of the major cases seen during the last decade. Special attention is given to the storm Gudrun of 2005 in Sweden and the Swedish electricity law about the customer compensations are summarized. II. Extreme Weather Condition Events and Protection Practices The major extreme weather related events that were seen during the last decade give an idea about the severity of these incidents and their impacts on electricity network. These events and the proposed protection practices are summarized in the following sections. II.1. Summary of Recent Major Events Due to geographical differences, different parts of the world are prone to distinct natural disasters. While the United States have been struggling with some serious hurricanes, flooding has been number one menace for Central Europe and wind storms have been a major concern for the Northern Europe. Heavy rainfall was seen over the southern regions of the central Europe from
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late May to early June, 2013. Excessive rain along the northern arcs of the Alps resulted in severe flooding throughout Germany, Czech Republic, Austria, Switzerland and Hungary. Because of the vast damages along the watersheds of rivers Danube and Elbe, Germany was the hardest hit country among others. The cost estimates of the losses due to flooding is about 17 billion , where Germany faced a loss of 12 billion [1]. During the disaster substations were flooded and long lasting black outs were seen. The 2013 flooding showed that the 2002 flooding was not examined thoroughly and the necessary lessons were not learned well. On 9th of July 2013 upon receiving heavy rainfall Toronto, Canada suffered from a flood. The utility that serves the city, Toronto Hydro, had 719,000 customers and up to 70,000 customers faced long interruptions [2]. About 300,000 customers were affected by short interruptions. The city center Toronto is fed by two substations; Manby Station and Leaside Station. The rain falls flooded Manby and then Leaside suddenly became overloaded [3]. The authorities had to start rotating blackouts to reduce the loads. In addition, the residents were asked to turn off nonessential lighting and electronic equipment. The hurricane Katrina hit the states of Alabama, Florida, Mississippi and Louisiana in the US in August, 2005 and about 2.7 million customers were left without power [4]. As it was estimated, the hurricane did do almost no damage on the generation side of the electric power system. Only one nuclear power plant was shut down in advance of the event and remained off for two weeks. Nonetheless, the power distribution infrastructure was hit harshly. Poles, overhead lines, transformers and electrical equipment were badly damaged. The city New Orleans was blacked out. After the hurricane, the utility Entergy New Orleans spent 260 ­ 325 million $ for restoration efforts in addition to a customer revenue loss of 147 million $ and then filed for bankruptcy in September 2005 [4]. Hurricane Sandy was a tropical storm that first caused major damage in the Caribbean and then moved on to the United States in October 2012. More than 9.3 million customers had power outages in the US and Canada [5]. 8 nuclear power stations had to be shut down briefly. Excessive destruction were seen in overhead lines and electric switch gears. The electricity infrastructure repair costs were estimated to be about 3.5 billion $ [5]. Heavy storms started to hit the United Kingdom in December 2013. According to the Environment Agency, Met Office, England has been suffering from the wettest winter seen in 250 years [7] and the country saw the wettest January since the first weather records in 1776. The storms and the rainfall resulted in severe flooding in February 2014. Strong winds and flooding has been causing extensive power outages throughout UK. On Wednesday 8, January 2014 the press release by the Energy Network Association (ENA) of UK and Ireland indicated that the extreme weather created some of the most considerable damage seen in decades and the
resulting power interruptions affected around 750,000 customers [8]. Fig. 1. Number of customers with power outages in the United States during Hurricane Sandy [6] The Storm Eino of October 2013 caused some 110 kV lines to trip in Finland and resulted in about 250,000 customer-outages [9]. According to Finnish high-voltage net-holder Fingrid lines dropped due to trees from the storm and the situation could be fixed within 40 minutes [10]. Major damage was also seen at distribution level companies. Elenia was the most affected company with 92 000 customer-outages [11]. Another extreme weather condition that poses a danger on the electricity supply is the crown snows. The paper [12] presents a case study conducted in Finland in 2006 and states the impacts of crown snows on the supply security. Ice storms threatens the electric supply security as well. The 1998 ice storm of Canada is an example that clearly shows the effects of such an event. The details of the storm and the power outage consequences are presented in [13]. In early 2013 due to snow storms large network disruptions were seen globally. On 8th and 9th of February, 2013, wet and heavy snow fall brought down both power lines and tree branches resulting in large network disruptions for 700,000 consumers in the United States [14]. In Plymouth, Massachusetts one nuclear power plant shut down automatically because of the outage. The situation was also spread to Canada where 21,000 customers were reported to be without electricity on February 9 [15]. On March 22, 2013 strong winds and frozen power lines caused power interruptions for 200,000 consumers in Northern Ireland [16]. In Poland, on April 1, 2013, over 140,000 businesses and homes were left without electricity due to problems created by heavy snow. Electric overhead lines were cut by the weight of the snow and by the tree branches that were broken off and fallen on the power lines [17]. The most severe ice storm seen in the last a couple of decades and large scale power interruptions following the incident were reported in China during the ice storm of 2008. The result of the long and heavy ice formation on the grid was devastating. The detrimental effects of the disaster include thousands of collapsed, damaged and broken transmission towers and more than 2,000 damaged transformers. More than 200 million people
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were left without electricity and the direct costs of the event was estimated to be more than 2.2 billion $. The paper [18] presents the impacts of wind storm of 2005 and ice and snow storms in 2008 on the electric power grid infrastructure in China in detail. II.2. Protection of Electrical Infrastructure against Extreme Weather Conditions and Disasters Extreme weather events bring abnormal conditions and potential threats to the electricity transmission and distribution infrastructure. Even the robust, well planned and well - operated infrastructures of developed countries suffer from natural disasters. As it was briefly explained by numerous examples at the Section 2.1 of this paper, the consequences of such incidents on the electric supply security are severe. Interrupted public services, cancellation of social activities, loss of revenue and loss of feeling of security are some of the major factors that attract attention on the significance of continuous electric supply. As it was seen during the infamous New York City black out of 1977, the fear for public disorder, looting and arson is another important aspect that drive authorities and the utilities, or the network operators, to take precautions in order to harden and increase the resiliency of the electricity transmission and distribution system. With respect to the time of occurrence of the incident, the necessary actions and precautions can be divided into three sections: i. Before the events Extreme weather forecast is possible via meteorological observations and measurements. Statistical data about weather and weather related extreme events are available throughout the world. However, what is lacking for the power system planning purposes is the availability and the usage of hazard maps. Such flood and hurricane maps are necessary when the new infrastructure is installed and when the upgrades are planned on the existing system. The problem with the developing countries is that their transmission and distribution system is already built and very little new constructions are needed. The cost of relocating the infrastructure in the hazard prone areas is extremely high and it is practically impossible. This fact leaves the option of hardening the existing system against possible disasters for the network planners and network operators. Another means of precaution is to define and provide coordination among authorities, network operators and municipalities in case of a blackout during a disaster. As it was seen during the storm Gudrun of 2005, in Sweden, the shortage of trained personnel is a serious problem during the power restoring and repairing efforts. One network operator might not have the sufficient number of personnel or the necessary equipment to overcome the urgent matters. At this point, the assistance of other utilities, personnel from public services, the civil
defense, or even the support from armed forces might be essential for the recovery efforts. In order to avoid chaos and confusion, all these coordination and crisis Management Planning should be predefined by the authorities: ii. During the events During the natural disasters, the first goal to achieve is to restore the electric power as quickly as possible. It is a fact that as the duration of the outage increases, the direct and indirect costs increase as well. Fast fault detection is crucial for power restoration purposes. Rather than waiting for the complaints of the customers, power system monitoring and fault detection technologies are the best way of detecting and managing extensive blackouts. It is customers right for the electricity consumers to receive information about the outages. The utilities are supposed to reach their customers by any means possible. Internet, televisions, newspapers, telephone calls and SMS, or even radio can be used to reach customers who experienced an outage. This is also important in terms of avoiding public fear and possible public disorders. iii. After the events In most of the cases blackouts continue after the extreme weather events. Especially for the customers in the rural regions, energizing back the power is tiresome and it might require much longer time than the ones in the urban areas. The incidents related to the extreme weather conditions cause considerable damages to the transmission and distribution system to the electrical equipment. This means comprehensive work for the repairing purposes. The electric towers, poles, overhead lines, transformers and etc. are likely to be damaged and they must be repaired, or replaced as quickly as possible. To avoid such future hazards, the necessary upgrading of the existing infrastructure should be defined and it must be carried out. One sound example for this action is to increase the degree of cabling in the distribution system. Although this kind of upgrade is highly expensive for the utilities, it is known that the reliability of the underground cabling systems is much higher than the reliability of the overhead lines. The hazard preparedness and the corresponding actions differ with the characteristics of the extreme weather conditions. The weather events can roughly be grouped into three as floods, storms and winter storms: i. Flood protection Flooding does not pose a considerable hazard for the distribution or the transmission lines. However, it is the major risk for the security of the power substations. Physical barriers are the primary precaution against flooding water. Levees and sandbags provide a protection to some extent. Water pumps are also necessary to pump out the water from the substation. Relocation of the critical equipment is the key element for the substation
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protection. Elevating the vulnerable components, such as controllers, switches, transformers and etc. helps to reduce the risks and losses. Changing the location of existing low ­ lying substations which are prone to floods is highly expensive and thus not preferable. However, flood hazard maps should be considered when new substations are to be designed and built. Cleaning up the debris and elevating the control rooms are other crucial points in flood protection. ii. Storm protection The primary concern about the storm protection of the transmission and distribution systems is the strong hurricane winds. In advance to the storms and hurricanes, upgrading damaged and weak poles and towers is a must. One practice is to follow the National Electrical Safety Code (NESC) of IEEE [19] when the strengthening of the poles is carried out. If changing the poles is economically unfeasible, then using guy wires to support the existing poles might be preferred. Falling trees over the overhead lines is the major reason behind the storm related outages in the Nordic countries. Cutting down the surrounding trees, providing wide corridors to the overhead lines and preventing vegetation are the cheapest remedies for this problem. Burying power lines to underground is the more expensive but at the same time more reliable solution for the wind related damages. Unfortunately, although the degree of cabling of distribution lines is high in the city areas, it is much lower in the rural regions. This results is longer outage times during hurricanes and storms for the customers residing in the rural regions. iii. Winter storm protection Winter storms bring heavy snow falls. When these snows are accumulated on the tower or on the overhead lines, there is a high risk for the towers to collapse and thus result in a power outage. The situation is similar with the ice storms. The China example [18] shows the catastrophic impacts of heavy ice accumulation on the electric power lines and towers. Ice monitoring systems, de-icing technologies and new materials that can be used to slow down the formation of ice are some of the possible ways in winter storm protection. All extreme weather conditions readiness and the practices for hardening the electric power system and its components mean extra investment and thus extra expenditures. The network operators are the Responsible parties for the natural disaster preparedness and for ensuring continuity of the electric supply. Naturally these companies will not be so willing to spend more money to enhance supply reliability in case of rarely seen extreme events. At this point the driving factor of the regulatory authorities is needed to provide the adequate motivation for the utilities. This motivation can only be achieved by the law makers via comprehensive policy changes. The storm Gudrun of 2005 and the following customer compensation scheme is a genuine example how a
natural disaster triggers the law makers to make decisions in order to sustain higher levels of power reliability. III. Storm Related Policy Changes After major natural disasters usually the governments go through policy changes to increase the reliability of their power system. Storm Gudrun of 2005 is a clear example of this practice. III.1. Storm Gudrun and its Impacts in Sweden In January 2005, the hurricane Gudrun hit northern Europe causing considerable amount of damage in Sweden, Denmark, Latvia, Lithuania and Estonia. In Denmark the winds damaged distribution overhead lines and resulted in power cuts for about 150,000 customers. The primary concern for the Danish was the fate of the extensive Wind Power stations. From a total of around 5400 wind turbines, most of them shut down automatically with the beginning of the hurricane. This lead in a power generation reduction of 2380 MW, which corresponds to almost 5% of the total electric energy generation capacity of Denmark [20]. However, the power production shortage did not give rise to any problems thanks to blackouts and to the electricity trade with the neighboring countries. In Lithuania, the low voltage overhead lines were largely harmed due to falling trees and the electric power network almost collapsed on 8th of January when the hurricane hit the country. 1.4 million people, about 40% of the total population, were left without electricity [20]. Long lasting blackouts were seen in Latvia along with 54,000 km of damaged distribution lines21 and about 40% of the customers experienced power cuts just after the events. 15% of the households underwent power cuts in Estonia [21]. Among all, Sweden is the hardest hit country by hurricane Gudrun. The falling trees on the overhead lines were the primary cause of the catastrophic impacts of Gudrun on the electricity network. Around 730,000 customers suffered from blackouts. For almost half of the affected customers the power was restored within 24 hours. Since the degree of cabling is higher in urban areas, the interruptions lasted up to only a few hours in these regions. However, the rural areas suffered from long lasting blackouts. 12,000 customers waited over 20 days to get the power back [22]. Gudrun did not do considerable damage on transmission lines and power generation facilities. 4 nuclear reactors shut down and one reactor went through downscaling and this reduction corresponded to 20% of the total electrical energy production of Sweden [20]. The Swedish electricity distribution system, on the other hand, was hit tremendously. The falling trees and collapsing poles harmed about 30,000 km of overhead lines [20]. A total of 100 network operators were affected by the storm. Table I shows the types of distribution lines of large network operators that experienced losses due to the storm.
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TABLE I THE AVERAGES OF DISTRIBUTION LINE TYPES OF 16 NETWORK OPERATORS [23]
Distribution lines in affected areas
Cable
Insulated overhead line
Uninsulated overhead line
Length (km) Percentage (%)
142631 100
68593 48
23193 16
50845 36
sek % of share
TABLE II
COST ESTIMATIONS BY NETWORK OPERATORS [23]
Loss of supply
clearence, repair and restorasion
compensation for loss of supply
other costs
53618000
1537315000
613700000
132050000
2
66
26
6
total 2344783000 100
The network operators and the authorities took immediate action to recover the damages on the infrastructure. Nonetheless, the hurricane and the falling trees had other consequences that hindered the repair efforts. The roads were jammed and it made it difficult for the personnel to reach the faulty areas. There were serious problems in radio, internet, telephone and GSM communications as well. The Swedish Armed Forces attended storm recovery endeavor due to the shortage of the trained personnel. The total cost of the hurricane due to electricity failures were enormous. The society suffered from 1,600 ­ 2,100 million SEK losses due to power outages and with the network operator losses added, this figure reached from 4,000 ­ 5,000 million SEK [23]. Table II summarizes the cost estimates of network operators for the storm Gudrun. As it can be seen on the Table II, the amount of compensations hold for 26% of the total losses. The majority of the costs were seen at the clearance, repair and restoration efforts. Gudrun and its outcomes were a shocking experience for the Swedish authorities. After the hurricane, it was realized that the current electricity market act and the existing policies were not sufficient enough to push the utilities to make necessary improvements in the electric power infrastructure for the sake of higher reliability. That is why, by updating the electricity market act the Swedish government introduced the plan of compulsory compensation schemes. According to the new legislation, the duration of maximum allowed interruptions for one single event was decided to be 12 hours. In case of outages lasting longer than 12 hours the utilities are supposed to pay compensations to their customers III.2. Governmental Action due to Storm Gudrun in Sweden Several law-changes were made as a result of the Storm. Also some major snow-storms of 2002 and 2003 showed that power-grid investments were necessary for a higher reliability. A governmental proposition [24] for changes in the electricity-law was handed to the parliament in October 2005, ten months after the storm.
A major change was an introduction of compulsory outage-compensations for the Distribution system operators (DSO). As a background to the compensationscheme proposed in 2005 was an inquiry for higher power-reliability in 2001. This inquiry resulted in a suggestion of outagecompensation as seen in the following Table III. This compensation-scheme was however not deemed necessary due to already existing voluntary goodwillcompensations from DSOs.
TABLE III
THE PROPOSITION FOR OUTAGE-COMPENSATIONS OF 2001, WHICH WAS NOT MADE INTO LAW
Hours of outage downtime
Amount compensated
12500 SEK 1000 SEK
483000 SEK
726000 SEK
Before 2005 no law-bound rights for compensations existed in Sweden. Although a majority of net-holders (over 90 %) provided compensations, the compensations were of varying amount while some companies had no schemes for compensations at all. Some existing laws gave the consumers some rights for compensations for expenses directly related to loss of power, however. The government law-proposals of October 2005 created the kinds of outage-compensations that are still in use. These compensated a percentage of consumers annual grid fee with a minimum amount bound to a yearly calculated index.
III.3. Electricity Consumers Right to Outage Compensation in Sweden The rights for compensation are defined in the Swedish electricity law [25]. The electricity law provides provisions for electrical utilities, electricity trade and electrical safety (chapter 1 §1). Chapter 10§9-16 includes the provisions for outage-compensation in Sweden. Outage-compensation is subtracted from other damage compensation paid according to the Swedish electricity law or other laws due to the same outage (chapter 10 §9). Right to compensation is provided if one or more phases are electrically disconnected from a granted
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energized grid during a period of minimum 12 hours (chapter 10 §10). Right to compensation is not provided if: the outage is due to failure from the electricity consumer, power is cut to take action driven by safety measures or by maintaining operation and reliable electricity delivery and the outage is no longer than the action craves, the outage is due to failure in the providers electricity grid resulting from obstacles out of the provider's control of which the provider could not reasonably have avoided or overcome, or the outage is due to failure in a grid with voltage of 220 kilovolts or more (chapter 10 §10). Compensation is paid by the grid-provider to which the consumer is directly connected (chapter 10 §11). When calculating outage-compensation the downtime is considered concluded at the time when power is back on and remains without fault for the next two hours. The outage-compensation for a downtime of minimum 12 hours and maximum 24 hours paid to the consumer is 12.5 % of the electricity consumer's annual electric grid cost, though at least 2 % of the price base amount (from the Swedish social insurance code chapter 2 §6 and §7) rounded up to closest 100 SEK. If the downtime is longer than 24 hours, additional 25 % of the electricity consumer's annual electric grid cost is paid for every additional 24 hour period, though at least 2 % of the price base amount rounded up to closest 100 SEK. Outage-compensation for one period of downtime should amount to maximum 300 % of the electricity consumer's annual electric grid cost (chapter 10 §13).
Example The price base amount from the Swedish insurance code of 2014 is 44 400 SEK. The minimum amount compensated for 12 hours downtime is 2 %Ч44 400=888 SEK 900 SEK. Additionally, every beginning of a new 24 hours-period after 24 hours of downtime will add another 900 SEK. Customer compensations are in accordance to the Swedish electricity law paid in 2014 according to Table IV.
TABLE IV THE COMPENSATION SCHEME BY SWEDISH ELECTRICITY LAW
Hours of outage Percentage of annual Minimum amount
downtime
costs compensated
compensated
1212,5
900 SEK
2437,5
1800 SEK
4862,5
2700 SEK
...
...
...
288300 (maximum)
12600 SEK
If the obligation to pay outage-compensation is unreasonably burdensome with consideration to the economic situations of the part obliged to compensate according to §11 or the part who finally pays the
compensation according to § 16, the compensation can be adjusted according to what is reasonable. The compensation can also be adjusted according to what is reasonable, if the reparation work for reestablishing electricity has been needed to postpone to not expose workers for significant risk (chapter 10 §13). The part obliged to compensate according to §11 shall pay the outage-compensation to the electricity consumer without reasonable delay and never later than six months from the end of the month the part obliged to compensate was informed or should have been informed about the outage. The part obliged to compensate shall pay according to law of interest §6, if not paid within the right time (chapter 10 §14). If the electricity consumer in spite of the provisions in §14 has not received outage-compensation and has not made demands from the part obliged to compensate within two years from the end of the outage, the right for compensation is lost (chapter 10 §15). IV. Discussion Europe is likely to be more vulnerable to climate change and its implications on electric supply security. The electrical energy production of 27 member states of EU plus Norway, Switzerland and Croatia was 2770 TWh in 1990 and it rose to 3598 TWh in 2008 [26]. When the distribution of power consumption among customers segments is checked, it is seen that there is a significant demand increase in residential and service sector customers 28. This means that the households and the daily services are more dependent on continuous electric supply and hence in case of interruptions, the impacts and the economic losses will be much higher in the future. Due to heavy precipitation, it is expected that Europe will be more susceptible to extreme weather conditions in the future [27]. Because of severe storms, floods and heat waves supply disruptions will be more common. The floods cause the majority of the damage at substations. Flood protection requires risk awareness. When substation planning is done, flood hazard maps must be taken into consideration and the construction must be done accordingly. For the existing substations, hardening against flooding is the only practice. Utilizing physical barriers, flood walls, sand bags and levees helps to some extent. If possible, relocating and rising the critical electrical equipment is another crucial point in flood protection. Restoring flooded substations is more time and effort demanding than restoring damaged power lines or towers due to ice or wind storms. The actions for substation safety during floods and recommendations before, during and after the floods are presented in detail in the study [28]. The reference [29] explains the changes in the weather causing extreme events and summarizes the impacts of these events on the substations and electric power system components. The hurricanes and wind storms usually damage the electricity infrastructure, in particular they pose hazard and risks to the distribution
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systems. Transmission system damages are rarely seen. Majority the outages due to storm related events occur along the distribution lines. Falling trees are the major concerns for the Nordic countries. In Finland, for the 110kV and 400 kV lines corridors the trees are cut in a width of 26 ­ 30 meters and over 40 meters respectively [20]. Cutting off the trees and preventing vegetation around the overhead lines and burying lines underground are the two primary practices to increase the resiliency against wind and lightning storms. Nevertheless, underground cabling systems have their major drawbacks also. The installation and repair costs and higher repair times are the biggest issues. Reference [30] shows that when compared to the overhead lines, underground outages occur less frequently, while the outages last longer. [30], [31] summarize the benefits and drawbacks of underground cables over overhead lines. In case of customer interruption costs we know that the outage frequency is more harmful than the outage duration due to restarting and damage costs. Upgrading the poles and structures, relocating towers, strengthening poles with guy wires are other means of storm readiness. The detailed storm hardening methods can be found at [31]. In case of ice storms, heavy snow falls and crown snows, collapsing towers and flashovers are the primary sources of disruptions. Design of the tower and tower location are important for storm protection. Ice accumulation monitoring systems and de-icing technologies that will slow down ice accumulation on the conductors are used as a means of storm protection [18]. There are some indirect impacts of extreme weather conditions on electric power reliability as well. Sudden temperature changes will result in an increase in the aging rate of the electrical equipment. This will bring in decreasing life time of the electrical equipment and hence it will boost the failures and losses. On the other hand, the heat waves cause a rise of the resistance of power lines with the consequent overheating and loss of capacity. They create an extra demand due to air conditioning and they lead to problems in power generation in hydro power plants. The cooling systems of thermal power plants are affected by high temperatures as well. The report [32] analyzes the impacts of extreme weather conditions on power systems and components in detail. V. Conclusion The influence of global warming on the frequency of extreme weather events is still debatable. However it is clear that the economic outcomes of these events are increasing rapidly each year. Uncertainties about climate change and therefore extreme weather conditions, poor forecasting, lack of extensive studies and insufficient data result in unpredictability of the needed enhancements of the electric power infrastructure. The generation side of the power system proved to be durable against extreme events. However, the distribution system is prone to
weather related damages. The infrastructure in the US and Europe is old. This makes the distribution system and its components to be more susceptible to the extreme weather related damages. Improvements and hence investments are necessary for overhead lines, poles, towers and substations. Flood and storm hazard maps and risk based planning are needed. Policy changes are key elements for increasing the resiliency of the infrastructure and for improving electric power reliability. By new legislations, it is possible to push the utilities to take action in order to maintain supply security. The customer compensation scheme of Sweden is a clear example of how to achieve such a goal. It is obvious that large scale case studies that will solely focus on the consequences of blackouts in case of natural disasters are compulsory for the operations and planning of the power system. Unfortunately the data about the impacts of the power outages due to natural disasters are limited. By the privacy concerns, some utilities tend to keep the outage information as a company secret. The lack of sufficient information creates obstacles to fully comprehend the economic costs of such events. The US Department of Energy introduced a regulation ordering that the power disturbances that will interrupt more than 300 MW of power or that will affect more than 50,000 customers must be reported by the utilities [33]. Again in the US, after Katrina in 2005, the state public utility commissions started to bring in new regulations in order to harden the infrastructure against natural disasters by paying special attention on transmission and distribution systems [31]. Analyzing major natural disasters and their impacts on electricity is crucial in terms of assessing the customer interruption costs. It is a first step for better understanding of the reliability worth of the electric power system [34]-[37]. Providing coordination among all parties of the system; distribution and transmission system operators, generation companies, regulation authorities and establishing quick and successful collaboration with the local authorities and with the public services during crisis is another task for the policy makers. Instead of waiting for an extreme weather related electricity crisis, the policy makers should pay attention to the potential risks and take action accordingly. References [1] Juni-Hochwasser in Mitteleuropa ­ Fokus Deutschland, Geoforschungszentrum GFZ und Karlsruher Institut fьr Technologie: CEDIM Forensic Disaster Analysis Group (FDA), 2013. [2] A. Toronto Hydro Corporation newsletter, 70,000 Customers Remain Without Power, Toronto Hydro Corporation, [Online]. Available: http://www.newswire.ca/en/story/1196483/70-000customers-remain-without-power . [Accessed 11 02 2014] [3] Toronto Hydro Corporation newsletter, Many Toronto Hydro customers restored after flooding, Toronto Hydro Corporation, [Online].Available:http://www.newswire.ca/en/story/1196707/ma ny-toronto-hydro-customers-restored-after-flooding. [Accessed 11 02 2014]. [4] Infrastructure Security and Energy Restoration, Office of Electricity Delivery and Energy Reliability,, Comparing the
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Impacts of the 2005 and 2008 Hurricanes on U.S. Energy
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