4200kVA Station type outdoor, exposed bushings, Pri 14.4/24.9kV, Sec 480/277Y three phase transformer.
External cable tray with multiple conductor runs per phase and neutral. Plant peaks at 3500 amps on 480V. Load is relatively balanced within 5%. Load is extruders, formers and lighting with an office on dry type transformer beyond their switchgear. 4-400HP AC motors on VFDs.
Y primary, Y secondary. SEL 735 metering the secondary.
Transformer has been in service 4 years. Plant reports there have been no changes in one year or more.
There is/was no voltage or plant operation's complaint.
Wildlife protection was on the secondary bushings. On X1 that wildlife guard started smoking and thermal showed 420F.
Extensive checks were made to include lifting manhole and looking at oil and connections. No definite cause but secondary bushing was called bad.
Transformer was replaced with similar unit.
24 hours later the plant is up and running normal. X1 on the new transformer is hot.
Today at 7AM the T Delta between X1 and X3 is 128F.
6PM, with 3500 amps, the T Delta is 325F. Bushing shows to be 450F.
SEL shows voltage harmonics under 3% and no voltage sag. PF is 90-92 across the phases.
If the wildlife guard had not smoked and no access to thermal, we would be unaware of any issue with the transformer.
Ther is no operation complaint from the plant. They are running full bore. Loss of production from the transformer C/O and start up time is the complaint now.
If it last until morning, the plan is to start looking for stray currents.
I am looking for a direction.
Thanks,
External cable tray with multiple conductor runs per phase and neutral. Plant peaks at 3500 amps on 480V. Load is relatively balanced within 5%. Load is extruders, formers and lighting with an office on dry type transformer beyond their switchgear. 4-400HP AC motors on VFDs.
Y primary, Y secondary. SEL 735 metering the secondary.
Transformer has been in service 4 years. Plant reports there have been no changes in one year or more.
There is/was no voltage or plant operation's complaint.
Wildlife protection was on the secondary bushings. On X1 that wildlife guard started smoking and thermal showed 420F.
Extensive checks were made to include lifting manhole and looking at oil and connections. No definite cause but secondary bushing was called bad.
Transformer was replaced with similar unit.
24 hours later the plant is up and running normal. X1 on the new transformer is hot.
Today at 7AM the T Delta between X1 and X3 is 128F.
6PM, with 3500 amps, the T Delta is 325F. Bushing shows to be 450F.
SEL shows voltage harmonics under 3% and no voltage sag. PF is 90-92 across the phases.
If the wildlife guard had not smoked and no access to thermal, we would be unaware of any issue with the transformer.
Ther is no operation complaint from the plant. They are running full bore. Loss of production from the transformer C/O and start up time is the complaint now.
If it last until morning, the plan is to start looking for stray currents.
I am looking for a direction.
Thanks,