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System Operations

You may ask, how do light rail trains run?  There are many components that allow the trains to operate.  There are communication houses, relay houses, traction power substations (TPSS), and overhead wires that all play an important part in the system's operations.  Below will explain each of the mechanisms and the safety precautions you should take when near these systems.

Communication Houses
The communication houses are conditioned metallic enclosures located at the end of the station platforms.  They contain the communications and Supervisory Control & Data Acquisition (SCADA) equipment necessary to inform and protect the light rail patrons, as well as to allow RTD dispatchers, supervisors, and security personnel to remotely monitor and control the West Rail Line system.  The station platform public address, variable message (electronic signs), emergency telephone, and closed circuit television systems are all part of the communications and SCADA network.  An extensive fiber optic network connects the various systems and remote devices along the West Rail Line with RTD's Operations Control Center (OCC) and the Security Command Center (SCC).

Relay Houses
The relay houses are metallic enclosures that contain the central signal system equipment (logic controllers) necessary to allow for movement of trains in a safe and efficient manner.  Similar to a traffic control system, the signal system is automated and used for safe and proper routing of trains.

Traction Power Substations (TPSS)
A traction power substation (TPSS) is an electrical station that converts the utility company provided 13.2 kV AC power to 750 VDC power, which is then transmitted to the train through the Overhead Contact System (overhead wires).  There is approximately one TPSS per mile along the West Rail Line.

Overhead Wires

There are two overhead wires.  The bottom wire, referred to as the contact wire, is needed to supply the electrical current to run the train.  The current is collected through the train's pantograph, which presses against the underside of the contact wire as the train travels on its route.  The Overhead Contact System (OCS) is a closed loop system where the current flows from the point of origin to its destination and back to the point of origin in a closed loop that includes the contact wire (primarily), the pantograph, the train's motor, the steel wheels of the train, the running rails, and the substation, which is the source of the power.  The top wire, called messenger wire, provides vertical physical support to the contact wire between structures and helps provide the OCS with more electrical conductivity.
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