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Voltage Stability Of Electric Power Systems

A new structure for doubly fed induction generator (DFIG) wind farms with coordinated power control under grid fault conditions are proposed in this paper. The proposed structure uses one grid side converter (GSC) and one energy storage system (ESS) for the entire wind farm unlike conventional structures, which have one GSC for each of the DFIGs. A converter loss decrease and a reliability enhancement are some of the advantages of the proposed wind farm, under normal operating conditions. The proposed wind farm follows the new grid codes to remain connected to the grid. In addition, it supports the network voltage and frequency stability by generating reactive and active power during and after faults. The ESS is coordinated with the wind farm to generate smooth active power under normal operation. This improves the low voltage ride-through capability of the wind farm under-voltage fault conditions and enhances the frequency response of the wind farm under frequency faults. MATLAB/Simulink software was used to simulate the proposed wind farm structure. An experimental setup was also provided to test the operation of the proposed power circuit topology.

ESS equipped DFIG wind farm with coordinated power control under grid fault conditions

The objective of the power system Generation Expansion Planning (GEP) is to determine the best investment schedule of capacity, type of technology, time and where to install new plants to satisfy forecasted load within the given reliability criteria over a planning horizon. Renewable Energy Resources (RES) implementation within the GEP model represents a challenging problem due to the RES uncertainty prediction and representation difficulty. This paper presents a mathematical model for the RES uncertainty prediction and proposes an optimal planning model for long-term GEP with high sharing of RES considering the uncertainty. The RES are represented as a conventional source with zero fuel cost and high forced outage rate within the GEP model. The GEP model considers the RES uncertainties impact, carbon dioxide gas emission reduction rate, inefficient generation units' retirement and the gradual penetration increasing of RES over the planning period. Mixed integer linear programming is carried out using MATLAB software to solve the proposed GEP model for a 20 years planning period.

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Generation Expansion Planning Considering High Share Renewable Energies Uncertainty

The prevalence of cabled infrastructure associated with wind farms, combined with the increase in power-electronic interfaces in wind turbines and reactive power plant, has highlighted the pervasive nature of harmonics on electricity networks. Insufficient consideration is given to the effects of harmonics through the low prioritisation of power quality in the Front-End Engineering and Design stage and a lack of awareness of the obligations of the respective parties involved. The resulting designs are incompatible with the requirements of the relevant Grid Codes. This can lead to delays, commercial exposure, restricted network access and subsequent loss of revenue. The obligations of the Transmission Owner (TO), System Operator (SO) and wind farm developer are discussed with respect to Grid Code requirements and the responsibilities of each party in ensuring compliance. The technical aspects of assessing harmonic compliance are described in the context of the design considerations which are made at the various stages of the project development. These include the shift in resonances within the host network, the modification of existing harmonic distortion and the propagation of injected harmonics into the network and through to the extra high voltage, high voltage and medium voltage substations. The ensuing challenges associated with ensuring compliance through filter design are discussed in the context of relevant international standards, including UK ER G5/4-1, IEEE 519, EN 50160 and IEC 61000-3-6. The results indicate that shifts in resonances are more problematic to resolve, compared to the propagation of injected harmonics: injected harmonics are readily absorbed through local filtering and thus the emissions are typically low; in contrast, the effects of shifts in resonances must be transferred back to the point of common coupling, resulting in complex local filtering. Early selection by the developer of appropriate transmission infrastructure and technology can lower the filtering requirement necessary to meet the harmonic specification issued by the host TO.

Ensuring Grid Code Harmonic Compliance of Wind Farms

The sensitivity and the highly connected modern power systems make Power quality problems a priority in these systems. Both utilities and consumers have essential role in dealing with these problems. It is utilities responsibility to provide a clean and reliable power. On the other hand, it is consumer’s responsibility to draw power with acceptable indices. In this Paper, the type of the consumer’s facility is chosen as a basis for managing power quality indices. In this paper, comprehensive power quality in Jordan Low-Voltage Electrical Power Grid is measured. The loads are divided into five categories: : (i) industrial loads, (ii) commercial loads, (iii) hospital loads, (iv) residential loads, and (v) office loads. Assuming each category will affect the grid in similar way, which will facilitate prediction of power quality problems. Also, this methodology will help proposing new regulation that governs the relation between utilities and consumers. The power quality indices considered in this paper are; THD, Crest factor, K-factor, Power factor, Harmonic to active power ratio, Voltage imbalance, and Frequency variations. The results show similar results for the loads with the same type. Also, the results show the correlation between the current total harmonic distortion and utility voltages and neutral-to-ground voltage, and between voltage and current imbalance.

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Investigation of Power Quality Indices in Jordanian Distribution Grid

This paper investigates factors which influence the power quality performance of the Dhofar Power Grid, based upon the first 50MW wind farm project connection. The wind farm consists of 20×2.5 MW wind turbines and will be integrated into the 132kV Dhofar network which is connected with the Maim Interconnected System via the Petroleum Development of Oman grid. As this is the first wind farm project in Oman, a review of fundamental aspects which influence power quality for connecting the wind farm is presented, as well as an initial view on Grid Code performance. The power quality assessment is required as part of the license obligation for a transmission operator and is vital to a wind farm developer for their filter design and compensation sizing. The paper addresses power quality topics such as voltage unbalance, flicker and harmonic compliance, in relation to network changes and potential future non synchronous connections. Simulation studies are carried out in DIgSILENT software and are presented in the paper.

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Power quality of Dhofar network with 50 MW wind farm connection

This paper describes the actual impact of the installed 400 kV shunt reactors on Oman grid. Supportive readings from the SCADA during off peak demand in the last winter period of 2018 are presented to show the the voltage profile at 400 kV and 220 kV busbars and the reactive power of generating units. The objective of installing shunt reactors is to limit the voltage rise in the grid during light loading conditions in winter period due to recently introduced 400 kV transmission lines. The recorded actual voltages and reactive power verified the effectiveness of the shunt reactors in improving voltage profile and shifting the operating points of generators into more stable region in addition to comply with the Security Standard.

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Impact of Installation of 400 kV Shunt Reactors on Oman Grid

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Grid Impact Study of the First Wind Farm Project in Dhofar Transmission System

This paper addresses the system planning and operational consideration in dealing with the first intermittent 50 MW wind farm project in Dhofar in Sultanate of Oman. The wind farm consists of 13 x 3.83 MW wind turbines connected into the 132 kV Dhofar network. The entire Oman power grid has been modelled for steady-state and dynamic analysis in DIgSILENT Power factory software tool. The aim of the paper is to understand the impact on wind intermittency on the Dhofar power grid with respect to power flows, dynamics and reserve considerations to minimize exchanges between the neighbouring grids. A five-month wind measurement campaign was conducted to fully capture the variation in wind speed such that the appropriate measures can be taken from a planning & control room perspective. Statistical analysis and simulation results are presented in the paper. The analysis shows that if the appropriate measures for intermittency are taken, no adverse effects are identified due to the wind farm connection to the Dhofar transmission network.

Integration of 50MW Dhofar Wind Farm Intermittency in System Planning & Operation

This paper presents techno-economic studies for grid connection of a new 1700MW generating plant in the vicinity of Sohar port area which is planned to be commissioned by January 2019. The objective is to justify the required capital expenditure on the basis of the submission of a full, complete and robust study, in the form of Pre-Investment Appraisal Document (PIAD), insuring the transmission system in Oman is planned, developed and operated in an efficient manner. Five options for connecting the Sohar generating plant to the Main Interconnected Transmission System (MITS) have been assessed and the most efficient financially, technically and lower risk option is selected. The paper describes the assessment for each option from different aspects, technically, financially and risk of deliverability of the project. The assessment of each option has been carried out on the basis of the following performance considerations: compliance with the Transmission Security Standard (TSS), capital cost, Net Present Value (NPV), environmental considerations, safety and flood risk assessment. Power losses have also been considered in the NPV calculation. In addition, the paper describes the optimal generation connection design in accordance with the TSS criteria. The compliance with TSS requirements has been assessed by steady state and dynamic studies for both peak and off peak demand with full evacuation of the new Sohar power plant, using the DIgSILENT professional software. The results include load flow analysis in N, (N-1), and (N-M-1) operating conditions, short-circuit levels, and transient stability.

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A. A. Al Nadabi

Papers

Power quality of Dhofar network with 50 MW wind farm connection

Impact of Installation of 400 kV Shunt Reactors on Oman Grid

Grid Impact Study of the First Wind Farm Project in Dhofar Transmission System

Integration of 50MW Dhofar Wind Farm Intermittency in System Planning & Operation

Techno-economic studies for connecting 1700MW sohar-3 power station to oman grid