GENERATOR ROTOR REFURBISHMENT
Generator Rotor Rewind
The rotor is the most susceptible component in the generator to operating incidents such as motoring or negative sequence currents. It is also subjected to very high centrifugal forces during normal operation. Thus, it is the component that requires the most maintenance in the generator. The rotor rewind involves a replacement of all field winding insulation.
TYPES OF INSULATION
There are three types of winding insulation used for generator rotors. The first type consists of taped winding turns (Fig. 18.7). Every other turn including the end turns is taped with mica mat tape. This system requires the most labor due to the hand taping required. However, it is the least expensive and provides the best contamination protection.
The second insulation system involves the use of strip turn insulation in the slots and taped ends. Every other turn is taped with mica mat tape. This system permits the use of wider copper in the slots, while still providing protection against contamination in the end winding region.
The third system involves the use of “all strip turn insulation.” It is normally used in applications requiring improved cooling in the end winding. The insulation strips are nor- mally made of Nomex or glass laminate (Fig. 18.8).
There are two types of material used for ground insulation (or slot armor). The first is a rigid armor made of a glass base. This material has high mechanical strength. The second type is Nomex. This material is tough and flexible.
The retaining ring insulation provides the ground insulation in the end winding region (Fig. 18.9). It is strong to be able to withstand the centrifugal forces. It normally has an outer layer of glass and an inner layer of Nomex.
The end winding blocking supports the winding and prevents distortion while allowing for thermal expansion (Fig. 18.10). The material used in modern rotors is epoxy glass laminates.