Advanced distributed control for Sual coal fired power plant22 January 1998
For the 1218 MW coal fired power generation plant in the small coastal settlement of Sual in Pangasinan on Luzon in the Philippines, the advanced distributed control system engineered by Cegelec PiC of the UK exploits the full capabilities of the Alspa 8000-P320 system architecture. A fast-track BOT project for which GEC Alsthom won the $1010 million contract to lead a consortium with CEPA Slipform Power Systems, the project is almost a standardized design along similar lines to the Shajiao C plant in China.
Located close to the coastal community of Sual in Pangasinan, the home province of Philippines head of sate President Ramos, the Sual electricity generating station will have two 609 MW high efficiency coal fired units to provide urgently needed power supply in a region in which demand is growing rapidly. The project is almost a standardized design along similar lines to the Shajiao B plant in China for which Cegelec also provided the electrical and C&I design and contracting.
The terrain around Sual presents massive logistics problems. All of the plant and equipment has to be delivered by sea on journeys taking from four to six weeks. This means that the fast track construction schedule, calling for first synchronization of Unit 1 by 15 September 1998, and Unit 2 by 15 December 1998 is a very ambitious undertaking.
To achieve this schedule, it helps to undertake as much as possible of the equipment checking, testing, and certification in the works before delivery. This is as true for the comprehensive state-of-the-art Alspa 8000-P320 plant control DCS as it is for power plant hardware and peripherals. The system is supplied by the PiC (Power Instrumentation and Control) division of Cegelec in Manchester, UK. Cegelec is the systems integrator and general C&I and electrical contractor in the Alcatel Alsthom Group.
A tool for functional testing of the control system equipment before delivery from Manchester to the site in the Philippines, developed by Cegelec under the designation Controtest, is already radically reducing the delivery schedule and augmenting the reliability of the application software configured for the Sual project. Controtest performs an I/O simulation which eliminates the need for hardwiring, greatly speeds up the testing process and proves the functionality of the systems software as configured.
The Sual plant
The customer for Sual, the largest coal fired power plant to be built in the Philippines, is the Pangasinan Electric Corporation. Great progress is now being made on the civil construction works by Sual Slipform Construction Corporation, part of CEPA. The plant layout is fairly conventional.
Boilers: The two huge two pass controlled circulation drum type boilers will each supply BMCR steam flow of 1990 t/h at a pressure of 182 bar(a) and temperature of 541°C, with 1698 t/h of reheat steam at 40 bar(a) and 541°C. The design feedwater temperature is 272°C and the flue gas stack temperature is 127°C. The steam temperatures are controlled over a wide range using water spray for superheat control and tilting burners for the reheat.
A low circulation ratio is used with the rifled water-wall tubes. The furnaces are of the balanced draft type, the high and intermediate temperature superheaters are of the vertical pendant type, the low temperature reheater is of the radiant wall type, and the high temperature reheater is of the vertical pendant type.
There are eight levels of corner firing, low NOx, tilting tangential burners. The coal is pulverized in four type BBD 4366 horizontal ball mills, and two trisector Ljungström air preheaters are used.
Seven stages of feedwater preheating are used – 4 LP and 3 HP – with a spray and tray type deaerator. A direct sea water cooled condenser with titanium tubes is designed to achieve a condenser pressure of 83 mbar with a cooling water temperature of 30°C.
Steam turbine-generators units: For both units 3600 r/min, 22 kV GEC Alsthom three-module steam turbines with three HP/IP stages and two LP stages are used with hydrogen cooled generators rated 771 MVA at a power factor of 0.85.
Instrumentation and control: Logic control, analogue control and data acquisition are all executed within the Cegelec PiC Alspa type 8000-P320 distributed control system. The P320 system is now used to control some 150 GW of energy projects as well as 120 dispatching centres around the world and 50 000 km of transmission lines.
Three major sub-systems, are integrated into the highly flexible, open systems power plant control system architecture:
Centralog: Provides the operator control interface and control room environment.
Controbloc: Links geographically distributed automation cells which execute the control and protection functions of the plant items using state-of-the-art field busses.
Controcad: Provides engineering tools for the design office and on-site documentation
The open systems architecture of the Sual power plant control system is highly dependent on flexible and reliable communications. The distributed elements of the Alspa 8000-P320 system, which is Cegelec's top-of-the-range solution for control and automation in the energy sector, are linked together by standardized networks at each level of the system hierarchy.
At the top level of the hierarchy, the plant network, based on standard IEEE 802.3 Ethernet busses operating on TCP/IP protocol, passes data and commands between the operator workstations and the Centralog data servers. Dual redundancy is used at this level to optimize system availability. The architecture schematic for the control room equipment, common services and FGD automation cells for Sual Units 1 and 2.
At unit network level – F900 – data and operator commands are passed between the automation cells and the control room standards on standard EN50170 WorldFIP busses. This again is a fast, deterministic network with a range of up to 7 km using copper or fibre optic busses in a dual redundancy network. The configuration schematic for Unit 1 (Unit 2 is similar in mirror image).
At the plant level – Locafip – automation cell controllers are linked to their associated smart I/O or instrument resources, also using WorldFIP busses and protocol.
Development of control schemes and operator screen displays using functional blocks, including both automation and supervision data, is achieved by the Controcad. A wide variety of information formats from plant designers is used to develop the application software in this way. Client server organization and communications links allow the number of workstations to the project team structure.
The facility can also be used for automation schemes for plant training simulators.
Operator workstations are based on proven platforms including Unix, Windows, X11. Centralog is both modular and scaleable – operator stations can be added to cater for increased project complexity, expansion or changes in manning levels.
Gateways for communications with other systems and interfaces to existing specialized control packages are becoming increasingly important. Connection to third party systems is facilitated by adherence to international standards and open systems design through out Centralog's Oracle SQL interface, X11 windows, Internet, etc. Interfaces to familiar office software packages such as spreadsheets are also available.
Data archiving, videowall displays, operator screen videocopier, and a wide range of mathematical calculation software applications are all available as additional function packages. For gas turbine power plants, a plant optimization package – Optiplant – uses GEC Alsthom's VEGA standardized power plant design mathematical model for GTCC plants to calculate:Gross turbine heat rate and efficiency Unit gross heat rate and efficiency Steam generator efficiency GT compressor efficiency.
The distribution of the multifunction controllers and field controllers gives Alspa 8000-P320 major advantage over non-fieldbus DCS systems including:Reduced field cabling Tolerance to local failures Unified approach to plant interfacing.
The MFC (multifunction controller) provides the computational power within the automation cells. Each controller is capable of executing any of the available control functions i.e. digital control/sequencing, analogue control, etc.
Each MFC is connected to a number of field controllers which hold the I/O cards that interface to the process and manage local processes. Interfaces are available to integrate HART protocol transmitters, electrical protection relays using IEC 870.5 protocol and intelligent motor controllers.
All of the advanced functions increasingly demanded by station operators, particularly to meet the requirements of economic operation under the strictures of privatization, are catered for including:Redundant controllers with automatic changeover to provide hot standby Redundant communications Continued autonomous operation in the event of loss of control function On-line maintenance including hot card replacement Synchronization and time stamping to 1 ms resolution.
The hot standby redundancy concept used provides immediate back-up without data loss. Both C370 controllers operate in parallel performing cyclical automation functions while being updated through the LocaFip and F900 network.
Both the duty and the standby controllers are synchronized by a dedicated link for periodic updating and consolidation of remnant values to avoid long term discrepancies. Each C370 controller is fully self tested cyclically and automatically becomes the active controller in the event of the loss of the other resulting in bumpless transfer of control.
Testing of software before delivery, and modifications testing is carried out without I/O test cabling using a computer simulator connected on the fieldbus using the Controtest facility.
This is done along with plant response modelling using test software for man-machine interfacing and control functions as a parallel process with delivery of equipment not required for software testing i.e. automation cells, termination bays, CCR desks, CVS and CIS.
As well as saving valuable time on delivery schedule and manpower commitments, this approach reduces site installation and commissioning effort as well as contributing to enhanced reliability.
Management of the power plant is normally exercised using P320 workstations in the control room. The architecture supports two separate Centralog systems, functionally organized so that an operator has access to Unit 1 plus common services equipment and FGD plant through one of the systems, or to Unit 2 plus common services equipment and FGD plant through the other. Interaction by an operator is through the Centralog workstations and is normally conducted by icon/pull-down menu selection using a mouse.
Decentralized installations such as water treatment, coal and ash handling, CW pumphouse are controlled from local panels with minimal status information provided to the DCS via serial links or hardwired connections as appropriate.
The turbine safety and governing system (EHG) is performed by the turbine supplier's dedicated equipment, which is interfaced via hard wired or serial kinks. The automatic turbine run-up system (ATRS) is implemented in the EHG but it is supervised by the DCS. Steam turbine load control and frequency trim are implemented in the Microrec electrohydraulic governor with overall co-ordination and supervision by the P320 system.