> What is Involved in Electrification? | Metrolinx Engage

What is Involved in Electrification?

How the System Will Work


  • Traction power substations transform the voltage of 230kV to the appropriate voltage (25 kV). 

  • Distribution of power along rail corridors is provided via Overhead Contact System (OCS), feeders and gantries. 

  • To ensure reliable power supply, switching stations and paralleling stations are needed.

Diagram of electrification

Power Supply - Hydro One

  • Electrical power will be supplied by Hydro One’s power grid through tap connections from existing 230kV transmission lines and transformer stations.
  • The Hydro One tap connections are part of the engineering and environmental assessment aspects of the project. The infrastructure required and environmental effects associated with the tap connections will be assessed under the TPAP.


Traction Power Supply

Transmission Tap

  • The point at which electric power is ‘tapped’ from the existing Hydro One power source. 


Traction Power Substation (TPS)

  • Part of the power supply components of the system; it is a traction power facility (TPF) that transforms the utility supply voltage for distribution to the trains via Overhead Contact System. 

Traction Power Substation

230kV Aerial Connections

  • Overhead electrical high voltage connection line from the existing Hydro One tap to the new TPS.

230kV Aerial Connections


  • The feeder wires from the TPS will be connected to the OCS with the help of gantries. The main gantry (also referred to as the catenary feeding gantry) is the one parallel to the track and closest to the TPF. 


Overhead Contact System (OCS)

  • OCS is a series of overhead wires which supply electricity to the electric trains. Power is supplied to the train through the pantograph which makes “contact” with the OCS.
  • OCS is supported by cantilever and portal structures.
  • OCS is designed to ensure trains meet minimum performance standards; maximum distance between OCS supports is approximately 65 m.

  • A design excellence review process will be carried out to review design options for enhancing certain aspects of the project design/ aesthetics wherever possible. 


  • One foundtation required.

Train on tracks


  • Foundations to be installed on either side of the tracks.


Bridge Modifications

Bridge Barriers

  • Barriers are required on overhead bridges to ensure safety of the energized equipment; height of the barrier is approximately two meters; barrier will extend beyond any electri ed wire(s) running under the bridge to ensure safety. 


OCS Attachments

  • Used for support of OCS wires in situations with restricted clearance such as tunnels and overhead bridges.


Vertical Clearance

  • There are a minimal number of bridges that do not meet the vertical clearance requirements for electrification. The options being explored include: raise the bridge, lower tracks, or modify OCS to t within the existing clearance/ opening (if possible). 

Ramp to bridge

Other Bridge Modifications

  • Minor bridge modifications (e.g., ash plates) will be required on some bridges to ensure that the electrification system passes safely underneath the bridge. 

Underside of bridge

Traction Power Distribution

Switching Station (SWS)

  • Switching stations are traction power facilities that are required approximately mid-way between Traction Power Substations in order to split the electrical sections. 

Power station

Paralleling Station (PS)

  • This type of traction power facility contains an autotransformer which helps support the OCS voltage in the electrified system. 

Paralleling Station

Underground Feeder Connection

  • An underground conduit carrying electrical connection between the overhead contact system and a traction power facility (i.e., traction power substation, paralleling station or switching station).

Underground conduit carryin electrical connections


  • Gantries are also used for traction power distribution. The feeder wires from the facility will be connected to the OCS with the help of gantries. 


Learn more about plans for your corridor and tell us what you think

You also can review the plans for each corridor and share your feedback as part of the TPAP.