Governor Response Modeling

Presented at WECC MVWG MeetingMay 2018

Dmitry KosterevBPA

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History• WSCC (WECC) defining moments –

July 2 and August 10 1996, as NERC defining moment was on August 14 2003

• 1996 – dynamic and voltage stability model failure to reproduce the actual system response during August 10, 1996 outage

• 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,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 studies

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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 = ActualRed = 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

Frequencyunresponsive generator (BL=1 or 2)

1= Governor is limited inupward direction2 = 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 eventhttps://www.wecc.biz/Reliability/May%2030%202013%20Model%20Validation%20Report.pdf

May 16, 2014 eventhttps://www.wecc.biz/Reliability/Model%20Validation%20Report%20for%20May%2016%202014%20RAS%20Event.pdf

August 18, 2016 eventhttps://www.nerc.com/pa/rrm/ea/1200_MW_Fault_Induced_Solar_Photovoltaic_Resource_/1200_MW_Fault_Induced_Solar_Photovoltaic_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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