Today’s global installed hydropower capacity represents about 20 percent of the world’s generated electricity. Hydropower provides about 50 percent of the renewable energy in the U.S., making it the largest part of the renewable energy sector.
The purpose of a hydropower plant is to convert the kinetic energy of water into electric power via turbines.
There are three typical turbine designs: Pelton turbine, Francis turbine and Kaplan turbine (see Image 1 and Figure 1). The primary criteria for selecting the appropriate design are the head and flow of the water.
Most larger turbines are designed in the vertical direction with the generator on top of the turbine (Image 2). Some smaller turbines are designed in the horizontal direction with either one turbine runner or two turbine runners, one on either side of the generator (Image 3).
Today, machine uptime is more important than ever before. Therefore, monitoring the machine status has become absolutely necessary. There are two levels of machine monitoring: safety monitoring and condition monitoring.
Safety monitoring for hydropower machines is based on vibration monitoring. Safety monitoring systems use permanently installed equipment that measures the overall vibration values across all measurement points simultaneously. This type of monitoring equipment sounds an alarm or shuts the machine down before a catastrophic failure can occur.
Since most hydropower machines have journal bearings, the most effective way to monitor the machine is by measuring the shaft relative vibration by means of two displacement probes per bearing plane. ISO 7919-5 provides recommendations for the type of equipment, what to measure, where to measure and acceptable vibration levels for evaluation.
In addition, ISO 10816-5 provides guidelines for measuring and monitoring the bearing housing vibration using seismic transducers, i.e. accelerometers or velocity transducers.
Both of these standards are currently under revision and being combined into one standard (ISO 20816-5), which will cover both applications in the future.
Image 4 is an example of two displacement probes measuring shaft relative vibration. Image 5 is an example of one velocity transducer measuring bearing housing vibration.
Condition Monitoring: Early Fault Detection
Condition monitoring for hydropower machines is based on vibration analysis and the influence of operating parameters. Machine condition monitoring is a step above safety monitoring and provides the user with early fault detection and information on possible machine failures before a catastrophic failure occurs.
ISO 13373-7 sets out guidelines and specific procedures to be considered when performing vibration diagnostics of various types of hydropower machines.
Hydropower machines are primarily influenced by:
- mechanical unbalance
- hydraulically excited forces in the turbine runner
- magnetic forces between stator and rotor in the generator
- mechanical forces in the bearings
Machine vibration is further influenced by different operational parameters such as:
- opening of wicket gate
- bearing oil temperature
When performing condition monitoring the ability to separate vibration changes caused by a failure mode from vibration differences based on operating modes is essential.
For success, it is necessary to simultaneously record all vibration and operating parameters.
Typical solutions for monitoring at hydropower plants include all or some of the following:
- displacement sensors for measuring shaft relative vibration
- seismic sensors for measuring the housing or bearing vibration
- safety monitoring equipment and condition monitoring systems.