Pratt & Whitney FT4 / GG4 Twin Pac
Manufacturer: Pratt & Whitney
Pratt & Whitney's J75-derived aeroderivative, sold by the thousand as 1960s and 1970s utility peakers and paired as the 42 to 53 MW Twin Pac.
This model is part of SecondWatt’s gas turbine research catalogue. Specifications and price observations are included where supported by sources. Equipment availability and commercial terms require confirmation.
Pratt & Whitney FT4 / GG4 aeroderivative and the 42 to 53 MW Twin Pac: history, ratings, fuel and water injection, support through independent GG4 shops.
The Pratt & Whitney FT4 is an aeroderivative gas turbine developed from the J75/JT4 turbojet; development began in 1961 for the US Navy and the engine first ran late in 1962 (Wikipedia). Delaware Power and Light installed a natural-gas FT4A package driving a 15 MW generator in 1963 (POWER). By June 30, 1976, more than 1,000 units had been sold with over 5 million operating hours (Wikipedia).
Two package configurations serve power generation: the Power Pac, one GG4 gas generator and FT4 free turbine driving a generator, and the Twin Pac, two trains driving one generator (POWER, Stratford Power Station). Stratford in New Zealand ran four 50 MW Twin Pacs on natural gas in open cycle from 1976 (Stratford Power Station). The FT4A-9 Twin Pac is rated 42 MW with one side alone at 21 MW (marketplace record), and the FT4C-3F Twin Pac 53 MW at 59 °F (packager sheet).
The product line became Pratt & Whitney Power Systems in 2000, PW Power Systems under Mitsubishi Heavy Industries in 2013 and Mitsubishi Power Aero in 2021 (Wikipedia). Mitsubishi Power Aero's aftermarket catalog covers the FT8 and FT4000 (Mitsubishi Power); GG4 and FT4 parts, component repair, overhaul and engine lease are carried by independent shops (Johnson Turbine Support, Worldwide Turbines).
Why it matters
The OEM lineage holder's aftermarket catalog covers the FT8 and FT4000 (Mitsubishi Power), so GG4 and FT4 support runs through independent shops with rotable-exchange and engine-lease programs (Johnson Turbine Support, Worldwide Turbines). A Twin Pac delivers 42 to 53 MW at 13,800 V and reaches full load in under four minutes (marketplace record, packager sheet).
Who buys it
Utilities bought FT4 packages as fast-start, black-start peakers in the wave of orders that followed the 1965 Northeast blackout (POWER). Twin Pac plants have served as national reserve generation; Stratford's four units ran on natural gas from 1976 (Stratford Power Station).
Key specifications
| Derivation | J75/JT4 turbojet |
|---|---|
| Development start / first run | 1961 / late 1962 |
| First commercial unit | Delaware Power and Light, 1963, natural gas, 15 MW generator |
| Units sold by 1976-06-30 | over 1,000 units |
| Fleet operating hours by 1976-06-30 | over 5 million hours |
| Twin Pac configuration | two GG4/FT4 trains driving one generator |
| Stratford, New Zealand, 1976 | 4 × 50 MW Twin Pacs, natural gas, open cycle |
| FT4A-9 output, single train | 20 MW |
| FT4A-9 Twin Pac output | 42 MW |
| FT4A-9 Twin Pac, one side | 21 MW |
| TP4-2 Twin Pac output, natural gas, 60 Hz | 50 MW |
| FT4C-3F Twin Pac output at 59 °F | 53 MW |
| FT4C-3F operating modes | 20 or 50 MW |
| FT4C-3F minimum load | 10 MW |
| FT4C-3F time to full load | under 4 minutes |
| FT4C-3F generator connection | 13,800 V |
| FT4C-3F demineralized water for NOx control | 20 to 50 gpm |
| FT4C-3F continuous operation | 14,000 hours |
| Lineage | PWPS 2000; PW Power Systems 2013; MHPS 2017; Mitsubishi Power Aero 2021 |
| OEM successor aftermarket scope | FT8 and FT4000 |
Major variations
FT4A-9: 20 MW per train (marketplace record); 42 MW as a Twin Pac and 21 MW on one side (marketplace record). TP4-2 Twin Pac: 50 MW on natural gas at 60 Hz (marketplace record). FT4C-3F Twin Pac: 53 MW at 59 °F, with 20 MW and 50 MW operating modes (packager sheet).
Configurations and options
The FT4C-3F Twin Pac is a self-contained outdoor plant with a 10 MW minimum load, 20 MW or 50 MW modes, black-start capability, full load in under four minutes and a 13,800 V direct main-breaker connection; NOx control uses demineralized water at 20 to 50 gpm, doubling in the 50 MW mode (packager sheet). A Twin Pac can run one train alone at half output (marketplace record).
Compatibility and dependencies
Fuel: the first commercial FT4A burned natural gas (POWER), Stratford's Twin Pacs ran on gas (Stratford Power Station), and FT4 peakers also run on diesel (marketplace record). Water injection on the FT4C-3F Twin Pac needs a demineralized water supply of 20 to 50 gpm (packager sheet).
Lifecycle and maintenance
The GG4 gas generator is serviced on an exchange basis: Johnson Turbine Support stocks new surplus, overhauled and newly manufactured GG4 and FT4 parts with a rotable exchange program (Johnson Turbine Support), and Worldwide Turbines overhauls and leases GG4 and free-turbine engines (Worldwide Turbines). A packager's FT4C-3F Twin Pac sheet cites 14,000 hours of continuous operation (packager sheet).
Thermal and emissions profile
The FT4C-3F Twin Pac uses demineralized water injection at 20 to 50 gpm for NOx control, doubling in the 50 MW mode (packager sheet).
Inspection checklist
Gas generator and free-turbine overhaul records and exchange history (Johnson Turbine Support). Water-injection system condition and demineralized water supply (packager sheet). Generator rating and the 13.8 kV main-breaker interface on Twin Pac packages (packager sheet). Fuel history: natural gas, diesel or both (POWER, marketplace record).
Procurement channels
Mitsubishi Power Aero aftermarket services cover the FT8 and FT4000 (Mitsubishi Power). GG4 and FT4 parts, exchange, overhaul and engine lease: Johnson Turbine Support (Johnson Turbine Support), Worldwide Turbines (Worldwide Turbines) and Global Turbine Support (Global Turbine Support). Used FT4 packages and Twin Pacs appear on industrial equipment marketplaces (marketplace record).
Regional notes
The FT4 fleet is largely North American utility equipment; the first commercial unit ran in Delaware in 1963 (POWER). Stratford, New Zealand, ran four Twin Pacs from 1976 (Stratford Power Station).
Content owner: Gary Martin, SecondWatt