Condition monitoring is the discipline of keeping tabs on the machinery in a nacelle, but getting data to the trending software and people who need it is the duty of IT technicians. The timely receipt of such performance data keeps wind farms properly maintained and profitable.
Ethernet on copper wires has been one way to get data from nacelle to ground, but that technology is good only for about 330 ft. before a switch (amplifier) is needed. Networks based on fiber-optic cable have become the preferred method for transmitting turbine data, and is easily implemented with Ethernet-to-fiber media converters in the nacelle. Fiber is good for transmitting data many miles without amplifiers, plus there is no worry about grounding issues or lightning strikes.
In addition to fiber-optic cable, wireless technology is being explored as an alternate means to get data from the nacelle to the ground. New monitoring systems are being introduced into existing nacelles for preventative maintenance purposes, and wireless technology can make it easy to achieve cost-effective deployment on a wide scale. For critical turbine control systems, however, it is still necessary to rely on the high communications performance and reliability of wired networks. This echoes the trend seen in other industries, where wireless technology makes new connectivity possible but does not replace existing critical infrastructure.
For the networks connecting multiple turbines to the control center, engineers have been using a topology called a collapsed ring and more recently, a chain network. In a collapsed ring topology, an Ethernet switch with at least three fiber ports is placed at the base of each tower. One port connects sensors in the nacelle, another goes to a previous turbine in the ring, and the third port to the next turbine. Crews would dig a trench and run the fiber in a conduit between towers up to the last turbine. To establish a redundant networking path back to the controls station, they run one long fiber without connections back to the control station through the just-laid conduit instead of digging a long separate trench. If a switch fails, a cable is cut, a connector disconnects, or another type of disruption occurs, the system can automatically route data around the problem using the redundant path. Recovery time depends on the redundancy scheme.
Network administrators like ring topologies because they use standard technology called RSTP (Rapid Spanning Tree Protocol, v802.1). RSTP is sufficient for email systems because a 30-second delay in email delivery is generally not a cause of serious concern. However, 30 seconds of network outage with no energy production data can be a major issue for a wind power farm. “A lot can happen in 30 seconds,” explains Moxa USA product manager Jim Toepper. “Without that production data, the wind-farm owner will not know how to bill, putting them in violation of a federal accountability act that requires them to be accountable for all production.” Producers need production data for every second so they can bill properly, and the government needs to know that the data is secure.
Wind power farms are therefore turning to industrial communication technology to ensure minimal network recovery times. Current technology makes it possible to achieve recovery times under one second or even 20 milliseconds.
Chain networks differ from the collapsed ring in that chains use several rings or links to connect the turbines. “Imagine three concentric circles each connecting 10 turbines in a 30-turbine farm,” says Toepper. “Each ring or link has two lines to the control station. Two big switches in the station connect to each other in a smaller ring for additional redundancy.” In the inner-most ring, switch A gets all of the primary connections and switch B gets backup connections from field circuits. If any one piece of equipment in the network goes down, farm managers have a redundant path to keep track of production data.
“So far, there is no problem with the amount of data transmitted because these networks generally run at 100 M bits/sec,” says Toepper. However, another trend happening in other industries is the widespread use of video for monitoring and surveillance. With video comes demand for more network bandwidth. Bandwidth requirements are likely to trend upwards toward Gbit/sec as asset owners begin installing network-connected cameras in the wind farm. WPE
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