Braking loads

Most turbines have the mechanical brake located on the high-speed shaft, with the result that braking loads are transmitted through the gearbox. If, as is usually the case, the mechanical brake is one of the two independent braking systems required, then it must be capable of decelerating the rotor to a standstill from an overspeed, e.g., after a grid loss. This typically requires a torque of about three times rated torque.

The mechanical brake is only required to act alone during emergency shutdowns, which are comparatively rare. During normal shut-downs the rotor is decelerated to a much lower speed by aerodynamic braking, so the duration of mechanical braking is much less, but the braking torque is the same, unless there is provision for two different braking torque levels.

Figure 7.26 is a typical record of low-speed shaft torque during a normal shut-

Braking Torque

Figure 7.26 Low-speed Shaft Torque During Braking at Normal Shut-down. Extracted from AGMA/AWEA 921-A97, Recommended practices for design and specification of gearboxes for wind-turbine generator systems, with permission of the publisher, the American Gear Manufacurers Association, 1500 King Street, Suite 201, Alexandria, Virginia 22314, USA.

Figure 7.26 Low-speed Shaft Torque During Braking at Normal Shut-down. Extracted from AGMA/AWEA 921-A97, Recommended practices for design and specification of gearboxes for wind-turbine generator systems, with permission of the publisher, the American Gear Manufacurers Association, 1500 King Street, Suite 201, Alexandria, Virginia 22314, USA.

down, in which the mechanical brake is applied as soon as the generator has been taken off-line. It is apparent that the braking torque is far from constant, taking about 2 s to reach its first maximum and then falling off slightly before reaching a higher maximum just before the high-speed shaft stops. Following this, there are significant torque oscillations due to the release of wind-up in the drive train. These result in torque reversals accompanied by tooth impacts and take some time to decay.

Although braking loads are infrequent and of short duration, their magnitude means that they can have a decisive effect on fatigue damage. The AGMA/AWEA document (1996) recommends that the time histories of braking and other transient events are simulated with the aid of a dynamic model of the drive train for input into both the gear extreme load design calculations and the fatigue load spectrum.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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