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New technology to enhance situational awareness for Eskom

ACCURATE MONITORING
Synchronised phasor measurement unit (PMU) technology will enhance monitoring and obervation of the country’s power system
New technology to enhance situational awareness for Eskom
New technology to enhance situational awareness for Eskom

Eskom Power Delivery Engineering division smart grid technologies and operational data chief engineer Reshin Moodley and Eskom System Operator, specialised studies senior engineer Brian Berry explain the advantages of the new PMU technology. Video and video editing: Darlene Creamer

ACCURATE MONITORING Synchronised phasor measurement unit (PMU) technology will enhance monitoring and obervation of the country’s power system

16th May 2014

By: Mia Breytenbach

Creamer Media Deputy Editor: Features

  

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Power delivery currently faces many chal-lenges, including decreasing reserves, an increase in renewable generation and changes in electricity loads – it is, therefore, important that State-owned power utility Eskom manages these challenges by having near-real-time observation of the health of the power system, says Eskom Power Delivery Engineering division smart grid technologies and operational data chief engineer Reshin Moodley.

“To improve Eskom’s power system reliability, as well as operational security during normal and highly stressed operating conditions, the utility has started to implement synchronised phasor measurement unit (PMU) technology at 15 substations across the country,” she says, adding that the project was initiated after several research projects.

A PMU measures electricity waves on a power grid, provides accurate, high-resolution data and monitors important metrics analysis.

The project comprises the installation of a wide-area monitoring system (Wams), comprising PMU modules, and substation phasor data concentrator (SPDC) equipment at key transmission substations across the country, as well as visualisation and stability applications at the national control centre.

Further, Eskom aims to increase coverage of critical nodes or substations in the network to install the system of PMUs at 52 substations in the future.

The budgeted value for the project, which includes the entire Wams, schemes installations, software, hardware, various applications and computer data storage equipment, is about R49-million, Moodley says, noting that the first phase of the project is scheduled for completion in March 2015.

About 60 PMUs will be installed at the first 15 substations, with about three to four PMUs per substation, each monitoring data from up to four live feeders.

The PMUs transmit synchrophasor data, which is time-stamped using a global positioning system (GPS) clock and transmitted to an SPDC. The SPDCs collect the data from up to eight sources, or PMUs, and combine it into a single stream that is trans-mitted to the Wams control centre.

This centre comprises computer and data-storage equipment running the Psymetrix PhasorPoint software, which supports data management applications, phasor measurement visualisation and synchronised measurement appli- cations. This system interfaces with Eskom’s Energy Management System, known as Temse, and the enterprise information system at the national control centre, Moodley explains.

Currently, Temse enables the control shift staff to monitor the electricity network with data comprising an update resolution time of around four seconds, Eskom system operator: specialised studies senior engineer Brian Berry explains.

While a four-second resolution is usually enough time to register changes in the network, such as the current system state, Berry says the PMUs provide controllers with even more accurate, high-resolution data of 50-times-a-second record- ings, which allows for observation of oscillations and other dynamics.

“In addition, the data is time-stamped by the GPS, whereas, in the past, data was time-stamped by clocks that could fall out of synchronicity,” he notes.

Advantages of Wams
Advantages of Wams include an improved state estimation of the power grid, Berry says, explaining that the state estimation provides the initial condition for all on-line applications, such as contingency and stability analysis for the network.

“As the PMUs are a highly accurate and trustworthy source, PMU measurements and data, as well as the measurement of voltage angle difference, allow for algorithm estimation to be improved,” he says.

In addition, Eskom will first run the Wams as a hybrid system, which is a combination of the PMU data, as well as the supervi- sory control and data acquisition (Scada), but the long-term goal is to use a linear state estimator, which uses noniterative, algebraic equations to find the system state, Moodley adds.

If enough PMUs are installed to provide network coverage of about 33%, the linear algorithm for state estimation can run every few seconds, as opposed to running every few minutes, which is what the Temse system currently does, Berry explains.

“However, for the system to be effective, PMUs at about 60 substations would need to contribute PMU data, which is why Eskom is initiating the second phase of the Wams project,” Berry says.

Another advantage of the Wams includes the real-time monitoring of important power system metrics and oscillations, as the system can calculate and monitor voltage magnitude as well as voltage phases, real and reactive power and frequency.

These metrics are important for understanding the stress in the network over a wide area at any time, Berry says, adding that alarms on these metrics enable the power system control staff to control power oscillations and ensure that they dissipate quickly.

Further, Berry says the system provides enhanced postdisturbance event analysis and aids in root-cause analysis during investigations.

“While the current recording systems are prone to missing crucial data because they record only for short periods and the Scada systems use a low resolution, Wams provides continuous time-stamped, high-resolution data over a wide area, which has proven critical for understanding system events,” he says.

In addition, the system enables Eskom to validate its system models with real-time recordings, which improves the simulation accuracy of offline studies, which, in turn, reduces risks to the network, Berry says.

Meanwhile, he cites the system’s improved ability to resynchronise islanded networks, which have split from the main grid. “Eskom is one grid, but the grid can split into networks that become isolated, which have to be resynchronised,” he says, noting that recoupling of the system can pose various challenges.

Nevertheless, when Eskom conducted a black start test using the pilot PMUs in 2012, as part of an emergency exercise, the utility managed to couple the networks on the first attempt, owing to the enhanced visualisation techniques of the Wams.

The Wams also functions as a platform for the development environment, which assists the utility in facilitating simulated exer- cises for its control shift staff, where strange events or disturbances can be observed and understood so that power system control staff can react accordingly and reduce the effect of similar future events, he says.

While Eskom has conducted initial training for field staff at the substations, Moodley adds that when the system is fully deployed, focus will shift to training control shift staff at national control.

Edited by Megan van Wyngaardt
Creamer Media Contributing Editor Online

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