Look ahead forecasting: the art and science of predicting near term grid reliability trends

Look ahead forecasting: the art and science of predicting near term grid reliability trends

By GE technical writers: power systems & project engineering manager James Moore, power systems engineer Rod Sulte, software build and release engineers Kottamasu Anil Kumar and Jalasutram Trinath, and principal software engineer Annangi Sriker

Power flow analysis is the most critical of all network calculations as it is concerned with the network performance in normal and abnormal operating conditions.

It has a great importance in future expansion planning, as a starting point in stability studies and in determining the best economical operation for existing systems. Power flow results are also very valuable for setting the proper protection devices to ensure system security.

Here, we discuss the PowerOn Reliance approach to running power flows and contingency analysis ahead of time using the forecasted values of load, interchange and generation obtained from various external sources. With this approach, violations related to power flows and each contingency can be determined in advance and planned for accordingly. This results in more effective maintenance of the power grid.

PowerOn reliance look ahead forecasting analysis application Importance

In a power system network, predicting the future state of the system is very much needed in order to prepare for any abnormalities. Power flow analysis and contingency analysis work on the current operating state of the network obtained from the state estimation process, hence these applications can’t be taken as a base for assessing the future state of the network. The look ahead forecast analysis (LAFA) module developed by GE gives a peek into the future state of the network.

Conventionally, the results of contingency analysis such as the number of real and reactive power violations are displayed per contingency for all the contingency cases defined. If users want to compare the effects of a contingency on a particular part of a network with multiple schedules, it takes significant time to navigate between various displays with results related to both time intervals.

The PowerOn Reliance LAFA module application filters and consolidates the data required to undertake analysis on multiple time intervals and contingencies. The user can select any element of interest and see the violations on that element for the selected contingency case and time period users have the flexibility to choose any part of the network, which is of interest, and assess the condition of the selected elements throughout a period of time for a predefined list of contingencies. LAFA allows this to be completed in a single action versus the multiple set up and configuration actions required under a conventional system.

Data initialisation

Inputs for analysis can be obtained from a number of sources already present in the PowerOn Reliance EMS system.

Sources of data

Load Forecast (LF): This module calculates the forecasted load values for the next seven days with a 24-hour resolution. Inputs to this module include historical weather data, historical load data and forecasted weather data.

Interchange Schedules (IS): This module calculates the tie-line exchanges between two different companies with a 24-hour resolution. Schedules are agreed to by both companies.

Unit Commitment (UC): This module calculates the generator operating plan for the next seven days with a 24-hour resolution. Inputs include forecasted load values and the interchange schedules between companies.

Power Flow Schedules (PFS): These schedules are needed for the power flow to run. They typically include generator MWs, load MWs, bus voltages and transformer taps.

Data initialisation priority hierarchy
and methodology

If the system is configured with UC, then the load generating schedules and interchange schedules will be taken from this module.

If not, a check is made to see whether LF and IS are configured. If both are configured, then the load schedules are taken from the LF module, interchange schedules are taken from the IS module, and generation schedules are taken from power flow schedules. If the system has the LF module and no IS module, then the interchange schedules are taken from power flow schedules.

If none of the systems are available, the application takes the required schedules from power flow schedules.

Process

Once data initialisation is complete, power flow is run to simulate a 24-hour period scenario with a minimum of
30 minute resolution. After that, contingency analysis is run with all configured contingencies on the system.

The LAFA application has the capability to divide the processing among multiple processors for faster performance and can be run either manually or periodically at the end of each hour for the subsequent 24 hours.

Results

Results from PowerOn Reliance’s LAFA can be visualised using tabular 3D and 2D graphs. The tabular format displays the number of voltage and branch violations during power flow and contingency analysis.

Users can configure a predefined set of buses and branches to view the results. This allows the user to view the buses/branches in the same graphical positions.

Users can select specific buses to view voltage variations – and branches to see the variation of flows – for next 24 hours in a 3D graph. Users can also select a particular contingency to view how the voltages and branch flows vary due to the contingency. The application is capable of showing how a particular contingency affects the violations for a particular hour.

Conclusion

The PowerOn Reliance LAFA module offers an effective solution to the control centre operator’s challenge of assessing the future state of network. It is a critical tool in detecting the deviations from normal bus voltages and branch flows in a day ahead scenario.

LAFA results are presented in terms of most severe violations and violations on any selected network element. These features enable user/operator to mitigate the most severe violations to protect the network from black outs. A converged solution from the LAFA module can be exported to CIM format, to enable exchange with other utilities or other software modules provided by different vendors.