Glossary

Look below for some terms to help you understand more about PSE's electric and natural gas systems as well as our ongoing and upcoming infrastructure improvement projects.

Co-location

When practical, PSE will build electrical infrastructure such as transmission and distribution lines on the same poles. This is typically done to take advantage of existing infrastructure corridors and minimize the effect of this infrastructure to the local community.

[Back to top]

District regulator

A district regulator is a device that is made up of piping, valves, control instruments and lines that automatically regulates natural gas pressure in the main pipeline to which it is connected.

[Back to top]

Distribution line

A distribution line is a medium-voltage (12.5 kV-55 kV) line that carries electricity from a substation to customers. Roughly half of PSE's distribution lines are underground. Distribution voltage is stepped down to service voltage through smaller transformers located along distribution lines.

[Back to top]

Fiber-optic line

A fiber-optic line is a glass or plastic optical fiber that transmits light and is often used for communication or data transference. Fiber-optic lines are lighter, less expensive and able to carry more information than radio or microwave communication. The fiber-optic lines used in PSE's electric system are relatively small, measuring only half an inch in diameter. PSE uses fiber optic lines to transmit system information to operating bases, allowing system operators to monitor system performance remotely.

[Back to top]

Gate and Limit stations

Gate and limit stations are devices in our natural gas system that regulate the pressure of the natural gas. Specifically, they decrease the pressure of the natural gas for use in residences and businesses.

[Back to top]

Kilovolt (kV)

A kilovolt (kV) is equal to 1,000 volts of electric energy.

[Back to top]

Liquefied natural gas (LNG)

Liquefied natural gas (LNG) is natural gas cooled to -260 degrees Fahrenheit. When cooled, natural gas becomes a liquid that is one six-hundredth the volume. In its liquid state LNG is easier to store and transport.

[Back to top]

Natural gas

Natural gas is a fossil fuel composed almost entirely of methane. Interstate pipelines transport natural gas to regional natural gas systems, where it is metered and delivered through a network of local mains, service lines and, ultimately, to customer homes and businesses. View How Natural Gas Gets to You or check out PSE's Source to Stove video.

[Back to top]

Service line

A service line is a lower-voltage (120 to 480 volts) overhead or underground electric line that is the last connection from PSE to the meter on customer homes or businesses.

[Back to top]

Substation

A substation is a vital component of electricity distribution systems, containing utility circuit protection, voltage regulation and equipment that steps down higher-voltage electricity to a lower voltage before reaching your home or business.

[Back to top]

Switching station

A switching station is a substation that reroutes power flow from one line or path to another and may integrate power from multiple transmission sources or operators on the local grid (e.g. Bonneville Power Administration and PSE). Rerouting power can isolate it in order to clear a fault (e.g. a fallen tree in the wires) or take a power line out of service for maintenance.

Unlike substations that serve neighborhood circuitry, switching stations do not step power voltage up or down.

[Back to top]

Town border station

A town border station is a facility where natural gas changes ownership from a transmission operator to a local distributor, so that it can be delivered to local customers. PSE receives natural gas from transmission operator Williams Northwest Pipeline at our North Seattle town border station, where we then reduce its pressure and deliver it to your home or business through our distribution system.

[Back to top]

Transformer

A transformer is a device that steps electricity voltage down from a higher voltage, or steps it up to a higher voltage, depending on use. Typically it steps voltage down from a distribution voltage to 120/240 volts for customers' residential use. Transformers are the green boxes in some residences' front yard or the barrel-like canisters on utility poles.

[Back to top]

Transmission line

Transmission lines are high-voltage lines that carry electricity from generation plants to substations or from substation to substation. Transformers at the substation "step down" the electricity's transmission voltage (55 – 230 kilovolts*) to our primary distribution voltage (12.5 kV).

[Back to top]

Tree wire

Tree wire is a specially coated, overhead wire that's designed to prevent an electric short (and subsequent outage) when a tree limb falls into a power line. Where installed, it significantly reduces the frequency of tree-related outages, but cannot prevent all disruptions (e.g. if an entire tree falls into a power line).

[Back to top]

Vegetation management

Vegetation management involves a variety of programs and techniques designed to protect power lines from the impact of nearby trees. These programs may include pruning, tree removal, herbicides and smart planting practices. The goal is to keep you safe and your lights on.

You can learn more about PSE's vegetation management in our Tree Trimming FAQ section.

[Back to top]