A brake system is provided for controlling a rotational speed of a drivetrain for a wind turbine. The drivetrain is coupled to a rotor shaft and a generator rotor shaft. The brake system includes a mechanical brake operatively coupled to the drivetrain. The mechanical brake includes a brake caliper and a brake disc coupled to the drivetrain. A sensor is configured to detect a parameter of the wind turbine. A controller is configured to actuate the brake caliper to apply a braking force on the brake disc. The controller is configured to control the mechanical brake based on the parameter to adjust a brake torque generated by the braking force.