Dingxiang Du

Design of a Real Time Digital Simulation System for Test of New Protection Schemes

This paper presents the design of new real time digital simulator (RTDS) based relay test systems. The background of the developments in protection relays and their associated technologies, such as optical transducers and IEC 61850, are introduced. The new developments in RTDS systems are described. It is shown that the recent developments in transducers and communication technology will have great impacts to the developments of protection relays and their associated RTDS based relay test systems. The paper further describes the existing, new developments and future trend in the development of protection relays and their associated RTDS systems.

An Integrated Current Differential Protection Scheme

This paper presents a new integrated protection scheme for transmission lines. The concept of the integrated protection is firstly introduced, in which a centralized protection system provides the protection of multiple power plant or a substation. A combined integrated protection relay for the protection of double circuit lines is then introduced, which combines the longitudinal current differential and the transverse current differential protection techniques. Studies show that the new relay offers more protection functions and significant economic advantages over the conventional current differential relays. A total integrated protection scheme based on current differential protection techniques is further described. In the proposed scheme, the specially designed protection relays are installed at each substation of a network and are responsible for the protection of every line sections connected to the substation busbar. The current differential algorithms with multiple settings are implemented into the relay to cover all the protected line sections. The scheme is supported by advanced communication network and standard. Studies show that the new scheme not only offer the new protection features for individual power line, but also provide the characteristics of integrated protection.

Research on dynamic simulation of the resonance fault current limiter

The resonance fault current limiter (RFCL), which avoids the disadvantages of the series reactor, is feasible for EHV and UHV grid. To contribute to project application of the RFCL, and study its running characteristic and impact on relay protection, the dynamic simulation lab of State Grid simulation center carries out the research on simulation technique for RFCL. The principle and technical properties of RFCL applied in EHV power transmission line are analyzed. Considering the features of dynamic simulation system in the lab, the approach to choose parameters of simulation model and corresponding structural design are described. This simulation model has been connected into dynamic simulation system and the simulation experiments for inspecting the control and protection function of RFCL are performed. Experimental results show that the performances of the developed simulation model for RFCL can meet the design requirement, and can be applied in dynamic simulation tests and researches.

The influences and countermeasures of wind farm access to transmission line differential protection

Large-capacity wind power will have impact on transmission line protection when short circuit occurs. This paper built the dynamic simulation model of different wind turbine generator through physical devices, and tested through operation and faults. By analysis of characteristics of wind farm model, this paper analyzed the influences of wind power to transmission line differential protection and proposed countermeasures to adapt and overcome the problem.

Analysis of protection performance in UHV transmission line with multi series capacitors compensation

Series capacitor can enhance transmission capability of power grid and optimize the power flowed to improve the transient stability of power systems. However, they change the magnitudes and the directions of fault voltages and currents in series compensated networks and impact the protection performances. This paper analyses the fault electric quantity characteristics and discusses the operation behaviors of protection relays on transmission lines with multi series capacitors. Some suggestions for improving the protection performance are proposed. The analysis results were tested extensively using RTDS (Real-time Digital Simulator) in a transmission line model. The simulation results show that the suggestions can improve the performance of protection relays applied in UHV transmission line with multi-series capacitors.

A novel substation area backup protection for smart substation

This paper proposes a new scheme of substation area backup protection system based on substation area range of information. A configuration scheme of relay protection in smart substation was proposed firstly, the structure of substation area backup protection (SABP) was introduced, the information matrix of SABP which can reflect the substation topology was established, the protection algorithm of SABP was proposed, the fault-tolerance performance of the proposed protection scheme was also analyzed. According to the analysis of fault direction information, fault current differential information, as well as the information matrix, the SABP can carry out fault location and make a reasonable tripping strategy. The result of case studies shows that the proposed protection algorithm can implement backup protection and circuit breaker failure protection for each electrical element inside smart substation, and has good adaptability to disconnection fault of CT.

High sensitive start element of transmission line protection

Sensitivity of start element impacts the performance of transmission line protection. Normally, start element is affected by data window length. A start element of transmission line relay protection based on current variation sample data of three phases at the same time is proposed in this paper. It includes two criterions. The start element performance is not impacted by data window and frequency. The sensitivity of criterion proposed was superior to present criterion. The criterion performance was proven using RTDS simulations in a 1000 kV power system.

Research on the distance protection performance for untransposed parallel transmission lines based on six-phase parameter information

For untransposed parallel transmission lines, the fault impedance measured by relays will be affected by both the mutual impedance between parallel lines and the coupling effect of different sequence components in the single line. Even the fault phase voltages are compensated by the zero-sequence current in the adjacent line, the errors of measured fault impedances are still quite large. The performance of distance protection may not reach the requirement. A distance protection algorithm based on fault circuit analysis, using the phase components of both lines at the local end and six-phase impedance matrix has been proposed in this paper. This algorithm is simple and immune to the grounding fault with big fault resistance. Simulation results show that this proposed algorithm can calculate the fault impedance more accurately, will almost not cause the cut-down and overreach of protection range, improving the performance of distance protection in untransposed parallel transmission lines apparently.

Protection algorithm based on spectrum characteristic of transient component

When a fault occurs on a transmission line, fault generated high frequency transient components are a series of natural frequencies in frequency domain. This paper proposes a protection algorithm for EHV (Extra High Voltage) transmission line based on spectrum characteristic of natural frequency. Spectrum correlation coefficient is used to determine whether a fault is internal or external fault. It can reduce trip time and not affected by swing, load current and power system operation mode etc. The scheme performance was proven using PSCAD/EMTDC simulations in 500-kV power system considering critical fault cases.

Analysis of pilot zero-sequence directional protection mal-function in double-circuit lines break-conductor fault and solutions

When asymmetric break-conductor faults occur in double-circuit transmission lines, the shift of load may produce large unbalance current in healthy line, leading to the malfunction of pilot zero-sequence directional protection with voltage compensation. This paper discusses the zero-sequence character of double-circuit lines in break-conductor fault, presents the malfunction mechanism of pilot zero-sequence directional protection with voltage compensation in healthy line after single-phase grounding fault tripping. The theoretical analysis was confirmed through simulation model. Moreover, preventive measures based on one-end single line or double lines electrical information was proposed.