Replacement of large components for wind turbines - What operators should know!
11.11.2025
After ten to twenty years of operation, wind turbines often reach the point where central components reach their wear limits. Large components such as gearboxes, main bearings, generators or rotor blades are particularly affected. Replacing them poses technical, logistical and economic challenges for operators – but at the same time offers the opportunity to significantly extend the service life and cost-effectiveness of existing systems.
The following article explains which components are typically affected, how a large component replacement works, what risks and planning requirements exist – and why this measure is increasingly becoming a key factor for the safe and sustainable continued operation of wind turbines.
1. Introduction
Wind turbines are designed for a technical service life of about 20 to 25 years. But like any complex technical system, they are subject to natural wear and tear. The large, central assemblies – the so-called large components – are subjected to particularly heavy loads. If they fail or show clear signs of material fatigue, operators have an important decision to make: repair, replace or shut down the plant?
Replacing large components is usually time-consuming, expensive and logistically challenging. At the same time, it can extend the service life of a wind turbine by many years and bring availability back to a high level. For many operators, replacement is therefore a key issue in the continued operation and service life management of their systems.
This guide explains in a practice-oriented way when a large component replacement is necessary, which components are affected, what the process looks like, what challenges can arise and when such an intervention is worthwhile.
2. What does "large component replacement" mean?
A large component replacement is the replacement of one or more central mechanical or electrical main assemblies of a wind turbine. These components are large, heavy, expensive and often can only be handled with special cranes, transport vehicles and specialist personnel.
Typically, large component replacements are not routine maintenance, but part of larger maintenance measures that are usually necessary after a defect, severe wear and tear or as part of service life extensions.
The goal of a large component replacement is to:
- ensure the operational readiness of the plant,
- extend the service life,
- and consequential damage that could result from continued operation with defective or worn parts.
3. Which components are affected?
The following components are considered classic "large components", the replacement of which typically causes the greatest effort and costs:
Rotor blades: They are among the largest and most expensive components. Damage is caused by cracks, lightning strikes or erosion.
Main Bearings: Carries the entire rotor mass. Typical damage: Pitting, wear, vibrations.
Transmission: Gears speed – prone to tooth chips, bearing damage, oil contamination.
Generator: Converts mechanical energy into electrical energy – often affected by overheating and insulation damage.
Rotor shaft: Transmits rotational motion, highly stressed by torsion.
Transformer / Power Electronics: Damage caused by thermal stress or overvoltage.
Gondola frame and hub: Rare replacement, but relevant in the case of structural damage.
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4. Typical causes and damage patterns
Large component damage rarely occurs suddenly. Common causes:
- Material fatigue due to load changes and turbulence
- Wear and Lubricant Aging
- Vibrations and imbalances
- Temperature changes
- Corrosion and moisture
- Lightning Bolt
- Improper maintenance
Signs are vibrations, temperature rise, oil particles in the transmission oil or conspicuous noises. Condition monitoring systems (CMS) help to detect damage at an early stage.
5. Challenges of large component replacement
A large component replacement is technically complex. Challenges include:
- Logistics: Transport of parts weighing up to 60 tonnes
- Crane work: expensive, weather-dependent, sensitive to wind
- Accessibility: Paths must be sustainable
- Spare parts availability for older systems
- Coordination of many trades
- Security requirements and insurance issues
6. Procedure for a large component replacement
Typical course of events in six phases:
- Diagnosis and planning: damage analysis, spare parts procurement, scheduling.
- Preparation: Shutdown, fuse, construction site equipment.
- Dismantling: Removal of the defective component with cranes.
- Transport: Removal and delivery.
- Installation: Assembly and calibration.
- Commissioning: Functional test, documentation, acceptance.
Advantages of a professional large component replacement
A professional exchange offers:
- Service life extension by 5-10 years
- Restoration of availability
- Cost control through planned measures
- Sustainability through refurbished components
- Technical optimizations through newer assemblies
8. For which systems does the replacement of large components make sense?
A large component replacement is usually worthwhile for systems between 10 and 20 years old with good substance and economical operation. Ideal for continued operation option or secondary market sale.
9. Manufacturers and plant types – practical examples
Enercon: gearless, replacement of generator bearings, pitch systems, rotor blades. (Enercon E40, Enercon E44, Enercon E48, Enercon E58, Enercon E66, Enercon E70, Enercon E82)
Vestas: frequent gearbox or main bearing changes (Vestas V52, Vestas V80, Vestas V90).
Siemens / Gamesa: modular design, typical exchanges for gearboxes, yaw systems.
Nordex: frequent bearing and gearbox replacements (Nordex N60, Nnordex N80, Nordex N117).
GE: Need for replacement of gearboxes (1.5 MW, 2.5 MW series).
10. Conclusion
The replacement of large components is a central component of the life cycle management of wind turbines. It extends the service life, increases availability and contributes to the profitability and sustainability of existing wind farms.
Interview with Falko Winkler (ENERTRAG)
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Falko Winkler
Project Manager Large Components Wind Power
ENERTRAG Service GmbH
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On what technical basis do you make decisions about the replacement of large components?
On a combination of plant history, condition data (e.g. vibration, temperatures, oil analyses), fault and downtime key figures as well as manufacturer documents (maintenance plans, service information, series statuses). The claim is clear: data-based, risk-oriented and economically comprehensible decisions.
What is a large component swap in a set?
The GKT is the planned replacement of central, heavy assemblies – in order to reduce the risk of failure, make downtimes plannable and extend the service life economically.
What typically counts as a large component?
Common: gearboxes, generators, main bearings, transformers, power electronics/converters, components in the yaw and pitch system, sometimes main shafts/couplings – depending on the type of system and the specific damage.
Why is "repair and drive on" often not enough?
Because risks shift with increasing operating time: A controllable defect can quickly turn into consequential damage – including emergency cranes, long downtimes and loss of yield. The GKT brings the decisive advantage: predictability. In asset management, this is often the difference between "claims management" and "risk management".
What is your specific goal with a GCT?
We want to bring the plant back into a condition in which availability and operational reliability are resilient – with a clear plan for costs, time windows, verifications and monitoring.
What are typical triggers for GCT?
Classic are trend deteriorations in condition monitoring, recurring alarms, oil particles/metal abrasion, temperature/vibration increases, leaks, series abnormalities or preparation for continued operation/service life extension. Important: It is not the individual event that decides, but the overall picture of risk, remaining life and business case.
Are there cases where a GCT is not the right measure?
Yes. When other limiting factors dominate (e.g. structural issues at the tower/foundation, critical leaf conditions, unsolvable logistics/approval requirements) or when the remaining service life is too short. Then an alternative is needed: graduated packages of measures or a clear exit strategy.
How do you ensure a clean process?
We work in clear phases, with clear responsibilities:
- Technical evaluation & business case (replacement vs. repair vs. continued operation)
- Engineering & Method Statement (assembly concept, tools, torques, tests)
- Crane and logistics planning (transport, areas, set-up times, weather windows)
- HSE & approvals (LOTO, rescue, circuit planning, construction site organization)
- Implementation (dismantling/assembly, documentation, quality assurance)
- Commissioning & acceptance tests (functional and safety tests, parameter levels)
- Follow-up (monitoring, follow-up checks, lessons learned)
What are the most critical project risks in practice?
Interfaces and time frames: crane, weather, mains circuits, material availability – plus the quality of assembly and final tests. Technically, many things can be solved; it becomes expensive if planning, approvals and responsibilities are not watertight in advance.
