A differential relay based UPFC compensated line

This paper discusses fault detection and classification in the double circuit transmission line of a differential based scheme in STATCOM (Static synchronous Compensator) compensated line applying FDST (Fast Discrete S-Transform). Here, STATCOM is placed at middle point of one of the transmission line and the other line is uncompensated. The proposed scheme starts processing by extracting the faulty currents signal (A, B or C-phase) from both end (i.e, sending and receiving end) of the transmission line synchronously through GPS system. The current signals are passed through FDST to derive the Spectral Energy (SE) of current signal at both end of the transmission line. Then the Differential Energy (DE) is computed by using SE of current measured at sending end minus SE of current measured at receiving end of transmission line. The scheme is very effective and works accurately for fault detection and classification of the transmission line.

A fast time–frequency transform based differential relaying scheme for UPFC based double-circuit transmission line

This paper describes the fault classification and detection of SVC (Static VAR Compensator) integrated differential relay based double circuit transmission line applying Discrete Wavelet Transform (DWT) approach. The SVC is placed at mid-point of circuit-I of double transmission line. The other circuit (circuit-II) remains uncompensated. The differential relay based protection scheme is used for the analysis of fault detection and classification. The process starts by extracting current signals (A, B or C-phase) from both sending and receiving end of the transmission line synchronously and processes through DWT to obtain the spectral energy (SE) at both the end of the line. The Differential Spectral Energy (DSE) of each phase current signals are obtained by SE of current measured at sending end minus SE of current measured at receiving end. This DSE value is used to register the fault pattern.

This paper addresses two issues in operation of a unified power flow controller (UPFC), enhancement of fault recovery and controller design accounting for filter dynamics. Performance of a UPFC is improved by a temporary modification of the UPFC into double static synchronous series compensator (SSSC) in order to double its capability in fault recovery mode. A battery is required as an energy source in the DC link of the double SSSC. The size of the battery for the SSSC has been be investigated. It was found that the double SSSC in fault recovery mode has almost twice the performance of the UPFC and the size of battery for the UPFC is reasonable for grid scale use. With the double SSSC in fault recovery mode, a combination control mode is suggested for the UPFC. One of the important parts of the UPFC is the filter at the output of the inverter. The function of the UPFC filter is to attenuate the harmonics generated by the inverter. In this paper a harmonic trap filter together with a low-pass filter are applied to the UPFC and investigated. Single-phase models are used to design cut-off frequencies whilst the d-q model is included in the UPFC controller design. It was found that if the filter dynamics are neglected in the control design, then the controllers response will be different. The test system used is a one-machine, two transmissions lines and an infinite busbar. All of the simulations were implemented using the EMTP. Additionally Matlab and Simulink programming environment were used to provide transfer function simulation for the controller design. The simulation results from both programs are compared.

This paper presents the measured impedance at the relaying point in the presence of a flexible alternating current transmission system (FACTS) device, i.e. unified power flow controller (UPFC). The presence of UPFC on a transmission line has a great influence on the tripping characteristic of distance relays. Distance relay tripping characteristic itself depends on the power system structural conditions (short circuit levels at the line ends), pre-fault operational conditions (load angle and voltage magnitude ratio at the line ends), and especially the ground fault resistance. In the presence of UPFC, its controlling parameters as well as the connection point of the instrument transformers of distance relay affect the tripping characteristic. Here, the measured impedance at the relaying point is calculated due to concerning parameters.

This paper presents a screening technique for greatly reducing the computation involved in determining the optimal location of a unified power flow controller (UPFC) in a power system. The first-order sensitivities of the generation cost with respect to UPFC control parameters are derived. This technique requires running only one optimal power flow (OPF) to obtain UPFC sensitivities for all possible transmission lines. To implement a sensitivity-based screening technique for guidance in optimally locating a single UPFC in a power system, we propose a new UPFC model, which consists of an ideal transformer with a complex turns ratio and a variable shunt admittance. In this model, the UPFC control variables do not depend explicitly on UPFC input and output currents and voltages. Accordingly, this model does not require adding extra buses for UPFC input and output terminals. IEEE five-, 14- and 30-bus systems were used to illustrate the technique

The characteristics of the distance relay are devised based on online and fault impedance. The relay uses fault information to react to the expected state; however, integrating the grid with a unified power flow controller (UPFC) might stop the relay from fault-triggered operations, requiring altered relay characteristics. Building relay tripping parameters are among the critical challenges that must be addressed for transmission line distance relays because current transmission networks face higher stress regarding power system operation. Furthermore, the use of flexible AC transmission systems (FACTS) instruments at the transmission level adversely affects distance relay performance due to impedance differences. The UPFC is among the essential FACTS instruments; it comprises shunt and series converters to alter the apparent relay impedance; hence, it was considered for this study, where a test system during fault was assessed to demonstrate the output of the distance relay before and after using the UPFC. MATLAB was used to build scenarios demonstrating the effect of a UPFC located in the transmission line's midsection or end or not using the UPFC. This research offers an analytical technique to determine the probable effects of UPFC on distance relay characteristics. The outcomes provide new relay characteristics for several fault resistances and locations for fault-specific impedance trajectory reactions.

In this paper, a fault detection and faulty phase selection of a two generator two bus system with unified power-flow controller (UPFC) is studied extensively by generating the data in EMTDC/PSCAD environment. Distance relaying of transmission line having UPFC is a very challenging task. Different fault cases are simulated by placing the UPFC at the sending end of a 230kV transmission line in two generator two bus system. A one cycle three-phase current data are collected at 1 kHz sampling rate for detection and classification of different faults by moving sum based technique. The results presents the proposed technique of frequency domain analysis possesses very fast and accurate protection for UPFC based power transmission lines.

The transmission line fault location algorithms are affected in presence of FACTS device like unified power flow controller (UPFC) due to changed voltage and currents signals at the relaying point after occurrence of fault. Additionally, these algorithms involve high computation burden associated with signal processing techniques and are proven to be in-efficient during severe power system conditions. To eliminate the limitations stated above, a novel travelling wave aided intrinsic time-decomposition (ITD) based fault location algorithm is presented in this paper for estimation of fault location in UPFC employed transmission lines. ITD offers several advantages over other time-frequency-energy (TFE) analysis tools such as presenting precise temporal information and involving less computation burden. ITD decomposes a given signal into a sum of proper rotation components (PRCs) followed by a monotonic trend. The proposed ITD based fault location algorithm estimates the arrival times of travelling waves from first PRC of modal voltage signals of the terminals to which the transmission line is connected. From the estimated arrival times, the fault location is calculated. For simulation, a 100 MVA UPFC controlling the power flows in a 500 kV transmission system is used. Different cases of faults with diverse power system conditions are applied to examine the robustness and efficacy of ITD based fault location algorithm. Further, ITD base method is compared to existing methods available in literature and found to be a better performer in the context of fault localization.

– The unified power flow controller (UPFC) is the most versatile and complex power electronic equipment that has emerged as the indispensable equipment for the control and optimization of power flow in electrical power transmission system. In this manuscript is investigated the control of real and reactive power flow through a transmission line with the use of UPFC at the sending end. Computer simulation using MATLAB Simulink is done and the behavior of the UPFC is studied. In the UPFC based control of transmission line parameter control systems, it is observed that whenever the SSSC sources some real power into the transmission line it is manifested as a voltage drop across the DC link. Reactive power demand is indicated as fall in the bus bar AC voltage. The fall of the DC link voltage is an indication of real power demand from the receiving end. Similarly a fall of the bus bar AC voltage is an indication of reactive power demand from the receiving end. Fuzzy Logic and PI controllers are used in this works, the control of DC voltage, AC voltage and power transfer.

Due to ever-increasing power demand, the power system is facing issues such as congestion, line outages, system reliability, and stability challenges. The impetus to revise the traditional power transmission theory and practice, and to introduce new concepts for improving the performance of the existing AC transmission system caused the development of flexible AC transmission system controllers (FACTs). Due to their capability of controlling transmission system parameters, the utilization of FACTs controllers has become essential to enhance the power system capability. To investigate the performance of FACTs controllers, this study incorporates the Unified Power Flow Controller (UPFC) in the power system. UPFC is used to mitigate transmission line congestion by controlling the transmission line power flow. In this paper, a modified control circuit for UPFC is implemented. Moreover, the selection of a suitable location for UPFC is necessary because of its techno-economic impacts. Therefore, this work uses a sensitivity-based approach for the selection of a suitable place of UPFC. To decide the suitable location, control parameters of UPFC along with system loss sensitivity indices are used. The model of UPFC along with the control circuit is simulated in PSCAD/EMTDC. To investigate the performance of UPFC, a five bus seven-line transmission system is used. After installing the UPFC at an appropriate location, the power flow results of transmission lines are compared with and without the usage of UPFC.

The Unified Power Flow Controller (UPFC) can inject voltage with controllable magnitude and phase angle in series with a transmission line. It can also generate or absorb controllable reactive power. UPFC is expected to be able to damp power system oscillations more effectively than power electronics devices such as SVG and TCSC. In this paper, a control system design of a UPFC for power system damping enhancement based on the eigenvalue control method is proposed. It is made clear that the best design method for the power system damping enhancement is to determine steady-state values of the UPFC control variables and the control parameters of the UPFC such as gains and time constants simultaneously, because the controllability of UPFC depends on the steady-state values of UPFC and the power flow condition. The effectiveness of the proposed control system taking into account UPFC inverter ratings is verified by digital time simulation. Furthermore the effects of the input signals to the UPFC controller on small-signal stability and transient stability enhancement are studied, and it is made clear that UPFC controllers using global information are more effective for power system damping enhancement than those using local information because global information has stronger observability for power system oscillations than local information. © 2000 Scripta Technica, Electr Eng Jpn, 133(3): 35–47, 2000

The flexible ac-transmission system (FACTS) family called distributed power flow controller (DPFC). The DPFC is derived from the unified power flow controller (UPFC) with eliminated common dc link. The active power exchange between the shunt and series converters, which is through the common dc link in the UPFC, is now through the transmission lines at the third-harmonic frequency. The DPFC is to use multiple small size single phase converters instead of large size three phase series converter in the UPFC. The large number of series converters provides redundancy, thereby increasing the system reliability. As the D-FACTS converters are single phase and floating with respect to the ground, there is no high voltage isolation required between the phases. The cost of the DPFC system is lower than the UPFC. The DPFC has the same control capability as the UPFC, which comprises the adjustment of the line impedance, the transmission angle, and the bus voltage. Due to the high control capability DPFC can also be used to improve the power quality and system stability, such as low frequency power oscillation damping, voltage sag restoration or balancing asymmetry.

Optimization of system capacity electric power transmission systems requires a reliable power flow controller. The power flow controllers must be able to control the level of electrical voltage and active and reactive power flow without reducing the level of stability and security of the transmission system. Latest technology in the control of power flow is a Unified Power Flow Controller (UPFC). The entire transmission line parameters are impedance, voltage, and phase angle can be controlled simultaneously by the UPFC. The method used in the conventional algorithms based UPFC is still firmly with logic. These algorithms have difficulties to electric power transmission systems multimachine very dynamic, i.e. systems that are experiencing rapid changes in the electrical load from time to time. Therefore, in this study was developed based on neuro-fuzzy method is applied to the adaptive UPFC for adaptively controlling the power flow in electric power transmission systems multimachine very dynamic. In this study, three phase fault is applied to the multimachine system. The results are taken to be consideration of PI and neuro-fuzzy controllers. The PI and neuro-fuzzy controllers show nearly same results but there is a low overshoot occurred during the fault in the neuro-fuzzy controllers results. According to results that UPFC improves the system performance under the transient and the normal conditions. However, it can control the power flow in the transmission line, effectively.

This paper discusses the distance relay ideal tripping characteristic in the presence of unified power flow controller (UPFC), one of flexible alternating current transmission system (FACTS) devices on the next line and pays especial attention to the distance relay over-reaching problem. This is done by presenting the measured impedance at the relaying point in the presence of UPFC at the near end of the next line. The measured impedance at the relaying point is greatly influenced in the presence of UPFC on the protected line or even on the near end of the next line. The measured impedance depends on many factors including the power system structural conditions, pre-fault loading, ground fault resistance, UPFC structural and controlling parameters.