Sean A. Kufel, P.E.

Power System Engineering, Inc.

April 20, 2015

Distributed Generation System Impact Analysis with Computer Modeling Tools

IEEE Rural Electric Power Conference

www.powersystem.org

© 2015 Power System Engineering, Inc.

Session SummaryGoal: Developing a reliable, efficient process for

performing DG system impact studies.• Data Requirements• Modeling Generation

– Types of generator models & adding generation– Types of analysis– Common modeling errors

• Focus on steps where errors or confusion are common• NOT: Instructions on using any modeling program• DISCLAIMER(S): I am not a programmer. I am not

endorsing any particular modeling application.

2

© 2015 Power System Engineering, Inc.

System Impact Analysis GoalsCommon impacts of DG that can be identified with computer modeling:• Voltage rise• Conductor/equipment overload• Inadequate device interrupt rating• Reverse power flow• Potential for islanding

3

© 2015 Power System Engineering, Inc.

Data Requirements• Utility side:

– Electrical model of distribution system area where DG is proposed, including:• Source impedance, including substation power transformer• System conductors• Major system equipment – transformers, regulators, capacitors &

protective devices• Substation area/feeder peak demand

– Historical minimum load in area/on feeder• Often estimated at around 25% of peak if historical hourly data is not

available

– Protective device settings– Regulator/LTC settings

4

© 2015 Power System Engineering, Inc.

Data Requirements• Applicant/Developer/Generation side:

– Number of generators to be installed and total aggregate capacity

– Proposed facility one-line/three-line diagram– Expected peak generator output & how the generation will be

used (back-up only, intermittent operation, on-site load service, power export, etc.)

– Location of proposed interconnection (preferably in reference to distribution system)

5

© 2015 Power System Engineering, Inc.

Data Requirements• Applicant/Developer/Generation side:

– Generator data:• Operating voltage• Ratings: kW, kVA, power factor• Fault information

– Steady-state, transient & subtransient reactance values or generator equivalent circuit for rotating machines

– For PV with inverter(s), fault current is typically a multiple of rated output (150% is often used)

– Other equipment data:• Inverter ratings, solar panel data for PV installations• Ratings & impedances of any generator step-up transformer units (GSU)

6

© 2015 Power System Engineering, Inc. 7

Impedance Data Equivalent Circuit

Generator Fault Information

© 2015 Power System Engineering, Inc. 8

Milsoft WindMil® Eaton CYME

Modeling Programs

• SynerGEE, eTap, Dapper, etc.

© 2015 Power System Engineering, Inc. 9

Types of Generator Models• Generic Generator

• Two operating modes:– Negative load (constant

kW output)– Swing kVAR (hold

desired voltage by adjusting kVAR output)

• Fault output based on generator impedances

© 2015 Power System Engineering, Inc. 10

Types of Generator Models• Specific Generators • Common types:

– Synchronous & Induction– Wind turbine– Solar array– Others

• Operating modes & fault contributions dependent upon type of generation

• Mostly the same as generic for synchronous machines

© 2015 Power System Engineering, Inc. 11

Generic Generator Pros/Cons• Con:

– Sometimes need to perform impedance calculations when only fault duty is available

• Pro:– Conversion utilities are often built in

© 2015 Power System Engineering, Inc.

Pro:• Possible to create extremely

detailed generator models with LOTS of specific data

• Possible (?) to run highly specific analysis depending upon program modules & capabilities

Con:• Hyper-specific data

generally not needed for snapshot analysis

• Lots of specific data can be overwhelming

Specific Generator Pros/Cons

12

© 2015 Power System Engineering, Inc.

Information Overload?

13

© 2015 Power System Engineering, Inc.

Add Generation to the Model

14

© 2015 Power System Engineering, Inc.

Peak Load Minimum Load

Voltage Drop/Load Flow Analysis

15

© 2015 Power System Engineering, Inc.

Common Error: Generators not included in analysis

Voltage Drop/Load Flow Analysis

16

© 2015 Power System Engineering, Inc.

Collecting Results• From on-screen result boxes:

17

© 2015 Power System Engineering, Inc.

Collecting Results• Via custom reports:

18

© 2015 Power System Engineering, Inc.

Voltage Drop/Load Flow Analysis• Other things to check:

– Substation/source power factor, before & after generation is added

– Native loads in all protective zones upline of the generation (with generation offline)• Aid in determining if islanding is possible

– Current flow through equipment with generation online– Reverse power flow through equipment and/or substations when

generation is operating (more likely and higher at minimum load)

19

© 2015 Power System Engineering, Inc.

Checking Protective Zone Loads

20

© 2015 Power System Engineering, Inc.

Turning on Power Flow Arrows (If Available)

21

© 2015 Power System Engineering, Inc.

Short-Circuit Analysis

22

© 2015 Power System Engineering, Inc.

Gen Z: Steady-state or “None” Gen Z: Subtransient

Short-Circuit Analysis: General

23

© 2015 Power System Engineering, Inc.

Coordination Analysis

24

© 2015 Power System Engineering, Inc.

CYME TCC Settings Device Coordination Check

Device-Device Coordination Setup

25

© 2015 Power System Engineering, Inc.

Generator Feeder Recloser

Short-Circuit Analysis: Fault Flow

26

End of Protective Zone 1

© 2015 Power System Engineering, Inc.

Short-Circuit: Reverse Fault Flow

27

Initiate fault immediately upline of protective device

© 2015 Power System Engineering, Inc.

Short-Circuit: Fault Flow• Locations to check during fault flow:

– End of protective device zones• Especially in direct path between generation and source• Especially for electronically-controlled reclosers

– Check ground pickup setting versus minimum fault flowing through device with generation contributing

– Source side of devices in direct path between generation and source

– Other feeders on substation

28

© 2015 Power System Engineering, Inc.

System Impact Study Model Use Keys• Develop a process and stick to it• Double-check entered data• Document analysis results clearly• Keep track of model changes made to improve system

conditions– Probably not a good idea to alter the working model of your

existing system if you are a utility, especially if it is an enterprise or shared model

• Step back and sanity-check results

29

© 2015 Power System Engineering, Inc. 30

QUESTIONS &DISCUSSION

© 2015 Power System Engineering, Inc. 31

Power System Engineering, Inc.

Name: Sean A. Kufel, P.E.

Title: Electrical Engineer

Direct: (740) 568-9220 x11

Mobile: (216) 544-8614

Email: kufels@powersystem.org

www.powersystem.org

Thank You:

IEEE 2015 REPC Attendees!