Search

This paper reviews the basics of series compensation in transmission systems through a literature survey. The benefits that this technology brings to enhance the steady state and dynamic operation of power systems are analyzed. The review outlines the evolution of the series compensation technologies, from mechanically operated switches to line- and self-commutated power electronic devices, covering control issues, different applications, practical realizations, and case studies. Finally, the paper closes with the major challenges that this technology will face in the near future to achieve a fully decarbonized power system.

There is a need to fulfill the electric power demand, and therefore, this chapter presents a discussion on various techniques available to do so including different FACTS devices, for example, TCSC, SVC, and STATCOM. A discussion on DG integration to the distribution system is also included.

Along with the development of extra-high voltage (EHV) and ultra-high voltage transmission (UHV) systems, series compensations (SCs) have attracted more and more attentions. Overvoltage protection performances of SCs are critical to the safety of SCs and project investments. Within the framework of system fault sequences and duty cycles of SCs, a series of external faults simulations are conducted. The setting values of MOV current protection and MOV energy protection are then determined accordingly. Moreover, comprehensive internal faults simulations are also performed to propose reasonable MOV energy. A test system of 500 kV with nine sets of SCs has been built, and the validity of the methodology proposed in this work has been confirmed by case studies.

The series compensation has been used at the main power transfer routes between northern and southern Finland, as well as in connections to Sweden, to increase the transmission capacity. In certain conditions the interaction between series compensated network and wind power plants may cause unstable subsynchronous oscillations. In Finland many new wind power generation sites will be built in the vicinity of the series compensated network, thus increasing the risk of subsynchronous oscillation phenomena. The subsynchronous oscillations can cause a disconnection of significant amount of wind power production and possibly damages in the wind turbines or series capacitors. This master’s thesis investigates the amount of potentially disconnecting wind power production capacity in the Finnish transmission system due to the subsynchronous oscillation phenomena and develops methods for validating the need and functionality of the subsynchronous oscillation protections in the wind turbines. The doubly-fed induction generator based (Type-3) wind turbines are identified to have a significant risk of causing undamped subsynchronous oscillations, while the full power converter based (Type-4) wind turbines are found to be generally immune to subsynchronous oscillation phenomena. The immunity of a single manufacturer Type-4 wind power plant model is also validated in the thesis. The maximum amount of potentially disconnecting wind power production capacity in single substation is defined using the estimated amount of production capacity from wind power plants with Type-3 wind turbines. The conservative estimations show that the highest amount of potentially disconnecting production capacity could be in range of 340–775 MW in 2022, 520–1225 MW in 2027 and 850–2225 MW in 2030. Fortunately, the amount of disconnecting wind power is likely not as great as the conservative estimation leads to believe, for example due to the risk of undamped subsynchronous oscillation being higher when the output power of the Type-3 wind turbine is lower. Defining more precise estimations will require additional studies in the future. The method for validating the need of subsynchronous oscillation protection in Type-4 wind turbines is developed in the thesis. The proposed method consists of three steps: 1) validation of the immunity to subsynchronous oscillations, 2) defining the worst-case scenario using parallel connected generic Type-3 wind power plant, and 3) discussions with the wind turbine manufacturer. It is proposed that if the investigated Type-4 wind turbines are not found to cause undamped subsynchronous oscillations itself and can withstand the worst-case subsynchronous oscillations caused by another nearby wind power plant, the specific subsynchronous oscillation protections should not be mandatory for the investigated wind turbine model. The method was illustrated on a single manufacturer Type-4 wind power plant model. Validating the functionality of Type-3 wind turbine subsynchronous oscillation protection can be performed for example by first injecting subsynchronous voltage or current of certain frequency on top of the fundamental voltage or current in the wind turbine terminal, and by varying the magnitude and the frequency of the injected current or voltage. Second, the selectivity of the protection should be more thoroughly investigated using another parallel connected Type-3 wind power plant in order to validate that the wind turbines that are most significantly causing the oscillations are disconnected first in the subsynchronous oscillation event. Sarjakompensointia on käytetty Suomessa kasvattamaan sähkön siirtokykyä pohjoisesta Suomesta eteläiseen Suomeen, sekä Ruotsin vaihtosähköyhteyksillä. Sarjakompensoidun verkon ja tuulivoimaloiden välillä on mahdollista syntyä alisynkronista vuorovaikutusta, joka voi aiheuttaa vaimentumattomia alisynkronisia värähtelyitä. Tulevaisuudessa huomattava määrä tuulivoimaa tullaan liittämään Suomessa sarjakompensoidun verkon läheisyyteen, mikä kasvattaa merkittävästi alisynkronisen vuorovaikutuksen riskiä. Alisynkroniset värähtelyt saattavat aiheuttaa merkittävän määrän tuulivoiman irtoamista, sekä mahdollisesti myös vaurioita tuuliturbiineissa tai sarjakondensaattoreissa. Diplomityössä arvioidaan alisynkronisten värähtelyiden takia irtoavan tuulivoimatuotannon määrää Suomen kantaverkossa, sekä kehitetään menetelmiä, joilla voidaan määrittää tuuliturbiineja alisynkronisilta värähtelyltä turvaavien suojauksien tarvetta sekä odotettua toimintaa. Kaksoissyötetyllä epätahtigeneraattorilla toimivalla tyypin 3 tuuliturbiinilla on tunnistettu olevan merkittävä riski joutua alisynkroniseen vuorovaikutukseen sarjakompensoidun verkon kanssa, johtaen tuuliturbiinin irtoamiseen verkosta. Täyden tehon taajuusmuuttajalla toimivat tyypin 4 tuuliturbiinit on todettu tavallisesti olevan immuuneja alisynkronisille vuorovaikutuksille. Yksittäisen tyypin 4 valmistajamallin immuniteetti validoitiin työssä. Alisynkronisten värähtelyiden takia tietyllä sähköasemalla mahdollisesti irtoavan tuulivoiman maksimimäärä arvioidaan asemalla olevien tyypin 3 tuulivoimaloiden tuotantokapasiteetin perusteella. Konservatiivisten arviointien perusteella alisynkronisen vuorovaikutuksen seurauksena suurin irtoava määrä tuulivoimatuotantoa voisi olla 340–775 MW vuonna 2022, 520–1225 MW vuonna 2027 ja 850–2225 MW vuonna 2030. Toisaalta pohdintojen perusteella todennäköisesti irtoava tuulivoiman teho olisi kuitenkin todellisuudessa reilusti alle konservatiivisen arvion johtuen esimerkiksi siitä, että tyypin 3 turbiinin riski joutua vuorovaikutustilanteeseen on suurempi mitä alhaisempi turbiinin tuottama hetkellinen teho on. Jatkotutkimukset ovat tulevaisuudessa tarvittavia tarkempien arvioiden selvittämiseksi. Tarve alisynkronisilta värähtelyiltä suojaavalle suojausfunktiolle tyypin 4 tuuliturbiineissa voidaan määrittää työssä kehitetyllä menetelmällä. Ehdotettu menetelmä koostuu kolmesta toimenpiteestä: 1) tyypin 4 laitoksen immuniteetin varmistaminen, 2) pahimman tilanteen määrittely käyttäen rinnalle kytkettyä geneeristä tyypin 3 tuulivoimalaitosta, ja 3) keskustelut tutkitun tyypin 4 tuuliturbiinin laitevalmistajan kanssa. Työssä ehdotetaan, että jos tutkittu tyypin 4 tuuliturbiini ei aiheuta alisynkronisia värähtelyitä ja kestää geneerisen tyypin 3 tuulivoimalaitoksen aiheuttaman pahimman vuorovaikutustilanteen, suojausfunktiota alisynkronisia värähtelyitä vastaan ei tarvitsisi vaatia kyseiseltä tuuliturbiinimallilta. Kehitettyä menetelmää käytettiin työssä yhden tyypin 4 valmistajamallin validointiin. Tyypin 3 tuuliturbiinin suojauksen toimintaa voidaan validoida syöttämällä alisynkronista virtaa tai jännitettä tuuliturbiinin terminaaliin, ja tutkimalla suojan toiminta-aikaa eri syötetyn virran tai jännitteen voimakkuudella ja taajuudella. Suojan selektiivisyyttä täytyy kuitenkin tutkia tarkemmin käyttämällä vähintään toista tyypin 3 tuulipuistomallia rinnalla, ja tutkimalla toimiiko suojat oikein, kun jompikumpi laitoksista pääasiassa aiheuttaa alisynkroniset värähtelyt.

Dynamic wireless power transfer can reduce the battery capacity of charged devices. This paper proposes a dynamic capacitive power transfer (CPT) system with a compact receiver structure and a reduced transmitter cost. Compared with the conventional solution, the specially designed coupler can reduce the transmitter copper usage by 50% while still achieving stable output. A series compensation with a compensating inductor is adopted on the transmitter side and there is no compensation on the receiver side to minimize the element count and size, especially on the receiver side. Design procedures of the coupler and the compensation network are provided. The mathematical model of the dynamic CPT system is established. Simulation results have verified the effectiveness of the proposed method.

The phase imbalance compensation concept is proposed in literature as an alternative way to mitigate classical subsynchronous resonance (SSR) problems in series-compensated transmission lines. However, a fundamental analysis to determine this concept’s ability to mitigate resonances between a doubly-fed induction generator (DFIG) and a series compensated transmission line, i.e., DFIG-SSR, is not reported in literature. Therefore, the objective of this paper is to investigate to which extent phase imbalance compensation is able to mitigate DFIG-SSR. For the phase imbalance compensation scheme, an analytical model that captures the relation between the level of series compensation, the degree of asymmetry between the compensated phases, and the resulting shift in resonance frequency is developed and validated using time domain simulations. Then, an optimisation framework is developed to search for an adequate level of compensation asymmetry, capable of mitigating the adverse interactions. The optimisation allows us to show that, even with the best set of parameters, phase imbalance compensation is not suitable for mitigating DFIG-SSR. The analytical model enables us to explain the underlying physical reasons for this and an attempt is made to explain why this concept is theoretically able to mitigate classical resonance issues. Lastly, directions for future research are identified.

The predominant reason for adding series capacitors in power systems is to increase power transfer capacity enhancing both the voltage and angle stability margins. The resulting decrease in series reactance can determine also undesired effects during faults: the fault current increases in dependence of the compensation degree and of the fault location in the system. This paper investigates the case of an Italian 230 kV – 50 Hz backbone spanning the Centre North – Centre South section, for which re-equipment with high-temperature conductors in conjunction with the installation of 60% capacitive series compensation are being evaluated. The impact of series compensation on faults levels (both phase-to-phase and phase-to-ground) and on the earth fault factors is systematically studied, within the backbone and in the nearby area. A parametric analysis is carried out, considering different generation, load and network scenarios evidencing the impact of series compensation is compatible with present equipment and system operation.

Sub-synchronous oscillations (SSOs) in doubly-fed induction generator (DFIG)-based series compensated power systems are mainly caused by sub-synchronous control interaction (SSCI). SSCI is the most recently found type of sub-synchronous resonances. In this article, SSCI is elaborated and investigated by performing eigenvalue analysis on a mathematically modeled DFIG system. The occurrence of SSCI is observed and the results of eigenvalue analysis are validated through a down-scaled 7.5-kW experimental setup of a grid-connected DFIG. Based on the analysis, the proportional control parameters of the rotor-side converter (RSC) are found to be very sensitive towards the sub-synchronous modes of the system. The results obtained from both the simulation and the experimental analysis show that if the sensitive proportional parameters of the RSC are tuned properly, then the DFIG system can become immune to the SSCI for any level of series compensation.

Emerging subsynchronous oscillation (SSO) issues in grid-connected wind farms have gained serious attention after several incidents occurred in the US and China. The temporal and spatial variation of wind speed, the diversified converter control structures, and the continuously varying number of in-service wind turbine generators (WTGs) greatly affect the equivalent impedance reflected by the wind farms. Such frequency-dependent equivalent impedance, as indicated by both theoretical analyses and practical experiences, has a huge impact on the mechanism and characteristics of SSO. In this regard, WTGs contribute to a more complicated type of SSO than those in conventional turbo-generators (CTGs). For instance, SSO in practical wind power systems can be triggered without the participation of series compensation in the transmission network. The emerging SSO phenomena observed in practical WTGs are relatively new, and cannot be properly interpreted by existing literature. This work will first review the historical development of SSO definitions and classification by IEEE, followed by discussions on recent incidents in practical wind farms due to the emerging SSO. Subsequently, new terminologies and classification of SSO are proposed with the aim to better understand SSO in large-scale wind integrated power systems. This paper offers a practical insight and a future perspective for the reader to properly deal with SSO associated with wind power systems.

This paper introduces a new three-phase dynamic voltage restorer (DVR) working in series compensation with an AC link, called AT-DVR. One of the main features of AT-DVR is an AC/AC buck converter, which is used to obtain the AC voltage for compensation. AT-DVR has the capacity to mitigate sag and swell events. A dynamic model of AT-DVR is presented in order to explain its advantages and its limitations. PI and fuzzy controllers were implemented to guarantee mitigation of sag and swell events, and these were evaluated using four performance indexes via simulation. Finally, a hardware implementation of the AT-DVR is described, and its behaviour when a fault occurs is demonstrated

ObjectivesThe aim of the study is to increase the energy efficiency of an arc furnace’s power supply system and low-voltage circuit. According to the aim of the research, the relevant tasks of determining the capacitor capacity for reactive power compensation and selecting a rational location for its installation are posed.MethodsWithin the framework of the previously developed concept of changing the parameters of the switching transformer in the series compensation circuit, issues of efficient use and consumption of electrical energy by a high power linear load under sinusoidal mode are considered. The installation of static compensators using a direct compensation method with automatic control including 12 stages of regulation is proposed as a means of increasing the efficiency of the arc furnace. Challenges involved in increasing the efficiency of electric power supply to alternating current arc furnaces using compensating reactive power in a low-voltage circuit are considered.ResultsThe viability of using the series compensation circuit of reactive power with the switching of capacitors in the winding of the higher voltage of the series switching transformer is demonstrated.ConclusionIt is shown that for efficient use and consumption of electric energy by highpower linear load under sinusoidal conditions, it is advisable to apply the series compensation of reactive power with the switching of capacitors in the winding of the higher voltage of the series switching transformer. This makes it possible to increase the efficiency coefficient of electric arc furnace power supply devices by reducing the power losses in the power supply system and in the furnace lowvoltage circuit by 1.6 times, as well as reducing the total load in the power transformer by 1.36 times.

TL (Transmission Line) congestion is a key factor that affects the power system operational cost. In addition of renewable generation in National Grid of Pakistan, transmission line congestion are frequent. Consequently, the network in this particular region faces severe congestion and dynamic stability problems. It has been planned that renewable plants shaved to curtail some available generation to minimize this inevitable congestion. However, one of the cost-efficient solutions to this problem is series compensation of lines using TCSC (Thyristor Controlled Series Compensation). It significantly increases the transfer capability of existing power transmission and enhances the dynamic stability of system at a lower cost, and has shorter installation time as compared to the construction of new TLs. This paper deals with the dynamic modeling of a TCSC in the NTDC (National Transmission and Dispatch Company) network with its applications to alleviate congestion during fault conditions. This study has been carried out using simulation software PSS/E (Power System Simulator for Engineers) which does not have a predefined dynamic model for TCSC, this leads to the necessity of creating a user defined model. The model of TCSC has been programmed in FORTRAN and compiled along with existing dynamic models of network components. The results indicate that power flow and dynamic stability of network is enhanced

This study demonstrates the capability and performance of the developed state-of-the-art hardware-in-the-loop (HIL) testing platform based on the real-time digital simulator (RTDS). The evaluations of (i) the effects of thyristor-controlled series compensation (TCSC) on the feeder protection first main (unit protection) and (ii) the performance of feeder protection second main (distance protection) of multi-ended transmission circuits with adjacent TCSC are carried out. Realistic parameters of transmission lines and TCSC are used for system modelling, and practical physical relays are used for the testing. The potential impacts of TCSC on both unit protection and distance protection are analysed based on the simulation results and relay measurements from the developed RTDS-based HIL testing platform.

To avoid the under/over-reaching problems of distance protection of extra high voltage/ultra high voltage transmission lines (TLs) in the presence of series compensation, pilot relaying scheme can ...

The rise in power electronic devices in power system has increased the problems of harmonics and power quality. In this paper I have discussed about the harmonics that are developed in power system due to non-linear loads. The damage of harmonics may rise from normal level to high level depending on their duration and the order of harmonic .So to mitigate this harmonics in power system I have introduced shunt active power filter by series compensation method. In this paper it is discussed how harmonics are reduced using shunt active power filter and it is shown through MATLAB/Simulink .The results of the simulation have been shown where the harmonics developed in power supply has reduced.