headsUP: Clutches

Install a clutch, increase cash flow by providing ancillary services

Morgan Hendry, SSS Clutch Company Inc, told the editors he’s seeing more interest in clutches these days as rapid deployment of intermittent renewables—wind in particular—forces grid companies to contract for ancillary services—such as fast-start generation, voltage support, etc.
   Having a clutch allows plant operators to disconnect the generator from its driver when, for example, it is more important to regulate reactive power for grid voltage support than it is to produce kilowatt-hours. The clutch typically is retrofitted on a non-geared machine by breaking the coupling that connects a gas or steam turbine and its generator and moving the latter a short distance to provide the space required. A geared retrofit is easier and less costly because the clutch is built into the existing gearbox.
   When the clutch is open, the generator behaves as a motor. Its field is controlled by a voltage regulator to either produce or absorb reactive power as needed. Advantage of the so-called synchronous condenser is the ease with which the amount of correction can be adjusted.
   Hendry said his company recently provided clutches to the engine OEM for four new LM6000s being installed at a major East Coast utility. They are replacing tired FT4s which suffer high losses in spinning reserve (fast start) service. With the clutch open on an LM6000 and its generator connected to the grid, the “motor” draws only about 400 kW, which is far less expensive than operating a hard-coupled turbine/generator at low load.
   When power is needed, the gas turbine is started and comes up to speed (the generator already is at speed). The clutch then engages automatically and the unit spins idle for a short time and is loaded to meet demand. The nameplate rating can be reached in about eight minutes.

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