OSIsoft PI System - An integral part of monitoring of the grid: Entergy applies synchronized phasor measurements to grid

By Floyd Galvan

Phasor technology and electric utility Wide-Area Measurement Systems (WAMS) in particular, are revolutionizing the electric utility industry. The OSIsoft PI System is an enabling tool which makes the collection, analytics, visualization and storage of phasor data possible in real-time.

The restructuring of the US electric industry has resulted in the formation of large control and reliability organizations (e.g. ISOs and RTOs). In addition, the competitive market has increased the level of energy transactions in the US and the interconnected, region-wide system. These developments have introduced greater uncertainty into real-time grid operations, along with increased congestion costs on the grid. Recently commitments by State legislatures have led to increased levels of renewable solar and wind energy commitments, further stressing an aging grid. In response, phasor technology has become a key component to manage and understand the effects of renewable energy and system events on the real-time grid.  Entergy is one of the industry leaders in phasor technology.

The Entergy Phasor system began in response to the 2003 New York blackout – the largest blackout in the US history.  Today, the system consists of 21 phasor measurement sites on the Entergy system which have been used to prototype various wide-area research initiatives, including wide-area visualization tools and post disturbance analysis.  The Entergy PMUs are connected via an OSIsoft PI system acting as both the Phasor Data Collector (PDC) and the data historian. The PMUs have proven to be accurate, low cost, and capable of providing a wide range of other power quality measurements. The outputs are in standard IEEE C37.118 synchro-phasor format. Data from all PMUs is sent to the OSIsoft PI System at the rate of 30Hz with approximately 80 signals being included. As noted by George Bartlett, Director of Entergy Transmission, “the PMUs that Entergy has installed to date have had tremendous value for both Entergy and the industry.”  These wide-area instruments are an important part of Entergy’s technological advance into the Smart Grid.

OSIsoft’s PI System acts as Entergy’s Phasor Data Collector (PDC) and retrieves the PMU data for Entergy’s system and for PMUs external to Entergy’s system.  Over 80 PMUs are reporting data to the PDC.  The data is used to monitor critical parameters associated with power system reliability: (1) frequency, voltage, real and reactive power; and (2) synchronized absolute and relative phase angle for all three phases of power flow and for the three sequence measurements for voltage, current, real and reactive power.  These measurements are GPS time-synchronized (to within one microsecond) and provide accurate, simultaneous, synchronized data of events occurring across the grid.

The PI System performs real-time advanced analytics on the phasor data being collected including: real-time frequency, frequency spike calculations, real-time FFT-Fast Fourier Transform, early alarming on instability or oscillation, un-wrapped relative angle calculations, real-time phase angle differences across the grid as well as, energy balance calculations. The PI System includes automatic alarm and notification software indicating both voltage and small signal instability.

Presently Entergy’s 21 PMUs are located in four states: Louisiana, Mississippi, Arkansas, and East Texas. These PMUs are placed throughout Entergy’s 500KV, 230KV, 138KV/115KV systems.  They continually monitor the Entergy grid and provide real time data to authorized users.  These users have access to OSIsoft client tools such as PI ProcessBook and PI DataLink, as well as, over 12 Tera-bytes (4 years) of historical Entergy and Eastern Interconnect PMU data for instant on-line access and analysis.

Entergy’s service territory includes the central Gulf of Mexico coastal region which is prone to the destructive nature of hurricanes.  Recently, Hurricanes Katrina (2005) and Gustav (2008), which caused outages to about one million customers individually, prompted the need for improved system understanding during periods of emergency operations. A clear example of this was the Islanding event caused during Hurricane Gustav.  On September 1, 2008, as Hurricane Gustav made its way across the Entergy grid, the Entergy Phasor System alarmed that a portion of the Entergy system had electrically islanded and separated from the Eastern Interconnect. The Entergy Phasor system made it possible for Entergy to successfully detect, monitor, and manage the island during the 33 hours the island was in place, and to successfully restore the island to the Eastern Interconnect without loss of load or generation.

The existing Entergy PMU system has become an important source for event information used by system planners, system operators and utilities throughout the Eastern Interconnect.  Of the 80 active PMUs in the Eastern Interconnect, Entergy’s PMU system represents roughly one third (1/3) of those PMUs.  As such, the significance of the Entergy Phasor system and its effects on the phasor information being shared throughout the Eastern Interconnect is profound. 

Gustav Island Reconnected 33 hours after Island formation – Picture depicts Entergy staff  manually reconnecting the island to the Eastern Interconnect on September 2, 2008.

 

 

 

 

 

The existing system, however, is still at a research stage and much more is needed to evolve the system to a reliable, robust, and intelligent wide-area monitoring system.  As such, in August 2009, Entergy submitted a proposal to the Department of Energy’s (DOE) Smart Grid Investment Grant (SGIG) program to upgrade its existing PMU system.  Entergy’s proposal outlined steps to harden the existing Entergy PMU System by:
•    Add PMU redundancy at PMU substations
•     Incorporating substation computers to record data during loss of communications and provide analytical and device management capabilities
•    Double the number of PMUs on Entergy system
•    Upgrade PMU computer infrastructure
•    Ugrade existing PMU visualization tools
•    New analytics for system monitoring
•    Changes to the State Estimator by incorporating Phasor Measurements
•    Provide extensive education to staff

In October 2009, Entergy was notified that it had been awarded a 50% grant by the DOE for its proposed PMU hardening project. The project is scheduled to begin in mid-2010 and last for 36 months. 

Conclusions

The WAMS implementation has enabled Entergy to build a strong foundation in scalability and grid measurement for wide area monitoring. This synchronized phasor measurement system is the most innovative measurement system the industry has experienced in the last 40 years and will continue to lead the industry as the system grows and matures in the years to come.

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Biography

Mr. Galvan is a licensed professional engineer in the state of Texas and the Lead Project Manager for Research & Development at Entergy Corp. His areas of specialization include wide-area monitoring and control, grid visualization, applications of phasor measurements, long-term planning and regional energy pricing.  He has held leadership positions within the North American SyncroPhasor Initiative (NASPI), the National Institute of Standards and Technology (NIST) Domain Expert Working Group for T&D Smart Grid Implementation, the Power Systems Engineering Research Center (PSERC) and the CEATI Power System and Operations committee.