Production improvement in ACM manufacturing company using lean manufacturing approach

ACM Sdn. Bhd. is a manufacturing company, in which to continuously commit on improvement process which based on the fundamental goal, to minimize or eliminate waste while maximizing production flow. The purpose of this study is to develop a value stream mapping for a ACM Sdn. Bhd. and it was begin with creating a current state map and understand the production flow and the current cycle times. This provides the information needed to produce a future state map. The goal is to identify and eliminate the waste, which is any activity that does not add value to the final product, in the production process. In order to collect the information needed, the study was conducted within the production facility to enable the researcher gained knowledge and familiarized with the production flow and the activities being performed at the shop floor. Parameters such as cycle times, down times, work in process (WIP) for inventory and material, and information flow paths were recorded. This information will enable the researcher to visualize the current state of the process activities by mapping the material and information flow and looking for opportunities to eliminate wastes. ARENA simulation software package was used to simulate and analyze the process flow and times. Result from the analysis shows that there are areas where the ACM Sdn. Bhd. can further improve their production system. Improvements in cycle times of 13-22% are possible by new arrangement of the layout. The results can be used as a guide to the ACM for improvement and implement the lean manufacturing concept in their manufacturing system

Voltage uprating of existing high voltage substations when transient voltage stress and available withstand strength are coordinated

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering in the High Voltage Research Group School of Electrical and Information Engineering Johannesburg, June 2017 South AfricaServitude availability in space-constrained built-up areas within the Johannesburg or Central Load Network (CLN) poses every-day challenges for power system engineers. Strengthening the backbone 88/275 kV transmission system within the CLN becomes even more difficult when multi-circuit transmission lines are required for increased power transfer capabilities. When uprating is considered to increase the power transfer capability, the withstand levels of existing external insulation demands an optimisation to find a new stress versus strength balance that allows reliable operation of substations at higher voltages. The research includes primarily an investigative simulation study to evaluate the current Eskom available design clearances in terms of their withstand capability when subjected to over-voltage transients. Two voltage range classes were evaluated and the results are discussed. For voltage range 1, it was found that the over-voltage stress was low enough to allow for a higher nominal operating voltage while maintaining the existing clearances. For voltage range 2, existing clearances are also found to be conservative and smaller safety margins will most likely be acceptable. From a transient analysis evaluation, voltage uprating is considered as a very attractive option to increase the power transfer capability of existing substations. Current Eskom clearances for 88 kV and 275 kV are expected to perform well during transients generated in uprated systems. Electrode grading to improve the field gradients in the substation will require attention to increase gap factors. Additional surge arresters are considered to be a cost effective solution to control over-voltages throughout the whole uprated substation. The physical modification of substations to replace strung conductors with tubular conductors, ensuring sufficient outage time to refurbish and rebuild with new equipment will be the most challenging part of uprating existing substations.MT 201

Transient Overvoltages in Gas Insulated Systems

Studio del transitorio elettrico di una linea di trasmissione mista a 400kV composta da OHL e GIL; utilizzando il software ElectroMagnetic Transient Program EMTP. Studio di sovratensioni interne, dovute a manovre di rete, e sovratensioni esterne dovute a fulminazion

Outdoor Insulation and Gas Insulated Switchgears

This book focuses on theoretical and practical developments in the performance of high-voltage transmission line against atmospheric pollution and icing. Modifications using suitable fillers are also pinpointed to improve silicone rubber insulation materials. Very fast transient overvoltage (VFTO) mitigation techniques, along with some suggestions for reliable partial discharge measurements under DC voltage stresses inside gas-insulated switchgears, are addressed. The application of an inductor-based filter for the protective performance of surge arresters against indirect lightning strikes is also discussed

Estimation of the Developed Overvoltages at the Entrance of a HV/MV Substation

External overvoltages can cause several damages to a HV/MV substation, leading to insulation breakdowns. The appropriate protection of the substation against external overvoltages is critical, in order to ensure the efficient, reliable and safe operation of the system. Shielding wires, mast and surge arresters are the main parts of a lightning protection system. The current PhD project deals with the effective lightning protection of HV/MV substations, examining the impact of various factors on the magnitude of the developed overvoltages at different positions of the system. The influence of the equivalent circuit model of the various components to the calculated overvoltages is also examined. Moreover, the substation outage rate due to lightning strokes is calculated, considering shielding failures and back-flashovers. In addition, special issues are discussed, i.e. induced overvoltages and installation of arresters in parallel. In comparison with other studies, main contribution of the thesis is that does not focus only on the role of the grounding resistance, but examines the dominant influence of other parameters; the improvement of the lightning performance of the substation can be achieved by the appropriate adjustment of various factors of the system. The current work highlights also the advantages and drawbacks of each equivalent circuit model, providing a guide to other researchers in order to select the appropriate models. As far as the risk assessment analysis is concerned, innovation of the performed study constitutes the inclusion of the arresters‟ failure rate to the total substation failure rate, since their possible failure results in malfunction of the nominal operation of the system. The induced overvoltages arriving at the entrance of the substation are also calculated, examining the role of the lightning hit position, the waveform of the lightning current, emphasizing to the role of the installation position of the arresters. Finally, the need for good matching of the voltage – current characteristics of the arresters is revealed, otherwise, the expected equal sharing of the injected lightning current will not be achieved. The current Thesis indicates that the combination of the arresters in parallel does not influence the expected overvoltages, but has to do mainly with the absorbed energy by the arresters

Electricity distribution networks’ analysis with particular references to distributed generation and protection

Electric power systems have served well the consumers need for continuous, uninterrupted power supply of good quality and at the minimum possible cost. However, nowadays, the worldwide increasing demand on electric power, coupled with governmental policy changes towards “green” energy and emissions reduction have led to significant changes in the electric power generation. These changes have introduced many serious issues and problems to the electric power systems and although they have been efficiently addressed in the past years, now they need to be restudied and reanalysed taking into consideration all new developments. Distributed generation (DG), constitutes one of the most important developments in modern electric power systems and introduced many benefits as well as drawbacks. DG units are connected to the electric power system near load centres, thus, directly to the distribution network. DG units are larger in number than the more massive conventional power stations and are linked to the introduction of bidirectional power flow. As a result, the configuration of the traditional electric power systems and the networks’ operation have been prominently altered over the last years as soon as DG was introduced into the electric network. This progress has offered many challenges that need to be addressed such as those in terms of control and protection of electric power systems and particularly of distribution networks. The current PhD Thesis attempts to offer a contribution to the electricity distribution networks’ studies with particular reference to distributed generation and protection. In particular, the problems and the issues arising from the installation of DG units in distribution networks are studied. Research on the methods for improving voltage profiles and for reducing real and reactive power losses in distribution networks caused by DGs installation is conducted. Moreover, a decision making algorithm is developed and proposed for selecting the optimum size and location of DG in distribution networks. Furthermore, a new technique based on syntactic pattern recognition for the identification of power system signals used by protective relays is developed in an effort to contribute in the deterrence and reduction of faults. Finally, extensive studies in a distribution network have been conducted, with and without DGs, which aimed to identify the influence of several important parameters in the network’s lightning performance and with its main goal the limitation of lightning faults

Investigation of transient and safety issues in gas insulated systems

This thesis investigates the occurrence, characteristics and effects of Very Fast Transients (VFTs) associated with disconnector switching operations in Gas Insulated Substations. VFTs are analysed and efforts are made to elucidate their behaviour through advanced simulation techniques. The initial motivation for this work was the occurrence of a surface flashover at a spacer, leading to a prolonged outage of the circuit in question and a significant repair effort. While post failure investigations were carried out by the manufacturer and yielded no significant observations, through modelling and measurements efforts while working towards this thesis, a phenomenon that could have led or contributed to the failure. VFTs at a live, operational 400kV Substation (un-named for confidentiality but termed throughout as Substation ‘A’) are quantified through both modelling and measurements. Significant progress in the modelling of VFTs and TEVs is demonstrated. Numerical Electromagnetic Analysis is shown to be most effective method in studying the behaviour of the GIS and earthing systems. Multiple NEA techniques are utilised, all solving a full-Maxwell’s equations through a Wave equation. The behaviour of the system (both internally and externally) is captured with great accuracy and lucidity, without the need to use analytic approximations or assumed parameters, which has traditionally been the case. Detailed models were built using equipment drawings from Substation ‘A’ for the GIB, spacer-flange assembly, double-elbow assembly, disconnector, gas to air bushing. Frequency and time domain behaviour is analysed and a potential contributor to the failure at Substation ‘A’ is identified. Furthermore, elements of the earthing system were evaluated for effectiveness in mitigating TEVs. The methods highlight some of flaws and inaccuracies that are present with existing ‘standard practice’ modelling efforts. The need for circuit-based modelling for VFT studies is apparent, as NEA techniques at very high frequencies are limited in their interaction with the wider system. Efforts are therefore made to enhance circuit-based models; utilising NEA methods and Vector Fitting to produce accurate, large bandwidth equivalent circuits, which demonstrate the computed frequency responses of the various GIS equipment types studied. Vector Fit models at lower orders of approximation are prone to unstable time domain responses, leading to numerical oscillations or even a complete divergence from a solution. A method was developed to identify model orders that demonstrate stability in the time domain, allowing the lowest model order of approximation to be selected, thereby reducing the additional computational requirements of very high orders of approximation, while retaining accuracy and stability in the time and frequency domains. The conversion process is augmented with a new method for identifying model orders that will be stable in the time domain. Several measurement techniques and sensors were developed to capture the entire cycle of transients associated with disconnector operations. Device prototypes were designed and optimised through NEA/circuit-based modelling, prior to undergoing laboratory-based measurements. Laboratory based testing was conducted using a custom built, half scale GIB, with impedance matching cones at each end to allow measurement and signal generating equipment to be connected with minimal interference. While, essential, laboratory-based measurements will never replicate the transient and high EMI environmental conditions seen at a live GIS, therefore, the bulk of the measurement efforts were focused on live measurements at Substation ‘A’. Throughout the course of this project several opportunities to undertake measurements were presented and a significant amount of data was recorded. Each measurement also identified areas for improvement of the measurement system

Modeling and Simulation of Varistors

This thesis treats various problems that arise in the context of varistors and microvaristors, which are are used for the suppression of transient overvoltages, due to their extraordinary nonlinear electrical conductivity. The present work is mainly motivated by the desire to simulate the behavior of high-voltage surge arresters used for lightning protection on the one hand and of microvaristors as materials for future applications in nonlinear resistive stress control on the other hand. The analysis of surge arresters requires the numerical calculation of mutually-dependent electric and thermal fields, whereby the principal difficulty resides in the extreme nonlinearity of the electric problem. For this purpose, the electro-quasistatics equation is solved in time domain by means of the finite-element method. The calculation of the thermally stationary state of a surge arrester and the evaluation of an envelope equation model for simulating the heating and cooling behavior of arresters are discussed in more detail. These simulations depend on sufficiently accurate models that describe the material properties. The estimation of nonlinear conductivity and permittivity of varistor materials is an inherent part of this thesis. Furthermore, nonlinear capacitance and conductance matrices are introduced. The presented approach is based on an equivalent circuit model. Its parameters are determined from field-simulation results