UDW Data Calculations, Post Disturbance Review, UI, and Backup | Part 2

In the previous article, we learned the basic concepts of the utility data warehouse (UDW) data model and related key concepts like data objects, data type objects, and time series data. The process-related data generally originating from a SCADA/EMS/DMS system is collected by using continuous or event sampling methods. The sampled data is further dumped into the UDW storage, where we can perform calculations on them.

 

Data Calculations

The calculations can be performed on the values defined in UDW object types. There are row calculations and column calculations. Here are some examples of calculations for the power system:

• Total production of the generation station.
• Water flows through a hydro turbine when the generator power output is known.
• Power factor when P (active power) and Q (reactive power) are known.
• Maximum, minimum, average, and total production during one day.

The column calculations can be min/max/average/summary/calculations. The values from one object type calculate a result for the same process object and store it in another object type. On the other hand in row/snapshot calculations, calculate results from one or many process objects within the same point of time and store the result in the same object type. An example of a row calculation is to calculate the total generation of the plant.

 

Figure 1. Calculation data for water flow, power factor, and energy production from a hydro facility. Image used courtesy of Adobe Stock

 

Post Disturbance Review Function

Post-disturbance review, also called PDR, allows the users to observe how the monitored process behaves before, during, and after a system disturbance. PDR records status and analog system point data (telemetered, calculated values like power factor, manually entered data, or coming from external systems like SCADA/DCS) over a time that spans a disturbance on the power system. A power system disturbance function is automatically activated upon a pre-defined indication state change or a measurand value limit transgression.

The PDR function consists of three sub-functions:

• Disturbance definition
• Disturbance recording
• Disturbance reviewing

When a disturbance is detected in the power system monitored process the UDW will be so notified by the SCADA/EMS system. An administrator can also manually start a disturbance recording. The disturbance recording function will start to record designated object types included in a data set called PDR, specified in the data engineering.

The recording function will include data for a certain amount of time before the disturbance and continue to record data for a duration after the disturbance, both of these times being configurable.

 

Archiving and Restore Method

The archiving function manages data older than the retention period. This data is removed from the online UDW database and stored as compressed files on the system disk, then the same data residing on the system disk in the form of a compressed file format disk is archived on external media like tapes if desired.

The different strategies can be deployed to archive and restore the SCADA/EMS/DMS data into the system. When data is archived and dropped from the UDW database, it can still be accessible and presented in curves and reports, given that the archive files are stored on a server disk; this approach is called “online archiving.” We can also configure the retention period and how long data will be available for reading from the online archives. When the second retention period expires, the archives are automatically moved for archiving to external media. Archived files stored outside UDW, like on magnetic tapes, can be restored to the UDW server.

 

Data Viewing

While data is online it can be viewed and data viewing can be achieved in different ways:

• The information in the server can be retrieved by using any third-party commercial tools connected to the UDW database. From all clients, information in the UDW server can be retrieved, calculated upon, and printed via commercial applications like browser and spreadsheet tools, and in some cases, with the help of an ODBC driver.
• It is also possible to create an SQL query with tools when creating local reports for the UDW server. As per user requirement, we can export query results to a file (e.g., CSV, Excel).
• Create charts of different kinds, such as pie and bar charts, based on the retrieved data.
• For the SCADA/EMS operators on operator workstations, tabular displays, trend pictures, and process pictures, such as single-line diagrams, are available.
• Users can define the powerful, SQL-based reports and view them on the client PC in the standard web browser, so no installation on the client PC is required.
• Another rich feature is the time select and playback function which enables the operator to perform studies of UDW data in process pictures. The UDW Data can be replayed at a slower, faster, or the same rate as the original recording frequency.

 

Figure 2. The control room of a power plant is the central point for monitoring data and making process corrections in response to calculations. Image used courtesy of Adobe Stock

 

Backup of the UDW Database

The UDW database is backed up to restore the database after a serious failure. Under certain circumstances, for example, in connection with hardware faults, the information stored on the disk memory can be destroyed. The most common failure may be a hard disk failure that cannot be handled by the RAID itself, or if a user accidentally drops a table in the database. To ensure that information is completely recovered, there should be routines for a regular copying of the system, so-called backup copying.

The Oracle export/import facility can back up the UDW database. A best practice is to have a standard backup schedule like a weekly total backup and incremental backups each day as well. The backups are stored on disk and can be copied to off-line media such as tapes and external drives for long-term storage.

 

Overview of UDW

In these two articles, we have covered the significance of the UWD server, a part of the heterogeneous SCADA/EMS/DMS network. The data calculation allows users to create reports by using SQL queries and data visualization in the form of trends and curves. The PDR function is related to reviewing and analyzing data before and after the disturbance in the system for data analysis and troubleshooting.

In short, the calculations and PDR, database backup, and user interface serve as a comprehensive analysis tool for ensuring smooth power plant operations through the collection, harnessing, and actionable use of critical data points.