Ethernet meets requirements of deregulated electric industries
Worldwide, electric utility deregulation is expanding and creating demands to integrate, consolidate, and disseminate information quickly and accurately between and within utilities. Recognition of these needs began as early as 1990 when Electric Power Research Institute (EPRI, Palo Alto, Calif.
Worldwide, electric utility deregulation is expanding and creating demands to integrate, consolidate, and disseminate information quickly and accurately between and within utilities. Recognition of these needs began as early as 1990 when Electric Power Research Institute (EPRI, Palo Alto, Calif.) launched the Utility Communication Architecture (UCA) project. Significant progress has been made to identify technologies capable of providing high-speed integration of Intelligent Electronic Devices (IEDs) (See Control Engineering , May 1998, 'HP Vantera Helps Companies with Deregulation,' p.75).
Similar to current Internet solutions, UCA provides a network solution to interconnect data sources (See UCA Application diagram).
Ethernet was chosen by UCA because of its:
Plentiful, low-cost hardware, such as bridges and routers; and
Scalability from 10 and 100 Megabit/sec (Mb/sec), with 1 Gigabit/sec (Gb/sec) becoming available soon.
Early concerns about Ethernet's ability to reliably deliver 'on time' (4 msec) messages were addressed through rigorous testing.
When 10 and 100 Mb/sec Ethernet was tested against 12 Mb/sec Profibus' token passing protocol, results showed either 100 Mb/sec Ethernet on a shared hub, or 10 Mb/sec Ethernet connected via a switched hub could meet the 4 msec 'on time' message delivery; Profibus spent too much time passing the token to meet the 4 msec message delivery requirements.
Testing was also conducted to determine electrical interference on Ethernet cables. In some cases, interference prevented packet transmission and/or caused packet corruption. To avoid electrical influences, UCA recommends using fiber-optic media to connect IEDs engaged in monitoring and protection functions in high-speed, automated substations.
UCA application model is a suite of existing standards assembled to meet
demands for real-time information from electric utilities.
Network, application layers
To allow data access from any device, anywhere, UCA adapted International Organization for Standards (ISO, Geneve, Switzerland) Open Systems Interconnect (OSI) standard and Transport Control Protocol/Internet Protocol (TCP/IP).
OSI's seven-layer model is implemented through standard protocols and does not require a buffer to be full before transmitting the its contents.
TCP/IP's streaming protocol normally waits until a buffer is full before transmitting, but controls are available to manage buffer size and delay times. Additionally, TCP/IP's built in congestion control permits 'dropping' packets when the network is busy-an undesirable feature in real-time delivery applications.
Both network layers support 'broadcast' messaging that allows devices being connected to the network to automatically broadcast their presence, address, and other common IED information.
The application layer is built on the 87 services available in the Manufacturing Messaging Specification (MMS). For now, only four services are used; Get Object Definition, Named Variable List, Unsolicited Event Notification, and File Transfer, but others may be added as requirements are redefined.
Deregulation will place greater demands for information on electric utilities than they have experienced before. EPRI's UCA project has produced a timely, cost-effective, and standardized solution to allow advanced IED functions to form the foundation for 'next generation' electric utility protection, control, and monitoring systems.
Dave Harrold, senior editor, firstname.lastname@example.org