The transmission system in Eversource’s service territory operates at three
voltage levels: 345,000 volts (345 kV), 230,000 volts (230 kV) and 115,000 volts
The 345 kV system is the backbone of the transmission system. The 345 kV transmission lines carry more power than the lower voltage lines and provide the ability to transfer large amounts of power between the New England states and beyond. The high voltage electricity carried by the 345 kV lines enter step-down substations to lower voltages for use in the transmission and distribution of electricity to commercial and residential areas. There are currently eight 345 kV substations in New Hampshire.
The 115 kV transmission system is the workhorse of the transmission network. It is responsible for transmitting power from intermediate-sized generation facilities and 345 kV substations throughout the entire service territory.
Eversource currently operates more than 1,000 miles of 115 kV transmission lines, connecting 45 substations where the voltage is stepped down for delivery to smaller commercial and residential areas. There are also eight 115 kV lines that connect Eversource to neighboring utilities.
Eversource annually invests many millions of dollars to maintain its transmission system to ensure a reliable and stable supply of electric power to its customers. These investments require careful planning to ensure adequate capacity to meet the increasing demand for electric power and to replace or upgrade equipment as it becomes obsolete or reaches its expected lifespan in service.