Hydraulic Pitch System for Wind Turbines: The Key to Enhancing Reliability
Have you had an issue with the reliability of your turbine blade pitch control hydraulics? We might have a solution for you to increase the life and precision of the control system.
Many of the top brands of wind turbines worldwide already trust the manufacturer Parker with filters, accumulators, and hydraulic valves. And now, some valves that are available for the US wind turbine market have been built in the USA. These proportional valves have been on the market for over 20 years in demanding industrial and mobile applications worldwide, with many upgrades and improvements over the years. Their use in the wind turbine market has been over ten years.
Hydraulically Controlling Wind Turbine Blade Pitch
Blade pitch control is a critical function of wind turbines for the overall control system. Wind turbines are designed to operate at steady rotational speed, usually about 15-20rpm for larger turbines. The gearbox increases the shaft speed to about 1,200–1,800 rpm to match the generator speed requirements to produce 60-cycle AC electricity at about 700V for the US market. The turbine controller starts the turbine when the wind reaches a given speed, usually about 10-16mph. A yaw drive keeps the turbine pointed into the wind to maximize electricity production efficiency.
The pitch control system, located within the turbine hub, adjusts the variable pitch turbine blades to control the generator speed based on a feedback signal from the control system. On the hydraulically controlled blade pitch systems, there is one pitch control proportional valve per blade on a wind turbine. The pitch system also “zeros” the blades so that there is no lift generated by the rotating blades, thus shutting off the turbine drive when the wind speed reaches above 50 mph to protect the turbine from physical damage. An electric brake is usually engaged when the blades stop rotation.
The pitch control system operates in a very demanding environment, and the proportional control valve is arguably the device that is exposed to the harshest operating environment in terms of temperature and weather exposure. Failure of only one of the three valves will force the wind turbine out of service. Data from turbine farm operators confirm this observation with many field reports of OEM, sub-standard, pitch control valve failures within weeks of its first operation. An unexpectedly large number of failures occur within the warranty window of service. Upon failure, a maintenance technician must travel to the turbine site and replace the hydraulic pitch control valve in the turbine hub.
As you know, all the wind farms are remote and do not have on-site technicians, so this trip can be costly from a personnel standpoint, but it is even more costly for lost electricity production. Performing this service can take one or more days, depending on the site location distance and technician availability. The cause of the failure has often been traced to circuit board failure due to inadequate vibration protection or the circuit board enclosure design does not prevent dirt and moisture ingression. The cost of replacing pitch control valves is secondary to the cost of maintenance replacement evolution and the loss of energy generation.
A pitch control valve must be designed to operate full-time in an extremely rugged environment. First, most hydraulic pitch control valves are in the turbine hub, which rotates and is thus exposed to heavy vibration, shock, and rotational forces (up to 50G on three axes). The valves are also subject to lightning strikes, so the valve electronics must be electrically isolated from the turbine electrical system. Also, the pitch control valve must be capable of withstanding ambient temperatures ranging from -40C to 85C. It stands to reason that the pitch control valve should be designed to comply with IP65 standards for protection against dirt and moisture at a minimum.
Increase Your Reliability with a Parker Proportional Valve
One pitch control valve that has proven itself in multiple wind turbine applications is the Parker D1FC (nominal size: NG06, 5gpm flow rate) and the D3FC (nominal size NG10, 16gpm flow rate) direct operated proportional DC valve with onboard position feedback. The control valves receive an input signal, 4-20ma or +/-10VDC, from the main turbine controller based on its monitoring of the generator output. Internal valve flow and performance specifications have been matched to the system requirements of the turbine to be compatible with the existing controls so a replacement valve can co-exist with valves on the other axis. These hydraulic valves are designed to meet IP65 standard designation, which inhibits moisture and dust ingression. The D1FC and D3FC units are built to meet IEC 68- 2-6, -7, and -36 vibration standards so that random noise and shock loads, respectively, are well accounted for in the design and build process. The electronic driver card is installed with anti-shock mounting technology, which minimizes vibrational effects, and all fasteners are thread-locked to guard against vibration as an additional measure of safety.
Field service reports often state that mating connectors are the root cause of a turbine outage. The connectors used on OEM pitch control valves do not have locking connectors, so vibration can cause them to disengage. The D1FC and D3FC valve assemblies use locking mating connectors, similar to those found in the automotive and agricultural industries, which are vibration-resistant.
Major Design Features of the Parker D*FC Proportional Valve.
Parker is certainly recognized as a global provider of motion and control technologies, particularly hydraulic controls, which is why RG Group is proud to be a full-line distributor of its equipment. There is a further advantage for cost-conscience owners: a single replacement D1FC valve may be used in conjunction with two existing OEM valves, thereby allowing an incremental replacement program. This approach may be preferable for those owners who would rather replace them with upgraded components as repeated failures occur over time. Other owners may determine that changing all three valves may be the most cost-effective solution when the technician labor cost for multiple repairs and lost electricity generation costs are considered in the long-term costs of maintenance.
Parker offers a wide range of options for the D1FC and D3FC models, tailored to meet the demanding needs of wind turbines in the US market. For more information on this particular valve, see the Direct Operated Proportional Directional Control Valve on Parker’s website.
This table of products is a guide to what we have to offer, but please consult with us to determine if it is the right solution for your model and generation of Wind Turbine.
RG Group’s approach to solving the toughest proportional and servo valve issues on a variety of industrial and commercial machinery will go a long way to determining potential upgrades for your wind turbine blade pitch control.
Download the Parker Wind Turbine product catalog for more information. With thousands of parts at our disposal, the chances are high that we’ll have what you need, when you need it.
Contact me at [email protected] to discuss your particular needs for extending the reliability, life, and maintenance intervals of your model and site.