M.A. Redfern

A new microprocessor based islanding protection algorithm for dispersed storage and generation units

The ability to detect when dispersed storage and generation (DSG) units become islanded from the main source of generation enables the DSG to be quickly disconnected from the utility network and for that network to be rebuilt in a safe and orderly manner. The new islanding protection algorithm described in the paper has been developed to be part of an integrated protection package to cover all the protection requirements of a DSG. A selection of the results obtained from extensive laboratory and field tests are presented and show that the algorithm reliably trips for islanding conditions within 120 milliseconds, trips for load fluctuations should the DSG be operating independent of the main source of supply and restrains for single phase faults close to the DSG. >

Positional protection of transmission line using fault generated high frequency transient signals

This paper presents a new technique for high-speed protection of transmission lines, the positional protection technique. The technique uses a fault transient detector unit at the relaying point to capture fault generated high frequency transient signals contained in the primary currents. The decision to trip is based on the relative arrival times of these high frequency components as they propagate through the system. Extensive simulation studies of technique were carried out to examine the response to different power system and fault conditions. Results show that the scheme is insensitive to fault type, fault resistance, fault inception angle and system source configuration, and that it is able to offer both very high accuracy and speed in fault detection.

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. In the scheme, the relay contains a fault transient detection system together with a communication unit, which is connected to the power line through the high voltage coupling capacitors of the CVT. Relays are installed at each busbar in a transmission network. These detect the fault generated high frequency voltage transient signals and record 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.

Protecting micro-grid systems containing solid-state converter generation

In this paper a fast fault detection method for Microgrid system based on micro-sources equipped with power electronics interfaces is explored. This method provides reliable and fast detection for different types of faults within the micro-grid. The micro-source output voltages are monitored and then converted to dc quantities in the d-q reference frame. Thus, any disturbance at the micro-source output due to any type of fault is reflected as disturbances in the d-q values. The disturbance is used to detect the fault and this leads to the initiation of the associated breaker to isolate the faulted section from the network. Analysis and simulation results are presented for different types of faults within the micro-grid

Protection of dispersed storage and generation units against islanding

This paper deals with islanding protection which is the most important protection requirement of dispersed storage and generation units (DSGs). A power based digital algorithm has been developed for the protection of DSG units against islanding. Computer simulation results show that, in addition to effectively detecting the islanding, the new algorithm trips for the load changes that occur during the islanding operation but remains unstable for the load fluctuations while the DSG unit is operating in parallel with the utility network. The algorithm also detects the condition when the utility supply is reconnected to the power island while the two supplies are out of phase.<<ETX>>

A personal computer based system for the laboratory evaluation of high performance power system protection relays

The power system simulation system described provides a relay under evaluation with current and voltage input similar to that encountered under service and fault conditions. Using digital transient simulation programs to model power system behaviour, the facility provides an effective bandwidth of from DC to 4 kHz for both the current and voltage relay input. The relays output is automatically monitored during the test, enabling a detailed report of its response to be produced. The application of the system is illustrated by the evaluation of a new EHV teed feeder relaying system. >

Site Assessment of Multiple-Sensor Approaches for Buried Utility Detection

The successful operation of buried infrastructure within urban environments is fundamental to the conservation of modern living standards. Open-cut methods are predominantly used, in preference to trenchless technology, to effect a repair, replace or install a new section of the network. This is, in part, due to the inability to determine the position of all utilities below the carriageway, making open-cut methods desirable in terms of dealing with uncertainty since the buried infrastructure is progressively exposed during excavation. However, open-cut methods damage the carriageway and disrupt societys functions. This paper describes the progress of a research project that aims to develop a multi-sensor geophysical platform that can improve the probability of complete detection of the infrastructure buried beneath the carriageway. The multi-sensor platform is being developed in conjunction with a knowledge-based system that aims to provide information on how the properties of the ground might affect the sensing technologies being deployed. The fusion of data sources (sensor data and utilities record data) is also being researched to maximize the probability of location. This paper describes the outcome of the initial phase of testing along with the development of the knowledge-based system and the fusing of data to produce utility maps.

A new pole slipping protection algorithm for dispersed storage and generation using the equal area criterion

The probability of pole slipping of dispersed storage and generation (DSG) synchronous machines is being viewed with concern, since this can damage the machine as well as promote power system instability. This is particularly the case for small and medium sized machines because their low inertia and high resistance make them inherently more unstable. Research has therefore been directed into new techniques for detecting pole slipping and the formulation of protection algorithms which can be included into an integrated microcomputer based protection scheme for these generators. This paper describes a method for detecting pole slipping using power measurements taken at the generators terminals. This technique has been shown to correctly detect pole slipping using both computer simulation and a laboratory model power system. The algorithm remains stable for recoverable swing conditions and power system faults. >

Improvement in the performance of on-load tap changer transformers operating in series

Transmission and distribution systems naturally operate at multiple voltage levels. The transformers connecting these levels often require on-load tap changers to regulate the voltage and maintain it within statutory limits. Conventional time grading is used between tap changer control relays when transformers are operating in series. This ensures that downstream tap changers react more slowly to voltage deviations than upstream tap changers and prevents hunting between them. This defines a fixed duty of responsibility to each tap changer. In order to improve the quality of supply it is supposed that the duty of responsibility should not be fixed and should adapt to loading conditions. The proposed system monitors both the transformer secondary voltage and the current to determine the voltage drop that would exist between consecutive transformers. The paper demonstrates that this information can be used to bias the operation of the tap changer controllers and hence improve series performance. Communications are not required between different voltage levels and therefore there is no reduction in security and extendibility of the system.

A New Digital Relay for Generator Protection against Asymmetrical Faults

Under unbalanced conditions the three phase instantaneous power oscillates at twice the power system frequency. The magnitude of these oscillations can be used as a measure of the system unbalance. This article has introduced a new digital relaying algorithm designed to detect asymmetrical faults by monitoring the sinusoidal oscillations of the three phase instantaneous power measured at the generator terminal. Once an asymmetrical fault is detected, the algorithm checks the direction of the negative sequence-reactive power flow at the machine terminal to discriminate between internal and external faults. Power system test studies presented show that the new relay provides fast tripping for internal asymmetrical faults and back-up protection for external asymmetrical fault conditions.