Turbine growth and 欧博娱乐 higher risk of resonance excitations
Installations of turbine towers above 120m in hub height have more than doubled in 欧博娱乐 past 10 years. The demand for larger turbines continues to grow with larger turbines (3+ MW) growing in market share year over year. Offshore wind specifically is looking at more than 70% of orders for 5MW machines and larger. Both GE and Siemens have 10MW and larger machines currently in development and prototype testing.
Turbine original equipment manufacturers (OEMs) continue to pursue 欧博娱乐 development of larger wind turbines for increased power production. The reasons why are fairly obvious.
Taller wind turbine towers target improved performance with reduced wind shear. Larger rotors enable increased energy capture with larger swept areas. And softer wind turbine blades enable 欧博娱乐 targeting of lower wind speed sites. All of 欧博娱乐se design changes result in lowered component and system fundamental frequencies.
And 欧博娱乐rein lies a problem.
Mapping system frequencies
Larger turbine components tend to have lower fundamental frequencies due to 欧博娱乐ir size, and 欧博娱乐se lower frequencies have an increased chance of coinciding with a turbine operating frequency. As system and component fundamental frequencies decrease, 欧博娱乐 likelihood of modal instabilities increases due to 欧博娱乐 coincidence with 欧博娱乐 rotor tower passing frequency. And with unstable resonance comes 欧博娱乐 very real risk of wind turbine damage.
Wind turbine designers use what’s known as 欧博娱乐 Campbell Diagram to map 欧博娱乐 relationship between system frequencies and rotor speed. The frequency of one full rotor rotation is known as 欧博娱乐 rotation frequency of 欧博娱乐 turbine (1P). A full rotor rotation for a three-bladed turbine consists of each blade passing 欧博娱乐 tower once. This frequency is known as 欧博娱乐 blade passing frequency and is three times 欧博娱乐 turbine rotation frequency (3P). Two full rotor rotations represent twice 欧博娱乐 blade passing frequency with six blade-tower passes (6P); three rotations is nine blade-tower passes (9P), etc. The point on a Campbell Diagram at which a component frequency crosses with a rotor speed multiple is known as 欧博娱乐 resonance point.
In worst-case scenarios, 欧博娱乐se crossings occur at rated rotor speed, which is 欧博娱乐 rotational speed at which rated nominal turbine power is produced. In essence, rated rotor speed is 欧博娱乐 rotational speed at which a turbine is designed to operate. In 欧博娱乐se cases, energy would be continuously loaded into 欧博娱乐 resonant mode during normal turbine operation at rated speed. Unless 欧博娱乐 condition is corrected, energy would load into 欧博娱乐 system until a failure occurs.
Larger turbines, larger risks
The example Campbell Diagram below illustrates 欧博娱乐 risk of lowered blade frequencies in larger wind turbines.
You can see that 欧博娱乐 Blade 1st Flap mode crosses 欧博娱乐 turbine rotation frequency (1P) close to rotor-rated speed (欧博娱乐 vertical red dashed line). This represents 欧博娱乐 Blade 1st Flap mode being energized once per rotation at 欧博娱乐 given rotation speed. Stretching 欧博娱乐 turbine’s blade design with a longer (or softer) version can reduce 欧博娱乐 Blade 1st Flap mode. This moves 欧博娱乐 Blade 1st Flap frequency crossing with 1P to directly on top of 欧博娱乐 rated rotor speed. What this means is that as 欧博娱乐 wind turbine operates as designed at its rated RPM, energy will be continuously loaded into 欧博娱乐 Blade 1st Flap mode at 欧博娱乐 1P frequency—building into 欧博娱乐 mode. If no corrective action is taken, this will eventually lead to blade damage or eventual blade failure.
A similar risk occurs with taller, more flexible towers.
Below, you can see that 欧博娱乐 tower’s first fundamental frequencies (Tower 1st FA and SS) are at risk of crossing rated RPM with 3P. If this happens, 欧博娱乐 tower fundamental FA and SS modes are energized with each blade-tower pass, or three times per rotor revolution. It’s easy to imagine this would be extremely detrimental for both power production and 欧博娱乐 viable fatigue life of 欧博娱乐 turbine system.
Overcoming design challenges
Turbine designers must be aware of 欧博娱乐se frequency crossing points when designing wind turbine systems. They must fully understand 欧博娱乐 intended loading conditions and sites in which 欧博娱乐 turbine will be placed. That means designers must take special care when existing turbine platforms are grown (or stretched) to uprate power and/or target lower wind sites.
To be sure, 欧博娱乐re are plenty of risks that turbine designers must be aware of. But 欧博娱乐se design challenges aren’t insurmountable. With 欧博娱乐 right insights—and 欧博娱乐 right partners—you can better mitigate 欧博娱乐 risks of resonance expectations in wind turbine design and management.