B. H. Zhang

A Novel Real-Time Searching Method for Power System Splitting Boundary

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.

Wide-Area Measurement-Based Nonlinear Robust Control of Power System Considering Signals' Delay and Incompleteness

With the wide application of synchronized phase measurement unit (PMU) in power system, the wide-area measurement system (WAMS) has enabled the use of a combination of measured information from remote location for global control purpose. However, the impact of time delays introduced by remote informations transmission in WAMS has to be considered, and the closed-loop power systems need be modeled as time-delay nonlinear systems. Moreover, the wide-area information is incomplete when not all generators in power system are equipped with the PMU. In order to eliminate the effects of power system models nonlinearity and wide-area informations uncertainty including time delays and incompleteness, a novel approach based on inverse system algorithm and linear matrix inequality (LMI) technique is proposed to design a nonlinear robust integrated controller. Digital simulation demonstrates that the four-machine system under the nonlinear robust integrated control has less settling time, swing times, oscillatory peak value and more critical clear time and better voltage stability performance for various time delays of remote incomplete measured information than that under PID control or nonlinear decentralized integrated control.

Research on order reduction of power system modeling for dynamic voltage stability analysis

Dynamic voltage stability analysis is mainly based on the time-domain solution of power system differential and algebraic equations. The modeling of each power element has a great influence on the correctness and complexity of stability analyzing. It is significant to model appropriately for simplifying calculation and drawing out principal contradiction. In this paper, the dynamical mechanism of voltage stability is summarized firstly. And based on the singular perturbation model taking into the fast and slow dynamics, this paper studies on how the quasi-steady-state model of power system approximates the dynamic of original system model. More, this paper employs the perturbation method and integral manifold theory as a tool for studying on the relationship of stability between the reduced-order system and original system. An important conclusion is reached that the power system quasi-steady-state model can be used for dynamic voltage stability analysis.

Flashover Characteristics along the Insulator in SF6 Gas under DC Voltage

In order to promote the flexibility about the selection of transmission corridor, DC gas-insulated transmission line (GIL) can be utilized to substitute part of the overhead line. One of the key factors that greatly threaten insulation level of GIL is the accumulation of surface charges along the supporting insulators under DC voltage. In this paper, the sphere-plane electrode system has been established to simulate the field distribution of the coaxial cylinder configuration in GIL. The effect of the insulators material and geometry on the insulators flashover characteristics under DC voltage in SF 6 gas has been investigated. Results show that the insulators surface conductivity has great influence on the surface charge accumulation as well as the flashover along the insulator in DC GIL.

A wind farm coordinated controller for power optimization

This paper presents a novel wind farm laguerre function based Nonlinear Model Predictive Control (NLMPC) coordinated controller for minimizing the wind farm wake loss and optimizing the capture power. According to the NLMPC with dynamic wake model, the controller can increase the farm capture power efficiently by regulating all WTGs in the farm. In the controller, the predicted effective wind speed error correction is proposed to compensate predictive model mismatch and the laguerre functions is introduced for reducing the receding horizon optimization burden. As the controller requires the predicted free wind from very-short term wind speed forecasting, the controller robust performance, which is critical for the practical application, is also discussed in this paper. Simulation study implemented in the testing wind farm shows that, the wind farm coordinated controller can increase the total wind farm power capture effectively in different wind conditions and reduce the time of receding horizon optimization considerably. In addition, the controller has attractive robust performance to the predictive model mismatch and free wind speed forecasting error.

Research on integration of transformer protection and winding deformation detecting

In this paper, the integrated conception of transformer protection principle based on equivalent equation and winding deformation on-line detecting has been presented. The transformer protection principle based on equivalent equation has been researched. Both of the equivalent equation protection criterion based on complete or fault component and the threshold on-line setting method are described in this paper. The on-line method uses the variation of the leakage inductance to monitor the transformer winding deformation. According to the parameter identification of winding leakage inductance, this paper puts forward a comprehensive and systematic integrated method of transformer protection principle and winding deformation on-line detecting. Using the transformer dynamic test data to inspect and verify, the conclusion can be brought that the winding parameter identification is accurate as well as be able to meet the requirements of transformer protection and online monitoring. The protection algorithm is theoretically clear and it can correctly and rapidly recognize the various transformer internal short circuits with distinct features.

The study on optimizing re-closing time to improve the transmission capacity

Based on the transient energy function (TEF) theory with classical models considered, the optimal re-closing time (ORT) can be calculated accurately. This paper mainly focuses attention on the validity and practicability analyzing of ORT obtained from this method. Firstly, the characteristics and influencing factors of the ORT are put forward and analyzed, and also the setting strategy of re-closing time for transmission line is presented. Further more, it will conduct simulations with a complex real system of China North Grid. Finally, the setting scheme is drawn to optimize the re-closing time of the key transmission lines in the network under current technological conditions. It is indicated that this method is an attractive counter-measure against transient instability and improving the transmission capacity of power system.

Optimizing the re-closing time to improve the transmission capacity of power system

The re-closing time of a transmission line has a distinct influence on power system transient stability. There is an optimal re-closing time (ORT) for all transmission line faults, no matter the instantaneous fault or permanent one. Based on the transient energy function (TEF) theory with classical models considered, the ORT can be calculated accurately. This paper mainly focuses attention on the validity and practicability of ORT obtained from this method. After analyzing the characteristic and influencing factors of the ORT, the setting strategy of re-closing time for transmission line is presented. And it will conduct simulations with a complex real system of China North Grid. Simulation studies show that this technique can significantly increase the security margin and damp the oscillation of the power system. It is indicated that the variation of ORT of a certain transmission line is insensitive to the influencing factors: the fault location, fault clearing time and pre-fault power flow. Finally, the setting scheme is drawn to optimize the re-closing time of the key transmission lines in the network under current technological conditions.

Combined Positional and Boundary Protection for Transmission Lines

This paper presents a novel relay for power transmission line systems, which is based on a combination of positional and boundary protection principle. The relay installed at a substation is responsible for the protection of the transmission lines associated with the substation. The relay is able to offer fast trip for any fault on its protected line sections without the need for communication link. The paper presents a detailed description to the basic principle, algorithm and design of the combined positional and boundary protection relay.

Integrated positional protection of transmission systems using Global Positioning System

This paper presents a new technique for the protection of power transmission systems by using the global positioning system (GPS) and fault generated transients, the integrated positional protection technique. The technique is based on the detection and processing of fault generated high frequency transient signals, in which a centralized protection relay provides the protection of multiple transmission lines. A specially designed integrated positional protection relay, which contains a fault transient detection system together with a substation communication network, is connected to the power line through the high voltage coupling capacitors of the CVT. The relay detects the fault generated high frequency voltage transient signals and records the time instant corresponding to when the initial travelling wave generated by the fault arrives at that busbar. The communication unit is used to transmit and receive coded digital signals of the local information to and from the associated relay(s) in the system. At each substation, the relays determine the location of the fault by comparing the GPS time stamps measured locally with those received from the adjacent substations. Extensive simulation studies presented in the paper demonstrate the feasibility of the scheme.