How do you monitor and control power system stability in real-time using PMUs and WAMS?

1 PMUs and WAMS

PMUs, or phasor measurement units, are devices that measure the voltage, current, and frequency of the power system at high resolution and accuracy. They can provide synchronized and time-stamped data from different locations of the grid, enabling a wide-area view of the system dynamics. WAMS, or wide-area measurement systems, are networks of PMUs that collect, transmit, and process the PMU data for various applications, such as state estimation, situational awareness, protection, and control.

2 Stability classification

Power system stability can be classified into different types, depending on the nature and duration of the disturbance, the mode and speed of the system response, and the control actions required. The main types are rotor angle stability, frequency stability, and voltage stability. Rotor angle stability refers to the ability of the generators to remain in synchronism with each other. Frequency stability refers to the ability of the system to maintain a balance between generation and load. Voltage stability refers to the ability of the system to maintain acceptable voltage levels at all buses.

3 Stability monitoring

Stability monitoring is the process of detecting and assessing the power system's stability status in real-time, using PMU and WAMS data. This process can provide early warning signals, identify critical components, and evaluate stability margins. Modal analysis is one method that utilizes PMU data to estimate the system's eigenvalues and eigenvectors, which indicate damping and oscillation modes. Transient stability assessment is another method that uses PMU data to simulate the system's response to a large disturbance, such as a fault or loss of generation. Stability indices are numerical or graphical measures that quantify the stability or instability of the system; for example, angle difference, frequency deviation, voltage magnitude, and reactive power margin.

4 Stability control

Stability control is the process of using PMU and WAMS data to apply corrective or preventive actions in real-time to enhance or restore the stability of the power system. This process can be local or wide-area, depending on the scope and coordination of the control devices. Examples of devices used for stability control include governors, automatic voltage regulators, power system stabilizers, under-frequency relays, under-voltage relays, demand response programs, distance relays, phase-shifting transformers, and flexible AC transmission systems. These devices adjust generator output, modify load demand by shedding or shifting, and change the network configuration by opening or closing circuit breakers in order to balance generation and load, reduce stress or congestion in the transmission lines, and improve rotor angle, frequency, or voltage stability.

5 Benefits and challenges

Using PMUs and WAMS for monitoring and controlling power system stability in real-time has many benefits, such as improving the accuracy and timeliness of system information and analysis, enhancing the situational awareness of operators and planners, increasing the security and reliability of grid operations and protection, and enabling the integration of renewable and distributed resources. However, there are also some challenges to be addressed, such as developing standards and protocols for data communication, managing the large amount of data generated, designing algorithms for stability monitoring and control, and evaluating risks associated with stability events and actions.

6 Here’s what else to consider

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