Intelligent cavitation monitoring in hydropower

Many hydropower plant operators know only too well the unavoidable phenomenon of cavitation in their machines. It is the formation of vapour bubbles due to localised areas of low pressure. When the vapour bubbles collapse, they create high pressure peaks that cause damage to the surfaces of the turbine runner over time. 

However, since the occurrence of cavitation is highly dependent on the operating mode of the machine, the extent of the damage cannot be predicted. Therefore, the machine is often subjected to maintenance too early. This is problematic as inspections and repairs require time-consuming tasks like draining, opening and checking the machine. This is especially true, since the damage caused by cavitation is usually minor and the machine could have otherwise operated for a much longer interval. 

“We want to significantly reduce this loss of valuable production time with our new system and our newly developed algorithms,” says Dr. Felix Lippold, Global Product Manager at Voith Hydro.

Therefore, Voith and the state-owned Icelandic national power company Landsvirkjun have initiated a joint pilot project focused on innovative cavitation monitoring in hydropower plants. The technology group will install its cutting-edge system at the Budarhals hydropower plant in Reykjavík, Iceland, the newest of six hydroelectric plants in the Thjórsá-Tungnaá area. It is an add-on function for Landsvirkjun’s condition monitoring system. The new system will be installed in the second half of 2020.

Optimal operation

Cavitation is usually avoided by effective design and generally does not occur within the normal operating range. Due to the increasing requirements to make existing plants more flexible in conjunction with other renewable energies such as wind power, it is becoming worthwhile for operators to exceed their plants’ normal operating range, even though this can cause cavitation to occur. With the help of Voith’s monitoring system, the incidence of cavitation in the event of an extended operating range can be evaluated against the additional benefit provided.

Budarhals – the place of action

The Budarhals facility has an installed output of 95MW and a capacity of around 585GWh per year. In 2014, Voith equipped the Budarhals hydropower plant with two modern, environmentally compatible Kaplan turbines featuring water-filled runner hubs and cutting-edge generators with specially developed brushless and Bluetooth thyristor-controlled excitation systems. Apart from the main components of the electrical and mechanical equipment, Voith also supplied the crane systems for the powerhouse and the control systems for the power plant. The highly automated Budarhals power plant is in a remote location and operates unmanned, so any undetected problems can cause severe damage to the equipment. 

Because cavitation damage occurs slowly, the observations will take place over a period of at least two years. “Our goal with the cavitation monitoring system is to gain more knowledge about the potential damage caused by cavitation in the machine and to extend the time between inspections,” says Georg Pálsson, Operations Manager of Thjórsá & Tungnaá River Plants at Landsvirkjun.

Cavitation damage on a turbine

A new system

Voith has continuously developed its cavitation monitoring system in recent years, using various data from experimental setups as well as plant measurements to make further refinements and improve the predictive accuracy. For this purpose, the experts used, among other things, modern methods such as machine learning with neural networks. It consists of a set of robust, high-frequency sensors and amplifiers, a high-speed data acquisition and signal processing unit, and an analysis software module. The sensors can be attached outside the turbine. Based on the measured acoustic emissions and additional machine data, such as rotational speed, the software module provides the cavitation state of the machine during operation.

The main advantage – compared to well-known analysis methods based on, eg an event counter in the time domain – is that individual calibration for each test case is unnecessary. This opens the path to flexible maintenance periods. Both long-term and short-term observations are possible, each giving important insights into the machine behavior and directions for the operation of the machine.

This also allows for better planning of maintenance intervals as well as a higher availability, both contributing to increased profit. This idea of individual and unit-tailored maintenance is incorporated in the Cavitation and Erosion Care service offered by Voith.

In addition to the detection of cavitation, it is also a matter of measuring the strength of the cavitation phenomenon. 

“We are in communication with the customer during our continuous development process and take into account their feedback on the use and behavior of the system. This allows us to improve the product even further,” Lippold says. “We will then successively further develop the algorithms so our customer can determine not only the current cavitation situation but also any damage to the material surface caused by cavitation, such as the material removal.”

A long tradition 

This close collaboration with Landsvirkjun, an innovation leader in their market, is a continuation of Voith’s long tradition of doing business in Iceland. As far back as 1912, the company built the first complete turbine installation at the Fjardarsel power plant.

The system has a capacity of 550kW, is driven by a horizontal Francis turbine, and is the oldest power plant in Iceland still in operation. In 1989, Landsvirkjun produced its first drafts for the Budarhals power plant that subsequently formed the basis for the current design. Budarhals was the first major infrastructure project in Iceland after the 2008 economic and financial crisis, which had a profound impact on the country.

Joint development

As a technology company, Voith focuses on very close cooperation with customers for the digitalisation of hydropower plants. Joint development has been a key factor of success for Voith over the years. This so-called “co-development initiative” is now increasingly being expanded globally and pursues two main goals: 

• To develop digital products that are consistently customer-oriented and digitally transform power plants and the entire customer fleet. 
• Aiming to strengthen customer relationships. 

The collaborations are primarily divided into three approaches:

• Individual product adaptation and expansion
• Multiple product adaptation, expansion and development of synergy effects, especially in the linked application
• Joint new development of digital solutions in the hydropower sector and beyond, ie across the entire energy ecosystem

The long-standing cooperation with partners such as Landsvirkjun leads to new insights and developmental tasks about technological and economic aspects, which bring both Voith and its customers a step closer to digital transformation. In addition to existing co-developments, this approach is to be pursued with other partners in the future.

“The concept of cooperation with customers to further develop our digital portfolio is extremely valuable for jointly shaping the future of hydropower,” says Dr. Thomas Mahnke, Global Product Manager at Voith Hydro. “After we started a pilot project with Landsvirkjun two years ago for our intelligent sound analysis system OnCare.Acoustic, we are pleased that we are now jointly launching a new innovative project for cavitation monitoring and are already talking about further cooperation in the digital field.” 

His colleague Markus Wirth, Director Sales Western Europe at Voith Hydro, adds: “By expanding the cooperation, Landsvirkjun is sending an important signal to the entire market to continue on the path of digitalisation.”