Variable Speed Control of Boiler Feed-Water Pump in the PowerGeneration Industry

Highlights

Improved power plantefficiency

Reduced maintenancecosts

Helsinki EnergyHelsinki Energy is one of theleading experts in the world inthe field of Combined Heat andPower (CHP) technology and oneof the biggest energy companiesproducing and distributingelectricity and district heat inFinland. The energy is mainlygenerated in the company's ownCHP power plants where aremarkable share of the fuel'senergy is used for district heating,instead of condensing it by seawater.In 1990 Helsinki Energy wasgranted the UN InternationalEnvironmental Award for itspioneering and determined workin developing CHP technologyand the consequent improvementof the city's air quality.

DriveIT ACS 1000 medium voltage drives for speed andtorque control of 315 kW 5,000 kW motors

Combined Heat & PowerThe basic indicator for efficiencyand environmental impact ofpower generation is the totalefficiency achieved. The moreeffectively the plant is able toconvert the fuel's thermal energy- either to electricity or to heat -the higher is the efficiency of theplant. Combined heat and powerprovides low cost energy andproduces much less carbon dioxidethan other power plants.

ChallengeAs the loading of a power plantcan vary from minimum load atnight time to peak load duringdaylight working hours, theplant's processes have to beadjusted accordingly. The processes,in the form of liquid or gas flow,

Case Study

Power generationHelsinki Energy, FinlandApplication: Boiler Feed-Water Pump, 4500 kW

A feedwater pump drive train: thegearbox in front, main pump to theright, booster pump behind the2-shaft induction motor.

Two of the four ACS 1000 splittablecabinets installed in the switchboardroom.

Helsinki Energy, Hanasaari B powerplant, located by the seaside in the cityof Helsinki. Its capacity is 220 MW forelectricity and 445 MW for district heating.The power plant's efficiency is 85%.

ABB Switzerland LtdMedium Voltage DrivesCH-5300 Turgi / SwitzerlandTel +41 58 - 589 27 95Fax +41 58 - 589 29 84Email mvdrives@ch.abb.comI-Net www.abb.com /motors&drives 3B

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Helsinki EnergyHelenEngineeringFIN-00090 Helsinki / FinlandTel +358 9 - 617 24 30Fax +358 9 - 617 24 42Email mikko.laakkonen@helsinginenergia.fiI-Net www.helsinginenergia.fi

are typically driven by large electric motorswith the power demand following affinitylaws. There are three main principles to controlthe flow: either throttling it (1), or adjustingthe pump speed by mechanical or electricalslip (2) or directly with a frequency converter (3).Driving the pumps with fixed speed motorsand controlling them at partial loads eitherby throttling or mechanically by fluidcoupling decreases the power plant'sefficiency tremendously.

Originally, the Hanasaari power plant'sequipment was selected among the bestavailable technologies at the time ofconstruction to fulfill the requirements ofhigh availability and efficiency. However,since the time of construction, variablespeed drive technology had taken a bigleap forward. Even though the old ASEAand Strmberg wound-rotor motors with sliprecovery control systems operated very well,Helsinki Energy decided to upgrade them inorder to reduce maintenance work and tofurther improve the plant's efficiency.

Additionally suppliers were challenged bythe limitations of the existing building.

SolutionGiven the efficiency problem of boiler feed-water pumps driven by fixed speed motors atpartial loads, the most economic control isachieved with a variable speed drive system.

In the spring of 1999, Helsinki Energy orderedfrom ABB four water-cooled DriveIT ACS 1000drive systems with AMB 560 motors and oil-immersed 3-winding supply transformers.

The Hanasaari B power plant's automationupgrade project was executed together withHelsinki Energy's HelenEngineering thatspecializes in the design of energy productionand distribution equipment as well as in therelated project management. The aim of thesedesign and construction services is to supportthe profitability of business operations

throughout the life cycle of theequipment.

As it was not possible to haulthe complete frequency convertercabinet with a total length of only4.7m into the building withoutmajor destruction, ABB designedand delivered the ACS 1000 driveswith splittable cabinets that fit intothe elevator.

Benefits

Power plant efficiencyBoiler feed-water pumps are oneof the biggest energy consumersin a power plant. Operating feed-water pumps with variable speeddrives can significantly increasethe efficiency of a power plant.

Outside the boiler feed-waterpump's nominal range, thecapacity needs to be sufficient tohandle rare but possible abnormalsituations in a boiler that operatesunder very high pressure.Depending on the local authorities'requirements, the pump - and thesupplying drive - have to becapable of delivering 10-25 %over pressure or overflow. As aconsequence, the drive operatespractically all the time under partialload, a situation where a variablespeed drive offers the bestavailable efficiency.

Reduced maintenanceUsing ACS 1000 variable speeddrives as level control device offeed-water drums can reducemaintenance of the feed-waterthrottling valves. These haven'tnecessarily been designed for thefull pressure differential resultingfrom throttling the flow with fixedspeed motors.

Further savingsFurther savings can be achievedby designing a new generatingunit's electricity distributionnetwork for feed-water pumpsoperated by frequency converters.As main loads, their across-the-line starting behavior typicallyimpacts on - depending onimpedance of the plant transformer- capital cost, either through amore expensive transformer,through higher fault currents, ora more expensive switchboard.Variable speed drives as such actas soft starters and cause nostarting current peaks.

The DriveIT ACS 1000 can beconnected via the most commonfieldbuses to become an integralpart of the plant's control system.

Key features & benefits

The ACS 1000 medium voltagedrive offers many benefits asstandard, including: highest reliability and availability high efficiency, > 98 % including

sine filter and auxiliaries lowest lifetime costs small footprint and overall

physical size greatest transformer flexibility high performance, through

Direct Torque Control (DTC) retrofit-ready, for fitting to any

standard medium voltagesquirrel cage motor, withoutderating

every drive fully factory-tested two-day on-site commissioning full compliance with international

standards including EN (IEC),CE, IEEE, and the first mediumvoltage drive to be UL Listed.