Stig Løvlund

Synchrophasor network, laboratory and software applications developed in the STRONg 2 rid project

This paper presents the activities carried out in one of the work packages of the Nordic Energy Research funded project Smart Transmission Grid Operation and Control (STRONg2rid). The main objective of the work package is to deploy a state-of-the-art software and hardware for developing power system operation, protection, control and automation applications. Several PMUs have been deployed at partner universities and a network of synchrophasors has been set up. In addition the Smart Transmission System Laboratory (SmarTS-Lab) has been established. This laboratory serves as a test-bench to develop and verify smart transmission grid technologies. A software development kit (S3DK) was developed within the project. The S3DK has been used to implement PMU-based applications and deploy them in different targets, including smart phones and tablets. Several tools and software applications which utilize synchrophasor measurements (from the laboratory or the deployed university PMU network) to perform power system monitoring, sub-synchronous power oscillation detection, etc., have been developed and are presented herein.

A method for real time voltage stability monitoring in sub-transmission networks

This paper presents a real-time voltage stability monitoring method based on estimation of maximum power transfer. The approach solely requires information from PMUs installed at concerned load buses at substations in addition to available information of system topology and load power obtained from SCADA/EMS or state estimator. The proposed algorithm estimates the Thevenin impedance seen at the load bus and consequently the maximum loadability. This power transfer limit is used as an indicator for voltage stability assessment when compared to the load power. It is emphasized that only topology of the considered subsystem is needed, not the whole network. This feature makes the method viable for online implementation since the computation requirement is insignificant. In principle, the proposed methodology is not limited to specific grids in terms of voltage level, but it is especially suitable for sub-transmission networks, where loads are supplied by bulk power source and voltage instability is imposed by long transmission lines. The proposed approach is validated by simulations on the Norwegian transmission grid.

‘In silico’ testing of a decentralized PMU data-based power systems mode estimator

This paper presents the software implementation of a Phasor Measurement Unit (PMU) data-based mode estimation application in a decentralized mode estimation architecture. This work builds from previous efforts in the development of a mode estimator implemented using a centralized architecture, meaning a set of modes were estimated for the whole system in a single processing location. One drawback of mode estimators that use centralized mode architecture is that the observability and therefore estimation of important low-damped local electromechanical modes can be affected by the higher observability of other dominant modes of the systems (e.g inter-area modes). This work proposes, implements and tests a decentralized architecture in order to increase the observation capability to provide better estimates of local low damped oscillations. In this architecture, the data from a single PMU or a group of local PMUs could be processed by a processor to estimate the modal parameters observed at a specific part of the grid or observed by specific group of PMUs. The decentralized architecture and results of tests are presented in this paper together with comparison with a centralized architecture.

Open source SCADA implementation and PMU integration for power system monitoring and control applications

This paper presents the implementation of an Open Source SCADA system in a laboratory and discusses methods for PMU data integration into SCADA. SCADA BR is a web-browser based SCADA that enables the user to access monitoring, control and automation equipment over multiple protocols. For implementation, protection relays from SEL are configured as DNP3 outstations to act as slaves and SCADA BR which is installed in one of the workstations in the laboratory acts as master. The evaluation of SCADA BR has been performed by executing a power system model in a real-time simulator and coupling its analog outputs with the protection relays. The integration of PMU measurements in the SCADA system and their use for monitoring is discussed. The limitations of the SCADA systems to fully utilize PMU data are also presented.

A comparative case study of online voltage instability monitoring

Online voltage instability monitoring based on estimation of the Thevenin impedance has been thoroughly studied in many works. This equivalent impedance can be approximated either by phasor measurements of the load voltage and current or by these measurements in combination with system topology. Both approaches have their own characteristics, which are closely examined in this paper. The study is conducted by simulation of the Nordic power system, where high power export on the transmission corridor between southern Norway and Sweden might cause voltage stability problems. Moreover, the proposed algorithms for estimation of the Thevenin impedance is also implemented and tested at the same location with real data from phasor measurement units. This has enabled interesting comparison of the Thevenin impedances obtained from simulations and the real power system.

Damping low frequency oscillations with hydro governors

This paper presents a novel approach into damping inter area oscillations during poor grid conditions and low oscillation frequency ranges at the generator side. The method is based upon the application of a single input Power System Stabilizer to the actuators of hydro governor systems (PSS-G). One constraint thereby is the decoupling of the damping application from the standard operational functionalities such as primary control. The investigation is based upon a two-step approach: A principal feasibility investigation utilizing a Single Machine Infinite Bus-SMIB Model and a second step using a four generator two area model focusing on the interaction of the governor control path and the voltage control path. Local signals and signals derived from Wide-Area-Measurement System (WAMS) like speed deviation or accelerating power respectively voltage angle deviation have variously been used as input signals and compared by their impact on system damping. This article is part of a special session at PowerTech 2013 which is being proposed by the EU FP7 Real-Smart Consortium, a Marie Curie Industry-Academic Pathways and Partnerships project1. Most of the work presented in this paper has been developed during a secondment at Statnett in Oslo, Norway.

‘In silico’ testing of a real-time PMU-based tool for power system mode estimation

This paper presents an overview of the software implementation of a real-time mode estimator application and its testing. The application was developed to estimate inter-area modes from both ambient and ring-down synchrophasor data from multiple phasor measurement units (PMU). The software application was implemented in LabVIEW using Statnetts synchrophasor software development kit (S3DK), to receive real-time synchrophasor measurements. The different features of the application were tested using two types of experiments presented herein. The first experiment is performed using emulated signals from a simple linear model. The second experiment was designed to use a linearized representation of the KTH-Nordic32 power system model. These experiments are used to carry out quantitative analyses of the tools performance.

PMU-based voltage instability detection through linear regression

This paper proposes a linear regression method using synchrophasor measurement for voltage stability monitoring. The method preprocesses synchrophasor measurements in order to eliminate inconsistencies and errors that embedded in them. This data is then used in the computation of sensitivities suitable for voltage stability monitoring. Some important electrical components such as Over Excitation limiter and On-Load Tap Changer which create discrete changes affecting in voltage instability have been included to assess the methods performance. Moreover, both process and measurement noises, obtained from real-time hardware-in-the-loop simulation and real PMU measurements from the Norwegian network, respectively, have been applied to validate robustness of the proposed methodology.

A scheme for coordinated secondary voltage control for systems with multiple VAr reserves

This paper presents a voltage control scheme for coordinating reactive power reserves, inspired by the concept of multi-agent system. Similar to an agent, the proposed controller takes on assigned tasks itself and contacts neighbors for support when needed. The control structure incorporates not only controllable VAr sources but also switched capacitor banks, resulting in increased online reactive reserves for critical contingencies. The approach is suitable for areas with penetration of FACTS devices, distributed generation connected to power systems by voltage source converter (VSC), or SVC-HVDC systems. The control structure is simple and very flexible in terms of coordination, implementation and expansion.

Implementation and testing of a real-time mode estimation algorithm using ambient PMU data

This paper presents a software implementation of a real-time power system mode estimator application which uses ambient synchrophasor data. The software is built using Statnetts Synchrophasor Software Development Kit (SDK) as a platform for fast prototyping of real-time synchrophasor applications. The SDK extracts synchrophasor data received in the IEEE C.37.118 protocol and provides them as LabVIEW signals. These signals are preprocessed and mode frequencies and damping ratios are calculated by Yule-Walkers method. The implemented LabVIEW software employs state machine logics which enables modifications and upgrades to the algorithm.