The impact of machine geometries on the average torque of dual-stator permanent magnet machines

The influence of leading design parameters such as rotor radial size and arc lengths, aspect ratio, stator yoke thickness, stator tooth-width and slot-opening/slot pitch-ratio etc. on the average torque of permanent magnet (PM) machines having dual-stator arrangement is investigated in this study. Further, the effect of their different rotor pole numbers is also presented and quantitatively compared. The analyzed machines are optimized using the evolutionary approach with a goal for optimum torque yield. The analysis shows that, each of the varied machine parameters has an optimum value for maximum torque production owing to their varying electromagnetic reaction which tends to saturate at some point on the magnetic path. Moreover, the best performance amongst the investigated machines is given by the machine type having eleven rotor pole number.Keywords: average torque, dual start, machine geometry, optimal value, PM machine

Effect of number of rotor poles on AC losses of permanent magnet machines having two separate stators

A study on permanent magnet (PM) eddy current and core losses of dual-stator PM machines is investigated in this paper. The analyzed core losses include: the rotor core loss, stator core loss and the total core loss of the machines. Further, the effect of their different rotor pole number is also presented with quantitative comparison. Due to the relatively high electrical frequency of the analyzed 14-rotor pole machine, it gives the largest amount of PM eddy current loss. Similarly, the 13-pole machine exhibits the largest amount of total core loss amongst the compared machines. Although, the investigated machine having 4-rotor pole has a low core loss value, likely due to its low electrical frequency. However, it has the poorest efficiency amongst all, due to its very low output torque. Overall, largest torque density is obtained in the 13-pole machine at rated current condition.Keywords: core loss, efficiency, PM eddy current loss, PM flux linkage, power and torqu

Coil- and phase-flux-linkage characteristics of dual excited permanent magnet machijnes equipped with different winding configurations

The flux-linkage characteristics of dual excited permanent magnet (PM) machines equipped with concentrated windings of single- and double-layer types is investigated in this paper. This includes precise comparison of the coil and phase flux-linkage waveforms of the machines having different stator and rotor pole topologies. It is observed that, the developed machine having double layer-wound configuration have unipolar coil flux linkage waveforms, although with a resultant bipolar phase flux-linkage waveforms on summation, while their corresponding single layer-wound counterparts are characterised by both bipolar coil and phase flux-linkage waveforms. Also, the opposite coils of the machines having single-layer windings as well as even rotor pole topology produces coil flux-linkage waveforms whose shape and magnitude are identical and same; thus, resulting to more phase harmonics unlike their counterparts that are equipped with odd rotor poles and single-layer winding configuration whose coil waveforms are shifted, thereby resulting to effective cancellation of harmonics in the resultant phase waveforms. In general, the single-layer-wound machines exhibit higher peak-to-peak and fundamental flux-linkage values than their double-layer-wound equivalents.Keywords: Dual excitation, flux-linkage, single- and double-layer windings, rotor and stator pole combinations

Fault-Tolerant Capability and Torque-Speed Measurements of Permanent Magnet Brushless AC Machines

In this paper, the fault-tolerant capability in terms of inductance profile of a dual-stator permanent magnet brushless AC machine is presented. Similarly, its power-speed and torque-speed characteristics are also predicted. Special reference is made to the impact of different rotor pole numbers. A 2D-finite element analysis (FEA) procedure is adopted in this work, and the cross-coupling effect of the machine inductances owing to the influence of direct-axis and quadrature-axis currents is also taken into consideration. The results show that, the investigated machine having odd number of rotor poles would exhibit better fault-tolerant capability compared to their counterparts with even number of rotor poles. Further, the machine having 6-stator slots and 13-rotor poles i.e. 6Slots-13P machine has the greatest field-weakening potential owing to its high full-speed to rated speed relation. The studies also show that, the investigated machines have negligible reluctance torque due to their basically unity saliency ratios obtained from the machines’ almost similar quadrature-axis inductance, Lq, and direct-axis inductance, Ld, values.Keywords: Direct-axis, Quadrature-axis, Inductance, Power, Speed, Torque, AC machines, Permanent magnet

Multi-Type FACTS Controllers for Power System Compensation: A Case Study of the Nigerian 48-Bus, 330 kV System

Flexible alternating current transmission system (FACTS) devices have provided proficient answers to power system instabilities faced in the systems operations today with very little infrastructural investment fund. This paper investigates the effects of the installation of the combination of two kinds of FACTS controllers; static VAR compensator (SVC) and thyristor controlled series compensator (TCSC) compared with the installation of SVC or TCSC alone in the system. Voltage magnitude profile, active and reactive power losses of the three scenarios were achieved in the Nigerian 48-bus power system network using power system analysis toolbox (PSAT) in MATLAB environment. Simulation results obtained without and with FACTS devices optimally placed using voltage stability sensitivity factor (VSSF), revealed that the percentage decrease of the net real and reactive power losses of the combined SVC and TCSC was the highest at 31.917% whereas that of the standalone SVC and TCSC stood at 19.769% and 30.863% respectively. This shows that in addition to their capabilities to maintain acceptable voltage profile, the combination of SVC and TCSC has better compensating effect as they mitigate against power losses which was observed in their high percentage decrease in power losses compared to the standalone FACTS devices. Keywords: FACTS, optimum location, PSAT, SVC, TCSC, VSS

Assessment of the incidence of microplastics at Ndibe, Cross River, Nigeria

The menace of microplastics in the aquatic ecosystems is of increasing concern worldwide mainly due to their impact on the entire ecosystem and human health. In order to contribute to knowledge, the incidence of microplastics in water and fish samples from Ndibe beach area of Cross River, Nigeria was studied. Ndibe beach is a recreational beach that hosts thousands of tourists and commuters annually. Recently, several residential and commercial areas have developed around the beach with attendant increase in the amount of plastics and other types of wastes deposited in and around the beach. Water samples collected from ten locations within the beach and fish samples (50 Chrysichthys sp. and 30 Clarias sp.) were analysed for microplastics using standard methods. The results showed that the water and fish samples contained microplastics of various sizes. The microplastics level was higher in water samples (68%) compared to the fish samples (32%). This calls for proper sensitization of residents and tourists around the area on the dangers associated with microplastics in aquatic ecosystem in order to regulate its discharge into and around the Cross River. This will help to mitigate the negative consequences of microplastics on the ecosystem integrity of the river and human health

Power sector reforms in Nigeria: opportunities and challenges

Constant power supply is the hallmark of a devel-oped economy. Any nation whose energy need is epileptic in supply, prolongs her development and risks losing potential investors. Nigeria, a country of over 120 million people, has for the past 33 years of establishment of the National Electric Power Authority (NEPA) agency empowered with the elec-tricity generation, transmission and distribution, wit-nessed frequent and persistent outages. Presently, the federal government has embarked on power sector reforms with the intention of improving the above unpalatable scenario and in turn reduce the scope of monopoly control of the nation’s power industry. This paper therefore looks at the overall power sector reforms as well as evaluates the opportunities and challenges there from; while advocating introduction of a demand side manage-ment (DSM) program by Power Holding Company of Nigeria (PHCN) as a way of reducing energy con-sumption among customers with emphasis on ener-gy conservation, energy efficiency and load man-agement

Investigating the steady state stability of the Nigerian 48- bus systems using facts devices

With the ongoing expansions and growth of the electric utility industry, including deregulation in Nigeria, numerous changes characterized by additional generating stations, increase in transmission lines and loads are experienced thereby pushing the transmission systems closer to their stability and thermal limits and hence, causing the transfer of reactive power during steady state operating conditions to constitute a major problem of voltage instability. Flexible ac transmission systems (FACTS) controllers have been utilized for finding solutions to various power system stability control issues such as voltage instability. This paper uses Static Synchronous Series Compensator (SSSC) and Thyristor Controlled Series Compensator (TCSC) to investigate the voltage magnitude profile, active and reactive power losses of the Nigerian 48-bus power system network for steady state stability enhancement using power system analysis toolbox (PSAT) in MATLAB environment. Optimal location of the FACTS devices was achieved through the computation of the voltage stability sensitivity factors (VSSF) for all the buses after continuation power flow (CPF) was carried out. Simulation results obtained without and with the FACTS devices revealed that the two FACTS devices especially TCSC has the capability to raise voltage profile of the buses and mitigate against power losses.Keywords: CPF, FACTS, MATLAB, Optimal location, PSAT, SSSC, stability, TCSC, VSS

Investigating the Magnetic Characteristics of 12/8 Switched Reluctance Motor for Enhanced Starting Torque

The switched reluctance motor (SRM) is among the special purpose electric machine family. It is simple in construction and avoids use of magnet so it is cheap to manufacture. The magnetic characteristics and simulation of three phase 12/8 switched reluctance motor (SRM) for enhanced starting torque is presented. The motor was analyzed using finite element technique (FET) and it was improved by focusing on the impact of important geometrical parameters on torque and efficiency. From the simulated results, the motor attained maximum efficiency of 91.7% at a speed of 1648.6 rpm and recorded a maximum torque of 321.1 Nm at a speed of 34.4 rpm. The magnetic flux lines and densities were also recorded. The maximum and minimum magnetic flux lines of the motor as observed were 1.2x10-3 Wb/m and -8.5x10-4 Wb/m respectively while the respective values of the maximum and minimum magnetic flux density of the motor were 3.8x10-1 T and 2.11x10-9 T. The results show that most of the field energy is confined within the motor and also concentrated in the air gap region of the motor. Dynamic analysis of the motor was performed for 0.02 s at a damping coefficient of 0.71 μNms/rad. The results showed that the motor has lower torque ripple. The preference to use this type of motor where high speed operation and better starting torque are needed has been highlighted in this study. Keywords:  Switched reluctance motor, static characteristics, transient analysis, torque, magnetic flu

Computational fluid dynamics modelling of an entire synchronous generator for improved thermal management

This study is the first in a series dedicated to investigating the airflow and thermal management of electrical machines. Owing to the temperature dependent resistive losses in the machine's windings, any improvement in cooling provides a direct reduction in losses and an increase in efficiency. This study focuses on the airflow which is intrinsically linked to the thermal behaviour of the machine as well as the windage power consumed to drive the air through the machine. A full computational fluid dynamics (CFD) model has been used to analyse the airflow around all major components of the machine. Results have been experimentally validated and investigated. At synchronous speed the experimentally tested mass flow rate and windage torque were under predicted by 4% and 7%, respectively, by the CFD. A break-down of torque by component shows that the fan consumes approximately 87% of the windage torque