Haiyu Li

A new type of differential feeder protection relay using the Global Positioning System for data synchronization

This paper describes a new technique for sampling synchronisation in a numerical differential feeder protection relay. The protection uses a Global Positioning System satellite receiver for sampling synchronization at each end of the protected feeder. The EMTP/ATP power system simulator was used to simulate a typical distribution feeder with faults at various locations. The current signals generated at both ends of feeder were used to evaluate the performance of the protection. These tests were carried out using a protection simulator. The results illustrate the effect of current transformer saturation on the sensitivity and stability of the protection. Finally it is shown that a precisely synchronized differential protection is fast, selective and accurate. On an internal fault it provides a high operating sensitivity, whilst it remains stable on all external faults.

Voltage sags pattern recognition technique for fault section identification in distribution networks

This paper presents a method to identify a faulted section in a distribution network using voltage sags pattern characteristics. The method starts with fault analysis to establish analytical voltage sags database. When a fault occurs, the voltage sag at the monitored node is compared with the established voltage sags in the database to find all the possible faulted sections. Finally, the method applied rank reasoning analysis to prioritize all the possible faulted sections. The method has been tested on an urban distribution network feeder. The results show that the most fault sections in the tested distributed network feeder can be located by the first attempt. All remaining faulted sections can be found by the second attempt.

Load shedding in a distribution network

Conventional methods of load shedding are too slow, do not effectively calculate the correct amount of load to shed and lack in operating in a coordinated way. This results in either unnecessary or insufficient load reduction. A new technique should be applied that will be fast and optimal relying on slow communication in order for the distribution network to maintain stability and to improve the reliability of supply to customers. This paper assesses the behavior of a 33 kV distribution network consisting of different type and size of loads and distributed generators, with the load shedding technique. The magnitude of the disturbance is determined using the swing equation, obtaining this way a more efficient system operation during emergency conditions with less customer interruption. Explanation of the load shedding architecture implemented and the investigation of its behavior are demonstrated through dynamic simulation using the power system analysis package PSCAD.

Increasing distributed generation using automatic voltage reference setting technique

The increasing connection of distributed energy generation in a distribution network may lead to unacceptable voltage rise. An automatic voltage reference setting technique, acting on the tap change control of the transformer supplying the network, can be used to address this problem. By measuring essential voltage points along the distribution network, an automatic voltage reference setting technique is applied to the automatic voltage control (AVC) relay. The AVC relay then controls an on-load tap changing (OLTC) transformer in order to maximise distributed generation while maintaining the feeder voltage within limits. The automatic voltage reference setting technique and its implementation are described. A closed-loop testing facility, based on a real time digital simulator (RTDS), was constructed and used to test the technique. The paper presents and discusses the results obtained and shows how this technique may be used to maximise the distributed generation that can be connected to a distribution feeder.

Assessment of Switched Communication Network Availability for State Estimation of Distribution Networks With Generation

Active management of complex distribution networks with distributed generation requires state estimation. As complete supervisory control and data acquisition systems are seldom available on 11-kV or lower voltage distribution networks, real-time measurements at remote points on 11-kV distribution networks are expensive. Therefore, the economical selection of a communication system for active management of distribution networks with distributed generation becomes an important issue. This paper presents the investigations into a leased communication system made of public-switched communication network channels for a distribution network state estimation application. It analyzes the effects of a different number of primary channels for real-time measurements on the distribution network state estimation accuracy. The leased communication system availability performance has also been analyzed and used to identify a number of reserve channels required to improve the leased system availability. The overall cost for improving the leased communication system availability has been calculated and compared with both a fiber-optic communication system and a power-line carrier communication system. The results show that the leased communication system is able to provide the lowest overall cost performance for the distribution network state estimation application.

Wideband impedance matching using Tchebycheff gain functions

A complete theoretical basis is proposed to achieve wideband impedance matching for any power line communication systems. We assume wideband impedance matching at the emission port. Static algorithms only for different types of load are developed. Tchebycheff gain functions are used for our purpose. Designing an impedance matching circuit should definitively allow an enhancement of the performances of power line communication networks.

Testing and modelling of voltage transformer for high order harmonic measurement

Harmonics have become an important concern in todays power system network. Conventional Inductive Voltage Transformers (IVT) are used as the essential instrument for harmonic measurement. However, the frequency bandwidths of the IVTs are limited. As a result, they are not suitable for high order harmonic measurement. This paper thus presents the testing and modelling of the frequency response of a 33kV single phase IVT up to 5 kHz. The test system setup for testing the IVT frequency response is described. The frequency response of a 33kV single phase IVT is measured and analyzed. A model of the 33kV IVT is developed and validated by comparing the simulation with the experimental results. Good correlation between the two results is observed. The impact of burden on the frequency response of the 33kV IVT is also simulated and discussed.

Fault location estimation for distribution system using simulated voltage sags data

This paper presents a new method for locating short-circuit fault in electrical distribution system. The method works by matching the actual voltage magnitude and phase angle with the simulated ones from fault analysis that stored in a database. The matching will give the possible faulty section/sections. A matching measurement algorithm is then applied to quantify the matching accuracy and to estimate faulty distance from particular bus on the section. In case more than one possible faulty section available, a ranking procedure is conducted to rank down the sections according to the degree of matching accuracy. A simulation test of the proposed method showed a satisfactory result.

Impact evaluation of IEC 61850 process bus architecture on numerical protection systems

The deployment of IEC 61850 process bus in substations calls for an impact evaluation of possible process bus architecture scenarios on the performance of numerical protection systems. Six alternative system architectures are proposed based on a component redundancy perspective. The functionality of each system is assessed using reliability block diagrams based on a success-oriented network. System reliability is calculated using the minimal tie sets method determined by the connection matrix. Sensitivity analysis is then carried out on the results using two approaches. One highlights those components with the greatest impact on system reliability and the other the importance of the task performed by each component in terms of how it affects the functionality of the system.

Improved adaptive voltage controller for active distribution network operation with distributed generation

The expected increase in connection of distributed generation (DG) may cause voltage rise problems on the existing distribution network. To address this issue, an adaptive voltage controller using On Load Tap Changer (OLTC) and Automatic Voltage Control (AVC) relay was proposed in previous research. In order to reduce costs of implementing large numbers of measurements, Distribution State Estimator (DSE) was used to determine the voltage reference setting for the AVC relay. This paper presents several improvements of the closed-loop testing system based on previous work. A graphical user interface (GUI) is developed to implement the adaptive voltage controller and to display the network voltages dynamically. In order to regulate busbar voltages remotely, control signals between GUI and the network are transmitted using ethernet communication technology. The case studies demonstrate that the proposed adaptive voltage control scheme is able to increase the output capacity of DG without violating voltage limits.