Governor Response Modeling

Presented at WECC MVWG Meeting

May 2018

Dmitry Kosterev

BPA

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History

• July 2 and August 10 1996 events became WSCC (WECC) defining moments, just as August 14 2003 was NERC defining moment

• Dynamic model failed to reproduce the actual system oscillation during August 10, 1996 outage (on right)

• Validation studies required many model adjustments, including blocking thermal governors to reproduce system frequency drop, COI response, and to some extent oscillations

• WECC staff developed “OCSGOV.p” EPCL to block thermal governors in transient stability simulations when its active power output above 90% of the turbine capacity

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History

Late 1990s:

• WECC started studying 2-unit outage as a credible contingency

• 2 Palo Verde outage became a limiting contingency for COI, voltage-

stability limited due to governor powerflow pick-up

• BPA expanded and deployed synchrophasor measurements

• BPA started baselining governor response, and found that COI pick up to

be about 50 to 55% of generation lost in the south

• WECC base cases at that time assumed that all generators are frequency

responsive, and COI pick-up was only 35%

• BPA and CAISO staff started blocking governors in post-transient

governor powerflow studies by providing a list of “blocked” generators.

The list was “tuned” to produce at least 50% COI pick-up for Palo Verde

outages

• Utilities continued to use “OCSGOV.P” EPCL to block thermal governors

in dynamic simulations

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Dynamic Response

(from 0 to up to 60 sec)

angular stability, oscillation

damping, frequency

response

Post-Transient Response

(a snapshot at 1 to 5 min),

post-transient voltage stability,

transmission thermal loading

Study Timeframes

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History

Early 2000s:

• WECC initiated efforts to establish a Frequency Responsive Reserve (FRR) standard

– California energy crisis, brown-outs because of insufficient reserves

– BPA wanted to achieve equitable frequency response distribution across the Western Interconnection

• FRR studies were planned to determine the required amount

The rest of FRR story

• WECC had several attempts to develop its own FRR standard, but came up short every time

• FERC directed NERC to develop a standard addressing frequency response in 2010

• NERC had Frequency Response Initiative work that led to the expedited development, approval and implementation of NERC BAL-003-1 Frequency Response Standard in 2013

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History

Early 2000s:

• WECC conducted governor response tests on May 18 2001

– AGC was disabled by BAs in the West

– Hoover and Grand Coulee generators were tripped

– Model validation studies once again showed deficiencies in the

frequency response modeling

• This led to the development of Thermal Governor Modeling

Recommendation in WECC:

• Les Pereira, John Undrill, Dmitry Kosterev, Donald Davies and Shawn

Patterson, “A New Thermal Governor Modeling in WECC,” IEEE

Transactions on Power Systems, vol.18, no.2, pp.819-829, May 2003.

https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1198319

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Thermal Governor Modeling

• Generator Owners used historic SCADA

data to classify generators as (a)

frequency responsive, (b) on-load

control, (c) baseloaded

• Load control model “lcfb1” was

developed, as well as a new thermal

governor model “ggov1”, which was a

better representation of gas-turbine

• Software programs added

“baseload_flag” to generator records

• Workshops were held to assist generator

owners with data preparation

• Dynamic model validation studies were

performed for multiple event

• The governor blocking list was updated

for post-transient studies7

Frequency Response Types

Frequency

Responsive

Load Control

Baseloaded

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Model Validation Studies for June 14 2004 Event

Model accuracy improved

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Blue = Actual

Red = Simulations

Dynamics vs. Post-Transient

Dynamics Post-Transient

Time Frame 0 up to 60 seconds a snapshot of system response

at 1 to 5 minutes

Frequency Responsive

Generator (BL=0)

Governor model is active Governor response is allocated

in proportion to generator’s

Pmax

Generator under Load

Control (BL=0)

Governor and load

controller models are active

No governor response

Frequency

unresponsive

generator (BL=1 or 2)

1= Governor is limited in

upward direction

2 = Governor is limited in

upward and downward

directions

No governor response

BL = “baseload” flag in powerflow base case10

Baseload Flag of 1 or 2

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What is the difference ?

• Flag “1” or “2” will not respond to frequency drop below nominal

• Flag “1” will respond to frequency increase above nominal

• Flag “2” will not respond to frequency increase

Why is this important ?

• Blocking thermal governors affects damping on inter-area oscillations

• A contingency of BC-Alberta separation (with high flows from BC to Alb) will result in system frequency increase and will start power oscillations, such as occurred on August 4, 2000

WECC MVWG developed a report in 2012 recommending using baseload flag of “2” for interconnection-level studies

https://www.wecc.biz/Reliability/WECC%20MVWG%20Thermal%20Governor%20Model%20Revision%202012-06-20.pdf

Fast Forward to Today

• Western Interconnection has experienced addition of significant amount of wind and solar generation, and some amount of gas-fired generation

• Loss of institutional knowledge – retirements and promotions

Post-transient governor powerflow

• BPA continues baselining system frequency response

• Actual COI pick-up is now about 45% because of the system changes on the east side

• Simulated COI pick-up with off-the shelf case is less that 30% in post-transient governor powerflow

– About 12 GW of wind and solar generators are modeled as frequency-responsive

– Program conversion issues

– HRSG in combined cycle plants are often represented as frequency-responsive

• BPA “tunes” base cases for historic governor response performance

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Fast forward to Today

Dynamic Simulations

• West-wide System Model and breaker-node modeling in GE PSLF enabled much more frequent verification of operating models

• WECC staff developed better tools to conduct periodic verification of planning models

• System provides plenty of events for model validation studies

• Studies show reasonable correspondence between simulations and reality

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May 31, 2013 event

https://www.wecc.biz/Reliability/May%2030%202013%20Model%20V

alidation%20Report.pdf

May 16, 2014 event

https://www.wecc.biz/Reliability/Model%20Validation%20Report%

20for%20May%2016%202014%20RAS%20Event.pdf

August 18, 2016 event

https://www.nerc.com/pa/rrm/ea/1200_MW_Fault_Induced_Solar

_Photovoltaic_Resource_/1200_MW_Fault_Induced_Solar_Photov

oltaic_Resource_Interruption_Final.pdf

Moving Forward

Let me propose to form a Sub-Task Team under PPMVTF to

develop processes and tools to ensure we have sufficiently

adequate governor response representation in dynamic

simulations and post-transient voltage stability

MVWG had some good ideas:

- Revisions to thermal governor modeling proposed back in

2012

- Model validation studies for July 4 2012, May 31 2013, May 16

and 26 2014 large generation drop events

Let’s make sure we will follow up this time….

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