Zurich Airport, operated by Flughafen Zürich AG, is heated by its own combined heat and power (CHP) plant. During a retrofit, at the end of 2009, the drive system for the boiler systems received a complete upgrade with modular variable speed drives from Control Techniques being selected as the drives of choice. Since that time, the new modular Unidrive SPM drives have been delivering optimum control of motors and pumps, giving greatly enhanced energy efficiency as well as 100% failsafe protection.

Every year, around 22 million passengers pass through Zurich Airport, with the airport handling more than 250,000 flights.  Every passenger and every member of staff – at the check-in desks, in one of the many workshops or in the control tower – needs to have a comfortable heated interior space, especially in winter. 

To keep everything running efficiently, the airport produces the heat it requires in its own combined heating and power plant. 

The airport operator, Flughafen Zürich AG, is the outcome of a merger back in the year 2000 of the former operator, FIG (Flughafen-Immobiliengesellschaft) and the airport directorate team.  The Energieversorgung (Power Supply) department, employing 30 people engaged in the operation and maintenance of the gas/oil power plant, is staffed primarily by control room operators (operations and heating), and by electrical and mechanical engineering specialists.  With a total of four gas and oil-fired boilers, this plant supplies heat and power to the entire airport complex, i.e. the terminals, office and hangar buildings.  To be specific, that means delivering 120 MW of heat, plus process steam for the catering and plating workshops, as well as every winter, an additional 10 MW of combined heat and power! The distribution network for the hot steam pipes, operated at a pressure of 12 bar, is 22km in length, of which eight kilometres are routed through ducting with pedestrian access.

In mid-2009, this 1980’s CHP power plant, that has both winter and a summer sections, underwent large-scale conversion.  Hans Peter Schröder, the man in charge of electrical maintenance in the Power Supply department recounts what it was that prompted this maintenance project: “The frequency inverter drives on the winter section were approaching the end of their service life.  Moreover, it was no longer possible to purchase spare parts. Quite simply, the technology and efficiency rating were no longer up to modern technical standards any more.  That’s why, back in 2009, we decided to replace the frequency inverters in the winter system.  This involved boilers 5 and 6 (each delivering 40 MW of power at a steam temperature of 485°C and at a pressure of less than 80 bar) – and we put the work out to competitive tender.  Needless to say, price was, of course, a major factor, but we also defined key technical aspects as criteria in our decision-making process prior to choosing the successful bid.  Particularly important criteria for us were the modular design of the frequency inverters and the simplified spare parts inventory associated with that. Control Techniques AG most closely matched our invitation to tender criteria."

“Two years before, we had first established contact with Control Techniques AG at the Go trade fair in Basle. This successful collaboration emerged from that first meeting.  In total, ten combined frequency inverter and switching units were replaced. These were designed for drives rated between 55 and 420 kW. Amongst other things, the two redundant 315 kW feed-water pumps are also controlled. These are tasked with pumping water into the heating boilers at a pressure of 120 bar, with each boiler already being at a pressure of 80 bar. The power grading scale for the various different motors was streamlined neatly to enable spare parts inventory for the two module types SPMC 2402 and SPMD 1424 to cover all potential requirements.”

The units that make up the Unidrive SPM range can be used to implement most types of system. The separation of the power circuit into rectifier and drive stages enables elegant and compact active input configurations to be implemented.  The modular nature of the power circuit allows drive systems to be constructed in non-standard enclosures. 

The range is part of the Unidrive SP ‘solutions platform’ AC variable speed drive range that spans 0.75kW right up to 1.9 MW.  It is configurable into five operating modes – open and closed loop, vector, servo and regenerating modes – and a wide range of feedback, networking and programming functions can be added with plug-in modules.

When it proved possible, back in April 2009, to shut down the winter section of the plant, demolition work commenced on the old plant.  In summer 2009, Control Techniques AG single-handedly took charge of the entire delivery and assembly of the frequency inverter plant.  Fredy Erb, the project manager responsible, comments: “In this time window, we installed switch cabinets on site, and at the end of the day, this formed the interface for connecting up the entire plant. Our assignment ended with the initial start-up of the plant, and a training course for operating and maintenance staff; everything ran very smoothly.”

 As well as the modular design, another important consideration was the geographical distance from the supplier to give confidence in support and spares – and, of course, peace of mind.  The two programmable controller modules employed (SPMC 2402 and SPMD 1424), which lend themselves to a very good and efficient cabinet design, assure very high levels of plant availability.  This also means that individual modules can be operated at partial load.  To cool the cabinet, the existing ventilation system was used in an ingenious manner, further enhancing the efficiency rating of the system. “The particularly important drives in the plant were implemented using a special kind of ‘bypass solution’: this makes it possible, in the event of some technical failure arising on the feedback-controlled frequency inverter section, immediately to switch over to a ‘bypass’ circuit that can accelerate the drives back up to speed using a ‘soft-starter’ solution (controlled by the Digistart IS family)”, explains Mr. Erb. 

Connection to the programmable controller and process control system is a conventional format with digital and analogue signals, as stipulated in the specification document issued by Flughafen Zürich AG: activation, nominal value specification for compliance with feedback control parameters, speed control, general faults, remote resets etc. – for this, all information is collected, processed and monitored right around the clock.  A retrofit option has already been implemented, using plug-in modules within the drives, for connecting them to a PROFIBUS system making this improvement a relatively simple matter.

All in all, this project ran very successfully for both sides.  Hans Peter Schröder summarised this positive experience:  “We now evaluate energy efficiency on a number of established criteria and have confirmed that there is a substantial improvement over the previous system. The entire project ran very smoothly and quickly.  Installation and collaboration with the installation staff all went really well and the full set of circuit diagrams arrived on site very promptly indeed.  Everything runs superbly!”

Evidence of customer satisfaction is demonstrated by the fact that Flughafen Zürich AG has already placed its next order.

As well as giving improved energy efficiency, the modular design has demonstrated benefits of increased reliability and safety, giving robust operation and zero downtime.  The flexible performance of the plant has simplified operation and the provision for future connectivity using Profibus is already in place. The new drive system allows both on-site operation and remote control when required, whilst its design is compact and space-saving.