Mary Bridge Children’s Hospital Substation Project

Project Overview

Tacoma Power is building a new substation, including new transmission and distribution pole lines to support the new MultiCare Mary Bridge Children’s Hospital. 

This project is being planned in partnership with MultiCare. MultiCare has proposed providing land at their 5th and M Street employee parking lot. Two aerial transmission lines will be required as part of the substation construction.  

Key project milestones

  • Project planning: Now to Q2 2024
  • Design and permitting: Q2 2024 to 2025
  • Construction: 2025-2026


What is a substation?

A substation is a facility within the Electrical Power System that includes overhead transmission and distribution lines. Substations transform voltage generally from high to medium voltage so it can be distributed down either overhead or underground power lines before being delivered to the customer where it is transformed to low voltage. A substation includes transformers, control equipment for switching, and system protection to transfer power to distribution lines.

How long is this project going to take?

We expect the project to take three to four years from planning to construction completion.  

Why do you need to add a substation?

We need a new substation to manage the increasing demand from the new hospital

Why do you need to put the substation here?

We wanted a location with proximity to our critical customer to ensure service reliability and near existing transmission lines to minimize the path and impact of new transmission lines.  Substations convert the power system voltage from transmission to distribution levels to be safely and efficiently delivered down our streets.  If distance thresholds are exceeded, low voltage levels will result in electrical issues for the customer

What steps does Tacoma Power take for substation aesthetics?

Some of the ways we anticipate improving the aesthetics of the substation include architectural walls and landscaping instead of a chain link fence. 

Why can’t you put transmission lines underground?

There are two reasons we have determined not to build underground transmission - higher costs and the complexity of the engineering and maintenance.  

The cost of underground cables of the same voltage level is generally five to ten times higher than that of overhead lines. 

The structure of underground transmission cables is more complicated than overhead lines. Underground transmission cables have high technical requirements and are difficult to manufacture and construct. 

Are the transmission lines safe?

Yes, transmission lines are safe. Whenever electricity is used, electromagnetic fields (EMF) are present; they are invisible fields that surround all electrical equipment and power lines.  

Electric fields are created around appliances and wires whenever there is voltage—the more voltage, the higher the electric field strength. Electric fields diminish with distance from the source and can be blocked by trees, walls, buildings, and other objects.   

Magnetic Fields are created whenever there is a flow of electric current, such as when an electrical appliance is running. Magnetic fields are measured in milligauss (mG) and diminish with distance from the source but cannot be shielded by objects. The magnetic field strength from power lines depends on many factors, including the line’s design, the amount of current the line carries, and the distance from the line.  

If you are interested in more information about EMF, here are some additional sources: 

WHO “What are electromagnetic fields?” 

US National Cancer Institute “Electromagnetic Fields and Cancer” 

US NIEHS Questions and Answers on EMF 

Is the substation going to make a lot of noise?

The prominent noise heard from a substation is a hum from the transformer.  A typical new substation transformer will produce approximately 70 dB of noise measured at 1.0 meters from the transformer, like the loudness of a newer, standard residential outdoor air conditioning unit.  The sound level diminishes further from the sound-producing source, so it will dissipate as it reaches the perimeter wall. 

What are the potential environmental concerns at a substation, and how does Tacoma Power address them?

The primary materials in substations are metals. The power transformer is filled with non-toxic and non-hazardous mineral oil for cooling and electrical insulation. In the event of a leak, the station has a designed secondary containment to prevent the oil from leaving the station.

Are there regulations are in place to ensure the public is safe from potentially dangerous materials used at a substation?

Electric power substations are required to meet various government regulations and industry standards.  There are many standards for equipment, maintenance, and operation of a substation including OSHA, IEEE, ASTM, ANSI, IEC, NEMA, NFPA, ICEA, NESC, and others. 

What type of maintenance is performed inside the substation, and on what schedule?

A monthly inspection of equipment is required at each of our substations Circuit breaker and transformer maintenance typically occurs annually or bi-annually depending on manufacturer specs, with routine testing scheduled approximately every three years. 

How can residents and property owners ask questions about the new substation?

Use the form below to submit a comment about this project.