Calculating MW in hydroelectric bypass using extended penstock

Discussion in 'The Projects Forum' started by Jan van Eck, Mar 21, 2015.

  1. Jan van Eck

    Thread Starter New Member

    Mar 21, 2015
    Hi, all!
    I am working on an interesting project for development of hydro power in the State of Vermont. Here is the background: there is a current dam located on the Lamoille River about 3 miles from the confluence with Lake Champlain, output elev. about 101 ft. MSL. (Near Milton, VT) The dam ["Peterson Dam"] is an old concrete beast about 51 ft high, but the effective generating head is about 45 ft. The current penstock is 8 ft diameter and the generating capacity is 6.23 MW. The idea is to remove the dam as it has hurt the fishery by wiping out the running-water area where certain fish spawn. The Power Board did not do that (reluctantly) because of the costs of replacing the generated power with new purchased power.

    When you look at the lay of the land then you see that the River upstream has two further dams about 2.7 miles up, with a vertical climb to the upper reservoir to 293 ft. MSL. Extending the penstock underneath a current open-lands pathway (has a local power line running over it) from the current generator to the upper pond would increase the generator head from 45 ft to about 190 ft., which is greater than the head at Niagara Falls (177 ft).

    Assuming direct proportionality, the existing-diameter penstock of 8 ft. should have an increased generating capability of 400%, boosting output from 6.23 MW to 25 MW. That is a significant boost. What makes this attractive is that the current generator house, transformers, switchgear, power lines, breakers, all the rest of the "stuff" does not have to be dismantled or scrapped; all that his happening is that the penstock pipe is moved from an inlet just above the existing Peterson Dam to the upper reservoir located North of the Town of Milton. Meanwhile, the old dam can be deconstructed, and the fish spawning grounds restored, all without disturbing the water flow rates that run from the intermediate dam to the current site.

    It would be optimal to boost the project to a baseline generating capability of 45 MW. To get there, one option is to simply "twin" any penstock pipe, so you run two parallel and independent pipes. This has the advantage of being easy (thus cheap) to build, but has the disadvantage of a greater system loss due to friction on the internal bore (more surface area). As a trade-off, going with a lower-cost, easy-to-build, simple system that can be expanded is better than a big fancy system that has a larger floor capital-cost base.

    Here come the technical questions: can the current turbine and generator be used, with the increased pressure head, by installing a restrictor to limit the power input to the existing 6.2 MW? I have to assume that this old turbine set-up has physical limits that preclude exposing it to this dramatic increase in pressure head. Since the machinery is in fine shape, it would be a shame to have to scrap it.

    How to design a splitter or diverter to put water into parallel generators?

    How do we get the parallel generators to synchronize properly? Will the system require a synchronous condenser, and if so, how big?

    The current power utilization factor is about 0.45. I would have to expect that any new installation would end up with about the same.

    Any and all ideas gratefully solicited. Thanks!
    Jan van Eck
    DJ Engineering