15 Sep 2023
By David Futter and Katy Huckle
The implementation of a Condition Monitoring System (CMS) to measure wind turbine health is no longer an optional extra. In many cases, particularly the offshore sector, CMS with Structural Health Monitoring (SHM) is mandatory—and the benefits are crystal clear. An effective CMS improves the efficiency of turbine maintenance, helps avoid major failures and downtime, and facilitates operating permit extension based on actual plant data, increasing the operational lifetime of an installation.
Typically, a wind farm can expect ROI from a CMS within 3 years of implementation. However, there are significant variations in quality on the current CMS solutions market. Unfortunately, procurement teams often fail to correctly estimate the total cost of ownership and select the cheapest system, which will eventually cost far more than its higher-quality competitors. As the saying goes: “Buy it cheap, buy it twice.”
Traditionally, CMS was focused on monitoring the health of the drivetrain. As installations grow, however, blade health monitoring is becoming essential, as is SHM for monitoring the condition of tower and foundations, particularly offshore. The current cost of a basic, 8-channel CMS with transducers lies in the range of $3,000 to $8,000 per turbine. Installation (including lost generation during installation) will be about $2,000 per turbine. These are the upfront costs that wind turbine owners and operators can be certain of. But what about the hidden costs?
Poor quality = hardware failures
In the language of condition monitoring, we generally refer to failure rate in failures per hundred item years. So, with 8 sensors on a 50-turbine wind farm, with a 20-year lifetime, the total runtime is 8000 sensor years. If a high-quality CMS delivers a failure rate of 1 per 100 sensor years, and a low-quality CMS delivers 2 per 100 sensor years, that low-quality CMS will fail an additional 80 times over the total installation lifetime.
Repairing a sensor is relatively simple, but still requires a visit from a technician, new hardware, and travel time—the costs of which can quickly escalate. If the total cost per failure is around $300, then this puts the price of 80 additional, onshore repairs at $24,000—for offshore installations, this could increase tenfold.
Don’t forget the cost of potential missed failures that could occur during downtime. While the sensor is out of action, no data will be recorded, which could lead to complications further down the line.
Poor quality = inaccuracy
An indirect cost of a low-quality CMS solution is lower monitoring accuracy. An advanced CMS may offer 1 percent better availability and greater storage capacity in the case of a communications loss. This could lead to a 1 percent improvement in fault detection. Typically, we see faults on 10 percent of turbines per year, of differing severities. So, on our 50-turbine wind farm, with its 20-year lifetime, we would expect to detect 100 faults throughout the lifetime of the park.
The savings associated with fault detection vary dramatically according to failure type and follow-on impact, but these can range from $1000 to $100,000. If we assume an average saving of $20,000 per fault, which equates to a saving of $1000 per turbine, then missing just one such event could have major financial consequences for the wind park.
The better the monitoring equipment, the lower the associated monitoring efforts, and the lower the cost of monitoring. If the monitoring fee for a low-cost CMS solution equates to €1000 annually, and the monitoring fee for a higher-quality solution equates to €500, the result over the 20-year lifetime of a wind installation is a cost difference of €10,000—much more than the original cost of the “expensive” CMS hardware. The advanced capabilities of the more expensive system have a significant downward impact on the total cost of ownership.
What if you have an inhouse condition monitoring team? System quality also makes a major difference here. Again, the advanced capabilities of a better CMS solution reduce the amount of post-processing and deliver clearer, more accurate results that are easier to interpret and lead to quicker responses to an imminent failure. This is especially true for high-quality CMS with process-oriented diagnostic software.
Low quality sensors may not have the capability or usable range necessary for wind turbines. This is not only in the low frequency region, but also at the high frequency part of the signal. Sampling at 10kHz is routinely used for envelope analysis—not only on the high-speed part of the machine, but also for slow rotating components requiring identification of impacting to enable diagnosis. However, some transducers (especially those based on MEMS) have a response limited to less than 5kHz, making them unsuitable for wind turbine monitoring. The consequential impact of undetected rotor bearing damage due to inferior, low-cost sensor technology can far exceed the minimal savings of a cheap CMS.
Some load monitoring sensors transmit data that can be instantly captured by the wind park controller system, making it immediately available to all corresponding monitoring and SCADA systems. Let’s take a strain measurement/IPC sensor as an example. There are low-cost models available on the market that, upon installation, require an expensive software module (around $4000) to connect to the controller module. Despite appearing initially as a low-cost sensor, the hidden costs of sensor integration massively inflate the price of such budget equipment, not to mention the additional costs of more complicated start-up and troubleshooting.
Despite the major financial potential impact from a predictive approach to maintenance (enabled by an effective CMS solution), many owners and operators still do not see CMS as a critical operational component of their wind park. When a CMS performs well, the potential cost savings are enormous, but if it does not perform (is inaccurate and requires regular maintenance and repairs), then it quickly becomes a cost driver, and operators lose trust in the entire process.
Lifetime warranties go some way to reassuring owners and operators that they are investing in a good CMS, but the hardware costs are one of the smallest parts of the hidden cost equation. The major hidden costs are due to maintenance visits to replace faulty hardware (especially offshore), missed failures during downtime, poor quality monitoring, expensive monitoring services, data processing, and networking.
Right from the start, investing in a higher-quality CMS with a lifetime guarantee will almost certainly save money over the total lifetime of an installation.
David Futter is the Head of Condition Monitoring Consultancy—an independent technical advisory service under the Bachmann Group—and a BINDT Vibration Analysis Cat IV practitioner and Approved Training Coordinator. He is a committee member of the BSI GME21/5 and GME21/7 as well as a member of the BINDT Vibration Analysis Expert Group.
Katy Huckle is a Marketing Manager at Bachmann electronic, specializing in Condition Monitoring. She holds an MBA from the HSG St Gallen in Switzerland.
Bachmann | www.bachmann.info
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