Research Papers

A Methodology for Protective Vibration Monitoring of Hydropower Units Based on the Mechanical Properties

[+] Author and Article Information
Mattias Nässelqvist

ÅF, Division Industry,
N. Kungsgatan 5,
Gävle 803 20, Sweden
e-mail: Mattias.Nasselqvist@afconsult.com

Rolf Gustavsson

Vattenfall Research and Development,
Kyrkogatan 4,
Gävle 803 20, Sweden
e-mail: Rolf.Gustavsson@Vattenfall.com

Jan-Olov Aidanpää

Luleå University of Technology,
Division of Solid Mechanics,
Luleå 971 87, Sweden
e-mail: Jan-Olov.Aidanpaa@ltu.se

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received March 23, 2011; final manuscript received January 16, 2013; published online May 13, 2013. Assoc. Editor: Marco P. Schoen.

J. Dyn. Sys., Meas., Control 135(4), 041007 (May 13, 2013) (8 pages) Paper No: DS-11-1083; doi: 10.1115/1.4023668 History: Received March 23, 2011; Revised January 16, 2013

It is important to monitor the radial loads in hydropower units in order to protect the machine from harmful radial loads. Existing recommendations in the standards regarding the radial movements of the shaft and bearing housing in hydropower units, ISO-7919-5 (International Organization for Standardization, 2005, “ISO 7919-5: Mechanical Vibration—Evaluation of Machine Vibration by Measurements on Rotating Shafts—Part 5: Machine Sets in Hydraulic Power Generating and Pumping Plants,” Geneva, Switzerland) and ISO-10816-5 (International Organization for Standardization, 2000, “ISO 10816-5: Mechanical Vibration—Evaluation of Machine Vibration by Measurements on Non-Rotating Parts—Part 5: Machine Sets in Hydraulic Power Generating and Pumping Plants,” Geneva, Switzerland), have alarm levels based on statistical data and do not consider the mechanical properties of the machine. The synchronous speed of the unit determines the maximum recommended shaft displacement and housing acceleration, according to these standards. This paper presents a methodology for the alarm and trip levels based on the design criteria of the hydropower unit and the measured radial loads in the machine during operation. When a hydropower unit is designed, one of its design criteria is to withstand certain loads spectra without the occurrence of fatigue in the mechanical components. These calculated limits for fatigue are used to set limits for the maximum radial loads allowed in the machine before it shuts down in order to protect itself from damage due to high radial loads. Radial loads in hydropower units are caused by unbalance, shape deviations, dynamic flow properties in the turbine, etc. Standards exist for balancing and manufacturers (and power plant owners) have recommendations for maximum allowed shape deviations in generators. These standards and recommendations determine which loads, at a maximum, should be allowed before an alarm is sent that the machine needs maintenance. The radial bearing load can be determined using load cells, bearing properties multiplied by shaft displacement, or bearing bracket stiffness multiplied by housing compression or movement. Different load measurement methods should be used depending on the design of the machine and accuracy demands in the load measurement. The methodology presented in the paper is applied to a 40 MW hydropower unit; suggestions are presented for the alarm and trip levels for the machine based on the mechanical properties and radial loads.

Copyright © 2013 by ASME
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Fig. 1

Components in a hydropower unit

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Fig. 2

Schematic figure presenting the bearing and brackets in a hydropower unit

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Fig. 3

Total damping and distribution of motions in the bearing and the bracket

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Fig. 4

(a), (b) Stiffness and damping properties as a function of eccentricity for a tilting pad bearing in the hydropower unit

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Fig. 5

Bearing load as a function of eccentricity

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Fig. 6

Position of the displacement sensors and the thermal change's influence on the bearing clearanc

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Fig. 7

Example of the calculated bearing load as a function of the bearing clearance and eccentricity for the tilting pad in a hydropower unit

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Fig. 8

Bearing load determined using strain gauges inside the pivot pin (upper figure) and the shaft displacement multiplied with the bearing properties (lower figure)

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Fig. 9

Bearing layouts in hydropower unit units

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Fig. 10

Design of the upper bearing bracket for the hydropower unit presented in Fig. 1 and the critical bolt (dashed box)

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Fig. 11

Bearing properties at the present bearing clearance and at a ±25% change of bearing clearance

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Fig. 12

Proposed levels for the alarm and trip




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