Power Delivery 101

From Power Generation to You

Seattle City Light is the nation's 10th largest public power system and first carbon-neutral utility, serving more than 410,000 customers. Approximately 90 percent of the utility’s power comes from clean resources from its hydroelectric facilities.

Before reaching its customers, power is generated, transmitted, and distributed through an extensive utility network. Here’s how it works:

1. Generation – Electricity is produced using turbines. At the hydroelectric dam facilities, for example, the force of water that pushes and turns the turbines produces the energy. Transformers at the dam then increase the electricity voltage to help it travel across many miles.
2. Transmission – Electricity is then sent through high-voltage transmission lines. Metals such as copper and aluminum are used in transmission line wires because of their flexibility and conductivity (a material’s ability to move electrical current).
3. Distribution – Electricity is then delivered to a substation. Here transformers lower the electricity voltage down to manageable levels so it can be sent in multiple directions through smaller power lines to customers.
4. Delivery – Before the electricity is delivered to customers, it passes through more transformers and protective devices to ensure it is at the right voltage. Electricity is fed into homes and businesses through the weatherhead (the pipe with the curved head that comes out of the top of a meter base that is either mounted to an exterior wall or pops up through the roof). Advanced meters attach to the meter base where they measure electricity use. The customer owns the meter base, and the utility owns the meter.
5. Energy-Use Data Collection – As customers use energy, advanced meters will record usage (measured in kilowatt hours). The energy-use data is then sent remotely to City Light through a secure wireless network and securely stored on City Light servers for customer billing.

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