It is highly recommended that turbine OEM's consider thermostatically controlled heater elements for their florescent lighting fixtures as a standard item when considering their lighting systems for use in extreme cold climate applications.
Extreme Cold Climate Emergency Lighting for Wind Turbine Towers/Nacelles
Chris Gilbert | Moltec Windpower Products
Wind turbines find homes in a wide range of climate conditions, and those that find their place in extremely cold environments have very special needs in many aspects of their designs. In the case of tower and nacelle internal lighting systems, such special needs are present. Florescent lighting fixture designs that are typical to these applications provide proper start-up and functionality between -20⁰C and -25⁰C (-4⁰F to -13⁰F) ambient temperatures, however, this low end temperature range falls short of the -40⁰C (-40⁰F) typically specified by various turbine OEM’s for extreme cold climate applications.
The possibilities for compromised functionality of lighting with this low end temperature range performance grows considerably as temperatures sink below -25⁰C (-13⁰F) at which point they can become virtually useless. Performance issues below this temperature range include very slow starting (several minutes), or no light start-up whatsoever. When the lighting is not starting properly, or not functioning at all, significant problems for technicians who are scheduled to perform maintenance or other work inside the turbine structure can be experienced. In this case, arrangements for temporary lighting suitable for the extreme cold climate must be made, which can be quite costly and time consuming.
In extreme cold climate applications, the functionality of these typical light fixtures is further compromised when optional emergency back-up battery systems are employed in the fixtures. The purpose of emergency back-up lighting is to provide short term, minimal lighting in the tower and nacelle to assist personnel as they exit the structure under power outage circumstances. The various battery types that provide power for the emergency back-up function in these fixtures are negatively affected by temperatures below 0⁰ C (32⁰F), just like your car battery, thus expectations for proper performance of the emergency lighting functions could be questionable. When a turbine OEM requires the emergency function in these light fixtures, there is an expectation that they perform properly in the environment for their intended purpose, namely “safety”.
Considering the effect of extremely cold climates on the performance of these typical light fixtures, with and without emergency functions, it is clear that OEM’s should highly consider their requirements and specifications, as compromised performance of the tower and nacelle lighting can, and usually does affect productivity and safety.
There is a very suitable solution for these types of light fixtures for use in extreme cold climates; however they are only available from a few light fixture manufactures serving these wind turbine applications. The solution is a factory installed thermostatically controlled heating element inside the light fixture. Such heating elements are available as a standard option from a few fixture suppliers, some located in North America, such as Moltec Windpower Products. It is required that these fixtures are UL Listed for US applications, and CSA Certified for applications in Canada, and better yet, agency listed specifically for use in wind turbine applications.
The heater element is controlled by a thermostat that is typically set to trigger around 10⁰C (14⁰F), and when triggered, the heater element heats the ballasts and emergency back-up battery packs (if so equipped), to maintain a proper internal temperature of the light fixture for expected functionality down to -40⁰C (-40⁰F).
Optional emergency back-up light functions are becoming a more frequent choice in tower designs for North America, and as previously mentioned, they also need to function properly in extreme cold climates. Interestingly, there currently are no agency requirements for emergency backup lighting systems in tubular wind turbine towers. Typical emergency functions will provide minimal lighting in most back-up equipped fixtures for around 90 minutes, dependent on the life cycle condition of, and available power from the batteries.
Keep in mind that emergency lighting is just that, emergency lighting; the emergency function should not be considered for use as a primary source of lighting, as the lumen output is very low and is unsuitable for these purposes. In the event of a power loss to the tower structure during occupancy, it should be assumed that the general lighting in the tower had already been functioning before an emergency light function was triggered. Since the light fixture was already functioning, it had created a considerable amount of heat within its housing, which is usually enough heat soak to maintain a suitable operating temperature for the ballasts and battery packs that operate this emergency function in the fixture, allowing enough time for personnel to exit the tower structure before the extreme cold climate has an effect on the performance of the emergency function of the light fixture.
It is highly recommended that turbine OEM’s consider thermostatically controlled heater elements for their florescent lighting fixtures as a standard item when considering their lighting systems for use in extreme cold climate applications.
For more information contact: Chris Gilbert, Moltec Windpower Products, firstname.lastname@example.org
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