By utilizing multiline voltage-source (VSC)-based flexible ac transmission system (FACTS) controllers, independent controllability over each compensated line of a multiline system can be achieved. While VSC-based multiline FACTS controllers emerged as a new opportunity to control two independent ac systems, the main constraints and limitations that are presented to the conventional transmission-line protection systems need to be investigated. In this paper, the impacts of VSC-based FACTS controllers on distance relays while controlling the power flow of compensated lines are evaluated analytically and by detailed simulations for different fault types and locations. Index Terms-Distance relay, flexible ac transmission systems (FACTS) controllers, generalized interline power-flow controller (GIPFC), generalized unified power-flow controller (GUPFC), static compensator (STATCOM), static synchronous series compensator (SSSC).
SUMMARYIn this paper, the impact of STATCOM on the apparent impedance seen by conventional distance relay protecting a transmission line is investigated. Analytical results are presented, and verified by detailed simulations. It is shown that the implications of applying STATCOM on distance relay are highly dependent on the sophisticated modeling of STATCOM especially its control system considering practical constraints. Accurate modeling of the distance relay, particularly the analog input signals are also important in extracting reliable results. Practical constraints of the STATCOM are modeled in full details. It is demonstrated that when the STATCOM's limits are modeled in detail, i.e., the STATCOM is not considered an ideal reactivepower source the STATCOM's impact on the performance of distance protection is less severe than in the case where limits are ignored and thus ideal controllers are applied. This is a remarkable point for the utilities as not to overestimate the severity of the impact of STATCOM on conventional distance protection of transmission lines. Six different phase-to-phase and phase-to-ground measuring units of the distance relay are simulated to resemble the behavior of the relay. Different power system operating conditions, STATCOM control system settings and fault scenarios are investigated. The STATCOM effects on distance relay tripping characteristics are also analyzed.
Existence of Generalized interline power-flow controller (GIPFC) in a transmission line changes the voltage and current signals which are measured with the protection relays of power system dynamically. In this paper, the effects of the GIPFC on the measured impedance by loss of excitation (LOE) relay of synchronous generator are firstly investigated by both analytical and computational methods for different operating modes of the power system. Results indicate that the presence of GIPFC causes a substantial delay on the operation of LOE relay. It is also shown that when partial LOE happens, the GIPFC redounds to the LOE relay under-reaching. Consequently, to readjust the relay in the presence of GIPFC, a new modified LOE protection algorithm on the basis of synchronized phasor measurements received from phasor measurement units (PMUs) is presented. The most important advantage of this modified algorithm is that it is a general algorithm which considers all VSC-based FACTS controllers. Regarding the simulations results, it is concluded that using the modified algorithm for the LOE relay can sufficiently decrease the delay and prevent the relay from under-reaching. The impacts of unified power-flow controller (UPFC) and interline power-flow controller (IPFC) on the LOE relay are also demonstrated. Index Terms-Flexible ac transmission system (FACTS) controllers, generalized interline power-flow controller (GIPFC), unified power-flow controller (UPFC), interline power-flow controller (IPFC), generator loss of excitation (LOE) protection, phasor measurement units (PMUs).
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