Roger Shuttleworth

Compact Patch Antenna Design for Outdoor RF Energy Harvesting in Wireless Sensor Networks

In this paper, two compact patch antenna designs for a new application - outdoor RF energy harvesting in powering a wireless soil sensor network - are presented. The first design is a low-profile folded shorted patch antenna (FSPA), with a small ground plane and wide impedance bandwidth. The second design is a novel FSPA structure with four pairs of slot embedded into its ground plane. Performance of both antennas was first simulated using CST Microwave Studio. Antenna prototypes were then fabricated and tested in the anechoic chamber and in their actual operating environment - an outdoor field. It was found that the FSPA with slotted ground plane achieved a comparable impedance bandwidth to the first design, with an overall size reduction of 29%. Simulations were also carried out to investigate the effects of different design parameters on the performance of the proposed slotted ground plane FSPA.

Investigation of PCB microstrip patch receiving antenna for outdoor RF energy harvesting in wireless sensor networks

In this paper the suitability of using a printed circuit board (PCB) microstrip patch receiving antenna for a novel application — RF energy harvesting to power a wireless soil sensor network deployed in an outdoor environment — is investigated. The performance of a conventional circular microstrip patch antenna using different microwave laminate substrates is evaluated in terms of return loss, radiation efficiency, and gain. Based on a chosen PCB material as the antenna substrate, an enhanced gain circular patch with a ring shaped parasitic radiator is presented. Simulations have been carried out using CST Microwave Studio to examine the antennas performance both in free air and in the presence of different soil conditions.

A theoretical study of a smart electromechanical tuned mass damper beam device

Research into piezoelectric vibration energy harvesting (PVEH) beams has so far largely overlooked the fact that these are, in many practical applications, mechanical absorbers of the vibration of the structure to which they are attached. This paper introduces the novel concept of utilizing a PVEH beam as a tuned mass damper (TMD)—which suppresses a particular vibration mode of a generic host structure over a broad band of excitation frequencies. This device comprises a pair of bimorphs shunted by resistor–capacitor–inductor circuitry. The optimal damping required by this TMD is generated by the PVEH effect of the bimorphs. The theoretical basis of this dual PVEH/TMD beam device is presented and verified by alternative analytical methods. The simulation results demonstrate that the ideal degree of vibration attenuation can be achieved through appropriate tuning of the circuitry for a device whose effective mass is less than 2% of the equivalent modal mass of the host structure. The proposed dual PVEH/TMD beam device combines the relative advantages of the classical (mechanical) TMD and the shunted piezoelectric patch (electrical vibration absorber), presenting the prospect of a functionally more readily adaptable class of ‘electromechanical’ tuned vibration absorbers.

Calculating the Surface Potential Gradient of Overhead Line Conductors

The surface potential gradient is a critical design parameter for planning overhead lines since it determines the level of corona loss, radio interference, and audible noise. The majority of existing surface gradient calculations are based on analytical methods which restrict their application in simulating complex surface geometry. This paper proposes a novel method which utilizes both analytical and numerical procedures to predict the surface gradient. With this method, stranding shape, protrusions, the proximity of tower, the type of tower, bundle spacing, and bundle arrangement can be taken into consideration when calculating surface potential gradients. A sensitivity study on the factors affecting surface gradient distribution is performed.

Experiences from over 15 years of on-line partial discharge (OLPD) testing of in-service MV and HV cables, switchgear, transformers and rotating machines

The authors present a paper on the application of online partial discharge (PD) testing and monitoring technology for the insulation condition assessment of in service medium voltage (MV — 3.3kV to 45kV)) and high voltage (HV — 66kV to 750kV) cables and plant. The paper begins with a short summary of the different economic ‘DRIVERS’ which apply to both public utility and industrial HV networks. The paper presents some of the test techniques employed and the on-line PD sensor technology used to test in-service power cables, switchgear, transformers, rotating machines, CTs/VTs and other HV plant. The paper concludes with some case studies of past projects carried out by the authors from on-line PD test projects testing a wide range of MV & HV assets in electricity networks around the world.

Experimental Tests of a Resistive SFCL Integrated With a Vacuum Interrupter

A resistive superconducting fault-current limiter (SFCL) has been developed using round magnesium diboride (MgB2) wire. The SFCL coil was wound using an interleaved coil arrangement to minimize the total coil inductance. The SFCL coil demonstrated reliable and repeatable current-limiting properties during testing. However, the wire temperature of the SFCL coil increases quickly during quench tests, and several minutes are required for temperature recovery after the fault is cleared. The SFCL coil therefore was fully integrated with a vacuum interrupter to quickly remove the SFCL coil from the circuit once a fault occurred. This allowed the SFCL coil to recover quickly while a bypass resistor acted as the current limiting resistance. A fast-acting actuator and its control circuit were designed and built to provide automatic control for the operation of the vacuum interrupter. The SFCL with the prototype vacuum interrupter was successfully tested. The energy dissipated in the SFCL coil was significantly reduced by integrating the vacuum interrupter. The fault tests with different potential fault currents also proved that the operation of the vacuum interrupter is independent of the fault current level. This prototype demonstrated the potential of a cost-effective and compact integrated SFCL and vacuum interrupter for power system applications.

Analysis and simulation of the proactive hybrid circuit breaker

High Voltage Direct Current (HVDC) short circuit protection is a fundamental requirement for any HVDC transmission system. Presently, all point-to-point links are protected using circuit breakers on the AC side of the converters. In order to enable HVDC grids, a more advanced protection system must be developed. HVDC circuit breakers are one solution for the protection of future HVDC grids. Several designs have been proposed for DC circuit breakers but few are suitable for Voltage Source Converter (VSC) applications. To date, only a few industrial prototypes have been developed, which are seen to be suitable for the VSC HVDC applications. This paper presents analysis and simulations on one of these prototypes, the Proactive Hybrid Circuit Breaker (PHCB). Equations are derived from a state-space analysis of the circuit breaker. A model of the circuit breaker is suitably parameterized for a +/- 300 kV VSC system in PSCAD. Fault simulations are then performed and compared to the equations developed in a state space analysis. Discussion is then given to the design and testing of the Load Commutation Switch (LCS).

Partial discharge pulse propagation, localisation and measurements in medium voltage power cables

This paper considers the measurement and propagation of partial discharge pulses on distribution class power cable circuits, with the idea of attempting to determine discharge location sites on cables based on the parameters of individual pulses. Single-ended discharge location techniques based on partial discharge pulse parameters and shape will not be as accurate as time-domain reflectometry methods but can be done on-line without the need for double-ended techniques. Power cables used for the transmission of 50/60 Hertz electrical power, are by design not intended to carry transients or partial discharge pulses. The geometry and construction of such power cables present a transmission line that can heavily attenuate and distort the partial discharge pulses, making their detection and discrimination all the more difficult. Experimental and field work has been carried out to develop basic knowledge rules to describe how the time-domain parameters of individual pulses alter as a function of the distance propagated from the discharge sites for medium voltage power cables.

A modular battery charger for electric vehicles

The next five years will see a substantial increase in the number of all-electric (EVs) and hybrid electric vehicles (HEVs) utilizing onboard electrochemical energy storage devices (batteries) that require full or part recharging by connection to a low voltage utility network that supply domestic or light industrial users. The utility connection requires a battery charger composed of a uni- or bi-directional power electronic converter that converts the AC supply to DC or vice versa. The expectation for future automotive power electronic converter products is lifetimes of 10 years and over, and operation in arduous temperature environments, factors that compromise existing power converter topologies, in particular those employing electrolytic capacitors. This paper discusses a 7kW battery charger design that is modular, has a balanced three-phase input, is near unity power factor and has no electrolytic capacitors. The paper discusses the charger design concepts and presents test validation results.

A review of technologies for MVDC circuit breakers

Medium voltage direct current (MVDC) distribution networks have been considered for various applications, such as offshore wind farm collector systems, all-electric naval vessels, and aircraft. MVDC circuit breakers are a critical technology to directly manage faults in multi-terminal DC (MTDC) networks. However, DC current breaking is much more challenging than in AC systems because there is no natural zero-crossing of the current waveform to aid fault isolation. This paper reviews existing MVDC circuit breaker technologies and also discusses their advantages and disadvantages. This paper also introduces new topologies that can be applied in MVDC applications. The operation of several hybrid DC circuit breaker topologies with aided commutation is included. The paper illustrates that a hybrid DC circuit breaker with aided commutation can clear a fault within 2-5 msecs with low losses, this shows great potential for future MVDC applications. The implications for the practical design of commercial MVDC circuit breakers are also discussed.