Multi-regional Modeling Working Group Case Building … Modeling Powerflow and Dynamics...RAW read warnings produced by PSSE. ... NMMS Facts • Since 9/1/2009

Eastern Interconnection Reliability Assessment Group

ERAG

Multi-regional Modeling Working Group Case Building Process

Presented by,

John Idzior ReliabilityFirst Corporation

NERC Modeling Workshop Minneapolis, MN

October 1-3, 2012


ERAG ERAG Structure

• Agreement signed by 6 EI Regional Managers

• Management Committee MMWG Regional Entity Coordinators

Other Representatives

Study Steering Committee 3 Working Groups

10/24/2012 2


ERAG Regional Coordinators

• FRCC (Fred McNeil, John Shaffer)

• MRO (Adam Flink)

• NPCC (Donal Kidney)

• RFC (John Idzior)

• SERC (Lee Adams, John Sullivan)

• SPP (Anthony Cook, Scott Jordon)

10/24/2012 3


ERAG Annual Development

• Series of Base Cases Power Flow 13 Cases

Dynamics 8 Cases

• Master Tie Line List

• Interchange Schedule

• Procedure Manual

10/24/2012 4


ERAG 2012 Series Models Developed

Year Season Dynamic

2013 Light Load X

2013 Spring

2013 Summer X

2013 Summer Shoulder X

2013 Fall

2013 Winter X

2014 Spring

2014 Summer X

2014 Winter

2018 Light Load X

2018 Summer X

2018 Winter X

2023 Summer

10/24/2012 5


ERAG Development Cycle

Member Companies

RE Coordinators

MMWG Coordinator

Regions/

SPOC

Industry

Users

10/24/2012 6


ERAG Data Checks

• Unrealistic PMAX and PMIN • Unrealistic QMAX and QMIN • PGEN outside range • Reactive device regulating node voltage more than one bus away. • Switch shunts with VHI - VLOW < 0.0005 • Controlled Bus Checks (CNTB) - Errors • Transformers with voltage band < 1.95 * step • RAW read warnings produced by PSSE. • Buses with duplicate bus names within the same control area. Duplicate bus names are defined as having the same twelve character name and six

character voltage fields. • Buses with blank voltage fields. • Machines connected to a Code 1 bus. • Code 2 buses with no machines modeled. • Machines with zero or non-positive RMPCT. • Machines with GENTAP > 1.1 or < 0.9. • Branches with Rate B < Rate A (Required) or Rate A = 0.0 and Rate B = 0.0 (Warning) for 100 kV and above. • Three winding transformers with Rate B < Rate A (Required) or Rate A = 0.0 and Rate B = 0.0 (Warning). • Transformers with RMAX <= RMIN or VMAX <= VMIN. Required for non-fixed tap transformers only. • Transformers with RMAX = 1.5 and RMIN = 0.51. Required for non-fixed tap transformers only. • Transformers with VMAX = 1.5 and RMIN = 0.51. Required for non-fixed tap transformers only. • Transformers with RMAX, RMIN, VMAX or VMIN = 0. Required for non-fixed tap transformers only. • Switched shunts with missing Block 1 steps. • Branches with loading above 100% of Rate A or B for 100 kV and above. • Bus voltages under 90% or above 110% for 100 kV and above. • Branches with resistance > |reactance| for 100 kV and above. • Buses with owner numbers out of range. • Buses with zone numbers out of range. • Buses with numbers out of range.

10/24/2012 7


ERAG Case Distribution

• ERAG Base Case Release Procedure (NDA)

• Regional Entity Members - Regional Coordinator

• Third Party Users - Single Point of Contact - ReliabilityFirst Corporation

• Secure Site

• Public Site - erag.info

10/24/2012 8


ERAG Software Tools Used

• Siemens PTI PSS/e

• Powertech Labs, Inc. Power Flow Database (PFDB)

Dynamics Database (SDDB)

10/24/2012 9


ERAG

10/24/2012 10

Questions?


ERAG

John Idzior

Lead Engineer, Modeling

ReliabilityFirst Corporation

330-247-3059

[email protected]

10/24/2012 11

Nitika Mago, P.E. Network Model Administration

NERC Modeling Workshop Bloomington, MN

Oct. 1, 2012

Network Modeling The ERCOT Experience

ERCOT

• 85% of Texas load • 40,530 circuit miles of high-voltage transmission: • -- 9,249 miles of 345 kV and 19,565 miles of 138 kV • 550 generating units • 84,000 megawatts (MW) total capacity: • -- 64,000 MW operational capacity • -- 9,600 MW wind generation • -- 4,400 MW net available private generation • -- 3,000 MW switchable resources • -- 3,000 MW mothballed resources • Capacity available on peak: 73,600 MW • -- Includes 8.7 percent of wind capacity • Reserve margin: 13.86% • Record peak demand: 68,379 MW (Aug.3, 2011)

Jan of 2012

NERC Modeling Workshop - Oct.1, 2012

Network Modeling Overview

Network Models

Planning Model

• Future Year Analysis • Production Cost Analysis • Voltage Stability

Network Operations Model

• Energy MS • Market MS • Steady State Analysis • State Estimator • Day Ahead • Outage Coordination • Voltage Stability

CRR Model

• Congestion Auction

Dynamics Model

• Stability Analysis


Old Model Release Process (2009)

Real-Time and Future Analysis

ERCOT Operations

Model Database

Non-Temporal

ERCOT Market and

Registration Database

SERVICE REQUEST


Problems with the Old Process

• Single Operations Model only valid for 2 weeks in advance. Planning Models were for following year, leaving a study gap.

• Market Information not integrated in Operations Model.

• Contingency files and One-lines not available to support future studies.

• Model database and Outage Scheduler had no dynamic link resulting in “broken” outages and no ability to outage future equipment.

• Differences in Planning and Operation Model topologies, element attributes, and naming conventions.

• Dynamic cases built from Planning Cases, but used to support decisions made in real-time.

• Market Participants had no access to the Model Database.


Current Model Release Process

Topology Processor

Topology Processor

Real-Time Analysis Temporal Models

Future Case Analysis


Model Consistency


Network Model Management System

The Network Model Management System (NMMS)

One system manages all model data


What is NMMS?

The Network Model Management System (NMMS) is an umbrella of applications used to manage, manipulate, prepare, validate, test, and provide consistent models to all model-driven ERCOT operational, market and planning systems. • Utilizes Common Information Model (CIM) standards for integration.

• Built around the Siemens’ Information Model Manager (IMM) and

Model on Demand (MOD)

• Uses temporal based tracking methodologies to store the network models data changes.

• NMMS serves as the single point of entry and maintenance for the network model topology used by external ERCOT market participants.


Time-Based Modeling

Base Model

Jul 20, 2012 1:00 pm

Jul 20, 2012 2:00 pm

Sep 1, 2012 8:00 am

Sep 1, 2012 9:00 am

Sep 1, 2012 10:00 am

Sep 30, 2012 9:00 am

Nov 8, 2012 8:00 am

– A projection of all network changes that are scheduled to occur on or before a given date/time on top of a “start of world representation of a electric grid” aka base model.


What Can NMMS Deliver?

• Accommodate Time Based Changes • Create models in the future • Generate historical models • Create Incremental and Full Models (in CIM/XML)

• Assign Ownership to every piece of equipment • Equipment owners own their data, with update rights • Uses CIM classes, attributes and associations

• Supply Outage Scheduler with equipment lists daily. • Provide NOMCR testing status notifications to data

owners.


NMMS Applications

NMMS Applications that handle Operations Data: • Project Tracker & Coordinator (PTC) • Information Model Manager (IMM) NMMS Applications that handle Planning Data: • Model On Demand (MOD)

Introduction : Slide 14 NERC Modeling Workshop - Oct.1, 2012

Four Types of Instance Editing options

NMMS User Interface

Single Instance Editor

Model or edit one

instance

Table Editor

Model / manage

multiple instances

Automatic Network Layout

View model

layout

Four different ways of viewing and

modifying modeling data

Module 2 : Slide 15

Incremental Data Imports

Model / manage

multiple instances


NOMCR Process Flow Diagram

Start Saved

Submitted

Deleted

Received

RejectedApproved

ForTesting

Incomplete

Withdrawn

AdditionalData Required

Approved forProduction In Production

Closed

T13

T14

Archived

T22

T20

T21

T25

T1

T2

T4

T3

T15

T5

T6

T7 T8

Resubmitted

T9

T16T19

Market TestComplete

T11

T12

T23

T27

T26

T24

T28

T18

T17

T10

T30

T29

T31

T32

T33

T34

Start Here

Enters Production HERE


Internally what is going on?

4 Levels of Testing prior to ITEST Release

Level 1

• Ran prior to “submission” • Range Checks • Association Checks • Completeness Checks

Level 2 • Model Coordinator Visual checks • Additional Programmatic Sanity Checks

Level 3 • Engineer Review • Assessment for Power Flow

Level 4 • Power Flow test with NOMCR incorporated with all other

NOMCRs for timeframe


So, What Does this Mean?

• In Short: TRACKING, COMMUNICATION, and COORDINATION – EVERY successful submission receives an automatic email that data was

submitted. – EVERY time the NOMCR state status is modified, both the submitter and

the owner of any effected equipment are notified via email.

• For emphasis: – EVERYONE listed as either an Owner or Operator of any piece of

equipment who is even tangentially effected by the change will receive an email that a NOMCR has somehow modified a piece of equipment that they own/operate.

– The email includes both the new status and WHO made the modification.


NMMS Facts

• Since 9/1/2009 NMMS is being used as the primary system to enter network model changes by ERCOT’s Market Participants and by ERCOT. – 16000+ change requests have been submitted into NMMS thus far. – Weekly CIM models from NMMS have been delivered to downstream

test environments.

• Since 6/1/2012 NMMS is being used as the source of record for planning models and planning model changes by ERCOT’s Market Participants and by ERCOT staff to build future planning cases. – Planners are now using NMMS to build base models for 5-year studies

• Quiet a few tools leveraging the flat structure of CIM/XML have been

developed. Some notable ones include, – Model topology tracer for Outage Scheduler, – Contingency definition builder, – Station one-line editor/generator, and – Granular model comparison viewer


What Does NMMS Do?


Building Network Models for Planning Studies

Network Model Build Process

• Two types of Model posting packages are released for future planning studies. These are available to all internal and external ERCOT Network Model customers. – Data Set A Model Package

• Intended to be utilized for short-term planning studies, systems operational studies, transmission loss calculations etc.

• Package contents – Four on-peak Seasonal Models for upcoming year (YR+1) with case load modeled

as maximum expected load in a season (Summer) and/or in a month corresponding to transmission topology cut-off (Spring, Fall, Winter)

– Four off-peak Seasonal Models for upcoming year (YR+1) with case load modeled as minimum expected load on day of corresponding seasonal peak case.

– Model Reports (As-Built Report, Data Validation Checks, etc.)

– Data Set B Model Package • Provides a preview to forthcoming models. Utilized for planning studies over the near-

term and longer-term planning horizon. • Package contents

– Yearly models for summer season for five future years following the upcoming year (YR+2 thru YR+6) with case load modeled as maximum expected load in season.

– One model in the five-year planning horizon with case load modeled as minimum expected load in the year.

– Model Reports (As-Built Report, Data Validation Checks, etc.)


Network Model Release Timelines

Jan

1 Jan Q1 Update

Apr Q2 Update

Data Set A

Jul Q3 Update

Oct Q4 Update

Data Set B

YRDSA YRDSB - 14 cases

YR+1 SPG-SUM2

Mar

1

May

1

Jul 1

Sep

1

Nov

1

YRDSA YRDSB

(YR+1)DSA - 15 cases

YR +1 FAL-WIN

- 7 cases

YRDSA YRDSB

(YR+1)DSA - 17 cases

(YR+4)MIN

(YR+6) SUM

- 2 cases

YRDSA (YR+1)DSA (YR+1)DSB

16 cases

MOD Environment

Posting date

Sync with Operations. TP Incremental Update

YR


Future Model Release Process

Temporal Long Term Models

Review Model

Iterative

Load, Voltge Profiles

Future & Stndrd PMCR

Gen Disptch Profiles

Topology Processor


Building Network Models for Operations & Market


• Three types of Model posting packages are released for every planned model to be migrated into ERCOT’s production environments. – Production Model Package

• Intended to be utilized to drive ERCOT Market & Operations applications in Production. • Package contents

– Model Profiles (Post-processed model, Redacted profile, Settlements & Billing profile, Outage Scheduling profile)

– Model Reports (Comparison, equipment details, Contingency report, etc.)

– Market Model Package • Provides a preview to the contents of a forthcoming Production model. • Package contents

– Model Profiles (Post-processed model, Redacted profile) – Model Reports (Comparison only)

– Future Study Model Package

• Intended to be consumed by internally by groups whose business is keyed off evaluating expected future changes to the electricity grid.

• Package contents – Model Profile (Post-processed model) – Model Reports (As Built Report only)


Model Release Timelines

• Picture above identifies the location where the Model Build process get triggered during a model’s content validation & testing lifecycle.



Build Validate Export Post Process NMG Release ERCOT Internal Release

Temporal Model

Validate

Review

Iterative

Submit Corrections Export Test Model

Bui

ld T

est M

odel

• All activities are executed in a Test Model Development environment

using the latest available Production data snapshot.


NMMS Development

Questions?

Nitika Mago, P.E. Network Model Engineer

Network Model Administration [email protected]

512-248-6601

mailto:[email protected]�

NERC MVWG Proposal for Node-breaker Modeling Eric H. Allen

October 1, 2012

2

RELIABILITY | ACCOUNTABILITY

MVTF White Paper

• Models form the foundation of power system studies

• Models need to be regularly compared against actual power system observations (i.e. validated)

• Approved December 2010

3


MVTF White Paper

WECC August 10, 1996 – reality vs. models

4


MVTF White Paper

• NERC Recommendation 14 from August 14, 2003 “The regional reliability councils shall within one year

establish and begin implementing criteria and procedures for validating data used in power flow models and dynamics simulations by benchmarking model data with actual system performance. Validated modeling data shall be exchanged on an inter-regional basis as needed for reliable system planning and operation.”

5


Recommendations

• 1. Periodic model validation should be an integral part of model maintenance

• 2. Operational planning (offline) models should be periodically validated by comparison with models from real-time systems. “Node-breaker” models

Standardized data transfer format

Universal identification of equipment

6


MVTF/MVWG Work Plan

• Task 2.2: The MVTF should draft a proposal for the Industry to institute node-breaker models in all off-line study models

7


Bus-branch vs. Node-breaker

Bus-branch Node-breaker

8


Benefits of Node-breaker

• Much better alignment with real-time models Greatly improved construction of historic powerflow cases

Real-time and off-line models can be constructed from the same database

• Greatly enhanced contingency evaluation Have computers identify breakers needed to isolate faults

and elements that trip in common

Stuck breaker contingency evaluation

Elimination of error-prone process of manually maintaining contingency decks

New TPL-001 standard

9


Different configurations

A B

10


Different configurations?

A B

11


Split buses

Bus-branch Node-breaker

12


Hurdles to Node-breaker

• Significant additional data Handling large interconnection powerflow cases

• Lack of familiarity in off-line study environments

• Transition costs

13


State of Node-breaker

• Being implemented by powerflow software vendors

• Computation time needed for additional topological processing is not significant, according to vendors

Interconnection-Wide Studies Goals and Studies

NERC Modeling Workshop – Bloomington, MN October 1-3, 2012

2 RELIABILITY | ACCOUNTABILITY

Forensic Analysis

1. Sequence of event analysis

2. Powerflow analysis

3. Dynamic Analysis a. May utilize all three time frames – transient, mid-term,

and long-term

4. Verification of protection operations


Transient Timeframe (< 20 sec)

1. Frequency response analysis a. UFLS system design

b. System separation studies – Frequency Response and under-frequency load shedding requirements. Includes study of restoration.

c. Resource mix change

2. Sensitivity Studies (including extreme contingency analysis – do an extreme contingencies spill over into other areas of an interconnection?) Includes study of system restoration.



3. Inter-area oscillations (small-signal stability) Sensitivity Studies (including extreme contingency analysis – do an extreme contingencies spill over into other areas of an interconnection?) Includes study of system restoration. a. Mode shape determination – Eigenvalue analysis

b. Challenging with user/proprietary models which do not translate into small signal study



4. Forensic analysis of disturbances a. ERCOT – ??

b. Western Interconnection – 2 to 3 weeks to develop

c. Eastern Interconnection – 4 to 6 months to develop

5. Inter-area transfer capabilities a. Regional and Interregional studies

6. GMD powerflow analysis – New developments

7. Reserve Assessments & deliverability a. Combination of capacity and deliverability analysis coming



8. Voltage stability a. Transient

b. Power-Voltage curve analysis

9. Cross-regional or interconnection-wide system expansion studies

10. Fault-Induced Delayed Voltage Recovery (FIDVR) analysis (more local, not interconnection-wide phenomena)

11. TPL Testing, including protection coordination analysis


Mid-term Timeframe (> 20 sec)

1. Frequency Response Analysis a. Crossing from Primary Frequency Response to Secondary

Frequency Response (AGC)

2. Plant and Unit controls interactions with: a. SVCs and StatComs

b. DC terminals

c. Electronically-coupled resources and loads

d. SPS / RAS

e. Other Control systems


Long-term Timeframe (> 2 min)

1. Frequency Response Analysis a. Crossing from Secondary Frequency Response (AGC) to

Tertiary Frequency Response (potential operator action)

2. Plant and Unit controls interactions with: a. SVCs and StatComs

b. DC terminals

c. Electronically-coupled resources and loads

d. SPS / RAS

e. Other Control systems


Questions?

1529pk - 1

Power System Stability Overview

presented by:

Prabha S. Kundur Kundur Power Systems Solutions, Inc.

Toronto, Ontario

NERC Modeling Workshop October 1-3, 2012

Copyright © P. Kundur This material should not be used without the author's consent

1529pk - 2 Copyright © P. Kundur

Power System Stability Overview

Outline

1. Brief Introduction to Power System Stability Basic concepts Classification Description of different categories of stability

2. Impact of new forms of generation: WTGs and PVs

3. Modeling requirements for each category of stability

4. Overall approach to model identification and validation

5. Where are the significant gaps?


Power System Stability

Refers to continuance of intact operation of power system, following a disturbance

Recognized as an important problem for secure system operation since the 1920s

Major concern since the infamous November 9, 1965 blackout of Northeast US and Ontario criteria and analytical tools used until recently largely based on the

developments that followed

Presents many new challenges for today's power systems


Power System Stability: Definition

Power System Stability denotes the ability of an electric power system, for a given initial operating condition, to regain a state of operating equilibrium after being subjected to a physical disturbance, with all system variables bounded so that the system integrity is preserved integrity of the system is preserved when practically the entire power

system remains intact with no undue tripping of generators or loads

Stability is a condition of equilibrium between opposing forces: instability results when a disturbance leads to a sustained imbalance

between the opposing forces

Ref: IEEE/CIGRE TF Report, "Definition and Classification of Power System Stability", IEEE Trans. on Power Systems, Vol. 19, pp. 1387-1401, August 2004


Classification of Power System Stability

Classification into various categories greatly facilitates: analysis of stability problems identification of essential factors which contribute to instability devising methods of improving stable operation

Classification is based on the following considerations: physical nature of the resulting instability size of the disturbance considered devices, processes, and the time span involved


Power System Stability

Frequency Stability

Small-Signal Stability

Transient Stability

Short Term Long Term

Large-Disturbance Voltage Stability

Small-Disturbance Voltage Stability

Voltage Stability

Rotor Angle Stability

Consideration for

Classification

Physical Nature/ Main

System Parameter

Size of Disturbance

Time Span

Short Term

Short Term Long Term


Rotor Angle Stability

Ability of interconnected synchronous machines to remain in synchronism after being subjected to a disturbance

Depends on the ability to restore equilibrium between electromagnetic torque and mechanical torque of each synchronous machine

If the generators become unstable when perturbed, it is as a result of a run-away situation due to torque imbalance

A fundamental factor is the manner in which power outputs of synchronous machines vary as their rotor angles swing

Instability that may result occurs in the form of increasing angular swings of some generators leading to loss of synchronism with other generators


Transient Stability

Term traditionally used to denote large-disturbance angle stability

Ability of a power system to maintain synchronism when subjected to a severe transient disturbance: influenced by the nonlinear power-angle relationship

stability depends on the initial operating condition and severity of the disturbance

A wide variety of disturbances can occur on the system

The system is, however, designed and operated so as to be stable for a selected set of contingencies usually, transmission faults

N-1 criterion


Small-Signal (Angle) Stability

Small-Signal (or Small-Disturbance) Stability is the ability of a power system to maintain synchronism under small disturbances disturbance considered sufficiently small if linearization of system

equations is permissible for analysis Instability that may result can be of two forms:

aperidic increase in rotor angle due to lack of sufficient synchronizing torque

rotor oscillations of increasing amplitude due to lack of sufficient damping torque

In today's practical power systems, SSS problems are usually associated with oscillatory modes local plant mode oscillations: 0.8 to 2.0 Hz interarea oscillations: 0.1 to 0.8 Hz


Voltage Stability

Ability of power system to maintain steady voltages at all buses in the system after being subjected to a disturbance

A system experiences voltage instability when a disturbance, increase in load demand, or change in system condition causes: a progressive and uncontrollable fall or rise in voltage of buses

in a small area or a relatively large area Main factor causing voltage instability is the inability of power system to

maintain a proper balance of reactive power and voltage control actions

The driving force for voltage instability is usually the load characteristics


Short-Term and Long-Term Voltage Stability

Short-term voltage stability involves dynamics of fast acting load components such as induction motors, electronically controlled loads and HVDC converters study period of interest is in the order of a seconds dynamic modeling of loads essential; analysis requires solution of

differential equations using time-domain simulations faults/short-circuits near loads could be important

Long-term voltage stability involves slower acting equipment such as tap-changing transformers, thermostatically controlled loads, and generator field current (over excitation) limiters study period may extend to several minutes


Frequency Stability

Ability to maintain steady frequency within a nominal range following a disturbance resulting in a significant imbalance between total area generation and load

Instability that may result occurs in the form of sustained frequency swings leading to tripping of generating units and/or loads

In a small "island" system, frequency stability could be of concern for any disturbance causing a significant loss of load or generation


Frequency Stability (cont'd)

In a large interconnected system, frequency stability could be of concern only following a severe system upset resulting in the splitting of the system into islands

Depends on the ability to restore balance between generation and load of island systems with minimum loss of load and generation

Generally, frequency stability problems are associated with inadequacies in equipment responses, poor coordination of control and protection systems


Examples of Major System Disturbances Caused by Different Forms of Instability

1. November 9, 1965 blackout of Northeast U.S. and Ontario Transient instability; Frequency instability

2. April 19, 1972, blackout of Eastern Ontario

Frequency instability

3. July 2, 1996 disturbance of WSCC(WECC) System Long-term Voltage instability

4. August 10, 1996 disturbance of WSCC system

Small-signal (angle) stability: inter-area oscillations

5. August 5, 1997 blackout of Southern California Short-term Voltage instability

6. July 30, 1999 blackout of Atlanta, Georgia Short-term Voltage instability

1529pk - 15

Impact of New Forms Generation: WTGs and PVs

Copyright © P. Kundur


Types of Wind Turbine Generator Technologies

1. Squirrel Cage Induction Generator, driven by fixed-speed, stall-regulated wind turbines

2. Induction Generators with variable external rotor resistance, driven by variable-speed pitch regulated wind turbines

3. Doubly-Fed Asynchronous Generators (DFAG), driven by variable-speed, pitch regulated wind turbines

4. Synchronous or Induction Generators with converter interface (back-to-back frequency converters), driven by variable-speed, pitch regulated wind turbines


Impact of Wind Power Plants on System Dynamics

Could have a significant impact on Voltage Stability Induction generators absorb high reactive power when voltage is low DFAG may “crow-bar” during a system fault, and act as an induction

generator A short-term phenomenon Overall solution requires coordinated voltage control of wind power

plants, including use of SVCs and STATCOMs

Type 3 and 4 WTGS do not contribute system inertia May contribute to Frequency Instability Result in higher rate of change of frequency

Detailed simulation studies using appropriate models essential for satisfactory integration of large wind power plants


Capabilities of Modern WTGS

With the significant growth in wind power, wind power plants will be required to perform like conventional power plants

Modern WTGs, based on Type 3 and 4 technologies, can contribute to reliability and efficiency of grid operation by offering the following capabilities: Voltage and VAr control Real power control, ramping and curtailment Primary frequency regulation Inertia response: special control


Modeling of Wind Power Plants

For system studies aggregated representation is sufficient Single WTG model to represent the wind farm or a sub-group of WTGs

Detailed models for WTGs developed by manufacturers and consultants for grid integration studies and design of WPPs are considered as Proprietary user-defined models

Further, maintenance of numerous vendor-specific models is unmanageable

Efforts are underway for developing “Generic” WTG models suitable for “system impact” studies


Solar Photo Voltaic Plants

Consist of multiple small sources of power, which are aggregated and injected into the transmission system at a single point Use converter interface to the power grid

Modern units have capability for reactive power control, voltage regulation and under-voltage tripping

Technical issues related to impact on power system performance

similar to those for Type 4 WTGs Voltage stability, frequency stability, and rate of change of frequency

may be issues that have to be addressed Units with constant power factor control may contribute to voltage

control problems

1529pk - 21

Modeling Requirements for Each Category of System Stability



Transient Stability

Short-term phenomenon Study period in the order of a few seconds

Devices that need to be modeled accurately:

Generators: rotor circuit dynamics, saturation Excitation system: AVR, PSS (continuous controls) Speed governors Loads: voltage dependent characteristics HVDC links, SVCs and other FACTS devices Protective relaying: transmission line

Initial operating conditions: transmission network, load levels, voltages and power flow conditions


Small-Signal (Angle) Stability

Short-term phenomenon Modeling requirements are generally similar to those

for Transient Stability

Particularly important to model accurately controls associated with excitation systems (PSS), HVDC links and FACTS

devices Proper “tuning” of these controls is the most effective

way to address the problems

For problems associated with inter-area oscillations Dynamic load characteristics may need to be

accounted for


Long-term Voltage Stability

Long-term phenomenon Study period extends to several minutes

Need to model generator over-excitation limiters (OXL), transformers

with under-load tap changers (ULTCs) and other voltage control devices

Voltage-dependent characteristics of loads Account for larger voltage variations than for TS Thermostatically controlled loads

Effects of speed governor response and AGC: steady-state effects

impacting on generating unit power outputs


Short-term Voltage Stability

Short-term phenomenon Can be faster than Transient (rotor angle) Stability

Modeling of dynamic characteristics loads and power electronic devices is important

Detailed representation of sub-transmission and distribution systems

and associated voltage control devices Load equivalents should include one or two dynamically modeled

induction motors, discharge lighting, and static loads Motors may include a small motor equivalent (air conditioners) and a large

industrial motor equivalent


Frequency Stability

Under-generated islanding conditions: short-term phenomenon Modeling of under-frequency load shedding schemes Simulations should account for voltage and frequency dependence of load

characteristics

Over-generated islanding conditions: long-term phenomenon Modeling of power plants and associated protections and controls: wide

range of protection and controls, including turbine over-speed controls Power plant auxiliaries and associated protective systems Network and load characteristics as impacted by large variations in

frequency and voltages In areas with significant amount of wind power, appropriate models for

WTGs

1529pk - 27

Overall Approach to Model Identification and Validation



Model Identification and Validation

For model identification of individual plants/units: Prepare test plan by reviewing plant documents and existing models Carryout pre-field-test simulations

At the plant, carry out tests for: Parameter estimation: tests on individual elements Verification of models: response of the plant to an external disturbance

Model parameter estimation using the above field test measurements Model validation by comparing with the measured response of the overall

plant with all facilities in service For new plants/units, during commissioning, carry out tests to check the

performance of various controls and protective systems


Validation Integrated Power System Model

Dynamic models of the overall power system are very complex Involve a complex array of devices and associated controls and

protective systems

Verification of the integrated power system model by comparing with the measured responses during system disturbances Based on accurate time synchronized PMU records (WAMS)

Reflect on the accuracy of models of elements having a

significant impact on the particular system disturbance Device models and parameters responsible for any discrepancies

1529pk - 30

Where are the significant gaps?



Significant Gaps in Power System Modeling

Models for loads: Dynamic characteristics of composite loads Impact of variations in load composition with time of the day,

weather conditions and state of the economy Models for limiters and protective functions associated with

generator excitation system: Over-excitation limiter (OXL), under-excitation limiter (UEL),

V/Hz limiter and protection Protective system settings and their coordination

Settings for protective systems associated with various elements of the transmission and distribution network

Coordination of various protective relays Coordination with emergency ratings of equipment to ensure

sufficient margin


Significant Gaps in Modeling (contd.)

EMS and State Estimator results of system and network operating conditions Measurement errors; errors due to analytical techniques used Measurement errors mostly associated with data from substation

instrument transformers Solution is to use advanced EMS using Synchrophasor Data based on

phasor measurement units (PMUs)

Representation of neighboring (external) systems

Status of transmission facilities and operating conditions

Lack of adequate real-time “Situation Awareness” and “Shared Decision Making” t'd

Documents

Multi-regional Modeling Working Group Case Building … Modeling Powerflow and Dynamics...RAW read warnings produced by PSSE. ... NMMS Facts • Since 9/1/2009