Wide-area monitoring and control are one of the key aspects of the Smart Grid. Some of the major applications of the phasor measurements units (PMUs) include wide-area monitoring and situational awareness.
Thus, PMUs are becoming an accepted and available technology for improving the prediction of the onset of voltage and transient instabilities.
The past and current efforts have mainly concentrated on the issues related to collecting the PMU data and establishing communication transfers of this data to the utility/ISO control centers, displaying the data, and using it for post mortem forensic evaluations, but not on using the data effectively for predicting steady-state instability in real-time.
ROSE, a real-time analysis tool, addresses the problem of utilizing the PMU data to increase the situation awareness of the operator and improve stability and reliability of the electric grid. ROSE increases situational awareness of the operators by allowing them to accurately and timely predict steady-state instability in real-time environment and avoid blackouts by using phasor quantities collected by PMUs.
ROSE continuously monitors power system conditions by incorporating high rate PMU data into calculation of stability margin and visualization and alarms the operator of the changes in the power system conditions (e.g., whether the system is “moving” closer to the boundary) before the next State Estimator case arrives. This will allow the operator to take timely remedial actions to prevent the system instability.
The Objective of ROSE
The main objective of ROSE is to provide the operator with both fast and accurate solutions in order to more quickly predict and more accurately determine system instability using phasor measurements.
What is ROSE?
ROSE defines the values of phasor measurements for which the system may securely operate. ROSE uses PMU, SCADA and SE data for real-time calculation and visualization of the current operating point and its proximity to the stability boundary.
The following constraints may be simultaneously monitored, enforced and
visualized on the boundary:
- Steady-state stability;
- Voltage constraint (voltage range and pre-to post contingency voltage drop);
- Thermal overloads.
Each point on the boundary corresponds to a “nose” point on the P-V curve or a
thermal or voltage constraint being violated. Operating within this region is secure;
operating outside this region corresponds to unreliable operation of a power system.
Use of PMUs allows us to incorporate the exact values of bus voltage magnitudes and angles. For the buses where PMUs are installed, the actual phasor measurements are used instead of power flow solution. Thus, state measurements, not state estimation, may be used in the ROSE.
The ROSE automatically identifies the limit values based on real-time phasor measurements.
The ROSE also computes and displays the current operating point. The location (e.g., coordinates) of the operating point is computed based on phasor measurements. The relationship between the current operating point and the boundary defines the “health” of the power system network and its proximity to steady-state collapse.
Answers Provided by ROSE
The ROSE provides continuous monitoring of the system conditions in terms of its proximity to voltage collapse, which allows us to alarm the operator before a new State Estimator will arrive.
The ROSE computes indices that can be easily understood and interpreted by the operators in order to increase their situational awareness:
- Time before the system collapse
- MW index (MW margin on the interfaces or at load pockets)
ROSE output includes:
- Visualization of the ROSE and its boundary on the plane of two phase angles;
- Displaying the current operating point inside the boundary;
- Tabular detailed results about limiting violation(s).
ROSE may be displayed on the plane of various system parameters, including:
- Phase angles
- Interface flows
- Power injections
The current operating point is shown inside the region to identify the closeness the boundary (e.g., limit). The closeness of the operating point to the boundary is an indicator of the severity of the system conditions while the shape and the size of the boundary itself are secondary.
For multiple PMU installations, ROSE offers the following solution:
- Identifying two most critical phase angles for each base case and contingency condition, and
- Displaying the current operating condition and the boundary on the plane of the most critical phase angles.
Depending on the computer used, it takes from 3 to 6 sec to construct a boundary for a SE model (the example is given for a 12000-bus SE model). There is no limit on the number of buses in the model, number of PMU installation, contingencies analyzed, etc.