Interlamination voltages in large turbogenerators

Currents flowing in the stator-core frames of large electricalmachines

“…When this happens, they cause overheating at the core-back contact with the building bars and they flow to the tooth roots and slot bottoms of the core plate, causing further local overheating. Core laminations may then become welded together, as described by Jackson [4] and Oberretl [8]. This confirms the proposal in Section 3.4 that, when frame currents flow into the stator core, they are controlled by the internal axial flux of the core, and the consequential current path can lead to overheating.…”

“…5. This behaviour has been described by Jackson [4] and is similar to the propensity of the building-bar currents to flow into the clamping-plate screen, if the frame construction permits it, as described in Section 3.…”

“…7 which was developed from Reference 4. Pattern of building bars to core, to core end currents proposed by Jackson [4] Flux directions compatible with Fig. 2 …”

“…5. This current constraint gives rise to substantial interlaminar potentials, as described by Jackson [4], which may break down the interlamination insulation and lead to bridging of the laminations and a removal of the current constraint. This can then cause significant heating and melting of the lamination steel and, hence, growth of the damaged area.…”

Experimental Model for Study of Electromagnetic Phenomena in Stator Core-End Laminations of Large Generators

“…However, it still induces high eddy currents and inter-lamination voltages in stator packets [7]. These effects might damage the stator core by breaking down the insulation layer between laminations and thus providing a closed path for a fault current.…”