ZANESLJIVOST PROIZVODNJE ELEKTRIČNE ENERGIJE Z UPOŠTEVANJEM ODPOVEDI S SKUPNIM VZROKOM

BRICMAN REJC, ŽIVA (avtor), Čepin, Marko (mentor)

Liberalizacija in deregulacija trga z električno energijo sta povzročili spremembo v elektrogospodarstvu, pri čemer je prišlo do ločitve monopolnega sektorja elektroenergetike na tržne in na državno regulirane dele. Liberalna in deregulirana ureditev elektrogospodarstva tako narekuje obstoj različnih podjetij za proizvodnjo, prenos in distribucijo električne energije končnim porabnikom. Tržni del sektorja zajema proizvodnjo, trženje in prodajo električne energije, državno regulirani del sektorja pa skrbi za vodenje elektroenergetskega sistema, za kar skrbijo sistemski operaterji. Ker trgi z električno energijo ne pokrivajo vseh funkcij, potrebnih za ustrezno delovanje elektroenergetskega sistema, je prišlo do uvedbe novih sistemskih storitev, kot so regulacija frekvence in napetosti v sistemu, izravnava odstopanj moči, razbremenjevanje omrežja, pokrivanje tehničnih izgub v omrežju. Za ustrezno izvajanje ter koordinacijo sistemskih storitev skrbi sistemski operater prenosnega omrežja. Cilj sistemskega operaterja prenosnega omrežja je čim večja zanesljivost elektroenergetskega sistema kot tudi čim večja zanesljivost proizvodnje električne energije. S stališča porabnikov električne energije to pomeni, da bo oskrba odjemalcev z električno energijo stalno zagotovljena s konstantno frekvenco in z določenim napetostnim profilom v omrežju, katerega velikost, odstopanja, upadi in hitre spremembe morajo biti znotraj predpisanih mej. Motnje in izpadi elementov v elektroenergetskem sistemu so lahko prehodne narave, lahko pa povzročijo razpad dela ali celotnega sistema in s tem izpad napajanja odjemalcev. Verjetnost izpada napajanja odjemalcev je mogoče zmanjšati z ustreznimi nadgradnjami in širitvami sistema, z zamenjavo ali nadgradnjo obstoječe opreme z bolj zanesljivo, s priključitvijo redundantnih elementov, z zagotavljanjem ustrezne raznolikosti elementov, z zagotavljanjem ustreznih prenosnih zmogljivosti omrežja, vendar pa izpadov ni mogoče popolnoma preprečiti. Razlogi za to so predvsem naključni značaji sistemskih napak, nepričakovane in časovno naključno razporejene visoke obremenitve v sistemu, spreminjajoča in negotova proizvodnja električne energije iz obnovljivih virov energije, zamude pri dobavi, vgradnji, zamenjavi in vzdrževanju opreme ter nepredvidljive vremenske razmere. Ena izmed karakteristik elektroenergetskega sistema je njegova nezmožnost ekonomsko učinkovitega shranjevanja električne energije. Zato morata biti za zagotavljanje zanesljive oskrbe odjemalcev v elektroenergetskem sistemu poraba in proizvodnja električne energije v vsakem trenutku uravnoteženi. Za zagotavljanje zanesljive oskrbe odjemalcev mora prav tako biti glede na napovedi porabe ter proizvodnje v vsakem trenutku na voljo zadostna rezerva moči za primarno, sekundarno in terciarno regulacijo frekvence. Ker se v sodobnih elektroenergetskih sistemih vsako leto priključuje vedno več obnovljivih virov električne energije, katerih proizvodnja je variabilna in negotova, prav tako lahko proizvodne enote, ki skrbijo za ustrezno regulacijo frekvence, izpadejo, je za zanesljivo obratovanje sistema potrebna dodatna rezerva moči ali višek razpoložljive moči v sistemu. Dodatna rezerva moči je lahko zagotovljena s turboagregati (npr. s plinskimi agregati ali s hidroagregati), ki niso namenjeni pokrivanju porabe v sistemu temveč služijo zgolj za rezervo, z zaviranimi vetrnimi elektrarnami, z baterijami in s shranjevalniki energije, s črpalnimi hidro elektrarnami, lahko pa jo uvozimo iz tujine. Nekateri sistemski operaterji predlagajo, da je za vsak MW proizvedene moči iz obnovljivih virov v sistemu razpoložljiv MW rezervne moči. Dimenzioniranje takšnih elektroenergetskih sistemov je lahko stroškovno potratno, saj lahko stroški zagotavljanja visokega nivoja zanesljivosti hitro presežejo stroške pokrivanja razpadov elektroenergetskih sistemov. Kot kriterij za določanje dodatne rezerve moči v elektroenergetskem sistemu pa lahko uporabimo tudi rezultate analiz zanesljivosti. V doktorski disertaciji smo se osredotočili na razvoj metode za določanje dodatne rezerve moči, ki je namenjena zagotavljanju zanesljive proizvodnje električne energije. Metoda temelji na rezultatih analiz zanesljivosti, pri čemer je upoštevana spremenljiva ter negotova proizvodnja iz obnovljivih virov električne energije. Metoda prav tako upošteva hkratne odpovedi proizvodnih enot zaradi skupnih vzrokov, kot so npr. ekstremne vremenske razmere. V prvem delu doktorske disertacije smo podali pregled ožjega znanstvenega področja disertacije: teorija verjetnosti in zanesljivosti, analize zanesljivosti proizvodnje električne energije, kratkoročne napovedi porabe in proizvodnje obnovljivih virov električne energije, zagotavljanje ustrezne rezerve moči v elektroenergetskem sistemu ter verjetnostne varnostne analize, v sklopu katerih so predstavljene odpovedi s skupnim vzrokom. Opisana znanstvena področja so podlaga za delo na področju zanesljivosti proizvodnje električne energije. V drugem delu disertacije smo predstavili novo metodo za zagotavljanje zanesljive proizvodnje električne energije. Nova metoda temelji na že uveljavljeni metodi za ocenjevanje zanesljivosti proizvodnje električne energije, to je pričakovano tveganje izpada napajanja (LOLE-Loss of Load Expectation). Najprej so v definicijo indeksa LOLE vpeljane odpovedi s skupnim vzrokom agregatov z uporabo metode beta faktorja, z uporabo metode grških črk ter z uporabo nadgrajene metode grških črk. Predstavljena je tudi nadgrajena metoda grških črk, s katero lahko natančneje definiramo izpade agregatov, saj lahko pri enem agregatu upoštevamo več izvornih vzrokov in povezovalnih mehanizmov, zaradi katerih lahko odpove skupaj z drugimi agregati, kar do sedaj ni bilo mogoče. Nato je definicija indeksa LOLE nadgrajena z vpeljavo obnovljivih virov električne energije, kjer je upoštevana tako spremenljiva in negotova proizvodnja iz obnovljivih virov, kot tudi njihove naključne odpovedi zaradi mehanskih napak in okvar opreme. Nadgrajen indeks LOLE je nato uporabljen za ovrednotenje zanesljivosti proizvodnje v vsaki uri prihodnjega dne, saj so kratkoročne napovedi proizvodnje iz obnovljivih virov najbolj natančne le za nekaj ur ali dan vnaprej. Dobljene urne vrednosti indeksa LOLE se nato uporabijo za določanje nivoja dodatne rezerve moči v sistemu tako, da se zadosti kriterijem zanesljivosti glede na predvideno negotovo proizvodnjo iz obnovljivih virov ter glede na predvideno porabo v sistemu v vsaki uri. V tretjem delu doktorske disertacije smo podali rezultate uporabe nove metode. Metoda je preizkušena na standardnem elektroenergetskem sistemu, t.j. poenostavljenem 39 zbiralčnem sistemu Nove Anglije, ter na realnem elektroenergetskem sistemu, t.j. sistemu Republike Slovenije. Rezultati analiz kažejo, da večja kot je vrednost predvidene porabe zmanjšane glede na predvideno proizvodnjo iz obnovljivih virov električne energije, manj zanesljiva je proizvodnja električne energije. Tako je zanesljivost proizvodnje v vsaki uri odvisna od predvidene porabe znotraj ure ter od predvidene injicirane moči iz obnovljivih virov. Velik vpliv na zanesljivost proizvodnje ima tudi negotovost proizvodnje iz obnovljivih virov. Večja kot je lahko napaka napovedi proizvodnje iz obnovljivih virov, višji je indeks LOLE, ter večji delež instalirane moči v sistemu kot predstavljajo obnovljivi viri, večji vpliv ima negotovost njihove proizvodnje na zanesljivost. Vpliv negotovosti proizvodnje obnovljivih virov kaže na problem vključevanja obnovljivih virov v elektroenergetski sistem z vidika zanesljivosti proizvodnje. Zaradi negotove proizvodnje obnovljivih virov je težko natančno določiti zanesljivost proizvodnje opazovanega sistema, kar ima lahko posledično velik vpliv na določanje ustreznega nivoja dodatne rezerve moči v sistemu za zagotavljanje zanesljivega obratovanja sistema. Rezultati analiz prav tako potrjujejo, da imajo odpovedi s skupnim vzrokom agregatov velik prispevek k tveganju izpada napajanja. Če predpostavimo, da lahko dva ali več agregatov odpove hkrati zaradi skupnega vzroka, se ocenjena zanesljivost proizvodnje zmanjša in posledično je potrebne več dodatne rezerve moči za doseganje želenega nivoja zanesljivosti. Več kot je agregatov, ki lahko odpovejo zaradi skupnega vzroka, večja kot je njihova instalirana moč, višja kot je njihova nerazpoložljivost ter večji delež vseh odpovedi agregatov kot predstavljajo odpovedi s skupnim vzrokom, nižja je zanesljivost proizvodnje. Posledično je predlagane več rezervne moči v sistemu za doseganje želenega nivoja zanesljivosti. Iz tega je razvidno, da ima upoštevanje odpovedi s skupnim vzrokom velik vpliv na zanesljivost ter na nivo dodatne rezerve moči v sistemu. Če so odpovedi s skupnim vzrokom upoštevane z novo metodo grških črk, se lahko izpadi agregatov še natančneje definirajo in s tem se omogoči podrobnejši vpogled v analize zanesljivosti proizvodnje električne energije. Z uporabo predstavljene metode se lahko zagotovi kratkoročno zanesljivo oskrbo odjemalcev električne energije v sodobnih elektroenergetskih sistemih, kjer se priključuje vedno več obnovljivih virov električne energije. Prav tako se v analizah upošteva vpliv hkratnih odpovedi agregatov zaradi skupnih vzrokov, kot je npr. udar strele, pri čemer se lahko identificira ter odpravi morebitne kritične odpovedi agregatov, s čimer se zagotovi še višjo zanesljivost proizvodnje. Nova metoda predstavlja izvirni prispevek doktorske disertacije, saj združuje vpliv spremenljive in negotove proizvodnje iz obnovljivih virov električne energije ter vpliv odpovedi s skupnim vzrokom proizvodnih enot na nivo dodatne rezerve moči v sistemu, ki je potreben za doseganje želene zanesljivosti proizvodnje, kar do sedaj še ni bilo narejeno.

• Jezik: Slovenski jezik
• Ključne besede: dodatna rezerva moči, metoda grških črk, obnovljivi viri električne energije, odpovedi s skupnim vzrokom, pričakovano tveganje izpada napajanja, zanesljivost
• Vrsta gradiva: Doktorsko delo/naloga
• Organizacija: FE - Fakulteta za elektrotehniko
• Leto izida: 2015
• PID: 20.500.12556/RUL-73272
• COBISS.SI-ID: 11080532
• Datum objave v RUL: 02.11.2015

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: RELIABILITY OF POWER GENERATION CONSIDERING COMMON CAUSE FAILURES

Izvleček

Liberalisation and deregulation of the electricity market led to changes among the previously monopoly electric-power industry, as it was separated to a market and a government-regulated part. The reconstructed electric-power industry requires various utilities for generation, transmission and distribution of the electrical power to the consumers. The market-regulated part includes utilities for electrical-power generation, marketing and electricity trading, while the government-regulated part is responsible for proper power-system operation and control. Since the power-system operation characteristics generally do not correspond to the reconstructed electric-power sector, introduction of new ancillary services such as frequency and voltage control, scheduling and dispatch, loss compensation and load following was necessary. These services are coordinated by the transmission-system operator. One of the main tasks of a power system is to supply all consumers with electrical power within defined reliability standards, including an uninterrupted power supply. Disturbances in power system can occur randomly at any time and may lead to power-system instability or even its collapse, where several consumers may be affected. The probability of disturbances can be minimized by proper power-system upgrades and expansions, by replacing or upgrading the existing equipment with a more reliable one, by providing an adequate diversity of the elements, by providing an adequate transmission capacity of the network, but nevertheless, the disturbances in the power system cannot be completely prevented. The reasons for this lies in the random occurrence of disturbances, the possible random peak loads in the system, the variable and uncertain power generation from the renewable energy sources, the delays in delivery, installation, replacement and maintenance of the equipment and in the unpredictable weather conditions. One of the characteristics of a power system is its inability to efficiently accumulate the electrical energy. To achieve an uninterrupted power supply reaching a balance between the generation and the consumption of electricity is needed. To ensure energy balance, additional generation operating reserves above the expected demand load are required. The operating reserves can be utilized in case of load and generation mismatch, which enables the power system to deal with unexpected changes in load or generation. Achieving the system balance has become more difficult with the increasing number of renewable energy sources, as the generation of electrical power from most of these unconventional energy sources is intermittent by nature. Operating reserves are most often ensured by an installed cold-capacity reserve, which is not considered as part of a reliability evaluation, by potential-energy storage facilities, by pumped-storage hydro-power plants, by de-loaded wind-power plants or they can be imported. Some transmission-system operators suggest that for each MW of installed power from renewable energy sources another MW of backup must be available. However, introducing such measures may lead to very high expenses, which may not justify the benefits of the high reliability. On the other hand, operating reserves can also be defined by reliability analyses. The doctoral dissertation is focused on a development of an analysis of power generation reliability level that will consider the impact of variable renewable energy sources in the observed power system for a reliable day-ahead operation. Additionally, common cause failures of several generating units are considered. In the first part of the dissertation a theoretical background is given: the probability and reliability theory, power-generation reliability analysis, short-term forecasts of the expected demand load and the expected power generation from the renewable energy sources, ensuring an adequate level of operating reserves in the observed power systems and probabilistic risk assessment, where the common cause failures are discussed. The discussed background is basis for working in fields of power-generation reliability analysis and assessment. In the second part of the thesis a new method for ensuring a reliable power generation is presented. The new method is based on an already well-established method for assessing the power-generation reliability, i.e., the Loss of Load Expectation (LOLE). Firstly, the definition of the index LOLE is expanded by the implementation of common cause failures of several generating units. The common cause failures are implemented using the Beta factor method, the Multiple Greek Letter method and the updated Multiple Greek Letter method. Additionally, an updated Multiple Greek Letter method is presented, which enables a more detailed definition of outage states of generating units, where several root causes and coupling mechanisms for one generating unit can be considered. Secondly, the LOLE definition is improved by the implementation of the renewable energy sources, whose power generation is variable and uncertain. Their random failures due to mechanical errors and equipment malfunctions are also considered. The upgraded index LOLE is then used to evaluate the power-generation reliability in each hour of the following day separately, as the short-term forecasts of the power generation from the renewable energy sources are accurate only for a few hours or a day in advance. The obtained hourly values of index LOLE are then used to determine, what amount of additional operating reserve within every hour is required to satisfy the reliability criteria. In the third part of the doctoral thesis the results of the application of the new method are presented. The method was tested on a standard power system, i.e., the simplified 39-bus system of New England, and on a real power system, i.e., the Slovenian power system. The results show that the larger the system balance is (i.e., the greater the expected demand load reduced by the power generation from the renewable energy sources), the lower the power-generation reliability is. Therefore, the power-generation reliability in every hour depends on the expected demand load within the hour and on the forecasted power generation from the renewable energy sources. Uncertainty of the renewable power generation also has a major impact on the power-generation reliability. The larger the forecast error for the power generation from the renewable energy sources is, the higher the value of index LOLE is. The larger the share of installed renewable energy sources is, the greater the impact of uncertainty of their generation on the power-generation reliability is. This represents the negative aspect of incorporating the renewable energy sources in power systems, as we cannot influence and precisely forecast their generation and can therefore not absolutely rely on their generation. Due to the uncertain generation from the renewable energy sources it is very difficult to accurately determine the power-generation reliability, which may consequently have a major impact on the determination of the appropriate level of additional operating reserve for ensuring a reliable day-ahead power-system operation. The results also confirm that common cause failures of generating units have a major contribution to risk. If it is assumed, that two generating units can share the same cause of failure, the obtained power-generation reliability decreases and consequently a larger amount of additional operating reserve is required to satisfy the reliability criteria. The more generating units that are susceptible to common cause failures, the higher that their installed powers and unavailabilities are and the higher share of all their failures that are represented by the common cause failures, the lower the power-generation reliability is. Consequently, more additional operating reserve is suggested to achieve the desired level of reliability. This suggests that common cause failures of generating units need to be considered within reliability analysis, as they have a large impact on the power-generation reliability and on the amount of the required additional operating reserve. More, if common cause failures are considered according to the new Multiple Greek Letter method, outage states of generating units can be more accurately defined and a more detailed insight into reliability analysis is enabled. By application of the presented method a reliable short-term electrical power supply to all consumers can be ensured; especially in modern power systems, where a large share of renewable energy sources is being installed. Additionally, the method takes into account the impact of simultaneous failures of several generating units caused by a common cause, such as the lightning strike. Consequently, the outage states of generating units can be more accurately defined, which enables the transmission-system operator to identify the critical failures of the generating units and to propose adequate measures in order to minimize the impact of common cause failures and therefore to ensure a higher power-generation reliability. The new method presents an original scientific contribution of the doctoral thesis, as it combines the impact of the variable and uncertain power generation from the renewable energy sources and the impact of simultaneous failures of several generating units caused by a common cause on the amount of the additional operating reserve, which is required for ensuring a reliable power system operation.

• Ključne besede: additional operating reserve, common cause failures, Loss of Load Expectation, Multiple Greek Letter Method, reliability, renewable energy sources.