TIGER STATIONS TO ENHANCE TRANSMISSION SYSTEM CHARACTERISTICS
The aggressive Distributed Energy Resources (DER) roadmap for California and other places around the globe stems from the proven benefits that distributed resources provide to the power sector industry. A large existing literature shows how DER helps in the fulfillment of long-term environmental goals by the use of alternative, and most times renewable, energy resources which are cleaner and likely more efficient –. On the technical side, DER has the potential to reduce losses in power lines, improve and the local power quality, particularly the local voltage profiles –, and to improve grid reliability , . Other operational benefits include peak shaving capabilities, reducing transmission load congestion, and reducing central generation reserve requirements . Lastly, DER can provide economic benefits by deferring traditional transmission and distribution investment for capacity and infrastructure upgrades , by reducing O&M and fuel costs, and by promoting innovative business models and most importantly incentives to different parties involved in DER interconnection such as utilities, independent generators, and the wider society .
Driven by many DER regulatory proceedings, utilities are facing already well-known substantial challenges with accommodating these active components into a grid that was traditionally designed for top-to-bottom power flows. These challenges, however, come with the opportunity that utilities will reduce reliance on conventional resources in favor of other preferred resources to meet existing reliability and sustainability needs. One opportunity, which is the focus of this work, is that of judicious installation of Transmission Integrated Grid Energy Resources (TIGER) to support reliability and sustainability. TIGER is here defined as a large-scale natural gas fed fuel cell power station on the order of 50 MW – 100 MW, which can be located in large substations (220 kV- 66kV) or in transmission Right of Way (ROW). Regarding the assessment of the effect of large-scale DER, more specifically, distributed generation on the transmission system, many research efforts focus on line losses and voltage profiles, the effect on transient stability, grid reliability, and optimal DER placement for greater grid benefits.
In , DER effectively reduced system line-losses, also, non-surprisingly, DER placed near longer feeders promoted higher loss reductions. This agrees with results shown in , which stresses that line loss reduction is location dependent, and higher if DER is placed in areas with heavy loads and low generation (low voltage). Authors in  show there can be a tradeoff between line loss reduction and voltage profile improvement: a larger DER allows a higher voltage improvement; however, if it creates a reverse power flow, it can potentially increase line losses.
In terms of grid reliability, authors in , assessed DER on its ability to improve the Voltage Security Margin (VSM) of the transmission grid. Results show that DER may only improve system voltage stability if the contingency takes place when the system is operating at a specific load “interval”, namely the “DG assistance interval”. The location of DG also plays a role, as higher benefits were obtained when DG was installed in the lower voltage region of the network.
Authors in  also studied DER effect on grid reliability in terms of annual availability, average failure rate, and average outage time. It was found that intermittent DG aggregate less reliability benefits to the grid compared to constant output DER. In addition, it is vital that the DER is able to island (and not be automatically disconnected) so it can support the system during the contingency.
Regarding transient stability, authors in  and  suggest that in transmission systems, stability depends upon the type of DER (i.e. synchronous, induction or inverter-based) and its penetration levels. When there is a fault, inverter-based DER will self-limit their fault contribution, while synchronous generator-based DER will still contribute with a large transient and sub-transient fault current from the rotor winding excitation current.
This research will focus on the effects of a large-scale DER to be integrated into high-voltage transmission substations. The key points this research will investigate are the ability of DER to assist local voltage profile of regions with poor load/generation balance, the ability to reduce resistive line losses, and optimal DER placement, as have the papers mentioned above. We will also briefly investigate the effects on the system voltage stability using P-V curve analysis methods. Although these impacts constitute a good case to determine if DER placement is attractive for achieving the aforementioned grid benefits, there are other impacts that are outside of this study's scope, for instance, the impact on existing voltage regulation or protection equipment, and the direct impact in system transient stability.
 B. Shaffer, B. Tarroja, and S. Samuelsen, “Dispatch of fuel cells as transmission integrated grid energy resources to support renewables and reduce emissions,” Appl. Energy, vol. 148, no. x, pp. 178–186, 2015.
 J. D. Eichman, F. Mueller, B. Tarroja, L. S. Schell, and S. Samuelsen, “Exploration of the integration of renewable resources into California’s electric system using the Holistic Grid Resource Integration and Deployment (HiGRID) tool,” Energy, vol. 50, pp. 353–363, Feb. 2013.
 M. F. Akorede, H. Hizam, and E. Pouresmaeil, “Distributed energy resources and benefits to the environment,” Renew. Sustain. Energy Rev., vol. 14, no. 2, pp. 724–734, 2010.
 M. A. Abdullah, K. M. Muttaqi, and A. P. Agalgaonkar, “Sustainable energy system design with distributed renewable resources considering economic, environmental and uncertainty aspects,” Renew. Energy, vol. 78, pp. 165–172, 2015.
 G. Pepermans, J. Driesen, D. Haeseldonckx, R. Belmans, and W. D’haeseleer, “Distributed generation: Definition, benefits and issues,” Energy Policy, vol. 33, no. 6, pp. 787–798, 2005.
 P. Chiradeja and R. Ramakumar, “An approach to quantify the technical benefits of distributed generation,” IEEE Trans. Energy Convers., vol. 19, no. 4, pp. 764–773, 2004.
 M. Jamil and A. S. Anees, “Optimal sizing and location of SPV (solar photovoltaic) based MLDG (multiple location distributed generator) in distribution system for loss reduction, voltage profile improvement with economical benefits,” Energy, vol. 103, pp. 231–239, 2016.
 M. A. Cohen, P. A. Kauzmann, and D. S. Callaway, “Physical Effects of Distributed PV Generation on California's Distribution System,” vol. 128, no. June, pp. 126–138, 2015.
 W. S. Andrade, C. L. T. Borges, and D. M. Falcão, “Integrated reliability evaluation of distribution and sub-transmission systems incorporating distributed generation,” 2009 IEEE/PES Power Syst. Conf. Expo. PSCE 2009, pp. 1–6, 2009.
 H. A. Gil, M. El Chehaly, G. Joos, and C. Cañizares, “Bus-based indices for assessing the contribution of DG to the voltage security margin of the transmission grid,” 2009 IEEE Power Energy Soc. Gen. Meet. PES ’09, pp. 1–7, 2009.
 K. L. Anaya and M. G. Pollitt, “Going smarter in the connection of distributed generation,” Energy Policy, no. January, pp. 1–10, 2017.  a. Tautiva, C. ; Dept. of Electr. & Electron. Eng., Univ. de los Andes, Bogotá, Colombia ; Duran, H. ; Cadena, “Technical and economic impacts of Distributed Generation on the transmission networks,” Innov. Smart Grid Technol. (ISGT), 2012 IEEE PES, pp. 1–6, 2012.
 M. Reza, J. G. Slootweg, P. H. Schavemaker, W. L. Kling, and L. Van Der Sluis, “Investigating impacts of distributed generation on transmission system stability,” 2003 IEEE Bol. PowerTech - Conf. Proc., vol. 2, pp. 389–395, 2003.
 V. V. Thong, J. Driesen, and R. Belmans, “Transmission system operation concerns with high penetration level of distributed generation,” Proc. Univ. Power Eng. Conf., no. 1, pp. 867–871, 2007.