Heavily Tracked Bushing Detected in Hydrogen Cooled Turbo Generator

Published Aug 29th, 2019


Italian Utility

Machine Description:

390 MW, 20kV, Hydrogen Cooled Turbine Generator

Two Bus Couplers per phase

CASE STUDY: Heavily Tracked Bushing Detected in Hydrogen Cooled Turbo Generator

During a partial discharge measurement using the TGA-B portable instrument, high levels of PD activity (over 3000mV position, well above the highest range, see Figure 1) were detected on the C phase outside of the hydrogen environment. As consequence, the user briefly shut down the unit for a visual inspection to verify the mechanical connections in the main lead areas and to inspect the generator bushing for cracks or signs of tracking. The user found that the generator bushing of phase C was heavily tracked (Figure 2). The plant had changed from a base to peak load operation, which may have accelerated the electrical tracking (due to condensation when the unit is off).

Figure 1. Graph showing high level system noise (OVR: out of range)

Figure 2. Heavily tracked generator bushing (photo taken after cleaning)

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