Commuter Rail AC Electrification Load-Flow Simulation Report - RTD

Commuter Rail AC Electrification Load-Flow Simulation Report Revision 1
• Two paralleling stations were located along the East Corridor,
• One paralleling station was located along the Gold Line, and
• Three paralleling stations were located along the North Metro Corridor
The purpose of the paralleling stations is to parallel the catenary and feeder systems, provide
feeder and catenary sectioning, and to supply power from the feeder/catenary system to the catenary/rail
system.
Two sets of traction power supply system studies were performed, with substations connected
to Xcel Energy’s 115 kV transmission network and configured as follows:
• In the first study set, both substations, Sandown and Argo, were equipped with two
traction power transformers.
• In the second study set, the Sandown substation was equipped with two traction power
transformers and the Argo substation was equipped with only one traction power
transformer.
The modeled autotransformer system provided a significant operating margin for the electrical
traction power system. Minimum voltages along the three corridors were well above industry
standards ensuring satisfactory operation under normal operating conditions, with all systems in
service, and under particularly severe contingency operation with one substation (both
transformers) out-of-service. The total system power demand averaged over 2 hours is
approximately 15 MVA. Taking into consideration the fluctuating power demand of the traction
power loads, short-term overloads and the requirement for transformer and substation
contingency operation, a preliminary continuous rating of 12.5 MVA should be considered for
each substation transformer when two transformers per substation can be installed. In the
event that only one transformer can be installed in Argo substation, it is recommended that 15
MVA rating for each transformer be considered. Further, it is recommended that a standard
continuous rating for each autotransformer be 2.5 MVA. These ratings would allow operation of
EMUs on the East Corridor, Gold Line, and the North Metro Corridor.
Since the autotransformer-fed system performed with a significant operational margin,
consideration should be given to the utilization of 1x25 kV direct-fed system. Preliminary results
indicate that the 1x25 kV system might be effective but more comprehensive simulations would
be required to ensure its viability. It is believed that this alternative system would be much
simpler, substantially less expensive to build and maintain, and provide more efficient utilization
of equipment.
Regardless of whether an autotransformer-fed system or direct-fed system is selected for
implementation, it is recommended that a utility impact study be performed. A key element of
the study should be investigation into the effects of the fluctuating traction power load on the
transmission system including a voltage flicker study. The unbalanced nature of the load due to
phase-to-phase substation transformer connections should be evaluated and the levels of
negative sequence currents in nearby generators determined. Further, the study should
evaluate the effects of harmonics generated by the rolling stock on total and individual harmonic
distortion of voltages and currents at the point of common coupling and assess the likelihood of
utility system resonance.
02/27/2009 FRSC Page 2 of 250