Threshold-Based Monitoring of Multiple Outages With PMU Measurements of Area Angle

Abstract

When power grids are heavily stressed with a bulk power transfer, it is useful to have a fast indication of the increased stress when multiple line outages occur. Reducing the bulk power transfer when the outages are severe could forestall further cascading of the outages. We show that synchrophasor measurements of voltage angles at all the area tie lines can be used to indicate the severity of multiple outages. These synchrophasor measurements are readily combined into an "area angle" that can quickly track the severity of multiple outages after they occur. We present a procedure to define thresholds for the area angle that relate to the maximum power that can be transferred through the area until a line limit is reached. Then in real time we would monitor the area angle and compare it to the thresholds when line outages occur to determine the urgency (or not) of actions to reduce the bulk transfer of power through the area. The procedure also identifies exceptional cases in which separate actions to resolve local power distribution problems are needed. We illustrate the thresholds and monitoring with the area angle across several states of Northwestern USA. Abstract-When power grids are heavily stressed with a bulk power transfer, it is useful to have a fast indication of the increased stress when multiple line outages occur. Reducing the bulk power transfer when the outages are severe could forestall further cascading of the outages. We show that synchrophasor measurements of voltage angles at all the area tie lines can be used to indicate the severity of multiple outages. These synchrophasor measurements are readily combined into an "area angle" that can quickly track the severity of multiple outages after they occur. We present a procedure to define thresholds for the area angle that relate to the maximum power that can be transferred through the area until a line limit is reached. Then in real time we would monitor the area angle and compare it to the thresholds when line outages occur to determine the urgency (or not) of actions to reduce the bulk transfer of power through the area. The procedure also identifies exceptional cases in which separate actions to resolve local power distribution problems are needed. We illustrate the thresholds and monitoring with the area angle across several states of Northwestern USA.

Threshold-based synchrophasor monitoring of multiple outages on a detailed WECC system using area angle

“…However, there are some exceptional cases in which the area angle does not respond inversely to the maximum power transfer. These exceptional cases usually correspond to local power redistribution problems as explained in (10) and further in Chapter 3 of this thesis. Depending on the nature of the lack of response, some of the lines giving exceptional outages need to be independently monitored to improve the accuracy of the interpretation of the area angle changes.…”

“…Previous work uses area angle to define thresholds to monitor stress across the area under various contingencies (10) and showed that area angle is a good indicator of stress. The strategy is to define thresholds based on the line limits in terms of maximum power transfer through the area and convert the maximum power transfer threshold to an equivalent area angle threshold to monitor stress across the area.…”

“…When a line is out, the participation factors for all the remaining lines are calculated with respect to power injections at the border buses. The maximum power that can be injected across the border buses such that line k inside the area reaches its limit is obtained by dividing the limit of that line by its participation factor according to equation (4) in (10). Then the amount of power to be injected into the border buses is the minimum of injections across all the lines.…”

“…Area angles were first developed for the special case of areas called cutset areas that extend all the way across the power system (4; 5; 6). This was generalized to an area with power flow in one principal direction through the area as illustrated in Fig.1.3 and demonstrated with the north-south flow from Canada to California through an area that included Washington and Oregon states (10). There are also AC versions of area angles (3; 15).…”

“…To evaluate the maximum power that can enter the area it is necessary to stress the area with additional power injections (10). These additional power injections can be made at border buses in proportion to the tie line flows entering or leaving at the border buses and in proportion to the net injection at the buses inside the area.…”