Fast-Track Redeployment of AVON Quad-Pack Improves Island's

THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 345 E. 47th St.. New York, N.Y. 10017 98-GT-455

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Fast-track Redeployment of AVON Quad-pack Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78668/V005T15A031/4219052/v005t15a031-98-gt-455.pdf by guest on 29 September 2021 Improves Island's Backup Power System by 11111111111,J111111111 OR EA Bjorn Blomberg Plant Manager Christer Liljigren Project Power Systems Advisor Vattenfall Generation Services AB Slite Kraftverk, Gotland, Sweden

Ian Jameison Triconex Ltd. High Wycombe, Buckinghamshire, UK

ABSTRACT Moving power generation equipment is a major undertak- ing under the hest of circumstances. This paper documents the project to provide more reliable backup power for the island of Gotland, off the coast ofSweden in the Baltic Sea. All the power for this scenic island is normally supplied by two sub-sea, HVDC cables from the Swedish mainland In the early 1990's, the power company started the planning to redeploy some of their peaking generation assets more effectively on Gotland. Providing the island with more generating capacity and faster recovery in the event of a partial or total loss of the DC tie-line was deemed a worthy en- deavor. Preparations to move the two 60 MW AVON Quad-pack gas turbine-generators were initiated late in 1994. In addition to commencing green-field site construction to receive the units, the company initiated a controls retrofit of the 1970-vintage units with new fault-tolerant combustion and generation automatic voltage regulation control systems to the relocated turbines. The scope and timelinefor this complex, fast-track project are described along with specific challenges. Results versus expectations are also documented

INTRODUCTION AND BACKGROUND A former Viking site, Visby, the largest city on Gotland island in the Baltic Sea (figure 1), was the main center of the Hanseatic League of the Baltic from the 12th to the 14th century. Its 13th-century ramparts and more than 200 ware- houses and trading establishments from that period make it the best preserved fortified commercial city in Northern Europe. The summer population of the island swells with Figure 1. Map of Sweden and Gotland Island (circled).

Presented at the International Gas Turbine & Aeroengine Congress & Exhibition Stockholm, Sweden — June 2-June 5, 1998 '

tourists from 60,000 to more than 400,000. Visby also serves ating Station must source the island's emergency power as an important port city for many tour boat lines, increasing requirements using the existing distribution system radiating significantly the island's power requirements. Another major from Visby. Furthermore, a cement manufacturing company, industry on this island is cement manufacturing, which re- pictured in the background of the figure 2, is perhaps the

quires continuous supplies for the large electrical loads used largest single power user on the island. Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78668/V005T15A031/4219052/v005t15a031-98-gt-455.pdf by guest on 29 September 2021 in the process. While the sub-sea tie-line is extremely reliable and is Since 1950, Vattenfall AB has provided Gotland's power sufficient to handle all but the most extraordinary situations, by way of a sub-sea HVDC power tie-line from the mainland in the early 1990's, the power company's planners sought to of Sweden. Presently, the link is made up of two cables for upgrade the island's backup power generation capability. The redundancy, installed in 1983 and 1986, which are capable of backup system included two 12 MW and two 19MW diesel- supplying 150— 160 MW of power per cable. This DC power engined generators; two oil-fired steam turbine generators of tie-line terminates on Gotland's west coast, just south of 17 and 30 MW capacity; and four 12MW gas turbine genera- Visby. Here the power is inverted to distribution voltages tor sets located around the island. Should any emergency which ultimately provide power to all the parts of the island. situation have developed requiring backup power to be gen- The Visby distribution site is connected to Slite, a town about erated, the oil-fired plant took more than five hours to come 40 km north and east of Visby on the east coast of Gotland, by on-line and the diesel generators required external electrical a 70 KV transmission line. supplies for starting. This left the gas turbines as the only There are two important reasons for the major transmission source of instantaneous electrical power generation, but they line connecting Slite to Visby. The Slite Gas Turbine Gener- could not maintain the island's grid.

Figure 2. Slite Gas Turbine Power Generation Station (and cement plant in background.)

2 PROJECT SCOPE The mechanical and structural design of the foundations The Gotland Island backup power upgrade plan called for and enclosures for the turbine generators and ancillary equip- moving underutilized gas-turbine power generation machin- ment was accomplished by a local construction company. ery from the mainland of Sweden. In 1995, Vattenfall AS Other local contractors performed the electrical systems de- constructed the SI ite Gas Turbine Power Plant to redeploy two sign, drawings and installation, including the high-voltage of these units. The gas turbine-generator units, two 60MW electrical transformers and switchgear. These companies were

Rolls-Royce AVON Quad-Packs, were originally installed at required to meet demanding schedules to ensure the success- Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78668/V005T15A031/4219052/v005t15a031-98-gt-455.pdf by guest on 29 September 2021 the Hallstavik Power Station, north of Stockholm. Each unit ful completion of this project. employed four AVON 1553 liquid-fueled gas generators and a 75 MVAR at IlkV generator. These two new units could New Control System Requirements supply approximately 80% of the island's load demand, or Due to the age of the control system, the Hallstavik units operate as synchronous condensers. The remaining demand became increasingly unreliable and also more difficult to could be supplied by the existing four smaller gas turbine service because of component obsolescence. In addition to generators. A benefit of using peaking gas turbine units such the difficulty of obtaining spare parts and knowledgeable as these is that they can be on-line within three minutes and service personnel, efficiency and environmental consider- generating to the maximum capacity within five minutes. Like ations made a more advanced monitoring and control system most gas-turbine-generators manufactured in the early 1970's, almost a necessity. To improve the efficiency, the latest however, these units were originally supplied with discrete- control methods had to be adopted. Total system availability component electronic and digital circuits along with separate had to exceed 99.9%. Furthermore, if a system could be found electromechanical relay-based sequencers. to do all the control tasks ofboth the turbines and the generator

Figure 3. Inside view of Block 1 gas turbine generator building.

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(usually called automatic voltage regulation), the design could The available control sequence options are: employ a single system and minimize the training and main- • Either end or block start tenance costs. • Start to generate These requirements led to the power company's project • Start to synchronous compensation

team decision to include new "fault-tolerant" digital controls Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78668/V005T15A031/4219052/v005t15a031-98-gt-455.pdf by guest on 29 September 2021 with extensive graphical supervisory human-machine inter- • Black start face (HMI) capabilities in the scope of the Slite Power Station Project. The following I/O list gives a measure of relative size and The decision was also made to proceed with the project on complexity of the system. a "fast-track" basis. The company began in 1994 planning to execute the entire project, from "green field" to operating I/0 Tyne Number units, in under a year. Analog Inputs 96 Thermocouples 64 Pulse Inputs 16 SYSTEM OVERVIEW Analog Outputs 8 Gas Turbine-Generators Digital Inputs 226 Each of the two units installed at Slite are a relatively Digital Outputs 82 unique configuration of aero-derivative gas turbines; four gas Total per system 492 generators, two free turbines and one synchronous generator comprise the 60 MW power block. The gas generators are Fuel Control operated in pairs to drive one or both of the power turbines, The control system's interface to the gas generators is accom- one at either end of the main synchronous generator shaft plished through the direct modulation of servo-valves using (figure 3). analog outputs via PID control loops. The servovalve in turn Such a configuration of turbomachinery brings additional adjusts the swash plate angle in the gas generator-driven fuel requirements for interlocking and controlling various pieces pump to regulate the fuel supplied to the burners. Compressor of machinery together. End-to-end load balancing, for ex- delivery pressures for each gas generator are used as the primary ample, is provided to keep the power input at both ends of the feedback for the thel control loop. generator equal while compressor discharge processor (CDP) balance is used to ensure equal power output from both gas Synchronous Generator Automatic Voltage Regula- generators to prevent unbalanced thrust across the power tion (AVR) turbine wheels. The total output of both generators (both The controls systems include the ability to directly regulate power blocks) must be controlled as well. the voltage output of the generator by modulating the static excitation to control the net rotor excitation current. A patented Digital Turbine-Generator Control Systems algorithm replaces much of the traditional interface equipment. Due to the potential consequences of a control system AVR features that improve the performance of the system are: failure, project personnel decided to employ fault-tolerant, • Soft startup and shutdown two-out-three majority-voting system control systems, de- • Voltage control signed for critical real-time control applications. • VAR or powerfactor control The two control systems installed at the Slite Gas Turbine • Stable PF control at low setting (VARs from MW) Power Station are relatively complex systems. Each is han- Min/max excitation limiting dling the control of auxiliary equipment, start-up/shutdown • sequencing, combuston control for four gas generators, volt- • Rotor/stator temperature limiting age regulation, synchronizing and load control, while commu- • Computation of rotor temp. from field volts & amps nicating essential information to the other power block's • Inverse time over-excitation limiting control system. Each system must be able to start-up (se- • Volts per Hertz (flux) limiting quence) and shutdown either pair gas generators in the block independently. The systems are also designed for "Black • Field overvoltage shutdown Start" operation and are set-up to auto-close the generator • Manual control with bumpless transfer breaker on a dead bus at 94% capacity. • Integration of turbine startup and operating modes with the generator control

Voltage Control Generator Protection This feature is designed to allow paralleling the generator To accomplish this important function, two standalone to the grid.by adjusting the excitation to match the generator protection relays monitoring phase overcurrent and trans- voltage to the grid voltage before paralleling. The voltage former differential protection and a multifunction program- control options available are: Generator Voltage (1 1KV), mable relay were provided. The programmable relay provides Grid Voltage (70 KV), or MVAR Control. time programmable "snap shots" of fault conditions, and

"online" monitoring of both primary and secondary voltage Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78668/V005T15A031/4219052/v005t15a031-98-gt-455.pdf by guest on 29 September 2021 Normal and Emergency Shutdown systems. It also monitors for and protects against the follow- Each control system provides a number of shutdown op- ing conditions: tions including normal (sequential) or emergency shutdown Phase distance of either or both ends simultaneously. A normal shutdown • Overexcitation reduces the speed of the gas generators to idling speed for a • Reverse power "Cool-down" period before interrupting the fuel supply to the gas generators. An emergency shutdown immediately inter- • Loss of field rupts the fuel flow and maybe initiated from within the control • Negative phase sequence logic or by manual action. • Breaker failure • Phase over and under voltage Vibration and condition monitoring • Neutral ground fault The control system incorporates vibration monitoring equipment so that the turbomachinery can be protected from both • Voltage Transformer Fuse failure catastrophic bearing and blade failures or normal system • Over and under frequency degradation. Vibration information is displayed in the F1M1 • Generator phase differential system so that maintenance decisions can be made with complete information.

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153000 Control System i— r - TS3000 Contro System Event-log Printer Workstations Workstation Screen Printer P-7 L. Auto-failover Workstations

-a- Local Control Room Active Hub

Quad Quad Peck mar e Pack Len View Workstation Event-log Printer Central Control Room re"--;

Figure 4. Control system block diagram

5 Electronic Overspeed Trip Each HMI workstation provides "Real-time" information In addition to the normal mechanical overspeed trip system on the equipment status and performance of all the sub- provided with most turbomachinery, the control system uses systems. The supervisory control system also stores historical redundant magnetic speed pickup to sense the various shaft data, performs trending and generates configurable reports to speeds in the unit and provides a precise voted trip signal to facilitate system fault analysis, diagnostic reviews, or operat- the fuel shut-off cocks and the servo dump valves should the ing documentation. The control systems and the two local Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78668/V005T15A031/4219052/v005t15a031-98-gt-455.pdf by guest on 29 September 2021 speed exceed preset limits. HMI workstations are located in the local control room situated between the two turbine buildings (figure 5). All Human Machine Interface (HMI} operations can be performed from either local HMI or the The systems include two TurboView HMI workstations in remote HMI. the local control room that are configured for"auto failover"and a remote LanView supervisory workstation located in the central control room (figure 4).

Figure 5. Turbine generator control systems located in the local control room

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PROJECT SCHEDULE AND INSTALLATION Following is a timeline of some of the major milestones in the project. It is clear that the schedule is quite aggressive for the scope of the project.

First proposal to move turbines 1993

Construction Company Selection 1994 Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78668/V005T15A031/4219052/v005t15a031-98-gt-455.pdf by guest on 29 September 2021 Disassembly of the gas turbine generating units 1994 Development of requirements for control systems 1994 Control system selection 1994 Order placed for control system Dec. 1994 Beginning of construction — ground breaking for installation Ian. 1995 Control system specifications completed Feb. 1995 Move the gas turbine generators to new site and reassemble Apr/Jun 1995 Factory Acceptance Test for control systems Jun 199$ Installation of Block 1 controls and field interface devices commenced 24 Jul. 1995 Installation of Block 2 controls and field interface devices commenced 21 Aug. 1995 First Start for Block 1 01 Sep. 1995 First Start for Block 2 07 Nov 1995 Site Performance Test and Block 1 Turnover 26 Oct. 1995 Site Performance Test and Block 2 Turnover 14 Mar. 1996

One of the most challenging aspects of this project was Once the project team had wrung out the equipment during synchronizing the production and operation of this remote tests at the manufacture's facility, these tests became the island site with the island generating grid. The tuning of the criterion for acceptance at the site. The installation and site response to power demand fluctuations required a realistic set verification test took approximately 5 weeks for each system, of circumstances. Synchronization and tuning had to be per- excluding external delays. formed on an isolated portion of the island. Since the system could never be taken down, training was done by isolating part RESULTS AND CONCLUSIONS of the island and using it as the load. As of this writing, the systems have not failed to respond The schedule required a proven control system to meet the during the quarterly tests. Fortunately, there has been no schedule. While the control system had previously been actual emergency need for power generated by this facility. applied to AVON engines, the control systems had not been The new Slite Gas Turbine Power Station is an asset to the applied to the Quad-pack configuration of AVON engines. people of Gotland. This is demonstrated during a readiness This fact alone required the development of additional verifi- test every 3 months. The project has met its original require- cation steps. Among them was a complete baseline of each ments and should therefore be deemed a successful project. unit's operating profiles — taken before disassembly. ACKNOWLEDGEMENTS Verification and Commissioning The authors wish to acknowledge the support ofthe follow- To facilitate the commissioning of this rather complex ing organizations in the writing of this paper. installation, detailed factory and site acceptance test plans • Vattenfall Generation Services AB for support were developed and approved by the owner and the control • Triconex Corporation -- turbine control system manu- system supplier. A formal procedure of signoff was followed to insure that the machinery was ready for each step of the facturer. The control system chosen to meet this facility's commissioning. The power and the HMI systems were checked requirements is the Triconex TS3 000 Fault-tolerant first so that the graphical display system could be used as Turbomachinery Control System. "eyes and ears" to document each test as it was performed. • SICANSKA Constructors -- mechanical and structural Next the HMI was used to test all the I/O points end to end. design and construction A fter the hardware was completely checked, the software was • AF ELTEKNIK -- the electrical systems design. then tested, followed by full functional testing of each sub- • Emil Lundgren Automation -- electrical contractor. system prior to the initial starts of the gas turbines.