The Hoosac Tunnel Electrification

[Trade Journal]

Publication: Electric Journal

Pittsburg, PA, United States
vol. 8, no. 10, p. 830-846, col. 1




IN September, 1910, it was decided to electrify the Hoosac Tunnel and approaches including the yards at each end. On May 18th, 1911, the first train was drawn through by electric power, while continuous electric operation of the total traffic was begun on May 27th.

The Hoosac Tunnel is the longest tunnel in the United States, being 25,081 feet long from portal to portal. It pierces the mountain range between the Hoosic and the Deerfield Rivers in the Berkshire Hills, its location and the general arrangement of tracks being shown in Figs. 1 and 2. Where the rock is soft the tunnel is arched with brick, but in the greater part the rock is hard and the walls are bare rock. To drain off the large amount of water en countered, the tunnel was run on a grade of 26.4 feet to the mile from each portal to a short level stretch in the center, at which point a 1,028 foot shaft extends to the top of the mountain for ventilation. The work of digging this tunnel was started in 1851, and the first train went through February 9th, 1875. It is straight and double tracked from end to end and cost about twelve million dollars.



The electric zone extends from the little tunnel west of the North Adams station to a point about a quarter of a mile east of Hoosac Tunnel station, the total distance being 7.92 miles. The electrification includes the yards at North Adams, about two miles of the main line between North Adams and the west portal where the grade is about 0.75 percent; then 4.75 miles of the tunnel which was constructed on a 0.5 percent grade leading from both ends up to the central shaft, and the yards at the east portal, including three-quarters of a mile of main line, having a grade of about 0.5 to 0.7 percent. In all 21.31 miles of single track is electrified.

The traffic at this point has been exceedingly heavy and with the smoke and steam incidental to steam operation, the tunnel has long been the limit of the capacity of the division, besides being exceedingly dirty and disagreeable to passengers. With the tunnel electrified automatic block signals have been installed and the capacity of the tunnel increased three-fold by allowing three trains on the same track at the same time. This was not safe before, as signals would not have been visible. Instead of being a nuisance the tunnel has become a pleasure in summer on account of its coolness and all passenger trains go through with the windows open.

The method of operation is for the electric locomotive to couple on in front of the steam locomotive as shown in Fig. 3, and pull the train, locomotive and all through the tunnel. Meantime the fires of the steam locomotive are left undisturbed so as to avoid filling the tunnel with smoke and gases. The success of this method is daily demonstrated, for it is usually possible to see out from the central shaft, a distance of 2.37 miles.


Fig. 2—Plan and Profile of Hoosac Tunnel


Overhead single catenary construction for 11,000 volts single phase was chosen as the system best adapted for this electrification, and the equipment is in many respects similar to that of the New York, New Haven and Hartford Railroad between Woodlawn, N. Y., and Stamford, Conn.




The power house has been built at Zylonite, about 2.5 miles south of the west portal of the tunnel. It is located near the old power house of the Berkshire Street Railway and uses a pond back of this station to supply cooling water for the condensers. From this location it will be possible to supply power to the street railway system without additional transmission lines if it is decided to abandon the old power house, and the station can be used entirely for this purpose if a hydro-electric plant is later built on the east side of the tunnel to supply the railroad. Water for the boilers is furnished by ten artesian wells 100 feet deep, and the coal is brought in from a switch on the Boston & Albany Railroad.


Fig. 3—Electric Locomotive Drawing Steam Locomotive and Train Out of Tunnel


The building is of brick on a concrete foundation 100 by 200 feet and is about 80 feet high. The basement floor is on a level with the ground, and is divided into three sections. The section at the east end or boiler room basement contains the Worthington duplex boiler feed pumps, the forced draft apparatus consisting of two steam turbines driving Sturtevant blowers, and the ash hoppers and ash cars. The middle section, or engine room basement, contains two Westinghouse-LeBlanc jet condensers, a service pump, the oil filter and gravity oil system, a battery room containing a 120 ampere-hour storage battery, transformers for supplying the lighting system and power for the station apparatus, and a machine shop.

The section at the west end contains the switch house. Here are located the two 60 000 volt oil circuit breakers, with heavy grid resistance and impedance coils to prevent excessive current during a short-circuit. The grid resistance is in shunt with automatically operated oil switches, so connected as to cut the resistance in series with the line load when a short-circuit occurs. The resistance is of such a value as to limit the current on a dead ground to 600 amperes which the main circuit breaker then interupts, thus completely opening the short-circuit.



On the second floor is the boiler room, which extends to the roof, and contains four 500 horse-power water tube boilers, equipped with underfeed stokers, the stokers being operated by a chain belt from the forced draft apparatus. Each boiler is supplied with a superheater which superheats the steam 100 degrees F. The other boiler room equipment includes a Sturtevant staggered tube economizer, two 12-foot induced draft fans, a feed water heater, a feed water weigher, two traveling combined hoppers and weighers for coal, and a service water tank which supplies gland water to the turbines, the jacket water for the compressor and water for the wash rooms. Space has been left in the boiler room for four additional boilers with their necessary equipment.

The coal is unloaded from hopper cars into a receiving bin under a trestle. From this it is raised 75 feet to the roof by a bucket conveyor, shown in Fig. 4, of 40 tons per hour capacity. Here it passes through a crusher to a 75 ton storage bin. Both the conveyor and crusher are operated by 20 horse-power induction motors.


Fig. 5—Power House and Spray Cooling System


As mentioned above, there is a pond near the station from which cooling water is taken for the condensers. In order to keep down the temperature of this pond a spray cooling system has been installed. This consists of two sprays or pipe lines about three hundred feet long mounted above the pond, Fig 5, from which the water is pumped through no spray nozzles. The water is pumped through the spray system by a centrifugal pump driven by a 100 horse-power induction motor. There is also an engine driven pump for use in emergency. The cooling water for the condensers is drawn in from the upper end of the pond, and discharged through a long flume leading to the lower end. The pumps supplying the sprays draw water from the discharge of the condensers and what is not used in the sprays goes out through the flume.

Like the boiler room, the engine room extends to the roof. In contains two main units, each consisting of an 11 000 volt, three-phase, 3,750 k.v.a. (single-phase rating) generator coupled to a double-flow steam turbine. The auxiliaries consist of a 100 kw steam turbine exciter unit, a 100 kw motor-driven exciter, a small motor-generator set for charging the storage battery, an air compressor and a 30-ton hand operated crane.

One end of the power house is given over to the switchboard alcove and the rooms containing the remote control switching apparatus, the lightning arresters and the chief engineer's office. The switch board is set at a slight elevation above the engine room floor. It is a dull finish slate board with eleven panels. All 11 000 volt circuits are controlled by oil switches operated from the board by remote control. The generator voltage is regulated by two Tirrill voltage regulators.

A diagram of the electrical layout is shown in Fig. 6. One phase of the generator supplies the trolley load, one phase the power load and one phase goes to ground. The Berkshire Street Railway, however, is supplied by an ordinary three-phase transmission line. For the railway locomotive system there are a set of three-phase station bus-bars and four separate feeder bus-bars which receive power through oil circuit breakers from the main bus-bars. The "trolley" bar of the feeder bus-bars furnishes power for the electric locomotive load and the "control" bar furnishes power to operate the circuit breakers which control the various sections of the track at the west portal and at the repair shop. The "trolley" and "power" lines are protected by an electrolytic lightning arrester, and the "control" line by a low equivalent lightning arrester. The "power" phase of the feeder bus-bar also furnishes power to a feeder for the hand-control operation of the circuit breakers at the switch houses. A reactance coil is located between the main station bus-bars and the feeder bus in the "power" and "control" phase to prevent excessive current during a short circuit.



This may be made clearer by assuming a short-circuit, say a flash-over of a pantagraph insulator, on one of the locomotives somewhere on the line. The rush of current through the series transformer in the switch house operates relays which make the connections between the ''control" wire and the mechanism operating the section breaker in the switch house which controls that particular section. The section breaker does not open, however, as the control wire is not yet energized. The rush of current then operates an overload relay at the power-house which opens the switches in succession cutting a heavy resistance in series with the trolley phase. At the same time the overload relay has operated a switch which energizes the control wire and thus, as the proper connections have already been made at the switch house, as mentioned above, the proper circuit breakers open to cut off current from this section. If for any reason these circuit breakers at the switch house do not open the circuit at the end of a given interval the switches at the power house will open, removing all power from the trolley phase.




The current is transmitted at 11,000 volts from the power house to the switch house at the west portal over a double circuit' transmission line 2.42 miles in length. The corner towers, Figs. 4 and 7, are formed of four uprights made of angle-iron strengthened by angle-iron cross pieces and diagonal braces. These uprights support at their top an angle-iron frame work on which are mounted the porcelain insulators that support the wires. The uprights are set in concrete foundation piers. The towers along the straight part of the line are formed of two eight inch channels connected together by angle-iron braces and diagonals and tied together by a cross piece at the top. These towers carry two angle-iron crossarms and are supported on two concrete foundation piers set at right angles to the direction of the line. They are spaced about 300 feet apart on the level.

The transmission line consists of five stranded copper cables, two of which carry current for the trolley or locomotive load and are suspended from the cross arms at one side of the tower, while the power and control wires are suspended in a similar manner from the other side. The cross tie at the top of the tower carries an insulator to support the ground wire which also serves as a guard wire protecting the transmission line against lightning. The line terminates at the switch house at the west portal which controls the entire system. The switch houses at the east portal and at the repair shop are not connected to the transmission line, but are fed through the trolley wires of one or both main tracks. Therefore, as long as current is on either one of the main track trolley wires the remainder of the system can be operated.

The same towers which carry the transmission line also carry two telephone wires supported on one of the cross braces between the channels about ten feet below the high-tension wires. Noise due to inductance on the telephone line is prevented by frequent transposition of the wires, the two wires being turned through 90 degrees between each tower. The effect of inductance is further reduced by one-to-one transformers put in series with the line, one wire being led through the primary and the other through the secondary. The static charge is taken off through impedance coils connecting the two telephone wires, the center point of the coils being grounded.


Fig. 7—View of Switch House and Overhead Construction at West Portal




Outside the tunnel two different systems have been used to support the overhead line. For two and three track sections on the main line the supporting bridges are built-up trusses of the type shown in Fig. 7, formed of seven and eight inch channel top and bottom chords with light angle posts and double diagonal rod braces in each panel. These bridges are supported at each end by A-frame towers formed of two eight inch channels braced with light angles, the plane of these towers being parallel to the center line of the tracks.

In the yards, where more than three tracks are equipped with overhead wires, instead of the steel bridges, cross catenary span wires are suspended from the apex of A-frame steel towers built of eight inch channels, with their sides in a plane at right angles to the track, Fig. 8. The messenger cable insulators are suspended from these stranded steel cross catenary cables by stranded steel wires of suitable length. Each tower is grounded by a cable clamped to the apexes of the towers. The anchor bridges are box trusses supported on heavy A-frame towers with latticed sides stiffened with double diagonal braces.


Fig. 8—Cross Catenary Line Construction in Yards at North Adams


The overhead trolley system is sectionalized into twelve units consisting of two tracks in the east portal yards; east bound main track and west bound main track of the east portal; east bound and west bound tracks of the tunnel; west bound main track from the west portal to the west end of the North Adams yard; a section of the east bound main track and a cross-over opposite the west portal switch house; two sections of the long siding between the North Adams yard and the west portal switch house; the shop yard; four tracks in the North Adams yard, and the east bound main track from the west end of the North Adams yard to the west portal switch house.

An interesting point in the overhead construction is the crossing of the double track 11,000 volt alternating-current railway trolley and the single track 600 volt direct-current trolley lines of the Berkshire Street Railway, just west of North Adams station. A view of this crossing is given in Fig. 9. The 600 volt trolley is sectionalized with wooden section insulators eight feet long on each side of the crossing, and is carried over the crossing under an inverted five inch channel which is supported by stranded steel cable span wires. This channel iron is on the same plane as the 11,000 volt alternating-current trolley wires but is insulated from them by similar eight foot section insulators. The direct-current trolley wire in this crossing section normally carries no current. On the north side of the crossing a feeder is connected to the 600 volt trolley wire and carried to a switch on top of a wooden pole. When this switch is closed by pushing up on a rod, 600 volt direct-current is fed to the crossing channel and trolley wire so as to permit a street car to pass over the crossing with current on. When the rod is released the switch opens by gravity, and by making another contact, grounds the channel iron and the direct current section of the trolley. The section insulators in the 600 volt trolley are grounded at the center of their length so that the 11,000 volt current can not leak past them in case of breakdown of any of the 11,000 volt section insulators.



The messenger cable outside the tunnel consists of a five-eighth inch stranded steel cable which supports a No. 0000 grooved copper conductor by rigid hangers of varying lengths at intervals of ten feet. The contact wire, which is No. 0000 grooved Phono-electric, is carried 1.75 inch below the copper conductor by double clips attached in the center of the ten foot spans between the hangers. On curves the conductor and contact wires are both suspended from the messenger by inclined hangers having double clamps.


Fig. 10—Overhead Construction in Tunnel


Inside the tunnel on account of the small clearance and the great amount of moisture present, the erection of an 11,000 volt trolley presented quite a problem. The supports are 100 feet apart and consist of U-shaped brackets parallel to the track, held in place by 1.25 inch wrought iron bolts extending 18 inches into the rock or brick arch. These bolts were split at the upper end and hammered home on a wedge, but prior to setting the bolts, the holes were filled with cement, and the cement rather than the wedges being relied upon to hold the bolts in place. Two U-pieces support a bracket of the type shown in Fig. 10, by means of two 150,000 volt triple petticoat porcelain insulators and these brackets, which extend across the track, in turn support the messenger cable through 150,000 volt insulators. As these primary and secondary insulators are in series, the combined dielectric strength is 300,000 volts.

Owing to the limited clearance in the tunnel the two contact wires are lowered to 15 feet 6 inches above the rails. For the same reason the messenger cables are supported 14 inches inside the center line of the track. This gives a minimum clearance of 12 inches between the messenger and the roof of the tunnel. In order to provide maximum conductivity a five-eighth inch stranded copper wire cable is used for a messenger. The twin contact wire hangers are designed to allow some vertical movement of the trolley wires. All parts of the tunnel hangers are made of bronze.