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News

Video smoke detection in challenging power station environments

D-tec Video Smoke Detection Systems : 01 June, 2009  (Application Story)
With steam and dust being potential false alarm triggers in conventional fire detection, Irish power stations have now moved to video smoke detection from D-Tec for higher levels of reliability
Video smoke detection in challenging power station environments
Increasingly, CCTV-based Video Smoke Detection (VSD) from D-Tec - part of AD Group - is being relied upon in today's power stations - including most notably seven operated by the Irish Republic's main generating company ESB - to keep a watchful eye on all important turbine halls, where the potential for disruption not only to a power station itself but to the electricity consumers it serves is tremendous.

Video Smoke Detection, because of its careful analysis of CCTV images, is ideally suited to this sort of voluminous, potentially, dusty environment. By contrast conventional smoke detection systems struggle in this type of situation, delivering a relatively slow speed of detection. Crucially, VSD using CCTV cameras as the means of detection is able to recognise genuine smoke patterns - something previously confused in power stations with dust and steam - and distinguish them from other vapours.

So how does VSD actually work? In practice, this approach to fire detection utilises standard CCTV images in real-time that can then be analysed by specialised image processing software. This seeks out the particular pattern that smoke produces by applying extensive detection and known false alarm algorithms.

By programming the software to look for anticipated motion patterns of smoke over a specified area, typically the turbines in a power station, within a camera image and looking for pixel changes, CCTV-based VSD has the potential to deliver an exceptionally fast response - typically in seconds. Crucially, once smoke has been detected the system can alert the operator as well as delivering a visual representation of the smoke on the system's monitor.

This ability to effectively detect smoke at source, unlike more traditional methods, means that VSD does not have to rely on the proximity of smoke to a detector and is therefore unaffected by distance. Whether the camera is situated 10 metres or 100 metres from a risk area, VSD has the capacity to detect smoke in the same amount of time, providing an early warning that would be impossible with conventional detection as it is not waiting for the smoke to reach the camera.

When it comes to the experience of an actual end user of Video Smoke Detection, the Republic of Ireland's Electricity Supply Board (ESB) is a logical place to start to appreciate the real impact which VSD is having on the ground.

The power generator - which is 95% government owned - has been close to this technology for nearly a decade now and boasts what is reckoned to be, the largest installed base of power stations covered by Video Smoke Detection anywhere in the world.

Currently there are seven ESB stations monitored by Video Smoke Detection. These include: Aghada (gas), Ardnacrusha (hydro), Marina (gas), Moneypoint (coal), Northwall (oil/gas), Poolbeg (oil/gas) and Dublin Bay (part ESB owned). Over the years two additional stations have featured VSD, namely Great Island - which saw the very first deployment of the technology by ESB back in 2000 - now used by another Power Utility - and Tarbert which also changed hands recently.

Kevin Grace from Safety Services at ESB Power Generation takes up the story of how the power generator has now come to depend on the protection afforded by VSD: "With regards to Video Smoke Detection, the first power station to actually have the system installed was Great Island in Wexford back in 2000.

Originally VSD, from D-Tec, was specified because of a requirement to protect the very large space of the turbine hall. The reality was then, and still is today, that conventional detectors simply don't have the speed of detection in this type of voluminous environment should there be an incident. With beam detectors near the roof, for example, we could be talking several minutes before anything actually happens - far from ideal."

Before turning to Video Smoke Detection, according to Kevin, Safety Services at ESB looked carefully at a number of other options: "Prior to 2000 Safety Services tried out, what was then one of the latest techniques, specifically, high sensitivity smoke detectors which were being promoted at the time as being able to cope with dirty environments typical of power stations. However in the case of ESB they simply did not work. This was due in part to the high propensity for smoke to diffuse in what are extensive, high roofed, turbine halls."

Having been unable to achieve the necessary performance, the next step for the Safety Services team was to consider more radical solutions such as CCTV-based Video Smoke Detection (VSD). This was seen as being at the forefront of technology at the time but also being very new, something of an unknown quantity. The upshot of this was extensive testing as proof of concept, before ESB would commit to any firm decision.

Said Kevin Grace: "At the request of Safety Services, in conjunction with D-Tec, an intensive test project was established at Wexford's Great Island power station. This necessitated smoke pellets being set off in the turbine area of the station to carefully simulate the effects of a fire. After the VSD system had settled in and been configured, and reconfigured, it was possible to achieve a detection rate in line with the time parameters Safety Services were looking for i.e. within a minute. The test was considered a great success and led ultimately to the roll-out of VSD across our thermal stations from 2000 onwards."

Typically, in ESB power stations, the VSD system is used in conjunction with standard B&W CCTV cameras all of which have hoods in place to help keep them clean of the dirt and grime which can build up.

Commented Kevin: "Normally when it comes to the optimum layout of the CCTV cameras they are positioned quite high up, with D-Tec's engineers ensuring that they are at the right angle as part of the commissioning process. As our power stations have anywhere from one to three turbines the number of cameras required will vary from site to site. The rule of thumb is two cameras per turbine, with each being used to focus on a specific half of the turbine concerned."

The initial phase of ESB's deployment of Video Smoke Detection was confined to thermal stations, specifically oil, gas, and coal, with a hydro plant only coming on stream much later in the process.

Said Kevin: "The real challenge for any fire prevention or detection measure is the environment into which it is placed. In our case a key defining factor is the type of station, as, from experience we feel that the risks are much greater for thermal powered stations, compared to hydro plants, where seal oil or control oil leaking onto very hot pipes - which can be above the auto ignition temperature of the oil - may heat-up, smoulder and ultimately start a fire. It was natural for oil, gas and coal station to be the focus at the inception of the programme and critical that the VSD solution would be able to pick-up early signs of smoke before the stage of potential ignition. By contrast hydro stations do not contain the hot surfaces of thermal plant required to ignite oil. A risk of fire still exists however and we did put VSD into one of our hydro stations - Ardnacrusha - and are currently investigating the possibility of expanding this to the remaining hydro stations."

For ESB the whole commissioning process has been critical to optimise the performance of the system in each station.

Commented Kevin: "Basically the system has to learn by building up a background reference image over time. Station-by-station, D-Tec worked with us over a few months, testing and refining the system parameters to increase sensitivity and avoid false alarms. They also come back periodically for fine tuning - typically every six months.

"Certainly from my perspective a key benefit with Video Smoke Detection is the immediate visual indication of what is happening when the alarm and associated image - with the area of interest highlighted - is displayed in the control room. During testing it is always instructive to watch as the system tracks smoke through the turbine hall, and the display highlights specific areas.

"One minor issue we have encountered is on turbine start-up as this tends to send a large amount of steam up to the roof, creating a pattern which is almost indistinguishable from smoke. Initially this was causing the VSD to alarm unnecessarily but was soon solved by D-Tec providing a pause button to press on start-up, briefly taking the VSD off-line. Other than this minor niggle the system has been extremely effective. In fact we have found that it tends to grow in accuracy over time as it gathers more data to compare with the site reference images it holds. There is also the potential to carefully balance the sensitivity of the system with the need to avoid false alarms. In power stations the system's algorithms must detect smoke for a defined period of time before an alarm will be sounded. This allows greater certainty over the result, in terms of whether it is or isn't smoke.

Commented Kevin Grace: "Overall we have been very pleased with the performance of D-Tec's Video Smoke Detection. There is the reassurance that incidents will be flagged-up, at the earliest possible stage, so preventative action can be taken. In addition to the obvious potential for injury to personnel or the loss of life, the possibility of a facility going off-line, unexpectedly, is a real nightmare scenario for any generator.

"However, the greatest fear of all is undoubtedly a major fire which could literally take away capacity for months or even years. Thankfully with VSD we are now well placed to stop this becoming a reality."

Looking ahead, D-Tec expects more and more operators to follow the example set in the Republic of Ireland by the Electricity Supply Board (ESB). Already we are seeing Video Smoke Detection (VSD) being used to protect the main turbine hall of the Kendall Power Station in South Africa - thought to be the world's biggest coal-fired station. Even more recently the latest VSD system - FireVu - was selected to monitor the turbines in two Portuguese cogeneration power plants through D-Tec's partner in the region, Technicon. In this case, one of the turbines, which required monitoring, was in a chemical plant complex and two other turbines had been installed in a paper waste plant. As well as developing power for their own needs the plants supplied much needed additional capacity to the main grid.

Said Ian Moore, D-Tec's Managing Director: "The evidence from South Africa and Portugal backs-up the Irish experience, with comparative testing in the cogeneration plants again showing that VSD offers a much faster level of detection. In fact in 75% of cases smoke was detected in less than 10 seconds, this is in stark contrast to conventional detection methods where this soared to 360 seconds to reach a similar percentage. By comparing the received images against reference images of a normal turbine hall operating environment VSD is best placed to spot irregularities, the instant they occur, rather than having to wait for smoke to actually reach detectors

"There is little doubt, that the effectiveness and ease of installation of VSD makes a compelling case for adopting this technology where, as ESB's testing programme amply demonstrated, conventional approaches are simply not going to provide the early warning necessary to minimise the very real risks associated with fire in power stations worldwide. It is important, at this juncture, to stress that VSD is distinct from other camera-based detection systems which are in reality motion detectors or obscuration-change detectors that are unable to differentiate between smoke and other sources of movement and are as such liable to generate a high level of false alarms."

For the future, the integration of VSD with an IP (Internet Protocol) based capability - such as in D-Tec's FireVu system - opens up the potential for the information and images it provides to be distributed to a number of viewing platforms for review or feed back from multiple power stations to one single ontrol room. The increased flexibility delivered by networking VSD is certainly something which D-Tec feels many power generators will want to build into their future fire detection programmes.
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