Hydro: Comerford 15 Mile Falls Project, Monroe NH

This project was accomplished in two years beginning in 1928. A special railroad was built to bring in construction materials and equipment. At its time, it was one of the largest hydro projects in the nation.

Our class drove north for an hour on Interstate 91 from Hanover along the Vermont side of the Connecticut River. A scenic overlook featured this sign and a view of the Comerford dam on the river. It is the second of three dams along the 15 mile descent of the river dividing New Hampshire and Vermont.

The 1928 constuction crew is installing a 16 foot diameter penstock, to lead the water from the reservoir down through the dam to the turbine 159 feet below.

We continued north then crossed the river into New Hampshire on I-93 to Monroe NH where we arrived at the Moore reservoir, dam, and hydroelectric power station, the farthest upstream of the three -- Moore, Comerford, and MacIndoes, generating respectively 192 MW, 164 MW, and 13 MW of power. TransCanada is the utility that owns and operates them. The view round this northern lake is unspoiled; there are no private cottages because the utility owns the land. There is boat and picnic access for the public

The dam is 178 feet high, with 159 of gross head -- the distance the water falls to the turbine. Looking upstream at the dam we see the turbine building, with four structures above the dam to raise or lower gates that let the water flow to the four turbines

Atop the dam, Merle Jones (distant) tells Walter Noll how these gates rotate up to allow water to flow down the sluice, without making power, if necessary. The utility makes money by selling electricity at the time during the day it is most valuable. Coal and nuclear power plants operate continuously, to satisfy base load requirements. When electric demand increases (at the beginning of the work day, at lunch, and and the end of the day), hydro plants like this can selectively dispatch the additional power by increasing the flow of water through turbines. Thus the water stored in the reservoid is an asset, to be expended at the most profitable times -- during peak demand.

There are environmental protection regulations about the levels of the ponds and rates of flow of water in rivers in the Comerford Project area. A minimum flow is required in rivers so that fish do not die. So a minimum amount of water always flows through the turbines, making electricity at all times, not just during peak (most profitable) demand. This base load power sells for about 3.5 cents per kWh. The utility makes most of its money during periods of peak demand, when the market will pay 5-6 cents per kWh.

TransCanada is concerned about safety of workers and visitors, so we all had to wear hard hats, safety glasses, and don arc suppression protection suits. If current-carrying high voltage switchgear happened to open up while we were near such a switch, there could be a temporary arc as current continues through ionized air until the switch is fully opened and the current flow stopped.

This large generator is on the top floor of the turbine building. It makes electric power by passing wires through magnetic fields. The magnetic fields are created by current from the smaller DC generator at the top.

The 56,400 horsepower turbine below the generator turns a common shaft at 128.6 rpm generating 39,000 KVA (kilovolt-amperes), about 39 MW.

The shaft turns relatively slowly, 2.143333 turns per second. There must be 28 windings around the stator to make electric power at 60 cycles per second.

The water discharged at the bottom swirls about. Seagulls and eagles hunt there for any dizzy fish swept through the turbine.

Here is a spare water wheel that goes inside a turbine.

Merle Jones showed us the control panels for the four generators at this plant. Today the plant is controlled remotely via microw
ave communications links.

Generator number 4 is sending out 38 MW of power at 1700 amperes. 

At the end of the afternoon we drove downriver to the next hydro station, Comerford, capable of an additional 164 MW of power. The public is welcome to picnic and launch boats on the sandy beach of the reservoir.
Thank you to Merle Jones, Matthew Cole, and TransCanada for ushering our Dartmouth ILEAD Energy Safari class through this impressive power source.

Oct 18
Host: Matthew Cole
Monroe NH by car pool
MacKay pp: 55-56
Robert Hargraves,
Oct 17, 2011, 3:27 PM