Page 8 - North American Clean Energy May June 2018 Issue

wind power
Space is very limited inside the hub, making it more difficult to do the troubleshooting of the pitch control system.
Extreme Weather Conditions vs. Proportional Pitch Control Valves
by Scott Smith
In many instances, performance of the hydraulic pitch control is scrutinized in suitable weather conditions. However, these control systems are exposed to a variety of extreme weather conditions that can greatly a ect both pitch performance, and longevity of the control components.
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valve was designed with a more robust electronic se failure rates in harsh operating environments.
Post-compensated, sectional, load-sense valve
Muncie Power Products has expanded its valve line with a new post-compensated, sectional, load- sense valve – the L125. A 33 GPM nominal ow rate valve, the L125’s inlet is capable of a maximum of 40 GPM and its work sections a maximum of 26.4 GPM. e L125 features good ow sharing parameters and multiple spool ow options. Electro-hydraulic and manual shift versions are available. Muncie Power’s new L125 post-compensated, sectional, load-sense valve is suitable for the utility, agriculture, snow and ice and refuse markets in addition to speci c applications such as truck-mounted cranes, forestry cranes, and plow and spreader functions.
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High Wind Speed will create high levels of vibration in the pitch
valve as it rotates in the hub of the turbine. e onboard electronics are susceptible to these rotational forces, subjecting the electronic driver card and enclosure to G-forces that loosen screws and wire connections; this results in loss of rotational position control of the blade.
Troubleshooting a fault or failure in wind turbines is not a quick and easy task. e tower climb and work process must be planned, and parts gathered; a climb safety meeting must be held before travel to the down turbine is even started. is controlled process can take many hours.
Once uptower and inside the nacelle – and especially the hub – space is
very limited, making it more di cult to diagnose the problem. Changing a
proportional pitch control valve in a turbine it can take 4-6 hours from start to nish, depending on the wind farm. Considering the maintenance costs, as well as lost production, the expense of constantly changing prematurely failing pitch valves can really add up.
Many pitch control valve designs
don’t account for potential extreme weather conditions or tough operational environments. After examining hundreds of failed proportional pitch control valves, it was found that over 90 percent of the failures were related to electronic component failure or degradation, or mechanical failures of the driver card housing. Failures are seldom caused
by wear or internal mechanical failure. ese failures ultimately a ect the
PID pitch rotation control loop (which often requires a rotational accuracy of
1 percent). A proportional pitch valve problem or failure will create a fault,
or error, in the pitch rotation system - ultimately shutting down the turbine.
Due to extreme weather exposure, the highest rates of failure are valves that
do not have a robust electronic control package. Heavy-duty valve construction, coupled with a robust onboard electronic package, with rugged wire connections and seals, is paramount for a proportional hydraulic pitch control valve to perform well and survive in these extreme conditions. Focusing on the design of the electronics (the electronic driver card,
the housing in which it must be mounted, and the electrical connections) results
in an improved life cycle. e goal for proportional pitch control valves is a 3 to 5 year life – without failure.
Ultimately, the pitch valve must be constructed with the understanding
that normal operating conditions will be exceeded. Valves are expected to perform in di erent wind and weather conditions around the globe. What performs well
in Europe may not perform well in certain parts of North America. e valve manufacturer’s original design must be analyzed and evaluated to determine if the valve can survive in the toughest wind and weather conditions.
Based in southern Oregon, Scott Smith (CFPHS) is a senior uid power specialist at Motion Industries. He has 35 years of experience in the
uid power industry with distribution and manufacturing companies, and earned his Certi ed Fluid Power Hydraulic Specialist certi cation in 2001. Smith has been heavily involved in the wind energy market for Motion industries, with a focus on hydraulic and lube systems.
www.motionindustries.com
|
Motion Industries
As in any hydraulic system, hydraulic pitch control systems experience the typical performance issues related to uid cleanliness, temperature, and viscosity. Wind turbines, however, are not your typical industrial or mobile application for these components. e majority of hydraulic pitch control turbines over 1mw have a proportional control valve manifold, hard-mounted to the pitch ram inside the hub. e hub, which rotates with
the blades, has much higher exposure to the external weather conditions; its only protection is a berglass nose cone that is not sealed. It’s not the easiest environment in which to function.
With turbines installed all over the world, in ever-changing climates, weather conditions can have a devastating e ect on performance and life of the proportional pitch control valve and system. Four primary weather conditions have a profound e ect on the life of the pitch control components: Extreme Cold, Heat, Humidity, and High Wind Speed.
Cold can cause loss of spool seal integrity,
as well as increased spool wear due to low viscosity. Extreme cold can also a ect control wiring and connections.
Heat creates low viscosity concerns, increasing wear, and reducing spool life. Varnishing can also result in spool sticking issues that can a ect the proportional-integral-derivative (PID) control loop.
Humidity will cause corrosion in coil pin connections, or any type of electronic connection that is not well sealed. Ultimately, this will result in accuracy problems in the rotational PID loop, often causing a fault in the turbine control system.
This 50-liter pitch package to decrea
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