Guibin Zou

A Traveling-Wave-Based Amplitude Integral Busbar Protection Technique

This paper proposes an extra high-speed busbar protection technique according to the propagation theory of traveling wave. When the fault occurs on the busbar, the detected initial traveling waves on all connected lines will come from their back, which are defined as positive direction traveling waves. While a fault occurs on any one of these lines, the detected initial traveling waves on all healthy lines are positive direction traveling waves; however, the traveling wave direction on the faulted line is negative. Within a short duration of postfault, a criterion discriminating fault direction can be established according to the amplitude integral relationships between the positive direction traveling wave and the negative direction traveling wave. Analyzing the detected traveling wave directions for all lines, a distributed busbar protection scheme can be constructed. To evaluate the proposed technique, a typical busbar model was built. Simulation results show that the proposed method can rapidly and reliably discriminate the internal faults from external faults, and the protection performances are immune to fault resistances, fault inception angles, fault types, and current-transformer saturation.

A Novel Busbar Protection Method Based on Polarity Comparison of Superimposed Current

This paper proposes a novel busbar protection method based on the polarity comparison of superimposed current. Analysis shows that all lines connected to the faulted busbar have the same polarities for the superimposed currents in case of an internal fault to busbar; but for a fault occurring on any one of these lines, the polarity on the faulted line is opposite of those on healthy lines. According to this important characteristic, the busbar protection criterion can be established. To improve the reliability of the busbar protection method, waveforms of superimposed currents are integrated within a short time after the fault. Moreover, a new phase-mode transformation matrix is proposed to realize that single aerial modulus can reflect all fault types. A real 500-kV substation busbar model was built in PSCAD to evaluate the performance of busbar protection. Simulation results demonstrate that the proposed protection method has good adaptability, fast operation speed, and high reliability. In addition, its performance is rarely influenced by the fault initial conditions, series compensation, and CT saturation, etc.

Identification of Lightning Stroke and Fault in the Transient Component Based Protection

To resolve the impact of transient traveling wave induced by lightning stroke on the transient component based protection of transmission line, a novel identification algorithm is proposed. Using the characteristics of symmetry of waveform induced by lightning stroke without causing fault and asymmetry of waveform generated by fault within a very short interval, the waveforms of transient current above and below time-axes are integrated respectively. First, through comparing the ratio of them with threshold value, the primary criterion identifying fault and lightning stroke is constructed; Secondly, to improve the reliability of discrimination between lightning stroke with and without causing fault, according to the difference of them, the secondary criterion is also defined. The simulation results from EMTDC demonstrate that the proposed integral criterions are valid and correct.

Algorithm for ultra high speed travelling wave protection with accurate fault location

Basing fault generated current travelling wave, a novel algorithm implementing ultra high speed protection and fault location for transmission lines is proposed. By applying wavelet transform to the current travelling wave signals measured at two terminals of a protected line, the corresponding modal maxima of the two current signals are obtained. The algorithm uses the polarity relationship between two initial modal maxima to determine whether the fault is internal or not. Simultaneously, the fault location can be easily calculated according to the interval between the two modal maxima. The factors influencing on travelling wave protection and fault location are analyzed and some measures are presented. Extensive simulation results based on EMTDC demonstrate that the algorithm is able to achieve double functions of ultra high speed protection and highly accurate location, which is just required by EHV/UHV transmission systems.

Realization scheme of directional unit protection based on travelling wave integral

A set of scheme of directional unit protection based on travelling wave integral is designed. For main components in this scheme, such as fault phase selection component, fault direction discrimination component, lightning stroke and circuit breaker operation verification, etc., the theoretical analysis and criterion construction and simulation test are all carried out. Simulation data demonstrate that the fault conditions hardly have any influence on the performance of proposed discrimination principle for fault direction; the identification criterion for different signals can correctly distinguish fault signals from various disturbance signals and fault phase selection criterion can precisely choose fault phase. This protection technique has clear principle and simple construction, which is promising to be used in practical power engineering.

A novel directional protection based on transient energy for HVDC line

Using the characteristic difference of transient energy, a transient energy based directional unit protection is proposed. Assuming the positive direction of current is from DC busbar to DC line, for an internal line fault, the detected transient energies on both ends of the line are all negative, which denote the positive direction fault. When an external fault occurs, the transient energy on one end is positive, which denotes a negative direction fault, but the transient energy on opposite end is negative, which means that the fault direction is positive. Through comparing fault directions on both ends, the internal or external DC line fault can be identified. Besides, according to the magnitude difference of transient energy, the faulty line can also be discriminated for bipolar line. Finally, this paper constructs a ±800kV DC transmission system model, and simulation results verify the validity and feasibility of the proposed method.

A Novel Distributed Busbar Protection for Digital Substation

For the digital substation based on IEC61850 communication standards, this paper presents a novel scheme of distributed busbar protection. According to the technical characteristics of digital substation, the configuration of distributed busbar protection without central unit is constructed; the requirements of data communication between merging units (MU) and distributed busbar protection units are analyzed and the process bus based on Ethernet is designed; last, the percentage differential algorithm for distributed busbar protection is introduced. Analysis shows that the proposed scheme is a simple, high reliable and feasible distributed busbar protection for digital substation.

Positive sequence differential impedance protection for distribution network with IBDGs

The fault characteristics of inverter-based distributed generator (IBDG) differ from those of traditional resources, which makes the conventional protection schemes ineffective in active distribution networks. This paper first analyses the features of measured positive sequence impedance at both ends of protected line section in internal and external fault cases. Based on the amplitude difference of defined differential impedance in various fault cases, a novel pilot protection scheme applicable to distribution networks with IBDGs is proposed. To diminish the negative influence of load branches, an operation criterion with restraining characteristic is constructed, and a current amplitude difference coefficient is introduced for the further improvement of the protection performance. The proposed strategy has no need for data synchronization measurement and owns stronger ability to resist transition resistance. Simulation results verify the validity and feasibility of the protection scheme.

Modeling and fault simulation of active distribution network based on RTDS

Active distribution networks (ADN) connect many distributed generators (DG), and compared with traditional distribution network, running state and fault characteristics of ADN change greatly, especially the ADN with connection of inverter-based DG (IBDG). To analyze and test the protection applicability in ADN, a model of ADN with IBDG is established based on RTDS in this paper, including primary system of distribution network, photovoltaic (PV) generation and control strategy for grid-connected inverter. Based on this model, both the characteristics of normal and fault condition are simulated and analyzed, and then compared with traditional distribution network. Meanwhile, based on the ADN model platform, a close-loop test for the protection device we developed is introduced briefly.

S-transform based pilot protection method for HVDC transmission lines

Traditional traveling wave protection of HVDC line is easily influenced by fault resistance, and the current differential protection as backup protection has disadvantages of slow operation speed and data synchronization, so this paper proposes a pilot protection method for HVDC line based on S transform. Theoretical analysis shows, for a fault occurring on the forward direction of the protection, the polarities of the fault components of voltage and current detected by protection are opposite, but for a backward direction fault, they are the same. According to these characteristics, a new method based on S transform angle differences to identify the fault direction is presented. In addition, for a pole-earth fault in bipolar HVDC systems, the faulted line can be distinguished from the healthy line in terms of ratio differences of S transform transient voltage energies. Simulation results show that the proposed method can effectively identify internal and external faults, the faulted line and lightning disturbance in different fault conditions.