Drives and Controls January 2023

28 n VARIABLE-SPEED DRIVES January 2023 www.drivesncontrols.com Unique UK wind tunnel takes off again after refurb T he UK’s largest pressurised wind tunnel has been extensively modernised using a digital control system for its AC and DC fan drive motors and auxiliary systems. Built in the 1970s, the wind tunnel, located in Farnborough and operated by QinetiQ, is used for aerodynamic testing and simulation to optimise the take-off and landing of civil aircraft. The 5m x 4.2m tunnel plays an key role in aircraft design. The £2m upgrade is aimed at cutting downtime and improving the efficiency of the facility, which is the only one of its kind in the UK. It was funded as part of the project led by QinetiQ and Boeing and supported by the UK Government through its ATI (Aerospace Technology Institute) programme. The £800,000 sub-contract to upgrade the tunnel’s main drive control system was won by ABB, which first conducted a feasibility study to determine the electrical and mechanical demands of upgrading the previous system, and ensuring that any alternative would interface with the current layout. The new HMI-based control system not only meets operational requirements but has been designed to enhance the user experience. A key upgrade has been to the main fan drive whose speed is controlled using a traditional method based on an 11MW slip- ring AC induction machine, piggy-backed with a 1.6MW DC machine. The AC motor’s torque is controlled via an hydraulically- actuated liquid rheostat on the rotor. The speed is then regulated using the DC machine. ABB also replaced the motor control centre, DC drive and a 11kV-to-690V transformer. The mechanical and electrical services contractor IME installed the upgrade. The wind tunnel’s previous control system has been replaced by a modern automation system that determines the switching routine for the AC machine as well as trimming the DC machine’s control and avoiding oscillations. It interfaces with an existing safety system and the tunnel control system while improving diagnostics, reliability and flexibility. “Beyond the obvious benefits of installing a current, supportable and reliable system, this project allowed the introduction of an HMI,” explains QinetiQ’s head of electrical for the wind tunnel, Paul Simons. “From the operator's perspective, the new automation system brings a comprehensive view of the plant through a well-constructed user interface for starting, stopping and monitoring the fan, and its auxiliary systems. “Where discrete steps were once required by the operator to start the system, this is now handled by an automatic sequencer that provides feedback on the state of the plant as it transitions through the different phases before starting the fan,” he adds. “The interlocks are managed through a trip and interlock cause-and-effect matrix that quickly informs the user on the state of readiness to start and what has caused a trip condition.” “As a modernisation project, the challenges of such an enormous application were not unexpected,” explains John Dixon, ABB Motion’s UK engineering manager. “For example, the wind tunnel is pressurised and totally replacing the motors was cost- prohibitive as this would have entailed cutting away the tunnel ceiling and nacelle and then welding it back into place. For this reason, the approach was to retain the existing machines, as they were in good condition, and to install a new DC drive, while retaining the liquid rheostat.” Achieving control stability for aerodynamic tests and good response times was a challenge because of the dual motor system and the dynamics of the liquid rheostat. “Attempting to replace the liquid rheostat would have meant having to de- rate the AC machine,” Dixon explains. “However, the facility requires the full motor capacity, plus occasional use of the overload limit, so de-rating was not an option. We therefore needed to retain the basic scheme and look at ways of modernising it.” Because of the wind tunnel’s large speed and pressure operating window, considerable time was spent capturing data to give a performance baseline before the upgrade. Models of most of the system components were built from this data and incorporated into the control system. Since the tunnel was restarted, testing efficiency and reliability have improved. QinetiQ is looking at introducing further improvements such as replacing the liquid rheostat hydraulic actuator with an electric linear actuator, for finer position control, improved stability and better system settling times. n A major upgrade to the control systems and drives on the UK’s largest pressurised wind tunnel has resulted in substantial improvements in flexibility, diagnostics, reliability and user experience. Wind of change: the upgraded wind tunnel is expected to be more reliable and efficient