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This paper analyzes the characteristics of equivalent dynamic power frequency impedance of the thyristor-controlled series capacitor (TCSC) and the integrated impedance, which is defined as the ratio of the sum of the voltage phasors across the two ends of the transmission line to the sum of the current phasors through the two ends of the same transmission line. The integrated impedance of the transmission line is used to determine whether there is a fault inside the protected line section or not. When an external fault occurs, the integrated impedance reflects the capacitive impedance of the protected line, its imaginary part is negative, and the absolute value of its imaginary part is large. When an internal fault occurs, the imaginary part of the integrated impedance on the fault phase is either a positive value or a small negative value. According to such characteristics, internal faults can be distinguished from external faults. Based on integrated impedance, a novel pilot protection scheme for the transmission line with TCSC and controllable shunt reactor is presented. Digital simulations based on 750-kV transmission systems show that the presented scheme offers high sensitivity and reliability with many advantages over conventional current differential protection. [ABSTRACT FROM PUBLISHER]

It is possible to prevent collapse of the whole post-fault power system, which is in unstable condition, by determining the splitting boundary so as to calm down the system oscillation. A fast method of searching for the splitting boundary of power system controlled islanding is presented in this paper, the aim of which is to minimize the load-generation imbalance in each island. The method contains three phases, namely, defining the domain of each generator according to power flow tracing algorithm, determining an initial splitting boundary based on the grouping information of generators, and refining the initial one to get the final splitting boundary. A real-time searching program for power system splitting boundary was developed based on the method. Simulations on the IEEE 118-bus power system and a practical power system show that the proposed method is effective and fast. [ABSTRACT FROM PUBLISHER]

A new algorithm for synchrophasor estimation is proposed to improve estimation accuracy under dynamic conditions. The real component of a constantly rotating vector and a low-frequency band-limited vector, which is linearized by Taylor series, is employed to model supplied signals in power systems. And dynamic characteristics of power systems are described in form of Taylor series' derivatives, which are calculated through consecutive phasors. The accuracy of phasor estimation was dramatically improved by the reassignment of estimation of short-time Fourier transform (STFT) with knowledge of these derivatives. Simulation results allowus to make the conclusion that the proposed algorithm improves the accuracy of phasor estimations under dynamic conditions dramatically, such as frequency ramping, low frequency oscillation, etc., at the cost of the calculation burden is a minimal increase whilst still meeting the requirements of the application for power systems. [ABSTRACT FROM AUTHOR]

Synchrophasors and frequency estimations play an increasingly important role in power systems. Discrete Fourier transform (DFT) may introduce errors into phasor and frequency estimations under dynamic conditions, such as power oscillation. A dynamic phasor and frequency estimator for phasor measurement units (PMUs) is proposed to improve accuracy by considering dynamic characteristics of power systems expressed as Taylor derivatives. Firstly, phasor estimations of sequence components of diffident data windows are attained via DFT. Secondly Taylor derivatives, expressed by adjacent phasors at different data windows, are employed to improve accuracy of estimations by reassigning estimations with the knowledge of dynamic characteristics. Finally, dynamic characteristics of positive sequence components are applied to estimate the fundamental frequency with less delay compared to a state-of-the-art algorithm, phasor-based synchronised frequency measurement (PSFM). To verify the performance, a set of digital dynamic tests and a power oscillation model using PSCAD/EMTDC are presented. The simulation results show that proposed algorithm can achieve highly accurate estimations of phasor and frequency over a wide range of dynamic conditions. Even though a minor increase in calculation burden is required, this technique provides accurate phasor and frequency estimations without changing the legacy structure of PMU devices. Additionally, it has been found that proposed algorithm really meets the needs of online applications. [ABSTRACT FROM AUTHOR]

An approach to numeric distance relaying is proposed that is suitable for EHV composite overhead line and underground cable circuit applications. The proposed relay incorporates a circuit shunt capacitance in addition to a series resistance and inductance. By modelling the protected circuit as a series of RLC sections within the relaying algorithm, greater reach point accuracy can be achieved. Unlike conventional distance relays that sense the fault loop impedance and compare this against a reach point value, the proposed relay uses a directional element that is based on the calculated reach point voltage and current values. Results are presented based on a composite 500 kV application study comprising two overhead line sections and two cable sections. Comparisons with conventional numeric distance relay algorithms show that overreach is virtually eliminated in the proposed relay. The simulation results have been verified with an implementation of the relay based on modern digital signal processing hardware. [ABSTRACT FROM AUTHOR]

The paper presents a technique for accelerated protection of distribution systems with tapped off loads. In the technique, the sequence and superimposed signals are used to determine the remote circuit breaker operation, from which a decision on whether a fault is inside the protected section can be made. Extensive simulation studies with respect to a typical ring main system with tapped off loads show that the proposed technique is able to significantly increase the speed of response of the conventional time-grading-based protection scheme. [ABSTRACT FROM AUTHOR]

This paper presents a new technique for non-communication protection of double circuit lines. In the technique, the sequence and super-imposed signals are used to detect the remote circuit breaker operation, from which whether a fault is inside the protected section can be derived. Extensive simulation studies with respect to typical double circuit transmission line systems show that the proposed technique is able to fast and correctly determine whether a fault is inside the protected line section without the need for communication links. [ABSTRACT FROM PUBLISHER]

The article presents comments of the author on adaptive non-communication protection for power lines. The researcher M.M. Eissa presented a paper discussing the adaptive protection based on changing the fault condition after breaker opening using two equations of voltage given in earlier articles. The author based his principle on voltage changing after breaker opening. The technique assumed that after occurrence of an internal fault, the voltage will drop to a specific value; after breaker opening by the relays, the voltage will drop to zero. This is actually not true and from the practical point of view, while after clearing the fault, the voltage does not drop to zero. Instead, it returns to its normal value. Hence, the proposed technique should change the principle of operation.

The article presents a discussion on the non-communication protection of double circuit line systems. The researchers Z.Q. Bo, X. Z. Dong and R. Millar are grateful to the discussers for pointing out their omission in not referencing the discussers' own excellent papers. It is clear that the authors failed to research these papers when writing their own. The author based his principle on voltage changing after breaker opening. The technique assumed that after occurrence of an internal fault, the voltage will drop to a specific value; after breaker opening by the relays, the voltage will drop to zero. This is actually not true and from the practical point of view, while after clearing the fault, the voltage does not drop to zero. Instead, it returns to its normal value. Hence, the proposed technique should change the principle of operation.

This paper presents a new high-speed protection scheme, transient positional protection (TPP) for power transmission lines. This scheme is developed using complex wavelet analysis, based on the concept of transient-based protection (TBP), in which the fault-generated high-frequency transient signals contained in the primary voltages are utilized to detect fault position according to their relative traveling time and polarities. Combined information (CI) is obtained from complex wavelet coefficients to extract and localize a band of specified high-frequency components propagating along the transmission line. A typical 400 kV EHV transmission system was simulated by PSCAD/EMTDC to evaluate the scheme. Simulation results show that this scheme is capable of providing correct responses under various system configurations and fault conditions. [ABSTRACT FROM PUBLISHER]

The reclosing time of a transmission line has a distinct influence on system stability. A new method of calculating the optimal reclosing time based on the transient energy function (TEF) is presented in this paper. It is shown that an optimal reclosing time can be used to set the autoreclosing device so that the system stability or power transfer capability can be significantly improved. Though power system TEF is based on classical models, the results from simulation studies of a real system (46 generators and 230 buses) with complex models show that the optimal reclosing time calculated using TEF can be used effectively. [ABSTRACT FROM PUBLISHER]

This paper presents the accelerated operation scheme of the adaptive noncommunication protection technique for power lines with complex configurations, such as multi-end feeder and ring main. In the scheme, the overcurrent directional relays are arranged in two operating modes, the fixed time operation and accelerated operation. The relays with faster operating time in the conventional time grading coordination remain unchanged. The new technique is employed to enable accelerated operation to be achieved for the relays that are in the positions for which slow operating time is set when using conventional time grading technique. For a fault occurring on the protected system, the relays of fixed time operation mode will operate at the preset time for the fault within its protected direction. The relays that are programmed to use accelerated operation mode will determine whether a fault is on the protected section or not by using the BO technique, that is, to detect the circuit breaker operation by determining whether the line section is in a balanced operation condition or not. The relay makes accelerated tripping decisions for a fault on its protected section. Simulation studies of the responses to various system and fault conditions show that the scheme can significantly increase the speed of the relay responses in the protection of power line systems with complex configurations. [ABSTRACT FROM PUBLISHER]

This paper presents the instant operation scheme of the adaptive noncommunication protection technique for power lines. In the technique, protection relays make tripping or reclosure decisions adapting to system and fault conditions without the need for communication links. The noncommunication is achieved by the detection of whether or not the system is in a balanced operation, in order to identify the breaker operation at the remote end of the protected section. In the scheme, the distance relay will trip instantly when a fault is detected outside its zone 1 but within its zone 2 reach. Subsequently it detects whether the fault is on the protected section or not, and recloses when a fault is cleared from the protected line section. Simulation studies with responses to various system and fault conditions have shown that the technique is able to give fast and correct response without the need for a communication link. [ABSTRACT FROM PUBLISHER]

This paper proposes a new technique in power line protection, the adaptive noncommunication protection. In this technique, protection relays make operate or restraint decisions, adapting to system and fault conditions, without the need for communication links. Operation without communication links to signal the remote end relay is achieved by the detection and identification of the operation of the circuit breaker at the remote end of the protected line section. An algorithm based on the symmetric components is proposed to detect and identify the balance condition of the system during the fault. The paper is focused on one of the three protection schemes based on the new technique, the delayed operation scheme. Simulation studies carried out for various systems and fault conditions have demonstrated the feasibility of the scheme. [ABSTRACT FROM PUBLISHER]