Xinzhou Dong

Fault Classification and Faulted-Phase Selection Based on the Initial Current Traveling Wave

Accurate fault classification and swift faulted-phase selection are the bases of protection for transmission systems. This paper presents the algorithm of fault classification and faulted-phase selection based on the initial current traveling wave. The characteristics of various faults are investigated on the basis of the Karenbauer transform. The criteria of fault classification and faulted-phase selection are put forward. In order to extract the traveling wave from postfault signals and to construct the algorithm, wavelet transform technology is adopted. The simulations based on the electromagnetic transients program have been done to verify the performance of the proposed algorithm.

Surge impedance relay

This paper presents a novel directional relay based on travelling waves for transmission line protection, referred to as the surge impedance relay (SIR). It determines fault direction by the ratio of initial voltage and current travelling waves under multiple frequency bands. In order to ensure the reliability of the relay, which has been a serious problem for travelling-wave-based relays, both the polarity and amplitude of the initial wave are used. In order to extract travelling waves from post-fault voltages and currents, and to construct an effective relaying algorithm, wavelet transforms were adopted. Because the fault information under the multiple frequency bands were used in the relaying algorithm, the SIRs reliability has been further improved. Theoretical analysis and EMTP simulations verified the directional relay. Finally, the paper introduces a scheme to implement the relay.

Identifying Single-Phase-to-Ground Fault Feeder in Neutral Noneffectively Grounded Distribution System Using Wavelet Transform

A scheme of single-phase-to-ground fault feeder identification in distribution networks with the application of a wavelet transform technique is presented in this paper. The scheme uses zero-sequence current traveling waves to identify the faulted feeder, and the busbar residual voltage to determine an event caused by fault or switch operation. The current traveling waves measured by zero-sequence current transducers are decomposed using wavelet multiresolution analysis. The local modulus maxima of the wavelet transform are extracted to determine the time of the initial traveling wave. The wavelet transforms on all feeders at the time are compared in magnitude and polarity with each other to identify the faulted feeder. The feeder identification is independent of the network neutral-point grounding mode. The proposed scheme was implemented and verified using Electromagnetic Transients Program (EMTP)-generated signals. The scheme proved to be robust against transients generated during normal events, such as feeder energizing and de-energizing as well as capacitor bank switching.

Fast detector of symmetrical fault during power swing for distance relay

Distance relay should be blocked during power swing to ensure the reliability, but still should trip as soon as possible after an internal fault occurs during power swing. It was very difficult to detect the symmetrical fault reliably and fast during power swing with complex power swing conditions and fault conditions considered. This paper presents a new fast detector of symmetrical fault during power swing. Based on the sudden reduction of absolute value of the change rate of power swing centre voltage (PSCV), the presented detector can detect the symmetrical fault reliably and sensitively in two cycles. This detector is easy to set and immune to the swing period, fault arc, fault location and power angle. EMTP simulations and real-time digital simulator system (RTDS) tests prove the presented detector is fast, sensible and reliable.

Hilbert-Transform-Based Transient/Intermittent Earth Fault Detection in Noneffectively Grounded Distribution Systems

Conventional relaying algorithms are mostly based on phasor computation. Since it is difficult to obtain accurate phasor results in fast transient situations, most of the feeder relays fail to correctly respond to transient/intermittent earth faults, which are, however, frequent fault cases in distribution systems. This paper presents a novel approach for fault detection and direction determination for these transient/intermittent faults. The basic idea is to extract the fault direction using the instantaneous powers direction. The instantaneous power is obtained by using Hilbert transform. The proposed direction element inherently utilizes the high-frequency components of the transient fault signals at a conventional sampling rate. Together with an intermittence detection algorithm, a scheme for transient/intermittent earth fault detection has been proposed. It has been implemented as a prototype relay. Electromagnetic Transients Program tests as well as physical model tests have proved the effectiveness of the proposed scheme.

Integrated protection of power systems

This paper reports on the development of integrated protection for power system. The concept of integrated protection is introduced, in which a centralized protection system (or relay) provides the protection of multiple power plant or a substation. Examples are given of the protection schemes with the features of integrated protection which are currently under development. A novel integrated protection scheme for substation and network protection is described. The technique is based on the detection and processing of fault generated transient current signals, in which specially designed protection relays are installed at each substation of a network. The transient detection unit of the relay detects the fault generated transient current signals. The transient polarity identification algorithm is then applied to the transient signals to identify the polarity of the signal detected. The direction of a fault is determined by comparison of the polarity of the signals derived from all the line sections connected to the substation. The actual faulted section is identified by processing the directional information from various substations

Adaptive noncommunication protection of double-circuit line systems

This paper presents a new technique for noncommunication protection of double-circuit lines. In the technique, the sequence and superimposed signals are used to detect the remote circuit breaker (CB) operation, from which it is to be determined whether a fault 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 rapidly and correctly determine whether a fault is inside the protected line section without the need for communication links.

Negative-Sequence Pilot Protection With Applications in Open-Phase Transmission Lines

Negative-sequence pilot protection (NSPP) is one of the most widely used protective principles for high-voltage/extra high-voltage transmission lines due to its excellent properties. Properties, such as immunity to system oscillation and the fact that it is not influenced by shunt capacitance, make it especially valuable for the protection of long-distances ultra-high voltage lines, which transfer large amounts of energy. However, negative-sequence pilot protection (NSPP) is not suitable for applications when a system operates with one phase open, which inevitably limits its overall application. To solve this problem and to achieve the selectivity and sensitivity for the NSPP algorithm, a novel algorithm for NSPP is proposed in this paper, which takes the load-phase voltage into the calculation of the negative-sequence voltage with a fault in the open-phase condition, and compensates the negative-sequence current in the open-phase operations for phase-ground faults. Simulation studies show that the proposed algorithm is able to produce excellent performance.

A New Current Differential Protection Scheme for Two-Terminal Transmission Lines

This paper describes a new current differential relay. A current differential plane is presented firstly to depict different system statuses. Two traditional current differential protection schemes are discussed by plotting their operating and restraint region in the current-differential plane. A relay characteristic with more appropriate operating and restraint region is plotted in the plane by analyzing the tolerances a current differential relay has. Based on the analysis, a new scheme of current differential protection is designed. It is tolerant of channel delay asymmetry, power system impedance nonhomogeneity and CT saturation. Finally we prove the relay performance using simulations. It enhances current differential relay performance without a significant increase in cost.

Adaptive Nonconmunication Protection of Double Circuit Line Systems

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.