A slewing apparatus, comprising a slewing bearing means for the operation of a reel. The disclosed improvements are field retrofittable. The outer ring may be mounted concentric to the inner ring and be movableslidable with respect to the inner ring. The encrypted Ethernet traffic is also tunneled within Multi-Protocol Layer Switching tunnels from the edge to the edge of the service provider network. In order to solve such problem, a generation system in the present invention is equipped with an exciter that estimates the slip frequency of the doubly-fed machine from each primary current I1 and voltage V1 and secondary current I2 and voltage V2 of the doubly-fed machine and excites the secondary of the doubly-fed machine at the estimated slip frequency.