New England’s Synchrophasor Initiative
- Written by Eugene Litvinov
PMUs with high sampling rates and GPS synchronization represent a critical smart grid technology that can enhance transmission system operations by providing wide-area monitoring of power system dynamic behaviors, an ability that was unavailable until recently. The New England Independent System Operator is two years into a project to expand synchrophasor infrastructure to give system operators a view of what is happening over the region's 3400 kilometers of 345-kilovott transmission lines.
In the great North American blackout of 2003, automatic protection systems fortunately worked well at the interface between New York and New England, so sustained outages in New England were limited to approximately 2,500 megawatts of load in Connecticut, Massachusetts and Vermont. Yet the outage still left 50 million people without power in nine northeastern and midwestern states and one Canadian province. A major contributing factor to the blackout was inadequate situational awareness. As a result, the US-Canada Power System Outage Task Force recommended evaluation and adoption of better real-time tools for operations and use of time-synchronized data in wide-area situational awareness.
In keeping with this recommendation, wide deployment of phasor measurement units (PMUs) got a big boost from the U.S. Department of Energy's Smart Grid Investment Grant (SGIG) program, with funding from the 2009 stimulus bill. With support from SGIG, the Energy Department, the Independent System Operator/New England (ISO-NE) and the region's seven major transmission owners are investing $14.9 million in a Synchrophasor Infrastructure and Data Utilization project. DOE provided a $6.4 million grant to ISO-NE through its SGIG program, while ISO/NW and the transmission owners are contributing the balance.
The major components of the New England synchrophasor project include:
- PMU installations at 40 substations in New England
- Eight Phasor Data Concentrators (PDCs) at the ISO and seven transmission owners
- Communication infrastructure to support streaming PMU data from substations to the owners and then to the ISO
- Alstom's PhasorPoint application for enhanced wide-area monitoring and situational awareness
- V&R Energy System Research's Region of Stability Existence (ROSE) application to compute the operational stability boundary and margin.
The selection of the 40 substations for PMU placement was jointly determined by the ISO and the seven transmission owners. The objective was to ensure complete observability of New England's 345 kV network. The transmission organizations have the freedom to choose PMU vendors as long as they meet the ISO-specified requirements. By the end of June 2012, PMUs had been installed at 28 substations in New England.
The openPDC application developed by the Grid Protection Alliance has been implemented at the ISO and seven transmission organizations. The openPDC receives PMU data at 30 samples per second and performs data synchronization across all the measurements using GPS time stamps to precisely align the signals with one another. Because the PMU technology and standards are still evolving, the open source platform of openPDC offers ISO-NE great flexibility to expand its functionality to meet our needs. For example, ISO-NE is developing a Data Quality Monitoring System based on openPDC to continuously examine all synchrophasor data to determine data quality in terms of availability, timeliness and validity, and record and report in real time relevant statistics and results.
The communication network developed for transmission of PMU data, from the transmission organizations to ISO-NE, supports one-way streaming transfer at full PMU data rate with an architecture based on the network connections supporting Inter-Control Center Communications Protocol (ICCP). Each organization supports a firewall and router combination at its site that is designed to isolate network access to only the phasor data stream coming from its own PDC as well as encrypt communication between sites. And each manages its own connections between substations and its PDC in order to leverage existing investments in network infrastructure and meet obligations for regulated operation of that infrastructure.
The network implemented between transmission organizations and ISO-NE consists of a simple hub-and-spoke topology comprising T1 circuits terminated in an eight-port router. ISO-NE manages the routers at the transmission organization endpoints as well as the central one and establishes the encryption used for the links. While the present implementation is not highly available with single circuits and instances of equipment, the design allows for the future addition of circuits and equipment to support fully redundant operation with failover (like the ICCP links).
The PhasorPoint application is a fully scalable solution for wide-area, real-time data visualization and situational awareness. Acquiring synchrophasor data from the openPDC at the ISO-NE, PhasorPoint provides ISO-NE with the capability to monitor, in real time, a host of critical system parameters including voltage magnitude, phase angles, system frequency, megawatt/megavolt-ampere reactive flows, oscillation stability, islanding identification and resynchronization.
The application can quickly detect real-time events such as a line trip or a loss of generator or load, and then estimate the megawatt amount and location and alert operators of abnormal system conditions. Two unique analysis techniques of PhasorPoint are Power Dynamic Extraction (PDX) and Mode Power Path (MPP). PDX analyzes observable modes of oscillation, mode shape and damping ratio to determine system oscillation stability. MPP tracks the path of the oscillating energy through the network and identifies sources of poorly damped or unstable oscillation so that appropriate remedial actions can be taken.
These state-of-the-art analysis techniques will help system operators manage the dynamics of the interconnected power system and provide a significant improvement in grid operation and reliability. In addition to monitoring the system in real time, the ISO can also access archived wide-area, time-stamped data to improve system planning and analysis, including power system performance baselining, event analysis and model validation.
The ROSE application is a new type of real-line tool for monitoring of the power system security. The main objective of ROSE is providing fast and accurate estimation of the stability boundary and operational margin as the distance from current operating point to the boundary. ROSE continuously recalculates and visualizes stability boundaries by using updated state estimation solutions and the set of credible contingencies. The boundary reflects constraints on steady-state stability, voltage limits and thermal overloads. The current operating state is updated with the rate of PMU data. Stability boundaries and operational margins can be reported in values of PMU coordinates or in traditionally monitored megawatt flows. The tool alerts the operator when the system is moving closer to the boundary and recommends preventive or corrective actions to avoid violation of the system transfer capability or instability.
In summary, the New England's sychrophasor project will build the smart grid technology platform upon which the next generation of monitoring and analysis tools will be developed. The entire New England region is expected to improve reliability through enhanced situational awareness, which will permit faster response to real-time system events, heighten the capability of monitoring system stability, yield more accurate system models and provide new capabilities in system restoration.
As part of the long-term smart grid implementation plan in New England, the sychrophasor project will serve as a foundation for future applications. As the continuation of this, ISO-NE is planning on implementing a PMU-only, real-time state estimator for the 345 kV backbone of New England's transmission system. This can serve as a backup to the current SCADA-based state estimator in the control center.
ISO-NE also plans to implement an on-line dynamic security assessment tool to compute transient stability limits in real-time. The PMU data collected from different real time disturbances will be used to compare with the simulation from the on-line tool. This will help us to validate and fine-tune our dynamic models, thus provide accurate operating limits and ensure reliable system operations. ISO-NE also expects to exchange synchrophasor data with other ISOs and regional transmission organizations (RTOs) so that we can monitor conditions in our neighboring systems as well.