Modeliranje omrežja in analiza dinamičnega obnašanja naprave SSSC pri majhnih pretokih energije

Kelava, Goran (author), Ažbe, Valentin (mentor)

SSSC (Static Synchronous Series Compensator) je naprava FACTS (Flexible Alternating Current Transmission System) za regulacijo pretokov moči oz. energije v omrežju. V omrežje je vezana zaporedno prek transformatorja, poleg tega pa vsebuje še AC/DC in DC/AC pretvornike ter GTO tiristorje. V omrežje oddaja napetost, ki ima ustrezno velikost in orientacijo glede na trenutno stanje v omrežju. Do problemov lahko pride, ker se ob prisotnosti SSSC v omrežju okrog majhnih prenosnih kotov pojavi dodaten nihaj v funkciji delovne moči v odvisnosti od prenosnega kota. To pomeni, da imata na določenih področjih statike kot in moč različen predznak, ob enakih amplitudah napetosti na obeh straneh SSSC pa se lahko pri prenosnem kotu 0 pojavi tudi stopnica. Namen te diplomske naloge je raziskati dogajanje ob kratkem stiku, ko v dinamičnih razmerah kot in moč zanihata čez 0. To je narejeno s simulacijo v programskem okolju Simulink, kjer je z modelom, sestavljenim iz že narejenih primerov »power_turbine« in »power_SSSC«, ustvarjeno simulirano omrežje z zahtevanimi pogoji. Izvedeno je bilo 7 primerov simulacij, ki so se razlikovale po trajanju kratkega stika, amplitudi injicirane napetosti in velikosti generatorja. Poleg tega je bil izveden še dodaten primer, ki prikazuje delovanje omrežja brez SSSC. Iz dobljenih rezultatov izhajata dve glavni ugotovitvi: - Generator vedno pobegne, ko imata po kratkem stiku moč in kot različen predznak, medtem ko se vrne v normalno obratovanje, če se to ne zgodi. - V nekaterih situacijah je možno, da pri daljšem trajanju kratkega stika generator ne pobegne, medtem ko pri krajšem pobegne. To je razvidno iz primerov z generatorjem 200 MW, kjer pri trajanju kratkih stikov do 0,19 s generator ne pobegne, pri kratkih stikih med 0,19 in 0,21 s pobegne, potem pa spet ne do trajanja 0,26 s, ko pobegne, ker je kratek stik predolg. Sicer se s podatki, pridobljenimi v teh simulacijah, tega ne da znanstveno dokazati, razlaga pa bi lahko bila, da se pri pobegih med 0,19 in 0,21 s delovna točka ujame na delu statike, kjer imata moč in kot različen predznak, zato generator pobegne, medtem ko se pri primerih okoli tega intervala delovna točka ali ne premakne dovolj, da pride v to območje, ali pa zaniha čez celotno območje. Glede na to, da se pri 500 MW generatorju to ne zgodi, je pojav bolj odvisen od amplitude moči kot od amplitude kota, pri kateri je moč pozitivna pri negativnih prenosnih kotih. V nadaljevanju poskusov bi bilo potrebno analizo izvesti tudi s kakšnim naprednejšim programom, da bi se dobila boljša razlaga in dokaz pojavov, prav tako pa bi dobili razlago ali pa prave rezultate za primere, kjer je injicirana napetost večja, saj so v teh primerih rezultati nepričakovani.

• Language: Slovenian
• Keywords: SSSC, kotna stabilnost, majhni pretoki energije
• Work type: Bachelor thesis/paper
• Organization: FE - Faculty of Electrical Engineering
• Year: 2023
• PID: 20.500.12556/RUL-149864
• COBISS.SI-ID: 164063491
• Publication date in RUL: 11.09.2023

Secondary language

• Language: English
• Title: Network modelling and analysis of dynamic behaviour of SSSC at low power flows

Abstract

SSSC (Static Synchronous Series Compensator) is a FACTS (Flexible Alternating Current Transmission System) device intended for control of power or energy flow in a grid. It is connected serially via a transformer, while also consisting of AC/DC and DC/AC converters and GTO thyristors. It injects voltage, properly sized and orientated, into the grid, given the current conditions. Problems can occur due to the fact that, in the proximity of the small voltage angles, an additional oscillation appears in a function of power in relation to voltage angle when SSSC is present, meaning that in parts of the statics, power and voltage angle differ in sign. Furthermore, when the voltages on both sides of SSSC are equally big, a step can appear in a graph. The purpose of this diploma is to explore the dynamic phenomena after a short circuit when both power and angle oscillate through 0. This has been done using a Simulink simulation, made of combining previously made examples »power_turbine« and »power_SSSC«, to create a model containing everything needed. 7 simulations have been conducted, differing in the duration of the short circuit, magnitude of injected voltage UT and size of a generator. An additional example is showing the behaviour of the grid without the SSSC. Upon completion, two main findings have been made: - Generator always escapes when power and angle are signed differently after short circuit has ended, while it returns to its normal state, when they are not. - There are situations, when the longer short circuit doesn’t necessarily mean a generators escape, and a shorter does. This is seen in some examples using a 200 MW generator, where short circuits shorter than 0.19 s don’t cause an escape, durations between 0.19 and 0.21 s do cause it, and durations from 0.21 to 0.26 s again don’t. Longer short circuits are too long to not cause an escape. Although this cannot be proven scientifically, using data gathered with these simulations, the likely cause for this is that, between the times of 0.19 to 0.21 s, the working point gets stuck in a part of the statics, where power and angle are signed differently, while shorter and longer durations cause the working point to either not reach this part of the statics, either it passes over it. Given the fact that this never occurs using a 500 MW generator, this phenomenon likely depends on the magnitude of power, rather than the width of the area with different negative angles. If one was to expand this research, the analyses s would require a more advanced program, in order to get a more suiting explanation and proof for what is happening. Also it would provide an explanation for simulations with bigger UT, where the results have been unexpected.

• Keywords: SSSC, angular stability, low energy flow