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Saeed Zaman Jamali,Muhammad Omer Khan,Syed Basit Ali Bukhari,Muhammad Mehdi,Gi-Hyeon Gwon,Chul-Ho Noh,Chul-Hwan Kim 한국조명·전기설비학회 2017 조명·전기설비학회논문지 Vol.31 No.10
Low voltage DC (LVDC) distribution systems are gaining attention as customer loads are shifting towards power electronics-based equipment. The DC distribution system has the advantage of supplying power to these power electronic-based loads with high efficiency and without undergoing an energy conversion process. However, the power electronic components used in the LVDC distribution system are vulnerable during short-circuit faults. These components must be protected during the short-circuit faults for a safe and reliable operation. Therefore, this paper proposes a protection technique based on DC short-circuit fault current behavior. The fault is detected via a superposition principle. A fault current limiter (FCL) is used to suppress DC fault strength and reduce the stress from the circuit breaker. Finally, a solid state circuit breaker (SSCB) is used to isolate the fault point. The simulation results show that the proposed protection Scheme operates quickly enough as per expectations to avoid damage to sensitive power electronic devices.
Frequency Profile Improvement of a Microgrid under Abnormal Conditions via a Demand Response Program
Muhammad Saeed uz Zaman,Raza Haider,Syed Basit Ali Bukhari,Yun-Sik Oh,Min-Sung Kim,Muhammad Mehdi,Chul-Hwan Kim 한국조명·전기설비학회 2017 조명·전기설비학회논문지 Vol.31 No.10
The frequency deviation of an electric power system from its nominal range is a significant indicator of the system’s instability. This issue is further highlighted when the system is incorporated with intermittent renewable energy resources. In this work, the frequency regulation of a microgrid is achieved by a demand response program. The proposed plan is implemented in a central controller that has two control sections. The frequency deviation is controlled by manipulating responsive loads. In the case of higher frequency deviation, the command of the first control section is proportional to the magnitude of frequency deviation and a large amount of responsive loads is manipulated to restore the frequency to its nominal range quickly. The other section of the central controller addresses minor frequency deviations. The proposed plan is implemented on a test system and outperforms the conventional methods in terms of frequency restoration. The improvement in voltage profile is also observed during abnormal conditions after the proposed plan is implemented.
One-stage Hip Reconstruction for Developmental Hip Dysplasia in Children over 8 Years of Age
Irfan Qadir,Saeed Ahmad,Atiq uz Zaman,Chirag Muhammad Khan,Shahzad Ahmad,Amer Aziz 대한고관절학회 2018 Hip and Pelvis Vol.30 No.4
Purpose: This study was performed to assess the clinical and radiological outcomes following one-stage hip reconstruction, consisting of open reduction femoral shortening and pelvic osteotomy, for neglected developmental dislocation of the hip (DDH). Materials and Methods: This is a retrospective analysis of 77 hips in 65 patients (46 females and 19 males; 12 had bilateral dislocations), operated at a Ghurki Trust Teaching Hospital in Pakistan between 2013 and 2015. The average age at surgery was 11.02±3.43 years. According to the Tönnis classification, there were 10, 14, 22, and 31 patients in grades 1, 2, 3, and 4, respectively. The pelvic procedure utilized in this study was triple osteotomy (47 hips) followed by double and Salter osteotomy (18 and 12 hips, respectively). Postoperative evaluations were conducted using the modified MacKay’s scoring system (functional outcomes) and Severin’s scoring method (radiological assessment). Results: Postoperatively, there were 38 (49.4%), 19 (24.7%), 14 (18.2%), and 6 (7.8%) hips in Severin grade I, II, III and IV, respectively. According to the modified McKay criteria, there were 22 hips (28.6%) in excellent condition, 44 (57.1%) in good condition, 9 (11.7%) in fair condition and 2 (2.6%) in poor condition. Both patients with poor outcomes had an unstable, painful hip with evidence of avascular necrosis of the femoral head. Conclusion: Based on the results presented here, we recommend the single stage procedure of open reduction, femoral shortening and pelvic osteotomy for treatment of DDH in older children with good to excellent functional and radiological outcomes.
Protection Coordination Using Superconducting Fault Current Limiters in Microgrids
Raza Haider,Muhammad Saeed Uz Zaman,Syed Basit Ali Bukhari,Zahoor Ahmed,Muhammad Mehdi,Yun-Sik Oh,Chul-Hwan Kim 한국조명·전기설비학회 2017 조명·전기설비학회논문지 Vol.31 No.10
Power generating units in the form of distributed generation (DG) are integrating with microgrid (MG) systems to supply reliable power to users. The trend of an integrated power supply is increasing continually to meet growing energy demands. Besides certain advantages of the MG system, some interconnection and system protection issues pose a challenge in terms of implementation. These problems need to be addressed in order to facilitate smooth operation of power systems. Superconducting fault current limiters (SFCLs) provide the best performance and unique protection features to electrical power systems during various fault conditions. This paper describes modeling, characterization, and implementation of SFCL in an MG system to enhance protection coordination. The proposed SFCL is modeled in MATLAB/ Simulink software and the performance of the system is validated through simulation results. It is also shown that the proposed SFCL provides a means of better relay coordination during various fault conditions. This is achieved by incorporating well-calculated design parameters of SFCL and its placement at optimal locations.
Muhammad Omer Khan,Saeed Zaman,Muhammad Mehdi,Chul-Ho Noh,Gi-Hyeon Gwon,Chul-Hwan Kim 한국조명·전기설비학회 2017 조명·전기설비학회논문지 Vol.31 No.10
Conventional AC power networks in recent decades have been in a process of continuous overhaul due to the development of power electronic devices and distributed energy resources (DER). This development has demonstrated great potential for the implementation of DC power networks and numerous effects on the employment of integrated AC/DC systems based on Voltage Source Converter (VSC) technology are underway. On the other hand, the integration of DER in a distribution network has emerged as a durable choice for fulfilling future energy need. In this study, a load flow analysis is performed on a Voltage Source Converter-Multi terminal DC (VSC-MTDC) based AC/DC Distribution system incorporated with DERs. An IEEE 14 bus distribution network was modified to include a VSC-MTDC network model for the implementation of the Newton-Raphson load flow algorithm. This paper also discussed the mathematical models for VSC, AC and DC networks along with the load flow study of the steady-state change in the AC/DC network as a result of converter and DC line outage.
Abdul Naeem,Shah Zaman,Muhammad Farooq,Ihtisham Wali Khan,Zahid Ali Ghazi,Tooba Saeed,Muhammad Hamayun 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.6
This work describes the practicability of utilizing bentonite clay as a cheap and raw support for heterogeneouscatalyst development. In the current research, ammonium persulfate (APS) impregnated bentonite heterogeneouscatalyst was designed for the conversion of waste cooking oil to biodiesel. The fabricated catalyst was analyzed byvarious instrumental techniques (FTIR, TGA, BET, SEM, XRD, and EDX) to study its various physiochemical properties. It was identified that the clay supported heterogeneous catalyst executed an excellent activity for waste cooking oilconversion as providing maximum biodiesel yield of 93% at optimal reaction conditions (reaction temperature 75 oC,oil/methanol molar ratio, 1 : 10; catalyst amount, 2.5 wt%; stirring rate, 600-rpm in 3.5 hr reaction time). Gas chromatographymass spectroscopy (GCMS) analysis confirms the successful conversion to biodiesel. Similarly, the variousphysiochemical characteristics of the synthesized biodiesel meet the international standard of American (ASTM6751)and European Union (EU-14214). Moreover, the designed acid catalyst showed catalytic activity for up to eight consecutiveruns demonstrate its good reusability.
Jose Bastidas Betancourt,Khawaja Khalid Mehmood,Muhammad Saeed uz Zaman,Chul-Hwan Kim 한국조명·전기설비학회 2018 조명·전기설비학회논문지 Vol.32 No.4
This paper proposes an Energy Management System (EMS) power dispatch algorithm for a set of various distributed energy resources (DERs) such as distributed generators (DGs) and energy storage systems (ESSs) connected to a 1-MW power grid system. The ESS is composed of a stationary Vanadium Redox Battery (VRB) and Li-ion Electric Vehicle (EV) charging parking lot at a workplace incorporating Vehicle to Grid (V2G) and Grid to Vehicle (G2V) charging capabilities considering no linear modeling of both battery technologies. The simulation study is carried out considering load profile curves of residential and commercial load connected to the system at peak of summer load. Effectiveness and simulation results of the proposed EMS dispatch model were confirmed on various scenarios under the presence of different levels of power mismatch, high intermittence of PV power output and EV penetration.