In 1971, General Electric finally offered a power plant of the size that most electric utilities wanted 6 years earlier after the Northeast Blackout of 1965. It was called the model series MS7001 package power plant.
Also known as the Frame 7, it was rated approximately 40 megawatts, making it nearly three times the generating capacity of a MS5001J (frame 5) at the time of the Blackout in 1965. This pleased many utilities. The first MS7001A (S/N 214053) was manufactured in Schenectady, NY. After significant testing, it was sold and installed at Long Island Lighting Company in West Babylon, NY. A bevy of other Frame 7s units soon followed. Those were designated the MS7001B power plants, they were all built at GE’s new facility in Greenville, SC. Notable power companies as Philadelphia Electric, Houston Lighting & Power and Florida Power & Light, Florida Power Corp, Tennessee Valley Authority and Georgia Power purchased hundreds of Frame 7s in the middle to late 1970s. Replacing the Frame 5 as the unit of choice, GE finally offered a peaking power plant of the rating wanted by most electric utilities desired. However, the Arab Oil Embargo of 1973-74 would soon change the entire climate of gas turbine power generation.
Fig. 11-1 below shows a typical MS7001B power plant in Greenwood, Missouri (installed circa 1975). This unit is rated approximately 50 MW. The rated speed for the turbine and generator was 3600 rpm. Driving a 2-pole, air-cooled generator, this meant that 60-cycle power could be delivered without the need for reduction gearing as is required on the Frame 5.
The Frame 7 retained many of the design features made popular with the Fame 5. It was a modular design. The generators were manufactured in Lynn, Massachusetts, meaning that they never met the gas turbine until at the installation site. The accessory base was separate too, so the interconnections (electrical, mechanical, pneumatic and hydraulic) were done for the first time at the jobsite.
For visual effect, as shown in Fig. 11-1 and 11-2, appearance lagging was installed around the major components to make the site more appealing to the passersby. This was particularly important for the exhaust stack which often rusted and become an eyesore because of its needed height (see left of Fig. 11-1).
Fig. 11-2 below shows a typical MS7001E power plant in Pleasant Hill, Missouri (installed circa 1980). This unit is rated approximately 65 MW.
One distinguishing feature of the Frame 7 is the turbine section. It has three stages as shown in Fig. 11-3 below. Each stage has nearly 100 blades (a.k.a. at GE as buckets) to develop the power to the aft turbine stub shaft which is bolted at the flange to the generator rotor.
A seventeen-stage compressor rotor was developed for the Frame 7 to increase air flow and deliver higher compressor discharge pressure to the combustion system. See Fig. 4.
Most of the auxiliaries required to support the operation of a Frame 7 (shown in Fig. 11-5) are all installed on a separate accessory base. The accessory gear box, shown on the left, drives such auxiliary pumps as the main lube oil, main hydraulic supply pump and the positive-displacement fuel pump. The power to drive the gear comes from the cranking motor (during start-up) and the gas turbine itself (during operation). The motor control center, with motor starters for such secondary pumps as the auxiliary lube oil, water pump and hydraulic supply pump, is typically on its own skid and installed at the front of the accessory compartment.
The accessory base has many auxiliary devices used to support the operation of the gas turbine. There are many devices driven by the accessory gear of a frame 7:
- Lube oil pump
- Atomizing air compressor (on some turbines, if applicable)
- Hydraulic supply pump
- Liquid fuel pump (if applicable)
Frame 7 gas turbines are always started with electric (cranking) motors. The schematic drawing (Fig. 11-8) below shows a motor (called 88CR). It has a flexible coupling on the output shaft connecting to a torque converter. A starting atomizing air (AA) compressor is identified. It was belt-driven by the starting motor to provide compressed air for atomization of the fuel during the firing, cross-firing and acceleration periods of the start-up. Once the overriding, jaw-clutch disengages (approximately 60% speed during start-up), a motor-driven AA compressor located on an off-base skid had to be operational.
If “black start” capability was required at the site, a separate diesel generator was utilized to provide power to the starting motor (88CR) and the off-base auxiliaries including:
- Fuel forwarding pump
- AA compressor
- Cooling water pump,
- AC lube oil pump
- 480 volt AC battery charger
The Frame 7 typically gas turbine had several off-base, skid-mounted auxiliaries:
- Liquid Fuel Forwarding (similar to the frame 5)
- Atomizing Air
- Cooling Water
- CO-2 Fire Protection
- Compressor Water Washing
- Water or Steam Injection
These auxiliary systems were connected to the turbine control panel and motor control center.
The MS7001B can be said to have “saved” GE’s Gas Turbine Division, because it met the demand for emergency power in the USA and Canada, as well as larger islands like Puerto Rico. This design has evolved to the MS7001EA forty years later, doubling its original power output to 80 megawatts.