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From the mid-1960s to the early 1980s, Curtiss-Wright, a famous name in the history of aviation, packaged and sold more than 50 MOD-POD gas turbine units.
Both 25 MW single-ended and 50 MW double-ended MOD-PODs were produced which featured gas generators from either Rolls-Royce or Pratt & Whitney paired with power turbines designed and built by Curtiss-Wright.
When serious problems with power turbine and expansion joint components of these units began to surface, Curtiss-Wright mandated a de-rating which resulted in a 20% reduction in maximum power output.
After Curtiss-Wright dropped out of the gas turbine business, Fern Engineering purchased all of their spare parts inventory and redesigned or reverse-engineered many of the original components, identifying deficiencies and developing improved replacements in the process.
Fern now offers MOD-POD owners six redesign hardware kits which are applicable to all of these units.
The kits can be fabricated and installed by Fern in 300-350 days and can boost the output of OEM units by as much as 25%.
Fern Engineering-designed hardware kits provide power solutions in six specific areas:
To eliminate thermal cracking, a complete redesign of the casing was required, utilizing an upgraded material, thermal shielding, and isolating segments.
The modification resulted in reduced operating temperature, reduced transient differential temperature, unlimited low cycle fatigue life and unlimited creep life.
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The redesign of the centering ring eliminates loose fitting keys and the associated vibration.
The assembly is effectively de-tuned by adding stiffening and damping to the inner core.
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The support ring has been redesigned to accomodate a restraining pilot diameter.
This restraint prevents the flange from outgrowing its mating part and eliminates bolt bending and failure.
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The blade tip seals have been strengthened by increased thickness.
Additionally, improved material has been utilized for the first stage.
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The rear flange has been replaced with a short conical section and conventional bolted flange.
This flange is fabricated from a much improved material which is shielded by the housing, minimizing distortion.
The conventional flange attachment to the turbine case eliminates hot gas leakage.
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The expansion joint has been upgraded by replacing the convolutions with improved material.
The inner flow liner has also been changed to minimize liquid entrapment.
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The components in the Fern kits are not merely reverse-engineered replicas of the OEM parts.
In many cases, they are completely new designs that feature upgraded materials and design elements that resist fatigue failures.
For example, the Fern power turbine casing in Kit 1 uses Inconel 625 which provides high creep and stress rupture strength while also giving good resistance to low cycle fatigue.
In addition, Fern's design includes isolating elements and radiation shields that allow the casing shell to operate at lower temperature than the original design.
The combination of improved materials and lower operating temperature results in a design that has effectively unlimited creep and low cycle fatigue life.
Since 1988, a total of 6 double-ended MOD-POD gas turbines have been upgraded with power turbine casings (Kit 1) and various other Fern Engineering MOD-POD kits.
The high-time unit has accumulated in excess of 6500 hours and 1000 starts.
Recent inspections have revealed the units to be in excellent condition with no distress.
Clients include Newfoundland & Labrador Hydro, Hydro Quebec and The Electricity Corporation of New Zealand (ECNZ).
At its power station in Cadillac, Quebec, Hydro Quebec implemented an upgrade of new turbine casings (Kit 1), blade tip seals (Kit 4), inlet housing rear flange (Kit 5) and transition piece expansion joint (Kit 6) on each of its three MOD-PODs.
Fern fabricated the components via source-approved vendors, arranged for packaging and shipment and provided installation supervision.
The upgrade, valued at approximately $3.5 million (USD), allowed Hydro Quebec to increase the rating of the station from 120 to 150 MW and recover the penalty imposed by the OEM at a cost of about $120/kW - significantly less than the cost of installing a new 30 MW simple cycle gas turbine.
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P.O. Box 3380