HYDRAULICS FEATURE
DETECTING DAMAGE EARLY By continually monitoring the gearbox, malfunctions and the resulting damage can be detected early and remedied through small repairs, before a total failure occurs. Recording and analysis of vibrations in the gearbox makes this possible to a large extent.
Of course damage that does not produce any vibrations or for which noise transfer is very inefficient, as in the case of problems in the planetary gear, cannot be detected.
This problem can be solved by monitoring the lubrication oil for metallic particles which are generated through wear and fatigue on the gearbox. These particles are carried along by the lubrication oil and thus can be detected by inductive particle sensors in the cooling lubricant circulation system.
FINDING LARGE PARTICLES In an inductive particle counter, a field coil produces an alternating magnetic field whose strength is measured with a pick-up coil. If ferromagnetic particles enter the magnetic field, it becomes stronger.
Non-ferromagnetic conductive particles induce eddy currents in the particles, which causes a magnetic field to be produced that weakens the original magnetic field.
Cumulative particle count in the early phase of damage to the gearbox of 1.5 MW wind turbine.
These particles are picked up by the oil circulator, conveyed through the MCS and are then completely separated out by the oil filter. In contrast to fine soiling, there is no consistent concentration of particles that would characterize the condition of the gearbox.
One challenge of this inductive measuring technology is eliminating its basic but unwanted sensitivity to air bubbles. The lubrication oil in the gearbox is, depending on its design, the suction point of the pump and the oil used is always more or less strongly frothed up.
A high performance signal processor takes care of the task of identifying the air bubbles as bubbles on the basis of their special signal form and not as particles. If the signals were processed purely on an analog basis, the air bubbles would cause false results in the error rate count and would severely limit the early detection of damage.
CONCLUSION
Integrating inductive particle sensors into vibration monitoring systems represents an excellent addition to the early detection system for gearbox damage.
Combining the systems makes it possible to jointly use the electronic data transmission and alarm system structures. MCS provides the necessary interfaces.
PARTICLE SENSORS Hydac MCS 1000 particle sensors were specially developed for such applications.
They can be installed seamlessly into the cooling lubricant circulation system, and at the moment they are the only sensors on the market that completely fulfill all the requirements of Germanischer Lloyd for particle sensors.
With a sensor diameter of 25 mm, ferromagnetic particles 200 µm and greater can be detected as well as nonferromagnetic particles of 550 µm and greater. Particles of this size are not normally found in a “healthy” gearbox, whose lubrication oil is typically constantly filtered with a filter fineness of 10 µm.
PARTICLE SWARMS
In the early phase of damage, large particles are normally not produced continuously, rather particle swarms sporadically appear. This occurs when material splits off from a surface and falls directly into the oil sump or goes through the tooth flanks and is crushed.
Hydac
www.hydac.co.uk
Global Wind Alliance
www.globalwindalliance.com
According to the needs of the system, parametrizable switching outputs that signal the detection of particles, or digital interfaces such as the RS485 and the ethernet can be used.
The probability of a complete failure of the gearbox with a correspondingly lengthy downtime for the wind turbine and the loss of electricity production and the associated financial risk can thus be minimized.
www.windenergynetwork.co.uk
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