Operation & Maintenance of Power Plants 


Eliminating unexpected cooling tower failures


Condition monitoring systems provide 30 per cent more cooling tower uptime for power stations.


Los sistemas de control de estado proporcionan un 30% más de tiempo de funcionamiento de la torre de refrigeración para las centrales eléctricas.


Mit Systemen für die Zustandsüberwachung kann die Betriebszeit von Kühltürmen in Kraftwerken um bis zu 30 Prozent erhöht werden.


M


edway Power Station in the UK is making significant reductions in downtime due to unexpected failures on the station’s induced draft


cooling tower. In particular, the integrated condition monitoring system is enabling engineers to assess the real-time performance and functionality of twelve large diameter cooling fans, together with associated drive motors and gearboxes, and to implement a long-term predictive maintenance strategy that has improved uptime by over 30 per cent and delivered tangible cost savings from these business critical systems.


690MW capacity Operated by SSE (Scottish and Southern Energy), Medway Power Station is located on the Isle of Grain on the estuary of the River Medway in Kent. Te station uses a combined cycle gas turbine, with a capacity of 690MW that enables it to power around 970,000 homes in the region. Te station has a single cooling tower, with


twelve individual induced draft cooling cells. Each is fitted with a motor-driven 6m diameter fan, with fibreglass blades, mounted in a cowl at the top of the cell, to enable cool ambient air to be drawn in from the base of the cell and across


heated turbine water as it falls through a series of baffles that maximise heat transfer. Te drive motors are located on the outside of the cowls and provide power through gearbox units, which are positioned within the body of each cell.


Extreme conidtions Fans, motors and gearboxes are all subject to extreme conditions. For example, as the site is in an exposed location, high wind speeds and downdrafts can affect fan operation, while the concentration of salt in the atmosphere, combined with dust and particulates from a nearby aggregate plant, cause corrosion and damage to motor and fan units. Similarly, the position of the gearboxes beneath the fan units means that they are continuously exposed to the flow of water as it is blown down each cell. Clive Davies, Control and Instrumentation


Project Engineer, explains, “Te nature of the application means that we have to pay particular attention to regular maintenance, as bearings and seals in drive shafts and fan spindles, in particular, can wear or fail. In the past, worn bearings on the drive end


of gearboxes led to excessive gear wear, reaching the point where gearboxes had to be replaced or removed for overhaul. Tis is an expensive operation, requiring partial dismantling of a cell, using heavy lifting gear.


A similar situation could occur if fan spindle bearings ran out of alignment, as excessive vibration would eventually lead to de-lamination of the fibreglass blades. In each instance, it means taking a cooling cell offline, which can affect our generating capacity and thus our revenue earning potential from the National Grid.”


Fig. 1. Medway Power Station is located on the Isle of Grain on the estuary of the River Medway in Kent.


Temperature monitoring Until recently, engineers at Medway Power Station had used hand-held vibration and temperature monitoring devices to check on the condition of the various systems used in each cooling tower cell. “Although reasonably accurate, this was a time consuming exercise, as motor, gearbox and fan units are difficult to access, and only provided us with historical data; so we only knew about


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