Competition, cross border trading activities and the increasing complexity of power networks is compounding power system stability issues. As grids get even more heavily loaded by sudden bulk power transfers, systems become very vulnerable and even minor equipment failures can result in cascade tripping and, eventually, blackouts. Real time wide area monitoring of electricity flows is essential in providing early warning of potential network stresses
ABB’s new wide area monitoring system (WAMS) technology uses GPS satellite signals to cost effectively ensure that the phasor measurement units, which monitor the condition of the power grid are synchronised with an accuracy of one millisecond. This enables system dynamics, such as frequency, voltage and power oscillations, to be observed in real time, regardless of the large geographical distances between measurement points and provides valuable early warning of potential network stresses.
PRECISE, SYNCHRONISED MEASUREMENTS
Large power outages are usually the result of multiple system failures that happen within minutes, and sometimes in seconds. The monitoring and control systems of individual utilities gather information from sensors within their own grid, and then evaluate this information to determine whether their system is operating to deliver the power to meet demand conditions. When things go wrong, the system either reacts automatically to take contingency actions, or displays information that allows system operators to take action. Using the component PSGuard, ABB’s wide area monitoring system gathers and analyses system data in milliseconds, compared with every two to five seconds in conventional network control systems.
This means emerging network problems, like shifts in frequency, can be documented and even predicted because precise and synchronised measurements can be taken consistently across the grid. Operators can also detect emerging problems in a neighbouring grid before they build up, allowing them to take preventative action.
WIDE AREA MEASUREMENT SYSTEMS
A typical wide area measurement system or WAMS, is built up on a reliable communication system connecting power stations, network control centres and substations. The GPS satellite system is used for timing accuracy and a number of phasor measurement units are deployed across the power network.
The phasor measurement unit or PMU streams the required real time data through the communication link to the WAMS. In some cases, PMUs could even include local instability protection schemes. To achieve value from the accurate and reliable data streams coming from these PMU devices, ABB has now introduced the PSGuard wide area measurement system.
The PSGuard system is a scaleable solution which can be implemented in stages, paving the way towards automatic wide area measurements by transmission companies. Application functionality packages can be chosen and implemented based on utility needs with the system being built on standard PC hardware and operating systems and having the required security standards built in.
First in Europe
Recognised in 2003 by the Massachusetts Institute of Technology (MIT) in the US as one of the top ten emerging technologies that can change the world, ABB’s WAMS technology became the first commercially operative wide area grid monitoring system in Europe during summer 2004.
Installed by Swiss energy company ETRANS in the critical Swiss north-south transmission corridor, ABB technology is helping keep the power flowing from Switzerland to Italy by faster detection of critical operating conditions.