P-HiL Evaluation of Virtual Inertia Support to the Nordic Power System by an HVDC Terminal

This paper provides an assessment of the effect from virtual inertia provided by an HVDC converter terminal on the Nordic power system. The analysis is based on results from Power-Hardware-in-the-Loop (P-HiL) tests with a laboratory-scale Modular Multilevel Converter (MMC) representing an HVDC terminal interfaced with a real-time phasor simulation of the Nordic grid. The applied control method for providing virtual inertia is utilizing the derivative of the locally measured grid frequency to adapt the power reference for the studied converter terminal. The power injection provided by the converter and the resulting impact on the frequency dynamics of the power system are investigated as a function of the emulated inertia constant and the frequency droop gain. The results demonstrate how the HVDC converter can effectively support the dynamic response of the power system when exposed to large load transients by improving the frequency nadir and reducing the Rate-of-Change-of-Frequency (ROCOF). Keywords: HVDC Transmission , Power-Hardware-in-the-Loop , Real-time Simulation , Virtual InertiaacceptedVersio

Rheological properties of emulsion of crude oil and water

In the paper the rheological properties of crude oil of White Tiger oil-field (Vietnam) and its emulsion with sea-water, including measurement results and analytical approximation formulae for wide range of pressure, temperature and water concentration, are presented. As it is known, the crude oil of White Tiger oil-field is a high-paraffin and high-viscous oil. At the low temperature (T ≤ 40°C) it behaves as non-Newtonian fluid of Bingham-Shvedov group. Therefore, beside the effective viscosity, the effective dynamic shear stress is also measured and approximated. The rheological properties of crude oil and emulsion of crude oil and water are also measured and approximated for the case when the mixture contains 0.1% chemical reagent ES-3363

Safety and efficacy of fluoxetine on functional outcome after acute stroke (AFFINITY): a randomised, double-blind, placebo-controlled trial

Background Trials of fluoxetine for recovery after stroke report conflicting results. The Assessment oF FluoxetINe In sTroke recoverY (AFFINITY) trial aimed to show if daily oral fluoxetine for 6 months after stroke improves functional outcome in an ethnically diverse population. Methods AFFINITY was a randomised, parallel-group, double-blind, placebo-controlled trial done in 43 hospital stroke units in Australia (n=29), New Zealand (four), and Vietnam (ten). Eligible patients were adults (aged ≥18 years) with a clinical diagnosis of acute stroke in the previous 2–15 days, brain imaging consistent with ischaemic or haemorrhagic stroke, and a persisting neurological deficit that produced a modified Rankin Scale (mRS) score of 1 or more. Patients were randomly assigned 1:1 via a web-based system using a minimisation algorithm to once daily, oral fluoxetine 20 mg capsules or matching placebo for 6 months. Patients, carers, investigators, and outcome assessors were masked to the treatment allocation. The primary outcome was functional status, measured by the mRS, at 6 months. The primary analysis was an ordinal logistic regression of the mRS at 6 months, adjusted for minimisation variables. Primary and safety analyses were done according to the patient's treatment allocation. The trial is registered with the Australian New Zealand Clinical Trials Registry, ACTRN12611000774921. Findings Between Jan 11, 2013, and June 30, 2019, 1280 patients were recruited in Australia (n=532), New Zealand (n=42), and Vietnam (n=706), of whom 642 were randomly assigned to fluoxetine and 638 were randomly assigned to placebo. Mean duration of trial treatment was 167 days (SD 48·1). At 6 months, mRS data were available in 624 (97%) patients in the fluoxetine group and 632 (99%) in the placebo group. The distribution of mRS categories was similar in the fluoxetine and placebo groups (adjusted common odds ratio 0·94, 95% CI 0·76–1·15; p=0·53). Compared with patients in the placebo group, patients in the fluoxetine group had more falls (20 [3%] vs seven [1%]; p=0·018), bone fractures (19 [3%] vs six [1%]; p=0·014), and epileptic seizures (ten [2%] vs two [<1%]; p=0·038) at 6 months. Interpretation Oral fluoxetine 20 mg daily for 6 months after acute stroke did not improve functional outcome and increased the risk of falls, bone fractures, and epileptic seizures. These results do not support the use of fluoxetine to improve functional outcome after stroke

Locating Generators Causing Forced Oscillations Based on System Identification Techniques

This paper presents a method to locate the source of forced oscillations in power grids caused by maloperation of turbine-governor systems. The transfer function between the grid frequency and the output active power is first estimated for each generator in normal operation condition. The turbine-governor acting as the source of the forced oscillations is then detected by identifying rather large mismatches between the predicted output of its estimated transfer function and actual measurements from the grid. The proposed approach can locate both single and concurrent sources of forced oscillations. The method requires synchronized measurements of the grid frequency and the active power of the generator, preferably from PMU measurements. Results from simulations of the Nordic 44 grid model, which emulates the Nordic power system, demonstrate the validity of the proposed method.acceptedVersio

A topology-based scheme for adaptive underfrequency load shedding

This paper presents a topology-based scheme for adaptive underfrequency load shedding (UFLS). By tracking changes of power system topology and information about power flow, the proposed method is able to identify islanded conditions, the number of islands and their deficits of active power, which are fundamental parameters for the adaptive UFLS scheme. The algorithm is also applicable to interconnected power systems, where islanding of the power grid can go beyond country borders and create new asynchronous areas that can comprise several national transmission systems. In this case, the proposed method can properly estimate the power deficit of each area and coordinate the load shedding of several affected power systems in the underfrequency area. The main idea of the proposed method is demonstrated by simulations of the IEEE reliability test system in PSS/E and real time coordination of the adaptive UFLS schemes in Labview

A Topology-based Scheme for Adaptive Underfrequency Load Shedding

This paper presents a topology-based scheme for adaptive underfrequency load shedding (UFLS). By tracking changes of power system topology and information about power flow, the proposed method is able to identify islanded conditions, the number of islands and their deficits of active power, which are fundamental parameters for the adaptive UFLS scheme. The algorithm is also applicable to interconnected power systems, where islanding of the power grid can go beyond country borders and create new asynchronous areas that can comprise several national transmission systems. In this case, the proposed method can properly estimate the power deficit of each area and coordinate the load shedding of several affected power systems in the underfrequency area. The main idea of the proposed method is demonstrated by simulations of the IEEE reliability test system in PSS/E and real time coordination of the adaptive UFLS schemes in Labview

Architecture and laboratory implementation of a testing platform for Wide Area Monitoring Systems

This paper presents a platform for testing wide area monitoring system (WAMS) applications in real time with a Hardware-in-the-Loop (HIL) approach. The power grid dynamics are emulated by performing real-time phasor simulations. Voltage and current phasors can be streamed to external systems based on the standard IEEE C37.118-2011, recreating synthetic synchrophasors. Moreover, phasors can be transformed into timedomain quasi-sinusoidal signals and transferred via a low-latency fiber optic connection to a 200 kW high-bandwidth grid emulator. The grid emulator can amplify the voltage and current signals, allowing Power Hardware-in-the-Loop (P-HIL) testing of physical hardware components. A graphical user interface has been developed to facilitate the interactions with the real time simulation and for better visualizing the power system dynamics. Two WAMS applications for assessing voltage stability margins and for detection of power oscillation are implemented and tested as examples. These examples demonstrate that the framework is a suitable platform to test WAMS applications in power systemsacceptedVersio

P-HiL Evaluation of Virtual Inertia Support to the Nordic Power System by an HVDC Terminal

This paper provides an assessment of the effect from virtual inertia provided by an HVDC converter terminal on the Nordic power system. The analysis is based on results from Power-Hardware-in-the-Loop (P-HiL) tests with a laboratory-scale Modular Multilevel Converter (MMC) representing an HVDC terminal interfaced with a real-time phasor simulation of the Nordic grid. The applied control method for providing virtual inertia is utilizing the derivative of the locally measured grid frequency to adapt the power reference for the studied converter terminal. The power injection provided by the converter and the resulting impact on the frequency dynamics of the power system are investigated as a function of the emulated inertia constant and the frequency droop gain. The results demonstrate how the HVDC converter can effectively support the dynamic response of the power system when exposed to large load transients by improving the frequency nadir and reducing the Rate-of-Change-of-Frequency (ROCOF). Keywords: HVDC Transmission , Power-Hardware-in-the-Loop , Real-time Simulation , Virtual Inerti

Voltage stability monitoring using a modified thevenin impedance

This paper presents a method for voltage stability monitoring based on the maximum power transfer to the load. The only required information is the system topology, the data from PMUs and the operational status of synchronous generators. With this information, the Thevenin impedance seen from a load bus can be estimated and by using the Thevenin theorem for maximum power transfer an impedance based stability index can be established. Since the Thevenin impedance is influenced by the operational conditions of the synchronous generators, it is consequently not a constant value and differs from the short circuit impedance of the bus. It is emphasized that the method requires only the information of the considered subsystem. Therefore, since the computation requirement is insignificant, the algorithm can be used for online monitoring. The validation of the approach is achieved by simulating a simple transmission system