Alstom: Ethernet for Plant Control System
Alstom's distributed control system uses Modbus and Ethernet Powerlink fieldbuses to address interoperability, speed, determinism, and safety.
Designed for energy applications, the Alstom control system, Alspa ControPlant, requires the highest levels for reliability and availability for industrial applications. Alstom, a provider of energy management, power generation, and rail transport systems, uses Alspa ControPlant as its distributed control system (DCS). The incorporation of Modbus and Ethernet Powerlink into the DCS makes the network a central part of the control system.
Modbus TCP and Ethernet Powerlink function as the fieldbus for the Alspa ControPlant control system. This decision by Alstom required the integration of Powerlink technology characteristics into the control system. The most important of these characteristics is redundancy, which Alstom implemented as a system standard. The redundancy and determinism of Powerlink provides the necessary level of availability for open and closed loop control of the power plant processes.
The site network, mainly located in the control room, has few industrial constraints, and is generally based on a standard Fast Ethernet switched network. A fault tolerant ring topology ensures high availability. Determinism is not needed, as standard Ethernet is used with IP protocol (TCP/IP and UDP/IP). The unit network has a speed of 100 Mbits/s or 1 Gbits/s and is made of fiber or copper.
Field networks and connected equipment are located at the field level and have the highest constraints. High-speed Ethernet meets the needs of new applications for the power market through increased network performance. To achieve this level of performance, Alstom selected two technologies, one without deterministic constraints and one with high real-time determinism requirements. For its non-deterministic field network, Alstom selected Modbus TCP for its openness to third-party devices.
Real-time deterministic field networks allow distributed I/O connections, and a simplified architecture that concentrates regulation processes inside the cell controller and reduces the cost of installation, maintenance, and engineering. Use of real-time and deterministic networks allows for time synchronization and time stamping via the network, eliminating the need for external specific wire to send synchronization information and signal to field controllers.
Reasons for a new architecture
Basing the overall network architecture on Ethernet has several advantages:
Users can standardize network equipment and protocols (TCP & UDP/IP);
Despite increased network costs because of the need for active network devices (switches and hubs), the overall cost is reduced thanks to the decentralized architecture, the standardized equipment and protocols, the reduced cabling (only Ethernet, bus topology) and the network synchronization of devices;
Using standard Ethernet technologies makes it possible to follow Ethernet evolution without additional R&D costs, thanks to Ethernet community R&D investments.
Powerlink, as a software solution based on standard Ethernet components, is compatible with standard Ethernet devices. It allows for use of fiber technology to access equipment up to several kilometers away. Fiber also permits networks to be located in electromagnetically disturbed areas.
The openness of the Ethernet Powerlink Standardization Group (EPSG) allowed Alstom to share expertise on highly available control systems. Alstom contributed to Powerlink's evolution by offering its "High Availability" feature for inclusion in the standard. The High Availability technical working group headed by Alstom introduced those features as an add-on of the existing Powerlink standard, avoided modifying the current Powerlink specification, and maintained compatibility with existing devices.
The High Availability feature of Powerlink has been validated and verified by state-of-the-art model checking. Simulations confirmed calculations and tested system functionality in many scenarios.
Alstom's implementation of a Powerlink network shows the necessary level of network availability to control power plant processes. Critical applications in a power plant must be secured in a way that prevents functional disruptions in case of control hardware failures or cable damage. If one PC with control functions breaks down, a second unit needs to "notice" the malfunction and assume the tasks of the failing unit, preventing risk-entailing delays in operation. Cable redundancy implemented by Alstom allows easy failure detection and localization and avoids data loss, cycle loss, and reconfiguration time.
See more below about Alstom, its Energy Management Business, and Alspa distributed control system.
Related reading: Powerlink specification V.1.1.0 integrates new features; contest for Euro students
Alstom and EMB
Alstom is a global leader in equipment and services for power generation and rail transport. In the field of power generation, Alstom is the world leader in integrated power plants, in power production services and air quality control systems. The company supplies 27% of the global capacity for power generation and covers all energy sources (gas, coal, renewable and nuclear). Alstom Power comprises five businesses: plant, turbo machinery, energy and environment systems, hydro and the new energy management business (EMB). EMB improves the efficiency of energy infrastructures from fuel supply to electricity production and consumption. Complementing Alstom's portfolio, EMB is in line with its clean power and Plant IntegratorTM strategies. Current developments will further strengthen Alstom's position for clean power generation, via the introduction of new technologies to monitor and control air quality in real-time in conventional plants and new clean coal plants that may be equipped with carbon capture and storage. With the development of carbon trading schemes, plant management solutions will require flexible integration with carbon registries and markets.
EMB focuses its expertise on four key areas of technology:
- automation - including -- plant DCS, machine control & instrumentation
- plant management - including plant & dispatch optimisation, asset condition monitoring and simulation
- grid connection & substation engineering - including isolated phased bus ducts
- power electronics - including excitation, automated voltage regulation and reactive power control.
EMB offers turnkey energy management solutions to optimise energy efficiency across the entire energy value chain, such as in the following areas:
- Plant efficiency increased through effective automation and control of the plants as well as new suites of power plant management software applications to manage plant scheduling, plant asset management as well as real-time plant simulation.
- Plant availability increasing plant operational flexibility to provide the proper amount of power at the right time to the grid. This means providing the ability to ramp power up and down several times a day.
- Power quality enabling customers to deliver the desired power quality, whether related to grid frequency (active power) or voltage management (reactive power).
Within EMB, Alstom has designed a complete product line for control systems called Alspa. Alstom's Alspa CONTROPLANT DCS system is dedicated to the power generation market.
The Alspa system consists of a flexible and open distributed architecture and is based on specific hardware components and standard communication networks. Alspa products support core functions for plant operation, and thus benefit from multiple safety and availability features such as self-testing, redundancy in controllers and communications, synchronisation and time stamping to 1 ms, fault tolerance, and continued autonomous operation in the event of the loss of control room equipment. Alspa products can be used for the DCS (thermal, hydro, nuclear, etc.) and for machine control. For machine control, Alspa includes the following controls:
- Alspa Field Controller
- Boiler Control and Protection and burner management system: Controflame
- Steam Turbine Controller: Controsteam
- Gas Turbine Controller: Controgas
- Generator Controller, AVR and Excitation: Automatic Voltage Regulator: dedicated to the excitation regulation of AC generator: Controgen.
The control system is built around three major components:
- the control room HMI with its software and hardware,
- the engineering tool manages a consistent engineering design of the complete power plant including: DCS, machine control and simulator with single point of entry and a unique database.
- perform the control and protection functions and are connected to the process. The multifunction controllers and field controllers offer a number of advantages e.g. reduction of field cabling, tolerance to failures and easy expansion of the system.
All these elements are connected by fast Ethernet networks.
Stephane Potier and Emma Cameron are with Alstom Power, Massy/France.
Tips for a robust industrial Ethernet infrastructure
Environmentally hardened design of communications network cabling, connectivity and active components is key to superior network performance, reliability and uptime, says Brian Shuman, RCDD, product development engineer for Belden.
"One major challenge in implementing an industrial Ethernet is ensuring that the infrastructure is robust enough to withstand harsh and demanding environments," Shuman says, providing advice for building a robust industrial Ethernet infrastructure.
Calculate the real cost of downtime: Analysts report that a large percentage of unplanned downtime in industrial operations is caused by network infrastructure failure. One report said 72% of network faults can be attributed to failure at the OSI (Open Systems Interconnection) Layer 1 (Physical Media), Layer 2 (Data Link) and/or Layer 3 (Network). Physical deterioration or electrical failure in data transmission components can lead to unreliable network performance, safety issues, data loss, system downtime, or failure, costing millions of dollars.
Evaluate environmental risks: Environmental risks may include physical stressors, such as temperature extremes, humidity, moisture, dust/dirt, oil, solvents, and corrosive chemicals. Mechanical and electrical stressors may include vigorous vibration, plant floor vehicles, EMI/RFI interference, and lightning strikes. All can seriously degrade components' physical integrity and result in intermittent outages or shutdown.
Specify industrial-grade components: Commercial off-the-shelf (COTS) Ethernet cables and hardware are not made to withstand conditions in harsh and potentially hazardous industrial settings. Rugged industrial-grade components deliver optimal performance over long service life, typically 10 to 30 years, significantly more than COTS products.
Design for end-to-end integration: Specify infrastructure components from a supplier capable of providing a high-quality, end-to-end Ethernet framework tailored to the application and environmental conditions. Learn more in a Belden white paper at www.belden.com/industrial .
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