Acoustical FEM simulation of partial discharge in large scale generators

The presented acoustic diagnostic routine is focused on insulation faults of gas-turbo generators. Finite element method (FEM) is used to model a void in bar insulation. Constant pressure is assumed for void. When partial discharge (PD) occurs, propagated sound energy in stator and surrounding air is simulated. Simulation shows that released sound from a PD pressure strongly influences in core sheets but it gets weak when arrives to air gap or surrounding air. It means most of the released energy by PD is detected with piezoelectric sensors which are placed across each slot or locally mounted on the stator. Sensors placed underneath the wedges or slots, find the PD locations. When used together with electromagnetic probe, piezoelectric sensors are reliable for pinpointing sites of high PD activity, such as slot discharge. For system modeling a Mitsubishi 85 MW, 11 kV gas-generator is used. Broken tooth caused this generator to trip. One of diagnoses for this trip is slot PD. Simulation shows sound pressure is limited to the PD point and is not affected by environmental acoustical noises. Acoustic sensors can distinguish between slotdischarge and internal coil PD, but are not able to make discrimination between positive and negative pulses.

Keywords:

Partial discharge , FEM simulation , acoustic