Coordinator: Paul Wright

Knowledge of network impedances is essential for power quality (PQ) measurements as they directly affect the propagation of disturbances such as harmonics and flicker. For example, system resonances amplify harmonics whereas shunt capacitances attenuate harmonics. Designs of expensive harmonic mitigation filters can be optimized if the harmonic frequency impedances of the network are known. As the network impedance varies according to the mix of connected loads and generators, it may need to be measured over a prolonged period to obtain its upper and lower bounds. 

Network impedance measurements are inextricably linked to the PQ propagation tools  and the PQ disturbance location tool also developed in this project. Knowledge of the network impedance is also essential for the power flow models that use phasor measurement units (PMUs)  to monitor network stability.  

Network impedance is usually estimated from models, but can be different from theory in a real smart grid with multiple distributed energy sources connected. Actual network impedance measurements are very difficult to make and various methods have been proposed. In the HVDC project, a feasibility study using an on-site digitizer was used to survey the harmonic impedance of a high-voltage (HV) grid, however the results were of limited success due to the approach taken as well as a poor signal to noise ratio. On the other hand, the SmartGrid I project successfully developed fundamental frequency impedance determination techniques using data obtained in a HV grid with two PMUs. The preliminary results achieved in this first study were very promising: not only could the grid impedance be accurately determined but also strong indication was achieved that the data could be used for on-site determination of VT errors.   

To build on the experience and first results achieved in the SmartGrid I project, the fundamental frequency impedance method using multiple PMUs has been refined, evaluated for its accuracy, and further tested using new PMU data obtained in sections of a HV/MV network. The method to the determination of harmonic frequency impedance is extended estimating the phasor at each harmonic frequency.  The feasibility of the method is tested using a laboratory test setup that can generate harmonic frequencies in a model grid. A final test is performed using real grid data acquired in one of the previous on-site campaigns. Finally, a method to determine ratio errors of voltage and current transformers using differential phasor measurements is developed, extending it to harmonic frequencies. 

For more information, see  the project webpage >>