Northeast Utilities (Connecticut) has purchased four of Siemens Power Transmission & Distribution, Inc's. new 550-kV dead tank circuit breakers with FA5 spring-spring operator technology – the first of their kind in the United States. The SPS2-550 outdoor SF6 gas-insulated breakers provide fast, reliable operation for utility applications at extra high-voltage transmission levels. The breakers will be used in the Long Mountain Substation upgrade in New Milford, Connecticut.

The FA5 spring-spring operating mechanism and 3AP arc-assist interrupter allows high speed closing, reclosing and two cycle fault interruption with minimal maintenance. The breakers are designed for zero crossing switching and protective duties at 550-kV maximum rated voltage, 2000, 3000, 4000 and 5000 A continuous current and 40, 50 or 63 kA maximum symmetrical interrupting capability.

Siemens has also received a second contract from Northeast Utilities for three variable capacitance/reactance shunt reactors for use in the utility’s 345-kV transmission line upgrade in southwest Connecticut.

The first shunt reactor contract was awarded in 2005 with the 2006 delivery of three of the highly specialized shunt reactors built in Nuremburg, Germany. The shunt reactors are part of the 345 kV Middletown-Norwalk, Connecticut project – a 69-mile transmission line with 57 miles of 115-kV line from central Connecticut to the southwest corner of the state. The project, built jointly with The United Illuminating Company (UI), is scheduled to be in service in 2009. UI has purchased the same shunt reactors for its portion of the project.

A shunt reactor is used to compensate for the capacitance of a power line or, in this instance, an underground power cable to keep the voltage at the proper level.

“These specialized shunt reactors are an integral part of the transmission line configuration that will provide NU with the ability to increase reliability to our customers,” said Jerry P. Fortier, project manager-NU Transmission.

Due to the location of the shunt reactors near residential neighborhoods, NU had a special requirement specifying a noise level of no more than 60 decibels. Siemens has invested significantly in low sound level technology – particularly for transformers – and has a great deal of experience in this area, largely because Siemens’ home country, Germany, has significant noise restrictions. Siemens built a sound enclosure around the main tank of the reactor consisting of a steel house with sound absorbing materials, rubber under the foundation, and other innovations to achieve a very low sound level.

The Middletown-Norwalk project is an important step toward meeting the growing demand for electricity while easing a major system bottleneck in southwest Connecticut.