Maximum Frequency of Low Frequency Oscillations

Maximum Frequency of Low Frequency Oscillations

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Q: Synchrophasors can capture the low-frequency oscillations lying in the range of 0.1 Hz to 1 Hz. What could be the maximum frequency of these low-frequency oscillations that can be detected with high accuracy using synchrophasor technology?

--P.M. (Germany)

A: Dominant inter-area electromechanical modes (where participating generators can be separated by large geographical distances e.g. British Columbia to Southern California) are a function of the actual power system under consideration (i.e., the strength of the grid and the inertia of the interacting generators). Generally these modes have a frequency lower than 1Hz. From signal progressing theory we know that in order to observe these modes you need to have a sampling rate at a designated processing location (e.g. control center) at least 2 -10 times the frequency of interest, hence with state of the art Wide Area Measuring Systems where a PMU (such as ABB's RES670) samples the real-time Voltage and Currents signals locally at the kHz range, but update the calculated Phasors at centralized processing center at 30Hz, you can observe electromechanical modes up to 15Hz, but with more confidence modes up to 3Hz. Therefore, most inter-area electromechanical modes can be observed using a state of the art WAMS systems.

Here are some references that may be helpful:

  • Korba, P.; Larsson, M., "Wide-area monitoring of electromechanical oscillations in large electric power systems," IEEE Power and Energy Society General Meeting, 22-26 July 2012
  • Turunen, J.; Thambirajah, J.; Larsson, M.; Pal, B.C.; Thornhill, N.F.; Haarla, L.C.; Hung, W.W.; Carter, A.M.; Rauhala, T., "Comparison of Three Electromechanical Oscillation Damping Estimation Methods," IEEE Transactions on Power Systems, vol.26, no.4, pp.2398--2407, Nov. 201

--Ernst Scholtz PhD
Global Program Manager for Grid Automation


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