Vishnu Malipeddi, Director of Engineering, DEX, Camarillo, Calif., dex.com/renewables
When a critical part fails, a wind-plant operator can be looking at months of downtime and dollar losses in many thousands. A little preparation, however, can help maintenance staffs get ready for the quick replacement of hard to come by parts.
All electro-mechanical components are destine to fail. Having the right strategy in place to manage that failure can be the difference between success and …well, failure. This is especially true for wind turbine owners and operators. Without an effective strategy at the ready, failure can be expensive in terms of lost output and revenue.
A coherent strategy
The question to ask before trouble arrives is: Do we have a coherent repair strategy in place? When a repair problem arises it is vital to have a cost-effective solution at hand. Can the part be repaired, or must it be replaced? Is inventory available? In this era of environmental awareness, one philosophy says repair the existing part instead of scrapping it and buying new.
The rapid expansion of wind energy in the last 20 years has often resulted in a rush to get new technologies to market. Inevitably this has led to reliability issues which can directly affect a wind farm’s revenue stream through down time. There is also a cost associated with additional operations and maintenance events. When compared with other designs, some new technologies have a propensity for higher failure rates within control systems and power electronics.
For example, about 54% of all wind turbine malfunctions are due to failures in control electronics, electrical systems, and sensors. Unlike many mechanical components in a wind turbine, most electronics and electrical systems have only one supply source – the OEM. These parts generally have a high unit cost so the cost of a new replacement part can be as much as three times the cost of repairing an existing part. If that is not bad enough, gaps in a supply chain can result in long lead times which aggravate the cost issues.
Obstacles and opportunities
As the industry continues maturing, many wind turbines are coming out of their manufacturer’s warranty. Owners and operators throughout the U.S. and Europe have had with some parts in their wind turbines declared obsolete (a few rotor current controllers and racks of insulated gate bipolar transistors (IGBT) for example), and there is no accompanying documentation to support their repair.
If one of these parts malfunctions, replacing it is no longer an option. Maintenance engineers must learn how the part works and carry out a root-cause analysis of why the part failed. Such complex electronics in today’s wind turbine assemblies requires a unique combination of skills and repair capabilities. The repair process must be carefully managed to ensure such parts are repaired within appropriate time frames and in a cost-effective manner. This involves use of detailed workflow and quality procedures so each repair stage is monitored and certified to ISO standards.
Often, the most difficult portion of this repair and recertification process is to ensure parts are exercised to their design specifications. Most electronic control parts are custom made for wind-turbine environments, therefore it is not practical or reliable to test these parts using standard off-the-shelf equipment. Nor is it practical to use a wind turbine to exercise the parts. This challenge has necessitated developing complex software, tooling, and test jigs to carry out full testing and validation procedures. Replicating an often complex series of electronic interfaces along with inputs and outputs means analyzing signals in detail. Software and hardware-emulation techniques will be needed to design equipment that ensures full test coverage on all functional areas.
Finding a repair facility with expertise in this arena can be difficult, but not impossible. Our company, for one, has facilities in the U.S. and Europe. At every stage of repair or refurbishment it is crucial that the staff adhere to quality assurance standards and provide a full audit trail showing the progress of the repair and certifying compliance with quality standards. These repair facilities have achieved certification by the International Organization for Standardization for ISO Certifications: ISO 9001, ISO 13485 and ISO 14001.
In all, a holistic engineering solution is necessary to report failure-symptom trends, epidemic failures, third-party-module issues, and evidence of design quality and reliability problems. Understanding how components fail is paramount to preventing future disruptions.
Proactive solutions, effective strategies
Efficiency and effectiveness in this business call for having a multi-faceted solution strategy in place before failure strikes. That makes it necessary to address the need for a component repair or replacement strategy, asset management strategy, and an inventory management system.
A coherent asset-management strategy ensures repairs are carried out quickly and efficiently with minimal downtime. For example, once a part is recognized as defective it should be swapped out and immediately sent for repair to ensure that a stock of working components is always available. Part pooling schemes between operators can also help ensure that contingency stocks are kept high.
The idea works this way: Buying enough spare parts to cover all potential failures is an expensive proposition. To offset such a major investment, some wind farm owners have formed “Parts Pooling” partnerships in which all members contribute to purchase an agreed inventory of spare parts that they can draw from as needed. As a part fails, the owner who needs a replacement pulls the spare from inventory and pays into the pool to replace it. This savvy strategy lets owners maximize financial resources instead of tying it up in inventory.
The location, storage, and transportation of spare parts is also crucial. Being close is not enough. Our research and experience finds that parts are frequently stored in warehouses close to wind turbine sites but without adequate protection from the elements. In many cases, such parts are unusable and must be refurbished or repaired before they can be fitted. This can be avoided by storing parts in a central location under strictly controlled environmental conditions. Sensitive electronics are particularly vulnerable to temperature changes, and humidity and can rapidly deteriorate electronics when they are not stored properly.
Too often we find that owners do not fully understand the financial ramifications surrounding the value of their defective parts inventory. With multiple and remote locations, plus little or no visibility into their defective parts inventories, owners do not realize the value of what they have locked away. For instance, one utility company after an inventory realized it had a high number of defective variable rotor current controller (VRCC) parts stored at various sites, but not tracked on any system.
They returned all of the defectives to our facilities to be repaired and recertified. When done, the spares were placed into a “good inventory” location for use as needed by any of their farms. This inventory became a significant asset on their books.
The experience shows that tracking spare parts is an important task. An asset management system should provide 24/7 visibility as to where all parts are located and their condition (good inventory, Work in Progress (WIP), or defective).
A case study
To illustrate the necessity of having a comprehensive strategy in place, consider these recent events. A European wind plant operator with turbines coming out of warranty experienced a series of failures with rotor-current controllers (RCC). These complex microprocessor-based devices let generators function with variable wind speeds which otherwise would cause undesirable power fluctuations. Control and monitoring systems allow variance in generator rotor resistance through a three phase resistor system. An Insulated Gate Bipolar Transistor (IGBT) power module switches the fluctuating power. A malfunction in the RCLS significantly reduced the wind plant’s production.
Without a repair strategy, the wind-plant operator simply turned to the OEM to purchase replacement parts. To his shock, the plant operator learned that the lead time for replacing the part was three to six months. In addition, the OEM’s pricing structure would significantly increase their costs. Then to make matters worse, the reduced production forced the plant operator to purchase power from the grid to meet contractual obligations. The turbines were offline for five months generating only production losses that cost owners an estimated $370,000. Not surprisingly they began searching for alternative solutions to resolve this situation and avoid reoccurrences.
The plant owner turned to DEX. Its engineering team evaluated the defective parts, and developed a repair procedure for the rotor-current-controller system.
Often the most difficult part of any repair and recertification operation is to ensure that parts are exercised to full design specifications. This is much the case with the RCC electronic control and power module assemblies. Signals must be analyzed in great detail to establish their proper function. Simulating the end application made it necessary to develop test hardware controlled by DEX software which ensures a repeatable, reliable test process that further ensures full test coverage across all product areas. A validation and verification process was carried out by repair engineers and quality personnel. This involved conducting tests and analysis on the equipment, software and process in line with ISO standards. In addition, tests were carried out over a six month period on site at wind farms.
Our company spent six months developing proprietary diagnostic software to ensure test reliability and repeatability during the product test phase. Upgrades carried out on the turbines improved their overall reliability included a 100% proactive replacement of known high failing components and a proprietary IGBT matching process in the power modules.
As a result, the turbines were brought back on line to full production, resolving their immediate need, while their material cost was reduced to one-third the cost of purchasing new components from the OEM. A comprehensive procedure has been set in place to prevent a repeat of long-term outages and disruptions in production.
In these challenging times, wind turbine operators must seize all opportunities for maintaining plant outputs at high capacity, cutting costs, and maximizing revenue. Putting a comprehensive strategy in place before failures occur is critical. Having a component repair or replacement strategy, asset management strategy, and an inventory management system in place can make a major contribution to achieving these goals.
Filed Under: O&M