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Hydro Generator Balancing

Rotating equipment experiences beneficial performance and life-expectancy improvements when properly balanced. Balancing is the process whereby the center of mass of the rotating equipment is moved to coincide with the desired axis of rotation, thus minimizing the vibration, heat, noise and wear that are symptomatic of imbalance. Balancing the rotating equipment in a hydro generator installation is therefore critical to the trouble free longevity of the entire system. Out of balance generators or turbines contribute to premature and uneven bearing wear, leading to excessive vibration & heat and often ending in unplanned downtime or necessitating shortened maintenance inervals.

Types of unbalance.

Static unbalance

Exists when the center of mass of the rotating equipment is not on the axis of rotation. It is explained as the condition when the principal axis of inertia is parallel to but offset from the physical axis of rotation.

Couple unbalance

Exists when the principal inertia axis of the rotating equipment is not parallel with the axis of rotation. To correct couple unbalance, two equal weights must be added to the rotating equipment at angles 180° apart in two correction planes. The distance between these planes is called the couple arm.

Two-plane unbalance (dynamic unbalance)

Dynamic unbalance is the vectorial summation of force and couple unbalance. To correct for two plane unbalance requires two unrelated correction weights in two different planes at two unrelated angles. It is a specification of the total unbalance that exists in a piece of rotating equipment. This type of unbalance can only be measured on a spinning balancer which senses centripetal force due to the couple component of unbalance.

Additional balance considerations

Unique, installation specific factors may create additional levels of complexity, and highlight the need to involve an experienced, qualified expert in the balancing process. A Kaplan turbine, for example, with only a slight misalignment of one turbine blade, may exhibit vibration that suggests imbalance, where in fact the problem cannot be solved by center of mass (balancing) adjustment.

Alan Towers Engineering is qualified to analyse complete generator systems and develop a customised balancing procedure to resolve hydro turbine and hydro generator balance problems.