Advanced Materials Research Vols. 18-19

Abstract: In determining the correct operation of relays of a protection scheme, proper representation of instrument transformers and their behavior in conditions where there can be saturation, is very critical. The main objective of this paper is to develop simulation model for assessing the operational performance of Current Transformer (CT). In order to test the validity of the developed model, three cases of CT operational conditions were considered, with data collected from Gombe, 330/132/33kV PHCN substation. The simulation results revealed various configuration performance responses that could affect relay protective schemes to different degrees. The CT responses revealed that the secondary current and voltage were distorted when the core flux linkages exceeded the set 9.2 pu saturation limit. It is concluded that the model developed for the CT of interest yield satisfactory results.

Abstract: The problem of precise control of the air – gap of magnetic levitation vehicles is considered in this paper. A sliding mode controller is designed for the levitation control task. Robustness of the controller was investigated using computer simulations. The results show that the controller is robust to parameter variations of up to ±13% and can tolerate disturbances up to ±400N/Kg.

Abstract: In this paper the normal regimes of the Nigerian 330-132 kV power grid at 2003-2005 year levels were analyzed. The load flow studies were also carried out at perspective load growth forecast up to 10 years based on exponential trend using a program (Newton’s method). An analysis of results shows that with existing available generation and maximum load estimate by the utility there is a deficit which will persist if generation, commensurate with load growth, is not immediately reinforced. The network lacks adequate reactive power sources to maintain permissible bus voltages and the power transfer capability due to thermal constraints.

Abstract: This paper is a survey and analytical work on the discovered potential hydropower sites in Nigeria by the authors. Hydrological data of dams and rivers have been collected from various locations in Nigeria. Mathematical model for energy conversion process to determine the plant generating capacities of the identified sites were developed. A computer program in Q- Basic has also been developed for fast analysis and accuracy. Simulations were done on the collected data. From the obtained results, about thirty-two potential sites have been have discovered suitable to generate between 16kW and 700kW electric power. Appropriate turbine types were suggested.

Abstract: This paper investigates harmonics in power systems especially harmonics produced by synchronous generators as well as those by distributed generation systems, particularly these days when private generating systems are on the increase in Nigeria. For the work done so far, we found that some generators have near square waves, and these are characterized by their odd harmonics. An investigation of the harmonic emf waves conducted shows that these generators produces harmonic alternating mmf’s and fluxes. All harmonic fluxes produce emfs which are undesirable. The effect of these harmonics results in additional losses, vibration and noise, interferences, and very often stall motors. However the useful torque of a machine is usually produced by the fundamental flux wave which is a pure sine wave. The work is on-going. The waveforms are being analyzed so as to determine the full spectrum of the harmonics present in each case and subsequently investigate their effects in telecommunication systems including the present day GSM.

Abstract: The problems facing the Power Holding Company of Nigeria PLC (PHCN) which was formerly called the National Electric Power Authority (NEPA), are numerous to the extent that every power electric engineer both in the industrial sector and in academic is being challenged to proffer possible solutions. In an attempt, to combat some of these problems, this paper is therefore focused on a problem, affecting frequent power interruption to consumers during rainy season by PHCN. A research carried out before now ascertained that more than 500 hours were lost annually on power interruptions due to lightning discharge in various substations throughout the country during rainy season. Therefore, this paper has suggested the use of double lightning arresters instead of one, for the protection of industrial and domestic electrical installation work. It recommended the use of Thyrite or Oriaghe low voltage lightning arrester to prospective power consumers for domestic application. Also, for the high voltage protection it recommended the use of the high voltage Thyrite lightning arrester for lightning discharge protection of transformers and switch gears, used by PHCN.

Abstract: The strategy of management of the existing capacity by proper illumination design and the use of energy saving devices in the residential sector is reported. Improper installation design and the use of all sorts of devices at homes has led to a lot of electrical energy wastages resulting in the need to increase the generation capacity. The study revealed that annual energy of 551.88kWh could be saved for a three – bedroom flat when energy saving fluorescent lamps were used. The corresponding naira savings was 2,207.52 per annum. In addition, the sizes of cable, fuses/circuit breakers required are reduced and hence reduction in the cost of installation. The paper advocates the need for proper design and installation of energy saving devices in homes. The paper will be of relevance to lighting installation designers, power systems engineers, power utility managers, and the general public.

Abstract: The Internet has emerged in the last few years, not just as another communication means, but as sheer power and access to it provides access to a lot of information. Lack of access to internet will bring strong digital divide between rich and poor countries and also brings strong divide within the rural and urban communities of a country which in turn will affect the socio- economic development of a country. So there is a need for low-cost information technologies that are suitable to the conditions prevailing in a developing or third world country. Broadband CorDECT is one of the cost-effective fixed wireless broadband Access Solutions used for networking and building knowledge societies in a developing country. It is based on the DECT standard specification from the ETSI. It provides a complete wireless access solution for new and expanding telecommunication networks with seamless integration of both voice and internet services. It has been designed and specified to inter-work with many other types of network, such as the PSTN, ISDN, GSM and more. Broadband CorDECT provides the basic telecommunications as well as broadband Internet services and thus bridges the digital divide and such a service cannot be provided by any other product today in the world even double the cost. This paper discusses the relevance of broadband CorDECT in the context of current trends and provides a description of the technology.

Abstract: Procedures for the preparation and rheological characterisation of coconut milk yoghurts are described. Coconut milk was fortified with soymilk, 50:50 (v/v/)% (coconut milk:soymilk), Nonfat dry milk, 60:40 (coconut milk:Nonfat dry milk), while whole coconut milk served as control. Milk preparations were homogenized, heated to 40, 60 and 80oC for 30 mins, inoculated with Streptococcus thermophilus and Lactobacillus bulgaricus and incubated at 43oC to attain pH 4.6. Rheological properties of yoghurts were studied at temperatures ranging from 10 – 80oC. All samples exhibited a pseudo plastic behaviour and described by a power law model. The effect of temperature on apparent viscosity was explained by a polynomial equation and gave a better fit than the Arrhenius relationship. The consistency coefficient exhibits strong dependence on temperature for which the activation energy of flow ranged from 4.57– 6.47kJ/mol. The flow behaviour index was low and nearly constant (~ 0.78) up to 40oC and then decreased with further increase in temperature.