Sunday, February 18, 2024

Harrisburg Power Office Gets Up and Running

Since my last update on the status of the former Pennsylvania Railroad Harrisburg Power Director's Office a surprising amount of progress has been made to get the equipment functioning in its 1943 configuration. For those of you who might not be aware, the Harrisburg Power Office used a relay based SCADA system to remote control all of the 1937-39 westward extension of the 12kv 25hz electrification network that first began operation in 1915.  The second phase of the PRR's electrification from New York to Boston had largely relied on tower operators to directly control the substation equipment via local control boards in the towers (although some substations may have been staffed 24/7 themselves). Although remote control SCADA equipment was installed in some towers and the Baltimore power office, the expansion of electrification west of Paoli, Morrisville and Perryville to Harrisburg and Enola would be under the purview of a single office in Harrisburg with a code based remote control system. 

The office was in service using most of the same equipment from 1939 through to 2013. When the Harrisburg Chapter NRHS took over the space in 2022, it was still in roughly the same condition it had been in when the doors were locked 9 years before. Known for their preservation work at HARRIS tower, including a fully functional and completely interactive Model 14 interlocking machine, the Harrisburg Chapter had its work cut out to achieve a similar level of interactivity for the Power Director's office. Based on the amount of time it took to restore HARRIS, my own personal estimate was on the better part of a decade. Therefore you can imagine my surprise when I learned that a good chunk of the active equipment had already been restored to functionality in only 18 months. In fact the video below records the moment I learned that the office relay logic had been hooked up to an Arduino mimicking the field stations.


Because the third phase of PRR electrification was financed with depression-era WPA loans, the PRR had to spread the wealth and contract half the system to Westinghouse and half the General Electric. Westinghouse and its Visicode scada system is the simpler of the two to reverse engineer and debug (one can send digits with a literal rotary phone) so currently it is the Westinghouse half of the equipment that has been wired up to modern digital logic simulating the field stations. The General Electric equipment uses a more complex protocol that requires another round of development, but that is not insurmountable. Interestingly the Westinghouse equipment was largely used on the low grade freight lines that last saw service in 1981 when Conrail discontinued its electrified operations. Therefore that equipment came back to life not after sitting idle for 10 years, but for 40 years!

The large display wall has also been restored to mostly full functionality, however compared to the SCADA consoles this functionality was somewhat limited. The indications on the display show switches being open (green) and closed (red), as well as the use of white lights to show de-energized track segments. These are wired to reflect the position of switches on the SCADA consoles or on the operator's consoles where remote operation is not in effect. Therefore the board is more of a visualization device than a real time status indicator. 

The longer term plans for the office are still under consideration. The equipment is a bit less interactive than a railroad interlocking machine with active train movements, however there are quite a few scenarios that can be played out including routine operations, breaker trips, transmission line problems and current load issues. Whatever the case may be, I'll be sure to report on it here.

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