Steady-State and Dynamic Performance of Oman Transmission System with Diesel-Engine Driven Distributed Generation Omar H
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Helwan University From the SelectedWorks of Omar H. Abdalla September 5, 2011 Steady-State and Dynamic Performance of Oman Transmission System with Diesel-Engine Driven Distributed Generation Omar H. Abdalla Rashid Al-Badwawi Hilal Al-Hadi Hisham Al-Riyami Ahmed Al-Nadabi Available at: https://works.bepress.com/omar/12/ Steady-State and Dynamic Performance of Oman Transmission System with Diesel-Engine Driven Distributed Generation Omar H. Abdalla1, Rashid Al-Badwawi2, Hilal S. Al-Hadi3, Hisham A. Al-Riyami4, and Ahmed Al-Nadabi5 Oman Electricity Transmission Company, P. O. Box 1224, P. C. 131 Al-Hamriyah, Muscat, Sultanate of Oman 1 [email protected] 2 [email protected] 3 [email protected] 4 [email protected] 5 [email protected] Abstract— The paper presents simulation studies of installing can contribute to improved operation of electric networks [10]. a number of diesel-engine driven generating units at selected DGs can provide ancillary services in power grids [11]. locations in the main transmission system of Oman. A total of This paper concerns with evaluation of the performance of 300MW generator units are proposed on a temporary basis to aid the main electric power grid of Oman with DGs at six in meeting the peak demand in summer 2011. locations. These DGs are required to aid in meeting peak A digital model is developed to simulate the system including central power plants, transmission system, loads and the demand in summer 2011. Benefits of installing new DGs are proposed Distributed Generation (DG). The model includes evaluated. These include improvement in voltage profile, representation of governor and excitation systems. The reducing transformer and line loadings, and reducing active simulation studies are performed by using the DIgSILENT and reactive power losses in the transmission grid. A digital PowerFacrory software package. The objective of the studies is to model of the power system [12] is developed to study the demonstrate effects of the DGs in improving system performance system performance with the added DGs using DIgSILENT in terms of voltage profile, line and transformer loadings, and PowerFacrory software. Section II describes the main transmission losses. transmission system in Oman and the associated generation The sizes and locations of DGs have been selected based on and distribution systems. Section III briefly describes the basis practical considerations; including availability of spacing, short- circuit ratings of existing switchgears, circuit capacity, feasibility of selecting the location and power of each DG. The results of connection, operation noise, site access roads for fuel delivery, are given in Section IV. Proposed key performance indicators environmental effects, etc. A number of performance indicators are given in Section V to provide a basis for evaluating the are defined to assess the contribution of the selected DGs. These improvements gained by employing DGs. Section VI include transformer loading index, line loading index, and describes the practical implementation and operation of the voltage deviation index. In addition, active and reactive DGs in summer 2011. Finally, conclusions are summarized in transmission losses are calculated and used for assessing the Section VII. benefits of the DGs. The results include comparison of the contribution of II. OMAN ELECTRICITY TRANSMISSION SYSTEM individual distributed generation at each site and the case with all proposed DGs. In addition the system dynamic performance is The transmission system extends across the whole of assessed by simulating various DG outages at peak demand. northern Oman and interconnects bulk consumers and electricity generators located in the Governorate of Muscat Index Terms — Distributed Generation, Electricity and in the regions of Batinah, Dhahirah, Dakhliyah and Transmission System, Performance Indicators. Sharquiya [13]. Fig. 1 shows a geo-schematic diagram of the system in 2011. It has two operating high voltages, i.e. 220kV I. INTRODUCTION and 132kV. There has been a growing interest in installing small-scale The main transmission system is supplied with electricity distributed generations (DGs) in electric power systems in generated from eight gas-based power stations located at recent years [1]-[3]. Although most DGs are based on Ghubrah (469MW), Rusail (687MW), Wadi Al-Jizzi renewable energy sources such as wind, solar and fuel cells, (336MW), Manah (279MW), Al-Kamil (297MW), Barka AES conventional small gas turbines and diesel engines can be (434MW), Barka SMN (681MW) and Sohar (605MW). For employed. Distributed generation can provide an alternative to updated generation information, see [14]. Rusail, Wadi Al- electric utility investments in system capacity [1]. Optimal Jizzi, Manah and Al-Kamel power plants have open-cycle gas investment planning for employing DG in a competitive turbines. The remaining plants are of combined-cycle type; electricity market is investigated in [4]. Introducing DGs in a gas and steam turbines. In addition, a number of direct main power system as Independent Power Producers (IPP) can customers are connected directly to the transmission system. help in meeting peak demand [5]. Determination of optimal The transmission system may be supplied from these direct location and size of DG is a key factor of successful operation. connected customers such as Sohar Aluminum Company, Evaluating the impact of network investment deferral on Oman Mining Company, Sohar Refinery Company and distributed generation expansion is explored in [6]. Evaluation Petroleum Development of Oman (PDO). Also, up to 300MW of technical benefits, impacts, and trade-offs of DG are can be supplied from DGs in 2011. investigated in [7]-[9]. DG units with their goodness factors Legend UAE Existing OETC Transmission System (2011) Power Station Al Batinah North G SRC G A lu 220kV Grid Station m in iu m G S o h SIP-A a r Shinas G I 132kV Grid Station IP Al Bureimi SPS 220kV Double Circuit Liwa 220kV Double Circuit Cable 132kV Double Circuit Auha 132kV Single Circuit Wooden Pole 132 kV Double Circuit Cable Oman Sea Sohar Private Customer Mhadah G SIS G (Alwasit) A Wadi Al Jizzi BA ES RK A SM Saham Al Batinah South N G G Bureimi Muscat Ghoubrah G Khaburah Seeb Main Madinat Barka Wadi Sa’a Wave 2 4 Muladah Qurum AlFalaj MIS Bawsher Muttrah Filaj Mabailah MSQ Wadi Kabir Rustaq Dank Wadi Adai Alhayl Mawalih Barka Main Nakhal Airport High Ibri KSA Al-Dakhiliah Rusail GG Misfah Yitti Sumail Bahla Jahloot Madiant Nizwa Ad Dhahirah Nizwa Izki Al-Sharqiyah Al Wusta Manah G G OMIFCO Sur Nahada PDO Adam Mudhirib G Mudaybi Alkamil JBB Ali Prepare By: Strategic Planning & Studies Section Fig. 1. Main Electricity Transmission System of Oman. The OETC transmission system consists of: In 2010 the system gross peak demand of 3613MW 835 circuit-km of 220 kV overhead transmission line occurred at 15:00 hours on 1 June, which was an increase of 2969.86 circuit-km of 132 kV overhead transmission line about 1.9 % from 2009 peak demand. The transmission system is interconnected at 220kV from 12 circuit-km of 220 kV underground cable Al-Wasit in Mahadah with the transmission system of the 63.798 circuit-km of 132 kV underground cable United Arab Emirate. This should provide increased security 6630 MVA of 220/132 kV transformer capacity of supply and benefits to both countries in the form of cost 9239 MVA of 132/33 kV transformer capacity savings from the sharing of reserve capacity and energy resources. 150 MVA of 132/11 kV transformer capacity Two 220 kV interconnection grid stations III. DISTRIBUTED GENERATION Two 220/132 kV grid stations Various sites for installing distributed generation have been Five 220/132/33 kV grid stations surveyed to determine the most suitable places. The sizes and Thirty seven 132/33 kV grid stations locations of DGs have been selected based on practical One 132/11 kV grid station considerations; including availability of space, short-circuit ratings of existing switchgears, circuit capacity, feasibility of connection, operation noise, site access roads for fuel delivery, The bulk of the power transmitted through the main grid, is environmental effects, etc. Six locations have been selected to fed, through 220/132/33kV, 132/33kV and 132/11kV grid install DGs to assist meeting peak demand in summer 2011. stations, to the three distribution licence holders, i.e. Muscat The locations and powers of these DGs are: Sur (80MW), Electricity Distribution Company, Mazoon Electricity Mudaibi (78MW), JBB Ali (24MW), MIS (19MW), Khaborah Company and Majan Electricity Company. In addition to the (59 MW) and Liwa (40MW) grid stations. The total power is distribution companies a number of large private customers 300MW. The DGs are connected at the 33kV busbars of the are directly connected to the main transmission system at 132/33kV grid stations. All generators are driven by diesel 220kV or 132kV level. engines and connected to the system through step-up transformers. IV. RESULTS only listed in the table. The 132kV busbars are connected to the 33kV busbars through 132/33kV transformers at grid Table I shows the percentage loading of power transformers stations. The DGs are connected at the 33kV load busbars. It at the concerned grid stations. Significant reductions in should be noted that the Grid Code [15], determines the transformer loadings are resulted by introducing the DGs. To allowable 132kV voltage range to be within ± 10% from its comply with the Transmission Security System Standard, the nominal value. loading on each transformer should not exceed 50%, thus Table IV shows the three-phase and single-phase to ground satisfying the N-1 security criterion. The non-firm loading faults when the DGs are connected to the 33 kV busbars. The conditions on the transformers at Mudaibi (66.41%), MIS fault current at all busbars increase significantly but these (51.18%) and Khaborah (50.55%) are completely removed values are still remaining within the allowable limit of the with the DGs as indicated in the last column.