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Their speed of response enable increased transient stability margins, voltage support enhancement, and damping of low frequency oscillations.
The main operational objective of both FACTS devices is to increase power transmission capability by voltage control at the point of connection of the power network. In this research both controllers are compared by their most important features, such as the following: the performance VI and VQ curves, the response time, the physical size, the cost and behavior in steady-state and transient stability.
Voltage magnitude throughout the network cannot deviate significantly from its nominal value if an efficient and reliable operation of the power system is to be achieved. Voltage magnitude regulation in the network is achieved by controlling the production, absorption and flow of reactive power throughout the system. Reactive power flow is minimized so as to reduce losses in the network, and voltage regulation is generally carried out locally.
Traditionally the following devices are used for this purpose: automatic voltage regulators AVR controlling a generator's field excitation so as to maintain a specified voltage magnitude at generator terminals, as well as sources or sinks of reactive power, such as shunt capacitors SCs , shunt reactors SRs , rotating synchronous condensers RSCs and SVC.
SCs and SRs are either permanently connected to the power system or can be switched on and off according to operative conditions. Nevertheless, they provide passive compensation since their production or absorption of reactive power depends on their rating and the bus voltage level at which they are connected.
Load-tap changing transformers LTCs whose main function is to regulate voltage magnitude at its terminals by changing their transformation ratio. Advances in power electronic technologies together with sophisticated electronic control methods made possible the development of fast static compensators namely Flexible AC Transmission Systems FACTS.
The FACTS technology has become one of the most valuable compensation techniques, because it applies the latest advances in power electronics to achieve additional and more effective control of the parameters of the electrical systems.
This represents the most efficient combination of conventional primary equipment, high power semiconductor devices, microelectronics and telecommunications equipment, allowing a most flexible power electric system.
The SVC has made the rotating synchronous compensator redundant, except where an increase in the short-circuit level is required along with fast-acting reactive power support. According to these, studying and comparing these controllers holistically would be useful. The objective of this paper is to present an integral comparison of the major aspects above. Applications of FACTS devices have continued to increase; accordingly, the results of this paper can be a reference to support engineers who are responsible for implementing these devices.
The remainder of this paper is organized as follows. Models and the general characteristics from both controllers are also described. Finally, in Section 4 simulations of the steady state and transient stability are presented and analyzed. The SVC consists of a group of shunt-connected capacitor and reactor banks with fast control action by means of thyristor switching.
A SVC can be considered as a variable shunt reactance, which is adjusted in response to power system operative conditions in order to control specific parameters of the network.
Depending on the equivalent SVC's reactance, i. Suitable control of this equivalent reactance allows the regulation of the voltage magnitude at the power system node where the SVC is connected.
SVCs achieve their main operating point at the expense of generating harmonic currents, and filters are normally employed with these kinds of devices. A SVC may include a combination of both mechanically and thyristor-controlled shunt capacitors and reactors; however, the most popular configurations for continuously controlled SVCs are the combination of either fixed capacitor-thyristor controlled reactor FC-TCR or thyristor switched capacitor-thyristor controlled reactor TSC-TCR Fuerte-Esquivel, From the point of view of steady-state modeling and simulation, however, both devices can be treated similarly.
Additionally, a SVC is connected to the system via a direct connection or by a coupling transformer. The function of a transformer has two main goals: i to connect the SVC at high voltage responding to an economic criterion and ii to filter the current of third harmonic that occurs as a result of the firing angle of the thyristors and by the presence of resonances in capacitor banks.
This device has become relevant because of the following: i it does not require major maintenance, since it has no rotating parts, ii fast response times of the order of milliseconds, iii voltage control can be independent of phase, iv minimal losses associated with its operation, v high profitability in comparison with the installation of new transmission lines and vi can help with reactive power during failures.
The SVC also has some disadvantages, however; the most outstanding is the generation of harmonics. Thus, expressions for the maximum and minimum susceptance are determined as follows: The thresholds of reactive power that can be exchanged to the system are defined as. Based on their principle of operation, the converters can be grouped as a VSC typically a capacitor or a current-sourced converter usually an inductor , with a DC signal input.
Each voltage is on phase and coupled to the corresponding AC system; moreover, the transformer reactance has a small value because of the reactors and the magnetic coupling. These output parameters can be varied to control specific variables of the power system at the point of connection. The reactive power flow is determined mainly by the magnitude of the voltage bus, V k , and the VSC output fundamental voltage, V vR. By the inspection of 1 — 7 and Figs. These characteristics are summarized and shown below.
Considering the curves which relate voltage magnitude to current VI or reactive power VQ for the aim of voltage support capabilities is common. A decrement in system load level results in an increase in voltage magnitude at all system nodes. On the other hand, an increase in the system load level produces a decrease in nodal voltage magnitudes.
For this condition, the devices maintain the voltage magnitude by injecting a capacitive current. In Fig. With reference to Fig. This can also be observed in Eqs. A similar approach is taken for reactive power compensation; in this case, Fig. Additionally, the SVC cannot transiently increase the generation of VAR since the high capacitive current consumed is determined strictly by the size of the capacitor bank and the system voltage magnitude.
Moreover, in the SVC if the system voltage is lower than the reference voltage, the impedance offered by the reactor is high. Additionally, if the system voltage is increased to exceed the reference voltage, then the mechanism of SVC switches the reactors to decrease the impedance of the inductive branch.
The impedance of the capacitive branch varies linearly with applied voltage according to the characteristic of the capacitor admittance.
Note that if the SVC has an upper voltage, it behaves as an inductive element absorbing reactives , and for any lower voltage the SVC is a capacitive element adding reactives. The function of the STATCOM is also to exchange reactive power capacitive and inductive, and the large capacitor bank including its protection and switching equipment is not required, which has been used in the conventional SVC.
The scheme of comparison is illustrated in Fig. Thus, STATCOM's small physical size is optimal for installations in areas where the floor has a high cost and for applications where the system can require a relocation of the installation.
For both FACTS, the costs can vary depending on voltage, land requirements, construction time, operation and maintenance, repair, workers, substation equipment, access, roads, service, permits, licenses and financing. Grouping these concepts, Table 1 shows a comparison between the costs of both.
Nevertheless, the physical size of the installation of an SVC influences civil engineering cost. A set of simulations are presented in order to analyze and compare the steady-state and transient performance of SVC and STATCOM, highlighting the advantages and benefits provided by each of these compensators in a power system.
The network operates with a frequency of 60 Hz; furthermore, the voltage and power value are kV and MVA respectively as the system base. Single-line diagram of the 5-bus test system. Power flow is the name given to the steady-state solution of a power electric system under prescribed conditions of generation, load and network configuration in order to find the nodal voltages, power flows, power losses and compensation requirements. In the case of reactive shunt compensation applications, the likely specific objective of the power flow studies are the following: i to determine appropriate location; ii to provide information about the power flows under normal and compensated conditions; and iii to identify required control, settings and limits.
The power flow results for the test network are illustrated in Fig. As expected, both devices can control the voltage magnitude at the specific value.
The power flow results indicate that in order to keep the nodal voltage magnitude at kV 1 p. In general, an improvement can be seen in the network's voltages profile. Furthermore, the reactive power flow has been increased almost 20 times to the Main node via L6, for the case without compensation. Clearly, the reactive power flow has been incremented between the Lake node and the South node through L3; the large amount of available absorbed reactive power is provided by the synchronous generator GEN2, with a value of In steady state, both compensators present similar improvements.
In this case, GEN1 significantly reduces the generation of reactive power since it has a value 2. Moreover, reactive power flow between nodes North and Lake, presents an increase of approximately 10 MVAR in the line L2, with respect to the case without compensation, which is also absorbed by the machine GEN2.
For completeness, it should be mentioned that the power losses decrease from 3. For shunt-controlled reactive compensation some applications of large disturbance studies include the following: i to determine appropriated locations and ratings; ii to provide information on the transient response and damping; iii to provide information about the interaction of the reactive source with the power system components; and iv to identify enhancement to power transfer limits, transient stability and system damping.
For these studies, power networks are modeled as a set of algebraic and differential equations. Using the results of power flow studies to provide initial conditions, the differential equations are solved by numerical integration. The test network of Section 4. A three-phase fault at South node has been applied to the network.
In both controls, reactive power as voltage at the connection point are important for calculating control variables. In these three cases, a failure occurs in the 1.
In Figs. Additionally, in Fig. The presence of a short circuit involving a voltage drop to zero at the node of the fault, increasing the value of the current that flows in the network. Without compensation, all voltages fall and remain low in the time in which the contingency of 1. In the figures, we can see that the only bus which reaches zero is the South node, which is where the fault has a major effect.
Consequently, the results of the fault are also reflected in the others buses with voltage drops. Once the fault is released, the system attempts to restore its initial conditions, but in this case the fault has been large and the system is disturbed, presenting oscillations and alterations that do not allow its recovery. In the interval of the fault, 0.
Despite the presence of the compensator, no change in voltage magnitude is observed, whereas in North, Lake and Main the effect of the installed STATCOM is clear; the compensator injects reactive power to the network, trying to raise the voltage magnitude of the nodes, in comparison with Fig. That is, the STATCOM has a high ability to respond, since the voltage is raised to a magnitude of a higher level than the SVC at the same time of operation, including bus Elm, which is far from the compensator.
Report Download. No part of this ebook may be reproduced in any form, by photostat, microfilm, xerography, or any other means, or incorporated into any information retrieval system, electronic or mechanical, without the written permission of the publisher. All inquiries should be emailed to rights newagepublishers. Modern power systems are highly complex and are expected to fulll the growing demands of power wherever required, with acceptable quality and costs. The economic and environmental factors necessitate the location of generation at places away from load centres. The restructuring of power utilities has increased the uncertainties in system operation. The regulatory constraints on the expansion of the transmission network has resulted in reduction of stability margins and increased the risks of cascading outages and blackouts.
Mitsubishi Electric has a range of FACTs solutions to meet a wide variety of needs and draws on a wealth of experience in the field, including a number of world-firsts. The modern power transmission system is rapidly changing. Closure of existing thermal plants and integration of new generation sources, such as renewables, requires additional grid support. Find out more about how FACTs devices can help in improving the transmission system here:. Mitsubishi Electric has a range of power-electronic based products to assist in grid stability. With over 50 years experience in power electronics- based reactive power compensation, we offer industry-leading reliability and performance.
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Power electronic based systems and other static equipment that provide controllability of power flow and voltage are termed as FACTS Controllers. It is to be noted.
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Show all documents It comprises two voltage source converters VSCs coupled through a common dc terminal. One VSC - Converter 1 is connected in shunt with the line through a coupling transformer and the other VSC - Converter 2 is inserted in series with the transmission line through an interface transformer. The dc voltage for both converters is provided by a common capacitor bank.
No part of this ebook may be reproduced in any form, by photostat, microfilm, xerography, or any other means, or incorporated into any information retrieval system, electronic or mechanical, without the written permission of the publisher. All inquiries should be emailed to rights newagepublishers. Modern power systems are highly complex and are expected to fulll the growing demands of power wherever required, with acceptable quality and costs. The economic and environmental factors necessitate the location of generation at places away from load centres. The restructuring of power utilities has increased the uncertainties in system operation. The regulatory constraints on the expansion of the transmission network has resulted in reduction of stability margins and increased the risks of cascading outages and blackouts.
The Journal of Applied Research and Technology JART is a bimonthly open access journal that publishes papers on innovative applications, development of new technologies and efficient solutions in engineering, computing and scientific research. JART publishes manuscripts describing original research, with significant results based on experimental, theoretical and numerical work. The journal does not charge for submission, processing, publication of manuscripts or for color reproduction of photographs. JART classifies research into the following main fields: Material Science Biomaterials, carbon, ceramics, composite, metals, polymers, thin films, functional materials and semiconductors. Computer Science Computer graphics and visualization, programming, human-computer interaction, neural networks, image processing and software engineering.
Enter your mobile number or email address below and we'll send you a link to download the free Kindle App. Then you can start reading Kindle books on your smartphone, tablet, or computer - no Kindle device required. This is based on modern high power electronic systems that provide fast controllability to ensure 'flexible' operation under changing system conditions.
Offering both an in-depth presentation of theoretical concepts and practical applications pertaining to these power compensators, Thyristor-Based FACTS Controllers for Electrical Transmission Systems fills the need for an appropriate text on this emerging technology.