Data networks in the electric power industry must be very resilient, because they often operate in the presence of strong electromagnetic and electrostatic fields.
Seamless communications from the power station through the transmission grid right down to the substation gives utilities new opportunities to increase their efficiency, flexibility and competitiveness. With the IEC 61850 we now have for the very first time a standard for communication networks and systems in energy generation as it is used in the so-called substations.
In terms of the impact which the new standard will have on the communications infrastructure, interoperability within and between the different parts of the electric power system is clearly the main issue. Communication interfaces, for example, have now been standardised to ensure that automation components supplied by different manufacturers will work together. It is also important that customers can replace or upgrade subsystems without problems.
By choosing Ethernet, the electric power industry benefits from the widespread use of the technology and ongoing development activities. Fast Ethernet (100 Mbit/s) has already become the standard in other industries (factory, process and material handling automation), and Gigabit Ethernet (1000 Mbit/s) is becoming increasingly popular. The higher speed versions are always backwards compatible with previous versions, giving Ethernet the flexibility to accommodate upgrades. High-speed redundancy mechanisms and wireless solutions continue to evolve, creating new applications. Rigorous use of the available security technologies and access protection for the data networks are vital, because communications extend beyond the local site to include data transfer between substations and control centres.
High EMC immunity
What requirements do network components have to meet to guarantee reliable data transmission? Communications between RTUs (remote terminal units), IEDs (intelligent electronic devices) and substation controllers are exposed to extreme electromagnetic and electrostatic fields, and the Ethernet switches have to be designed for that harsh environment.
Ambient conditions can vary significantly, from the standard range of -5°C to +45°C to an extended range of -40°C to +85°C. The Ethernet switches must be built to withstand these temperatures without a fan, because the short service life of mechanical components would otherwise lead to early failure. The availability of the data network is vital, and high-speed redundancy must compensate for the failure of a managed switch.
The Rapid Spanning Tree Protocol (RSTP) is the most familiar method which is used to compensate for network interruptions. However, switchover can take several seconds even in small networks with only 10 devices. To work around this problem, some manufacturers have developed proprietary extensions which are based on this technology and which reduce switchover times.
At first glance, ring switchover times of 5 ms seem to indicate that this approach does actually work. However, switchover time only applies from one switch to another, and every switch must be multiplied by 5 ms. Switchover time increases even further in practical application under load. Moreover, each switch requires elaborate, individual configuration.
High-speed redundant rings
Hirschmann has developed the HIPER Ring to maximise availability. All of the components in the network are connected together to form a ring. A redundancy manager, which is built into every switch, sets a physical link to standby. If a line break occurs, the affected devices send a signal to the manager which activates the stand-by link. Only one switch has to be defined as the redundancy manager to configure the HIPER Ring. Other than allocating the ring port on the other switches, no further configuration is necessary.
With the current version of the technology, the Fast HIPER Ring, switchover on the new MACH 1000 and RSR switches for a complete ring with 10 devices takes place within 10 ms after a fault occurs. The technology supports large rings with up to 200 network components, and switchover times are only slightly longer (<60 ms).
Military standards
Besides redundancy techniques, data network availability also depends on the average time it takes until a failure occurs. This time frame is defined as the mean time between failures (MTBF). There are various ways of determining the MTBF of an Ethernet switch. The most stringent method is based on military standard MIL-HDBK-217F, and this is the method that Hirschmann uses. Our open rail switches have an MTBF >70 years. Should it nevertheless become necessary to replace a switch, it is important that the swap can take place quickly and easily without any special network expertise.
The full set of configuration parameters and the switch software can be saved on an external storage device. Once this data is loaded into a new switch, the switch becomes a fully functional replacement.
Switches with high-voltage protection
The new IEC 61850-compliant MACH 1000 and RSR families of Gigabit Ethernet switches were designed specifically for deployment in power automation applications. They feature outstanding immunity to electrostatic discharge and magnetic fields. The MACH 1000 family switches are designed for installation in a control cabinet, whereas the compact RSR switches can be rail or panel mounted.
Both product families offer a wide choice of port count and transmission media. The operating software includes extensive management, diagnostic and filter functions, and it supports high-speed redundancy mechanisms such as Rapid Spanning Tree and Fast HIPER Ring. Other features include a -40 to +85°C temperature range and redundant power supplies.
Summary
The International standard IEC 61850 creates the engineering framework for deployment of Ethernet to support automation of the power grid. Open architecture and interoperability provide good investment protection. Extremely rugged network devices, which are suitable for use in the electric power industry, are now available. There is no longer any reason not to migrate to the latest technology during substation construction or modernisation projects.
For more information contact Fons de Leeuw, Profitek Industrial Communications, +27 (0)12 664 4998, [email protected], www.profiteksa.com
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