The Hidden Costs of
Cheap Condition Monitoring
What WTG Owners and Operators need to watch out for when selecting their next CMS
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.
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. But there is huge variation on today’s market in quality of different CMS solutions. Unfortunately, procurement teams often fail to correctly estimate the total cost of ownership, often selecting the cheapest system that 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, but, as installations grow, 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 system 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, then, over the total installation lifetime, the low-quality CMS will fail an additional 80 times.
Repairing a sensor is relatively simple, but it still requires a visit from a technician, new hardware, and travel time – all of which can become very expensive for offshore parks. We estimate the cost of 80 additional, onshore repairs at $24,000 (Technician Time + Hardware: $200. Transportation to site: $100. Total per failure: $300) and, if these repairs are offshore, the costs could increase tenfold.
Still to consider is 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% better availability and greater storage capacity in the case of a communications loss. This could lead to a 1% improvement in fault detection. Typically, we see faults on 10% 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, then missing just one such event has major financial consequences for the wind park and equates to a saving of $1000 per turbine.
Own Monitoring
But 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 therefore lead to quicker responses to an imminent failure. This is especially true for high-quality CMS with process-oriented diagnostic software.
Data Processing
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. But 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.
Connectivity
Some load monitoring sensors transmit data that can be instantly captured by the wind park controller system, therefore 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 in maintenance visits to replace faulty hardware (especially offshore), missed failures during downtime and due to poor quality monitoring, costly monitoring services, data processing and networking.
We recommend investing in a higher-quality CMS right from the start, with a lifetime guarantee, which, as we have shown, will almost certainly save money over the total lifetime of an installation. Purchasing teams must consider all the factors outlined above when calculating Total Cost of Ownership for a CMS solution to ensure a complete and accurate picture.
Condition Monitoring Consultancy is an independent technical advisory service under the Bachmann Group. Find out more!
David Futter is the Head of Condition Monitoring Consultancy, part of the Bachmann Group, 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.
