UK grid outgrows its SCADA

National Grid Company, owned by National Grid Transco plc, the largest investor-owned utility in the UK, runs the power grid in England and Wales, a system that consists of 4500 miles of high-voltage overhead electricity transmission lines, 400 miles of high-voltage electricity transmission underground cable and in excess of 250 substations.

The existing NGC energy management systems was composed of 2 SCADA systems (north and south) and an overseeing system, which managed data relating to power management. By 2003 this system was considered no longer capable of meeting dramatically increasing demands for real time data and control capacity. It was therefore necessary to design and implement a more flexible integrated EMS to meet the evolving requirements of a larger and more complex network. The new system, an integrated EMS supplied by GE Energy, is based on the company’s XA/21 distributed control system and.has been designed to monitor, control, and optimise the operation of NGC’s high voltage transmission grid – in effect it will manage the entire grid. Moreover the new control network, consisting as it does of modular hardware and software, is “evergreen” – it can be upgraded as required without the need for wholesale replacement.

Creating the IEMS

GE Energy started with the XA/21 product and tailored it to meet National Grid’s specific IEMS requirements. The new system was sized to support a database of 1.2 million points, and in excess of 150 dedicated user consoles. It consists of 5 configurations, namely the main active system, the DBU (disaster back up), DDS (database development dystem), PDS (program development system) and DTS (dispatcher training simulator).

The IEMS includes a comprehensive suite of supervisory control and data acquisition (SCADA) and power network applications designated ‘network analysis’, ‘network configuration’, ‘state estimator’, ‘complete model estimator’, ‘contingency analysis’, ‘dispatcher power flow’, ‘equipment outage scheduler’, ‘voltage VAR scheduler’, and ‘remedial & preventive action’. Tailoring the system, says GE, was a truly global activity with NGC and GE teams demonstrating an unprecedented degree of collaboration throughout the project.

Prior to ‘go-live’ the system was run through a series of exhaustive test phases, including a preliminary factory acceptance test, factory acceptance test and a site acceptance test. In the event the IEMS went live on 2-March 2004, followed by a 1000-hour availability ‘soak test’, which was successfully executed.

Upon final system acceptance, a long term customer support agreement took effect. This includes 24x7 support and two full time GE employees working at the National Grid facilities. Long-term plans include upgrading of the system to take into account new trading arrangements due to take effect in 2005.

The XA/21 system

The XA/21 transmission management system is designed to control generation and the associated high voltage transmission network in such a way as to optimise generation and transmission of power. It manages generated power in response to system disturbances, by vigilant monitoring of system conditions against operating limits and by development of corrective and preventative strategies. It is designed to ensure that accurate information is available exactly when needed based on a system architecture drawing from three sources – data acquisition and control, the database, and the graphical user interface.

. It is intended to:

• Minimise the impact of power system problems

• Aid risk management and help avert potential outages

• Enhance operational efficiency by reducing fuel costs and extending equipment life.

Its makers justify their description of it as ‘one of the industry’s most advanced EMS/SCADA systems’ by reference to its advanced open system architecture, with full graphics, power system application, historical information storage and retrieval and relational database technology. It has been around since 1990 and has accumulated over a million hours of, on the whole, reliable operation. What might be regarded as the exception occurred during the August 14 2003 northeast USA blackout, when an XA/21 operated by FirstEnergy was implicated in the causal chain by the NERC, who ordered FirstEnergy to replace it. Eight weeks after the blackout exhaustive tests revealed an obscure candidate bug, a programming error that allowed a data storm to create a condition of silent failure, though ultimately it was not conclusively proved to be a main cause. Nonetheless, GE acknowledged the existence of the bug and promptly issued a patch to all 100-plus XA/21 users.

As a distributed control system XA/21 allows the monitoring, optimising and controlling of the operation of geographically dispersed system components in real time, automatically and manually. It is scaleable from a single node non-redundant system to a widely dispersed network containing dozens of interconnected processing nodes and aquiring data via. The common computing foundation can be configured for specific system functions.

A given system can be entirely interfaced and interconnected. It shows a real time view of the entire electrical network, and can be viewed by operators and management using an array of information management tools. It can analyse alternate operating strategies, corrective and preventive, based on current or postulated system conditions.

BETTA arrangements

To prepare for implementation of the British Electricity Trading and Transmission Arrangements (BETTA), National Grid is in the process of adding the Scottish network to the existing IEMS. To accomplish this, National Grid asked GE to handle a significant portion of the scope including the creation of displays, conversion of database, installation, training and commissioning support for the additions. This resulted in a 40% increase in the amount of data in the system, which was well within the sizing and capabilities of the IEMS. Going live is set for April 2005.