Prime-mover dynamo plants – Electric control – Fluid-current motors
Reexamination Certificate
1998-11-30
2001-07-24
Enad, Elvin (Department: 2834)
Prime-mover dynamo plants
Electric control
Fluid-current motors
C290S042000, C290S043000, C290S053000, C290S054000, C290S055000
Reexamination Certificate
active
06265785
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to wind turbines. More particularly, the present invention relates to overspeed protection for wind turbines.
BACKGROUND OF THE INVENTION
Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) typically include a “fail-safe” mechanical braking system that is applied in the absence of electrical power in the utility grid, or excessively fast rotation of the turbine hub (overspeed). However, for wind turbines having large rotors (e.g., 30 or more meters in diameter), application of a mechanical brake results in structural loads to the turbine blades, the gear box and the tower. These structural loads shorten the useful life of the wind turbine.
One braking solution is aerodynamic braking of the turbine by pitching the blades of the turbine to reduce rotational speed of the hub. Aerodynamic braking reduces structural loads applied to components of the wind turbine when power is provided by the utility grid. However, when power is not supplied by the utility grid, the mechanical fail-safe braking system is applied to stop rotation of the wind turbine. In an environment where utility grid interruptions are common, caused by, for example, multiple power outages, poor line conditions, or other interruptions, frequent use of the mechanical braking system can shorten the useful life of a wind turbine.
What is needed is a braking system for a wind turbine that applies a mechanical brake for overspeed conditions during short power outages and not automatically upon loss of power.
SUMMARY OF THE INVENTION
A method and apparatus for a non-volatile overspeed protection for wind turbines is described. The wind turbine includes a sensor coupled to sense a rotational speed of a hub and a braking system to reduce the rotational speed of the hub when activated. A control circuit is coupled to the sensor and to the braking system to activate the braking system if the rotational speed of the hub exceeds a predetermined rotational speed during a predetermined time period after external power supplied to the wind turbine is lost. A low-pressure trigger valve activates the braking system when hydraulic pressure in the braking system falls below a predetermined threshold. In one embodiment, a non-volatile power supply provides power to the control circuit in the absence of external power.
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Christenson Craig Leonard
Cousineau Kevin Lewis
Blakely , Sokoloff, Taylor & Zafman LLP
Enad Elvin
Zond Systems Inc.
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