AOC 15 user manual Braking System

12.0 Troubleshooting 96

This section contains a brief discussion of each major wind turbine component and the control system. See Section 12.7 for a summary of troubleshooting guidelines and recommendations.

When troubleshooting it can generally be assumed that only one fault exists. A failure can be due to a malfunctioning component, one that still works but with reduced capacity, a broken connection (mechanical or electrical), a set point which has drifted from its original calibration, a loose or poor electrical connection, an improperly grounded cable shield or an intermittent problem, i.e. one that can fall into any one of the previous categories after a certain period of time.

Multiple failures can occur but are not typical and normally it will not be clear from the outset whether a failure has single or multiple causes. The best course of action is to assume a single failure and proceed to correct the obvious symptoms first. As troubleshooting progresses, additional causes or failures can come to light.

12.1Braking System

The braking system comprises three independent subsystems: the dynamic brake, the parking brake and the tip brakes. The dynamic brake employs a resistive capacitive circuit to slow rotation by dissipating rotational energy in the resistive network while maintaining some excitation. During normal shutdowns the parking brake is delayed to prevent excessive loading of the wind turbine transmission system. During emergency shutdowns the parking brake is applied immediately and to prevent overloading of the turbine the dynamic brake is detuned by switching out part of the capacitor circuit. The capacitor network consists of two distinct, relay controlled stages and for a shutdown due to power loss, one stage of the capacitors will not be active. See Figures 12.1-1 to 12.1-4 for depictions of the brake systems.

The tip brakes are electro-magnetically controlled. The tip brake magnets receive their power from the rotary transformer through a bridge rectifier located in each tip brake. Should the rotor over-speed, power to the magnets is cut and the tip brake plates swing away from the blade end due to centrifugal force, slowing the rotor down. Should a power loss occur in the grid, all three braking systems (dynamic, tip, and parking brakes) deploy simultaneously.

Should all tip brakes deploy prematurely, their electric circuits should be checked, as well as the rotary transformer, which could have developed a fault. If only one tip brake deploys prematurely, its magnet’s setting should be checked, in addition to its electrical circuit. The surfaces of both the magnet and catch plate should be checked for nicks, corrosion and debris. Both must be smooth and flat for optimal operation. The vertical position of the magnet with respect to the hinge block should also be checked. It can be adjusted using the threaded rod attached to the magnet.

A deployed tip brake can also indicate a failure of a drive train component or of the dynamic brake. Deformation of the tip brake plate could be caused by an excessive holding force, due to a faulty magnet or corrosion, combined with rotor over-speed, heavy hailstone impact or by ice being shed from the blades.

NOTICE: Use of the material contained in this document is subject to the warning on page Iv and the disclaimer on page v of this document.

DOC012R02 AOC 15/50 User Manual Nov 2001