NSTAR Electric is seeking approval from Massachusetts state regulators to build two new 115-kV underground transmission lines in order to maintain reliability and address the capacity needs of the electric system in a part of Boston.
The company filed its petition with the Massachusetts Department of Public Utilities (DPU) on July 30.
The pipe-type cable (PTC) lines would be built between NSTAR Electric’s Station #385 (K Street substation) located at East First Street in South Boston and a connection point past two existing wye joints located within the median of Columbia Road near its intersection with G Street, also located in South Boston.
“The project is needed because two existing 115 kV underground cables that supply two major Boston area substations are expected to exceed their thermal capacity under an N-1 contingency in 2013,” the company added, noting that the facilities “will serve the public interest by providing a necessary source of transmission in the Boston area in order to ensure the reliable operation of the transmission grid.”
The need for the project is documented in the company’s 2013 annual filing with the DPU, namely, its ten-year outlook analysis on the transmission system, which stated: “The line sections from K [Street] to the wye joint are seen to overload in the 2013 cases for loss of the companion line and stuck breaker contingencies at K [Street] which also take out one of the lines. These overloads range up to 120% in 2013.”
NSTAR Electric further said that from 1990 to 2012, its summer peak grew at about 1.8% per year and is forecast to grow by 1.8% per year from 2012 to 2023.
The company began pre-construction activities for the project in mid-2012 with consultations and preliminary permitting meetings with the applicable state and local permitting agencies. Cable installation for the project is scheduled to occur in the spring, summer and fall of 2014, with the desired in-service date set being by the end of that year.
The project’s current total cost estimate, based on a conceptual estimate (+50/-25%), is $20.5m, and it includes costs associated with the new underground line and the modifications to the K Street station.
There are currently two 115-kV underground PTC transmission lines (#483-524 and #483-525) that begin at the K Street station and both follow a route along H Street, with each line connecting to a separate wye joint located in the median of a divided roadway near the intersection of Columbia Road and G Street in South Boston.
One wye joint splits Line #483-524 into two line segments, with one segment proceeding to the company’s Station #106 – known as the Andrew Square substation and the Ellery Street substation – in South Boston. The second segment proceeds to Station #483 – known as the Dewar Street substation in Dorchester. This line section, the company added, also provides a backup supply to National Grid USA’s North Quincy station through a normally open tie.
National Grid is a subsidiary of National Grid plc.
Likewise, the second wye joint splits Line #483-525 into two line segments, one of which proceeds to the Andrew Square Station and the other to the Dewar Street station, and to the North Quincy station through a normally open tie.
As currently configured, NSTAR added, Line #483-524 and Line #483-525 carry the entire load of the Andrew Square and Dewar Street stations, which serve about 32,300 and 53,700 customers, respectively.
The project includes replacing the two wye joints with four straight joints, with two of those straight joints connecting to the two existing lines from the K Street station to create two single lines to the Dewar Street station (Line #483-524 and Line #483-525). NSTAR also said that the two new lines from the K Street station will be connected through the remaining two new straight joints to create two new single lines to the Andrew Square station (Line #106-526 and Line #106-527).
The result will be four lines beginning at the K Street station, with two proceeding to the Andrew Square station and two proceeding to the Dewar Street station.
The total length of the transmission corridor created by the project, as measured from the boundary of the K Street station parcel to the southern terminus on the Columbia Road median, is 4,933 feet.
NSTAR also noted that it is in the process of determining whether the median strip and the portion of Columbia Road in the project area is protected parkland under the care, custody and control of the state Department of Conservation and Recreation or part of the state Department of Transportation’s roadway system.
Among other things, the company said that with the proposed project in place, under N-1-1 contingency events, the loss of two stations will be reduced to loss of one station only, thereby effectively reducing the amount of load and customers lost.
Also, the total amount of distribution generation currently available or in NSTAR Electric’s distributed generation queue is about 3.7 MW as of June, so, at its current projected growth rate, distributed generation is not contributing to a sufficient reduction in demand to eliminate the need for the project.
NSTAR is a Northeast Utilities (NYSE:NU) company.