Coordinated automatic voltage control of power transformers

Zahtjevi na rad regulatora napona energetskih transformatora su u uvjetima poremećenog pogona odnosno pri propadima napona potpuno različiti od onih za vrijeme normalnog pogona. Podešenja regulatora napona prilagođena su uvjetima normalnog pogona. Ista podešenja u uvjetima poremećenog pogona mogu dovesti do sloma napona prijenosnog sustava. Dokaz tomu su poremećaji napona poput gubitka proizvodnih jedinica, prijenosnih vodova, povećanja zahtjeva prema potrošnji jalove energije i posljedično dugo vrijeme oporavka napona. Navedeni poremećaji zabilježeni su u svijetu posljednjih desetak godina i jasno su naznačili potrebu za drugačijim načinom rada regulatora napona energetskih transformatora u uvjetima poremećenog napona. Ova disertacija je orijentirana prema problematici rada regulatora za vrijeme poremećenog pogona i u tu svrhu su predložene i detaljno opisane korektivne mjere. Korektivne mjere su razrađene u obliku algoritma koji se zasniva na mjerenju napona na strani višeg napona energetskog transformatora. Osim dodatnog mjerenja napona na strani višeg napona energetskog transformatora, za potrebe rada algoritma, nužna je i komunikacija između transformatorskih stanica u skladu s IEC 61850 normom. U disertaciji je detaljno objašnjena izvedba komunikacije između transformatorskih stanica za potrebe koordinirane regulacije napona energetskih transformatora neovisno o proizvođaču numeričkih uređaja. Predloženi algoritam je prikazan dijagramom toka, lako je primjenjiv i može se implementirati u distribuiranoj ili centraliziranoj inačici koordinirane regulacije napona energetskih transformatora. Razvijeni algoritam izvršava korektivne mjere na osnovu predefiniranog postotka propada napona na strani višeg napona energetskog transformatora. U disertaciji su opisane korektivne mjere poput privremene blokade regulacije napona, isklopa prekidača visokonaponske prigušnice, promjene postavne vrijednosti napona regulacije, potpune blokade i na kraju podnaponskog rasterećenja dijela prijenosnog sustava. Nadalje, dana je tehno-ekonomska analiza predloženog rješenja koordinirane regulacije napona energetskih transformatora. Na kraju rada su prikazani rezultati kao i usporedbe postojeće i koordinirane regulacije napona dobiveni računalnim simulacijama s različitim parametrima propada napona na strani višeg napona energetskog transformatora za svaku navedenu korektivnu mjeru zasebno. Računalne simulacije, algoritam i model su napravljeni u programskom paketu Matlab u vremenskoj domeni.Requirements on voltage regulator operation for power transformer OLTC’s are completely different during disturbances in power system then during normal operation. During disturbances inadequate functioning can lead to the voltage breakdown of the transmission system. Evidences and examples of this are disorders caused by loss of power generating units, transmission lines or increasing demand of reactive power which have as a consequence long voltage recovery times. Such (similar) disturbances are taking place around the world over the past decades, and clearly indicate the need for a different operating mode of voltage regulators. Furthermore, the goal is to achieve voltage regulator function valid during abnormal operation as well as during disturbances. This dissertation addresses the problem of common voltage regulators during abnormal conditions and for this purpose certain remedial countermeasures are proposed. Remedial countermeasures are described and designed in the form of an algorithm which is based on communication between substations according to standard IEC 61850 and additional measurement of the voltage from high voltage side of power transformers. Measurement of the voltages from both sides of power transformers is also needed. The proposed algorithm is explained in details as well as communication between substations for automatic voltage regulation of power transformers, and it is independent of the numerical device vendors. The proposed algorithm is presented in the form of easily applicable flow chart and it can be implemented in a distributed or centralized version of power transformers automatic voltage control system. The developed algorithm performs corrective measures based on a predefined percentage of voltage drops on the high voltage side of power transformer. The dissertation describes the countermeasures as a temporary blocking of voltage regulation, high voltage reactor circuit breaker switching-off, changing of set value ??of voltage regulation, complete blocking and at the end load shedding of the transmission system. Furthermore, the analysis was focused on the automatic voltage regulation and its effects on voltage, tap changer position and the amounts of active and reactive power in a given period of time. The period of time for analysis is time domain between ten of seconds up to ten of minutes. Techno-economical analysis of proposed solution of coordinated voltage control of power transformers is given. At the end of the dissertation, compared results of the common and the proposed advanced voltage regulation of power transformers, achieved through computer simulations considering different parameters of voltage drop on the high voltage side of the power transformer are presented. The Computer simulations, algorithm and model are made in software Matlab and its package Simulink. For every proposed countermeasure, case by case, algotihm was tested separately in relation with predefined voltage drop respectively on the high voltage side of power transformer in substation Ernestinovo. From the results of the computer simulations were expected to provide savings in positions of tap changer for all OLTC power transformers connected in seria and potential savings in active and reactive power. The main improvements compared to the existing common voltage regulation of OLTC power transformer is application of secure and reliable communication between substations using GOOSE messages in accordance with standard IEC 61850. Proposed countermeasures such as changing of set value of voltage regulation and total blocking confirmed its flexibility, applicability and proved the expected positive effect on conservation of voltage stability during disturbed power network conditions. Distributed generation of renewable energy nowadays and in near future will have significant role in delivery of electric energy within any power system network. When a story about electric energy, the issues is will be in solving how to plan, build and run power system network in a sense how to properly take produced electric energy from distributed sources. In general, the issue will not be frequency of the system; the issue will be stability of voltage on certain voltage levels. Besides so called three levels of voltage regulation and reactive power systematically is coming to use of smart grid solutions. The smart grid has a task to run and keep power system network in optimized state. It means development of pilot projects with tasks to apply smart grid solutions which will take into consideration energy, economy, ecology, ethics and education