Up Time Magazine - February/March 2009 - (Page 58) turbine monitoring systems. Centralized or De-Centralized — The monitoring system must not only acquire data when the turbine is operating within pre-defined bands, but it must compare the data to alarm limits and take the appropriate action. There are at least two approaches: perform all of these operations within the system that is installed in the nacelle and communicate directly with a central monitoring service, or install a more sophisticated system centrally within the wind park and use it to communicate with both the wind turbine monitoring systems, and with the central monitoring service. Many wind farms have a wired or wireless network, and the monitoring system may be allowed to tap into that network. The Effectiveness of Alarm Checking Software — Many vibration analysts running ‘normal’ vibration monitoring programs do not have an effective set of alarm limits set up for their machines which allows them to run an exception report that provides useful, actionable information. The solution is to manually analyze each and every measurement. This is not possible when performing on-line monitoring. It is therefore very important that the alarm Figure 11 - One critical decision in determining the success of monitoring wind farms is the number of sensors to place. cussed the issue related to varying speed and load, but let’s take a look at some of the other challenges: The Number of Monitoring Points — One of the most critical decisions is selecting the number of sensors that should be installed on the gearbox, generator and bearings, and selecting their location. Every sensor costs money, and it requires another channel in the monitoring system. And when you multiply these additional costs with the number of wind turbines (see Figure 11), you can see that it is a very sensitive issue. As with all vibration monitoring applications, it is essential that the monitoring system can at least acquire enough data to warn when the vibration levels are increasing – even if there is not enough data to actually diagnose the problem remotely. But, as discussed previously, when monitoring large planetary gearboxes, the spectral data can be very complex. Knowing the failure modes of the turbine can help immeasurably. If you know which gears and bearings are most likely to fail, then you can position the accelerometers accordingly. The Central Monitoring Service — The “central monitoring service” is the group of people who will respond to the alarms, analyze the data and make final recommendations. It is essential that this group has access to the required data and has the experience to make recommendations. Obviously a communication link must be established with the wind CMS CMS Figure 12 – Centralized vs. De-Centralized communication pattern with the Central Monitoring Service (CMS). The light blue rectangles represent the wind farm and the blue circles represent individual wind turbines. 58 february/march 2009
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