WE HAD A MIGHTY RIVER - THE PINE PORTAGE GENERATING STATION

From: FORTY-THIRD ANNUAL REPORT OF THE ONTARIO  ELECTRIC POWER COMMISSION 1951
pages 84 - 87

PINE PORTAGE GENERATING STATION - NIPIGON RIVER

The Pine Portage Hydro-electric development, where one unit was placed in service on July 17, 1950, and a second unit on September 15, 1950, provides additional generating resources for the Thunder Bay System. The installed capacity is 60,000 kilowatts but this will ultimately be doubled by the installation of two more units.

The station is situated on the Nipigon River about 12 miles up-stream from Cameron Falls Generating Station and is the third and final project for the development of the whole potential of the Nipigon River between Lake Nipigon and Lake Superior. It is connected to Alexander Generating Station and to Port Arthur by 13 and 90 miles of transmission line, respectively.

The project comprises a gravity-type concrete dam, approximately 3,100 feet long with a maximum height of 140 feet in which the intake, spillway, and log-chute head-block are incorporated; a flood-water channel below the spillway; a power-house immediately down-stream from the dam on the west bank of the river; and a tail-race channel 600 feet long carrying the discharge from the draft-tubes to the Nipigon River.

DEWATERING THE SITE AND CLOSURE OPERATIONS

To dewater the site of the dam, a diversion channel (approximately 800 feet long) was excavated in the rock bluff on the west bank of the River. A section of the main dam with two concrete diversion ports was constructed in the channel with provision for steel gates which were later used to cut off the flow through the diversion channel when the dam was completed.

Rock-filled timber-crib cofferdams were then built across the river up-stream and down-stream from the limits of the dam and the river-flow was diverted through the channel.

The closure operation presented an exacting problem because it was necessary to maintain sufficient flow in the river at all times to ensure continuous operation of Cameron Falls and Alexander Generating Stations down-stream. It was found that this could be accomplished by carrying out the closure in three stages. In addition to  the diversion ports mentioned previously, two closure ports of equivalent size were constructed in the dam approximately half-way vertically between the diversion ports and the spillway.  Due to the steep slope of the river up-stream from the dam and the high banks through which it travels, it was possible to close off the diversion ports and raise the water to provide sufficient flow through the closure ports in a matter of hours. The second stage of the closure was accomplished by slowly throttling down the flow through the closure ports as the head-pond level rose. This maintained satisfactory flow for the stations down-stream until the head-pond reached the level of the spillway. The closure ports were then closed, and the flow to the plants down-stream was maintained by adjusting gates and stoplogs in the spillway sluices.

The two steel gates used first in the diversion ports and later in the closure ports were finally installed permanently in the spillway.

THE DAM

The main dam, except for 400 feet at the west end, has a standard gravity cross-section with an up-stream batter of 1 to 24 and an 8 and one half to 12 sloping face on the down-stream side. The dam has a top width of 12 feet west of the head-works and 14 feet 9 inches east of the head-works. The westerly 400 feet of the dam consists of a concrete bulkhead with a vertical up-stream face and a down-stream slope 8 and a half to 12. The elevation of this top of the bulkhead is 3 feet below that of the remainder of the dam. The bulkhead is covered with an earth fill having an up-stream slope of 2 and a half to 1, a down-stream slope of 3 to 1, and a top width of 20 feet. As several parts of the dam were constructed with form work supported by Bailey bridging, the vertical construction joints were spaced throughout to accommodate this type of construction. The joints were spaced alternately at 36 feet and 33 feet 4 inches. Horizontal construction joints were established at intervals not exceeding 50 feet. Some of the pours near the bottom of the dam were considerably less than this.

Steel water-stops 16 inches wide and one quarter inch thick were placed in both the horizontal and vertical construction joints  near the up-stream face. Half the width of the water-stop was embedded in the first block of concrete poured and before the adjacent block was poured the entire vertical face of the first pour and the exposed half of the vertical water-stop were treated with a heavy coat of mastic. Semi-circular drains of 7 and a half inch radius were located directly down-stream from the water-stops.

The dam is provided with inspection tunnels, one running west from the power-house for a distance of 700 feet and one running east from the diversion ports for a distance of 300 feet.

HEAD-WORKS AND PENSTOCKS

The head-works section consists of four intakes, one for each unit. Water from the forebay enters each intake through two openings which merge before reaching the penstocks. Steel trash-racks are installed on the up-stream face of the head-works . Head-gates controlled by separate motor-driven hoists are provided for each intake.

The penstocks are 20 feet in diameter with a thickness of three-quarters of an inch throughout. They are encased in concrete envelopes having minimum thickness of about 18 inches. The purpose of the concrete envelope is to protect the steel, eliminate periodical maintenance, and prevent expansion and contraction of the penstocks due to large variations in temperature. Only those portions of the penstocks for the third and fourth units which had to be embedded in the head-works' concrete were installed.

POWER HOUSE

The power - house is a steel and concrete structure 175 feet by 60 feet and is located close to the face of the dam.

Water discharged from the turbines passes through concrete elbow-type draft- tubes to the tail-race below the power-house. The draft-tubes have been constructed for the third and fourth units that will be installed at some future date.

The generators , built by the Canadian Westinghouse Company, are rated at 33,000 kilowatt-amperes at 90 percent power factor, 13,800 volts, 60 cycles. In construction they are the umbrella type and totally enclosed. Rototrol-type voltage regulators are used on these generators. They are the first of this type installed in Canada on generators driven by water-turbines.

The transformer bank is installed immediately west of the power-house. This bank comprises three transformers, each rated 22,000 kilovolt-ampere, single-phase, 13,800 to 138,000 Y volts. A fourth transformer has been provided as a spare for the bank.

The low-voltage switching equipment, supplied by the English Electric Company is of the air-blast type.

The power-house is equipped with a travelling crane having a capacity of 180 tons. There is an erection bay on the west end of the power-house to provide space for the erection and dismantling of turbines, generators and transformers.

....end of report...


This is likely why PEW in their " Forest Of Blue" site Lake Nipigon as a RESERVOIR and not as the great LAKE that it is.