Distributed Generation and the Impact on a Distribution System Brian Lassiter Technical Sales Engineer
Company Overview Founded in 1989 in Abilene, TX Industry leader in Engineering and Operations Utility Software WindMil & LightTable T&D Circuit modeling and engineering analysis DisSPatch Outage Management Communications IVR Over 1,000 utilities, consultants, and universities use Milsoft Applications
Overview Regulations Typical DG Interconnections Impact Studies Utility Example Summary
Installed Capacity by State Solar Wind State Installed MW State Installed MW California 4,316 Texas 16,406 North Carolina 396 California 6,022 Nevada 339 Iowa 5,710 Massachusetts 308 Oklahoma 4,300 Alaska Does the sun shine here? Alaska (35th) 62
Regulations Alaska Regulations R-09-02 Applicable to utilities subject to net metering requirements Requirements may be developed using, as applicable, standards from IEEE 1547 Only 9 of 37 regulated utilities meet the criteria some of the economically regulated utilities that do not meet net metering requirements are simply too small to be able to handle the interconnection of a DG of appreciable size
1547 Series Applicable Docs 1547 2003 and 2014 Amendment 1- Standard for Interconnecting Distributed Resources with Electric Power Systems 1547.2 Application Guide for IEEE 1547 Standard for Interconnecting Distributed Resources with Electric Power Systems 1547.7 2013- Guide to Conducting Distribution Impact Studies for Distributed Resource Interconnection
IEEE 1547 System Impact Study Areas DER Grounding cannot cause over voltages on the EPS for ground faults Shall not energize the EPS when EPS is deenergized. Shall detect island and disconnect within 2 seconds Shall cease to energize the EPS for faults on the connected circuit Shall not reconnect until EPS voltage is maintained for 5 minutes within ANSI C84.1 Range B
IEEE 1547 System Impact Study Areas DER cannot actively regulate voltage DER cannot adversely affect EPS coordination Shall cease to energize EPS when PCC voltage falls outside of limits in voltage/clearing time table Shall not create objectionable flicker according to IEEE 519 or IEC 6000RDA
Other Resources UL 1741 NRECA Toolkit UWIG library of turbines and analysis tools available FERC SGIP Small Generator Interconnection Procedure FERC 661-A - Transmission Interconnection
Generator Types
DG Types Rotating Type Synchronous Generator (adjust kvar by field winding) Induction(needs external source of excitation) Wind Turbines Types 1-4 machine based coupled with grid via converters(types 3-4) Inverter based PV
Load Behavior Negative Load (kw/kvar) kw based on sunshine or wind speed Constant kvar PF Control Mode (Fixed PF) kvar adjust with kw VAR controlled to maintain voltage kvar increases or decreases to offset voltage rise/drop(synchronous Generators)
Impact Studies Regulator Operations the effect of DG on the number of equipment operations performed by voltage regulation equipment(ltc, Regulators, Capacitors) System Voltage DG impact on voltage delivered to connected loads Voltage Flicker visible light flicker at end users System Protection effects on OCDs and fault contribution of generators
Typical PV Daily Profiles Content 4 3 2 1 Average Daily Profile 0 2 4 6 Average Daily Profile 0 6 12 18 24 4 2 0 2 4 Average Daily Profile 0 6 12 18 24 0 0 6 12 18 24 8 10 6 8
Load Models Typical system planning studies use peak loading DG Interconnection studies require the analysis of multiple load models Max Peak Min Load Average Load Different times of year
Load Models Typical load data in EA systems Billing system Monthly kwh, Peak kw SCADA Control Point Values Substation Metering DG Simulations provide best results if AMI kw values are provided Ability to analyze all loads at specific points in time
Shortcomings of Typical Load Data Traditional static load model is missing time component DG Output is highly variable over time Control systems monitor load constantly, not just at single instances in time Time series analysis evaluates the magnitude and frequency of the impact
AMI Load & Time Series Analysis Typical intervals 1 hour or 15 mins DG Interconnection requires shorter interval to match up in frequency of PV load changes Interpolation of data may be required to acquire the desired load data
DG Variability Estimating plant output requires data from like systems Irradiance/wind patterns can also be used to determine DG estimated output for area being evaluated
Time Series Study Tools OpenDSS GridLab-D Both great for analysis, but difficult to use for system modeling Some commercially available options Milsoft WindMil provides exports of system models to OpenDSS and GridLabD
Sample Impact Study La Plata Electric Durango, Co 41,000 Meters (12 per mile) Winter Night Peaking 650 DG Installations Used Peak and Min Load models 80 kw Proposed Solar Site Single phase tap 80 %AMI kw 15% kwh 5% non-ami kw
Study Area 80 kw of solar generation
Analysis Voltage Profiles 126 124 122 120 Voltage 118 116 114 112 110 0 1 2 3 4 5 6 7 8 9 10 Miles from Source Peak Loading Min Loading Min Loading w/ Generation
Peak Loading Voltage Profile 125 123 121 119 Voltage 117 115 113 111 109 0 1 2 3 4 5 6 7 8 9 10 Distance from Source Peak Loading Meters Modeled Meters Actual
Min Loading with Generation 128 127 126 125 Voltage 124 123 122 121 120 0 1 2 3 4 5 6 7 8 9 10 Distance from Source Min Loading w/ Generation Meters Modeled Meters Actual
Considerations Utility looked at solution options for voltage Reconductor area Installing Line Regulators Utility evaluates all interconnection projects Continue to evaluate areas with other existing generation in place Several small DG of same type eventually add up to larger impact
How much is too much?
How much is too much? No silver bullet answer If DG is significant the impact to the system will vary throughout the day Significant depends on the system Load Impact Conductor Size Distance Answer depends on system, loads, and DG
Utility Hurdles Interval Load Data Not only AMI system to get loads, but system to manage loads for retrieval Tracking DG installations(gis, EA, CIS) Not only impact of new system Total impact of installed DG Loss of revenue vs. operating costs System must still be designed as if DG doesn t exist
Questions/Comments
References PV Voltage Rise Dan Harms, La Plata Electric DG Impacts on Distribution Systems Greg Shirek, Milsoft Sandia Report Time Series Power Flow Analysis for Distribution Connected PV Generation Seia.org Awea.org
Thank you Brian Lassiter Technical Sales Engineer brian.lassiter@milsoft.com