aolalde
Electrical
- Dec 16, 2003
- 1,022
We have four Synchronous Generators Diesel Engine driven and a Static Reactive Power Module 20 MVAR, all synchronized to the utility power line. The four generators are identical size and manufacturer; 15 MVA, 12 MW, 400 RPM, 13.2 kV. 60 HZ, field Voltage 267 VDC, and current 231 DCA. The generators are brushless excited, with a rotating 6 diode rectifier and AC 59 kW, 26.7 HZ, 3-phase armature. The main rotor field has 18 poles one circuit series, the rotor outside diameter is 10.5 Foot.
The four generators under normal conditions provide 10.5 MW and 6 MVAR each one.( Very conservative load).
After 7 years in service, generator #1 failed. We found 3 of the 17 rotor field series jumpers fused.
Three poles were re-wounded, the jumpers were replaced and the unit reconnected in line. It last 2 days and the very same type of failure developed in the field connections again.
This time all 18 poles were rewound and all field connections replaced. The unit ran five days and developed the very same type of failure. Four jumpers making the interpole connection were totally melted and six pole windings were grounded. This time one pole shoe had five amortisseur winding bars totally fractured, each pole shoe has 12 bars. The rotor paint shows signs of overheating.
The stator winding does not shows signs of any damage and it test OK, insulation resistance, PI and comparison surge test.The rotor failure has been similar but involving different random poles.
The electric records during the days in operation show, that this generator #1 was generating an average of 10.5 MW but only around 3.9 MVAR and for the last 1.5 hours it worked as induction generator, taking reactive power from the line bus.
Questions:
1- Has somebody experienced a similar problem?
2- Why the series connections are melted but not the pole windings?
3- In theory when one jumper in the series connection melts, the field circuit is opened, what feeds the current to melt three more jumpers?
Any comments will be appreciated.
The four generators under normal conditions provide 10.5 MW and 6 MVAR each one.( Very conservative load).
After 7 years in service, generator #1 failed. We found 3 of the 17 rotor field series jumpers fused.
Three poles were re-wounded, the jumpers were replaced and the unit reconnected in line. It last 2 days and the very same type of failure developed in the field connections again.
This time all 18 poles were rewound and all field connections replaced. The unit ran five days and developed the very same type of failure. Four jumpers making the interpole connection were totally melted and six pole windings were grounded. This time one pole shoe had five amortisseur winding bars totally fractured, each pole shoe has 12 bars. The rotor paint shows signs of overheating.
The stator winding does not shows signs of any damage and it test OK, insulation resistance, PI and comparison surge test.The rotor failure has been similar but involving different random poles.
The electric records during the days in operation show, that this generator #1 was generating an average of 10.5 MW but only around 3.9 MVAR and for the last 1.5 hours it worked as induction generator, taking reactive power from the line bus.
Questions:
1- Has somebody experienced a similar problem?
2- Why the series connections are melted but not the pole windings?
3- In theory when one jumper in the series connection melts, the field circuit is opened, what feeds the current to melt three more jumpers?
Any comments will be appreciated.