In hydropower, reliability has a direct operational and financial impact. Water is most valuable when it is moving through generators, producing power, and supporting grid needs. A unit must be ready to start when needed, change load with control and alarm, or trip before abnormal conditions lead to catastrophic failure.

Mechanically, that reliability starts with the bearings. The unit’s ability to spin depends on properly loaded, concentric bearings. Good alignment helps equalize thrust-shoe loading, reduce runout-related cyclic loading, keep guide bearings concentric, and maintain proper clearances between the rotating and stationary components.

A thorough alignment also establishes a baseline set of measurements. That record can become invaluable later if the unit develops increased vibration or changing bearing temperatures.

One of the challenges of hydropower alignment is that every unit is different. Units may be similar across sites or manufacturers, but they are often custom-built for the site’s available head pressure, watershed flow requirements, and equipment configuration. Hydropower facility and generator design have evolved over the decades and can be observed in facilities still operating today.

That means alignment is not a universal step-by-step process. The same principles apply across designs, but teams must interpret those principles based on the configuration of the unit, bearing arrangement, clearances, and available measurement points.

Good alignment depends on repeatable, high-quality measurements. Teams typically use shaft runouts, shaft angle, elevation measurements, and clearance measurements to understand how the shaft is positioned and how it moves. Dial indicators are commonly used to capture shaft runouts at bearing elevations, while tight wires, laser systems, or digital inclinometers may be used to measure shaft angle.

A key concept is the “free shaft.” Before every individual measurement, the shaft must hang freely, without being influenced by a turbine seal, guide bearing, outside force, or even someone leaning on the equipment. Without a free shaft, measurements can be misleading.

Repeatability is equally important. For vertical units, measurements are commonly taken at 0, 90, 180, and 270 degrees, then checked again at 0 degrees. If the starting and ending measurements do not repeat, then something changed, or the measurement set may include an unacceptable error.

The best alignment work begins before the outage. Historical records can reveal prior settings, known construction or unit configuration issues, and past troubleshooting lessons. Without that information, teams may spend time rediscovering conditions that were already understood decades earlier.

Original equipment manufacturer (OEM) drawings and design documents are also essential. They help teams understand how the machine is designed and assembled, where critical clearances are located, what bearing settings should be, and how far apart measurement points are.

Proper tools, qualified craftspeople, alignment training, and outage planning all contribute to a smoother process. Alignment takes time, and rushing the work can make an already precise task much more difficult. These practices are especially important in hydropower O&M programs, where planned outages must be executed efficiently and units returned to service on schedule.

Alignment methods must account for the unit’s equipment configuration. Suspended (underhung) and umbrella (overhung) units have different thrust bearing locations, which affect how the shaft pivots and how runout readings should be interpreted.

Turbine type also matters. Francis turbines rely on seal ring clearances, Pelton units may have shaft seal assemblies that affect free shaft conditions, and Kaplan or propeller units use blade tip clearances when centering the turbine in the casing.

Bearing type affects the adjustment strategy as well. Adjustable shoe thrust bearings allow individual shoes to be adjusted, while spring bed and self-equalizing thrust bearings handle load distribution differently and require adjustments to the supporting bracket or structure to change the bearing plane.

Guide bearings play an equally important role in unit reliability. Their job is to maintain concentricity between rotating and stationary components while minimizing uneven loading. Depending on the unit design, facilities may use shell/sleeve bearings or segmented shoe bearings, each requiring a different approach when setting clearances and making alignment adjustments.

Perfect alignment is the ideal: a shaft plumb to gravity, a thrust runner perpendicular to the axis of rotation, a straight shaft, and concentric rotating and stationary components. 

In practice, perfection is not required. Manufacturing tolerances, plant settlement, measurement limitations, and field adjustment precision all affect what is achievable. The practical standard is repeatable measurements within acceptable tolerances and a unit that is left better than it was found. 

Unit alignment should be considered:  

• During initial construction. 
• Before and after major overhauls or generator rewinds. 
• When bearings are removed or replaced. 
• When vibration or bearing temperature concerns emerge.  

Because concentricity cannot be seen while the unit is operating, changes in temperature or vibration may be the visible signs that alignment should be evaluated.  

Ultimately, alignment is about giving hydropower units the best chance to operate safely, reliably, and predictably. It protects bearings, supports outage decisions, and gives maintenance teams the baseline information they need to understand what the unit is telling them over time. 

Vertical hydropower unit alignment is a technical discipline that requires preparation, precision, and an understanding of how each unit is configured. As you plan your next outage or evaluate your O&M program, keep these fundamentals in mind: 

• No two units are the same.  
• Measurement quality determines outcome.  
• Preparation starts before the outage.  
• Better is the standard, not perfect.  

If your team is planning an overhaul, evaluating alignment concerns, or looking to establish better baseline records, GFT’s hydropower mechanical engineers can help. Contact us to discuss your unit’s needs.