Analysis and simulation of vector controlled bearingless induction motors

The concept of bearingless motors, which combine both motoring and rotor bearing capabilities, is appealing especially in high speed and high power machine applications. Although extensive research has been carried out on permanent magnet and reluctance types of bearingless motors, studies on the induction motor type are less successful. This thesis addresses the bearingless induction motor based on the concept of dual-pole windings, one controlling the motor torque and the other the generated radial forces. A modelling approach is undertaken to investigate the effect of induction machine design on radial force generation and motor levitation under both steady state and transient conditions. The simulation is based on the dynamic reluctance mesh model embedded in vector control systems for the decoupled control of torque, flux and radial force. This is achieved through modification of a previously developed computer software for modelling induction motors in order to model the control of bearingless induction motors. Both the squirrel cage and wound rotor induction motors are investigated and their suitability for generating controlled bearing relief forces assessed. Vector control schemes for the bearingless cage and wound rotor induction motors were also designed and simulated. A mixed field oriented vector control scheme, which incorporates the simple rotor field orientation for motoring control and an airgap field orientation for rotor levitation control, is introduced and found to be advantageous in bearingless induction motor control. Apart from investigating totally bearingless conditions, the study also investigates bearing relief capabilities for a vector controlled cage and wound rotor induction motor in which the rotor movement is restricted by bearings but with the bearing load cancelled by suitably directed radial force. The effects of real winding topologies, stator and rotor slotting and iron saturation on the performance of bearing relief and bearingless induction motors are also presented. Finally, suggestions for future work is included In order to further investigate bearingless induction motors and its applications

Electrical performance of polymer-insulated rail brackets of DC transit subjected to lightning induced overvoltage

The fourth rail transit is an interesting topic to be shared and accessed by the community within that area of expertise. Several ongoing works are currently being conducted especially in the aspects of system technical performances including the rail bracket component and the sensitivity analyses on the various rail designs. Furthermore, the lightning surge study on railway electrification is significant due to the fact that only a handful of publications are available in this regard, especially on the fourth rail transit. For this reason, this paper presents a study on the electrical performance of a fourth rail Direct Current (DC) urban transit affected by an indirect lightning strike. The indirect lightning strike was modelled by means of the Rusck model and the sum of two Heidler functions. The simulations were carried out using the EMTP-RV software which included the performance comparison of polymer-insulated rail brackets, namely the Cast Epoxy (CE), the Cycloaliphatic Epoxy A (CEA), and the Glass Reinforced Plastic (GRP) together with the station arresters when subjected by 30 kA (5/80 µs) and 90 kA (9/200 µs) lightning currents. The results obtained demonstrated that the GRP material has been able to slightly lower its induced overvoltage as compared to other materials, especially for the case of 90 kA (9/200 µs), and thus serves better coordination with the station arresters. This improvement has also reflected on the recorded residual voltage and energy absorption capacity of the arrester, respectively

Comparative analysis of ACSR and ACCC conductors on corona effect for lightning surge studies

Corona effect plays an important role in determining the distortion and attenuation of the surges travelling along overhead transmission lines and thus could possibly cause the backflashover. This this paper presents a comparative analysis between the two conductors used for 275 kV transmission line in term of corona effect when subjected to the lightning surge propagation studies. The two conductors are the Aluminium Conductor Steel Reinforced (ACSR) and the new High-Temperature Low Sag (HTLS) conductor, known as Aluminium Conductor Composite Core (ACCC). Simulation using section by section method for a single conductor were simulated using PSCAD/EMTDC software. The analyses were done by comparing the results with three parameters that known to be affected the corona, namely the different conductor radius, the heights of the conductor above ground level, and the segment length used for a single conductor. The finding that can be drawn from the study is that the presence of ACCC conductor are found to be more efficient in reducing the corona effect than the ACSR conductors apart from other advantages such as higher current capacity and lesser losses as compared to ACSR

Effect of Earthing Enhancing Compound (EEC) on improving tower footing resistance of a 500 kV Tower in a rocky area

This paper presents a comparative analysis of different earthing designs’ performances, with particular interest on the use of earthing enhancing compound (EEC) for a selected earthing design of 500 kV transmission towers in a rocky soil, using the SESCAD tool of the Current distribution, electromagnetic field grounding and soil structure analysis (CDEGS) software. The simulation included the interpretation of soil profile and comparison between designs A, B and C, which are currently used for the 500 kV tower footing resistance (TFR) improvement. Results showed each design had reduced the TFR by 66%, 54.7% and 63.2% for the towers T42, T48 and T50, respectively. In some cases, further improvement of TFR is required, especially in the rocky area where the soil resistivity (SR) value is of more than 500 Ω⋅m. In this case, EEC was used in Design C, encasing both the vertical and horizontal electrodes, and it reduced the TFR further by 16% to 20%. The characteristics of the soil and earthing arrangement design play an important role in achieving a low TFR value, which is directly proportional to the backflashover occurrence and thus to the transmission line performance

Analysis and simulation of vector controlled bearingless induction motors

The concept of bearingless motors, which combine both motoring and rotor bearing capabilities, is appealing especially in high speed and high power machine applications. Although extensive research has been carried out on permanent magnet and reluctance types of bearingless motors, studies on the induction motor type are less successful. This thesis addresses the bearingless induction motor based on the concept of dual-pole windings, one controlling the motor torque and the other the generated radial forces. A modelling approach is undertaken to investigate the effect of induction machine design on radial force generation and motor levitation under both steady state and transient conditions. The simulation is based on the dynamic reluctance mesh model embedded in vector control systems for the decoupled control of torque, flux and radial force. This is achieved through modification of a previously developed computer software for modelling induction motors in order to model the control of bearingless induction motors. Both the squirrel cage and wound rotor induction motors are investigated and their suitability for generating controlled bearing relief forces assessed. Vector control schemes for the bearingless cage and wound rotor induction motors were also designed and simulated. A mixed field oriented vector control scheme, which incorporates the simple rotor field orientation for motoring control and an airgap field orientation for rotor levitation control, is introduced and found to be advantageous in bearingless induction motor control. Apart from investigating totally bearingless conditions, the study also investigates bearing relief capabilities for a vector controlled cage and wound rotor induction motor in which the rotor movement is restricted by bearings but with the bearing load cancelled by suitably directed radial force. The effects of real winding topologies, stator and rotor slotting and iron saturation on the performance of bearing relief and bearingless induction motors are also presented. Finally, suggestions for future work is included In order to further investigate bearingless induction motors and its applications.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Indirect lightning surge analysis of insulated rail bracket and station arrester in a fourth rail LRT system

This paper presents a study comparing the performance of a fourth rail direct current (DC) urban transit system when affected by an indirect lightning strike. Two different designs were used: one with a Cast Epoxy (CE) bracket equipped with a 3EB4-010 arrester, and the other with a Glass Reinforced Plastic (GRP) bracket equipped with a PDTA09 arrester. To replicate the indirect lightning strike, a lightning induced overvoltage was generated using the Rusck model. The model utilized the sum of two Heidler functions as the input for the lightning channel base current, assuming a perfectly conducting ground. The objective of this study is to determine whether an indirect lightning strike has any impact on the performance of the insulated rail bracket and station arrester of the LRT Kelana Jaya line, considering their different materials and residual voltage limits, respectively. Simulations were conducted using the Electromagnetic Transients Program - Restructured Version (EMTP-RV), and the performance of the two designs was compared when subjected to a 30 kA (5/80μs) induced current. The results showed that the GRP bracket, which has a higher permittivity, performed better when paired with the PDTA09 arrester, which has a lower residual voltage limit. This combination resulted in slightly lower induced overvoltage and significantly lower residual voltage being clamped by the station arrester

Transient fault detection and location in power distribution network: a review of current practices and challenges in Malaysia

An auto-restoration tool to minimize the impact of faults is one of the critical requirements in a power distribution system. A fault-monitoring system is needed for practical remote supervision to identify faults and reduce their impacts, and thus reduce economic losses. An effective fault-monitoring system is beneficial to improve the reliability of a protection system when faults evolve. Therefore, fault monitoring could play an important role in enhancing the safety standards of systems. Among the various fault occurrences, the transient fault is a prominent cause in Malaysia power systems but gains less attention due to its ability of self-clearance, although sometimes it unnecessarily triggers the operation of protection systems. However, the transient fault is an issue that must be addressed based on its effect that can lead to outages and short-circuits if prolonged. In this study, the authors summarize the guidelines and related standards of fault interaction associated with a monitoring system. The necessity of transient fault detection and location techniques and their limitations, the need for signal processing, as well as recommended practices, are also discussed in this paper. Some of the practices from local power utility are also shared, indicating the current approaches, key challenges, and the opportunities for improvement of fault-monitoring systems due to transient fault, which can be correlated with the reviews provided

Techno-economic analysis of commercial size grid-connected rooftop solar PV systems in Malaysia under the NEM 3.0 scheme

Commercial grid-connected rooftop solar PV systems are widely applied worldwide as part of affordable and clean energy initiatives and viable long-term solutions for energy security. This is particularly true in a crowded city where space is a constraint and at the same time, there are unutilized rooftops. With the recently announced Net Energy Metering (NEM) 3.0, commercial buildings in Malaysia can apply up to 75% capacity of the maximum demand (MD), which can be connected to the grid. Apart from reducing electricity bills, the owner can offset energy for 10 years. This paper presents a design analysis with the details of the sizing of a rooftop PV system. The PVsyst software tool is used to estimate the energy produced by a 380 kWp system, and this study provides a financial analysis to evaluate the profitability of the system with a particular interest in commercial buildings under the NEM 3.0 policy, which has resulted in 8.4 years return of investment (ROI). PVsyst is a software used to size the PV system and provides technical, financial, and environmental analysis. This in-depth analysis could provide a useful case study for asset owners in deciding the way forward for sustainable energy production, cost saving, and combating the energy security issue, since Malaysia is blessed with an abundance of sunshine throughout the year

An ELM based multi-agent system and its applications to power generation

This paper presents an implementation of Extreme Learning Machine (ELM) in the Multi-Agent System (MAS). The proposed method is a trust measurement approach namely Certified Belief in Strength (CBS) for Extreme Learning Machine in Multi-Agent Systems (ELM-MAS-CBS). The CBS is applied on the individual agents of MAS, i.e., ELM neural network. The trust measurement is introduced to compute reputation and strength of the individual agents. Strong elements that are related to the ELM agents are assembled to form the trust management in which will be letting the CBS method to improve the performance in MAS. The efficacy of the ELM-MAS-CBS model is verified with several activation functions using benchmark datasets (i.e., Pima Indians Diabetes, Iris and Wine) and real world applications (i.e., circulating water systems and governor). The results show that the proposed ELM-MAS-CBS model is able to achieve better accuracy as compared with other approaches