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Intelligent Utility
Dr. Nokhum Markushevich
Dr. Nokhum Markushevich
·Posted in Intelligent Utility
Thu, Mar 23

The Challenges of Load Reduction via Voltage Reduction in Active Distribution Networks

Voltage reduction is a common component of emergency load reduction measures in many utilities [1]. Typically, the size of the voltage reduction and the expected load reduction is predefined in the utilities opearating manuals, see e.g., [2] - [3]. These numbers are based on voltage tests periodically performed by the utilities, e.g.,  once a year.  It implies that under the conditions of the “passive” disitribution networks, the load sensitivity to voltage reduction is approximately the same during an extensive time interval.

The situation can significantly change with the high penetration of Distributed Energy Resources (DER), especially, when they are equiped with smart inverters. These components and other active elements in the disitribution systems constitute the Active Disitributin Networks.

Different circuits of an Active Distribution Network of the same utility may be of different designs (e.g., OH or UG). They feed different combinations of conventional loads (without embedded DERs), loads with  embedded DERs, stand-alone DERs, microgrids, and other kinds of prosumers. The DERs can be connected either to the secondaries, or to the primaries. They may have different setups of the volt/var control functions [4], different injections of real power, different rated power factors, etc. The results of the voltage reduction tests may be significantly different under different combinations of the mentioned above factors. Many of these factors are changing in near-real time, which means that the test results obtained under the test conditions may not be applicable to the actual situations.

Also, currently, the real load-to-voltage sensitivities are presented and used as linear dependencies (e.g., as slope coefficients of a linear regression equation derived based on the test measurements). In an Active Distribution Network, the real load to voltage dependencies are non-linear due to non-monotonic nature of the DER volt/var curves. It means that for specific voltage reduction intervals, the load sensitivities may significantly differ from the regression factors extrapolated for a wider or different voltage reduction interval.

Based on the challenges of the testing and conducting the emergency voltage reduction for load reduction in the Active Distribution Network, it is worth considering a methodology for voltage reduction test aimed only at determining the natural load dependency on voltage without the impact of DERs. These dependencies are similar to the current dependencies for the”passive” distribution networks.  They can be attributed to the nodal loads and be used in near-real time modeling of the operating conditions of the Active Distribution Networks. The models should also include the near real time individual models of the performance of major DERs, groups of DER, microgrids, and other significant prosumers [5]-[8].

In order to perform such modeling and subsequently the voltage control based on this modeling, adequate information exchange between the major actors in the Active Distribution Network and Distribution Management Systems (DMS), as well as between DMS and the transmission Energy Management System (EMS) should be provided [5]-[11].

More details on this topic are presented in [12] and[13].

 

References.

  1. NERC Reliability Standards for the Bulk Electric Systems of North America. Available: http://www.nerc.com/comm/OC/Documents/Reliability_Standards_Complete_Set.pdf  

  2. PJM Manual 13 Emergency Operations Revision: 62. Available: http://www.pjm.com/~/media/documents/manuals/m13.ashx

  3. NYISO Emergency Operations Manual. Available:  http://www.nyiso.com/public/webdocs/markets_operations/documents/Manuals_and_Guides/Manuals/Operations/em_op_mnl.pdf

  4. Common Functions for Smart Inverters, Version 3. Available: http://www.epri.com/abstracts/Pages/ProductAbstract.aspx?ProductId=000000003002002233

  5. Coordination of Volt/var control in Connected Mode under Normal Operating Conditions, Use Case Description. Available:  http://smartgrid.epri.com/Repository/Repository.aspx/  

  6. Update aggregated at PCC real and reactive load-to-voltage dependencies, Use Case Description. Available:  http://smartgrid.epri.com/Repository/Repository.aspx/

  7. Updates of capability curves of the microgrid’s DERs, Use Case Description. Available:  http://smartgrid.epri.com/Repository/Repository.aspx/  

  8. Updating information on microgrid dispatchable load, Use Case Description. Available:  http://smartgrid.epri.com/Repository/Repository.aspx/

  9. Nokhum Markushevich,”New Aspects of IVVO in Active Distribution Networks,” Presented at IEEE PES 2012 T and D conference

  10. Nokhum Markushevich, Cross-cutting Aspects of Smart Distribution Grid Applications, Presented at IEEE PES GM 2011, Detroit. Available from IEEE Explore.

  11. Development of Transmission Bus Load Model (TBLM), Available: http://collaborate.nist.gov/twiki-sggrid/pub/SmartGrid/TnD/TBLMUseCase_V14-03-13-13-posted.pdf

  12. Nokhum Markushevich, Voltage Reduction Effect in Active Distribution Networks. Available:     https://www.scribd.com/document/376755241/Voltage-Reduction-Effect-in-Ac...

  13. Nokhum Markushevich,  Analysis of electric heating load dependency on voltage. Available: https://www.energycentral.com/c/iu/analysis-electric-heating-load-depend... Â