HomeMy WebLinkAbout20210920PAC to Bayer 117-1 Q0542 -Transient Stability Study Report.pdf
Transient Stability Analysis Report
Completed for
Bowler Flats Energy Hub, LLC
Bowler Flats Energy Hub
LGIQ# Q0542
Proposed Interconnection
To the Existing
230 kV Frannie - Yellowtail
Transmission Line
August 22, 2014
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Table of Contents
Executive Summary ........................................................................................................................ 2
1. Description of Project .............................................................................................................. 3
2. Study Assumptions .................................................................................................................. 4
3. Transient Analysis ................................................................................................................... 6
4. Conclusions .............................................................................................................................. 7
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Executive Summary
Bowler Flats Energy Hub, LLC (“Interconnection Customer”) proposed interconnecting 240
MW of new generation to PacifiCorp’s (“Transmission Provider”) Frannie – Yellowtail
transmission line approximately 2.75 miles north of the Frannie Substation located in Carbon
County, Montana. The Bowler Flats Energy Hub project (“Project”) will consist of 120 Gamesa
2.0 G114 wind turbines generators for a total output of 240 MWs. The requested commercial
operation date is approximately December 1, 2015.
Interconnection Customer will [NOT] operate this generator as a Qualified Facility as defined by
the Public Utility Regulatory Policies Act of 1978 (PURPA).
The Transmission Provider has assigned the project “Q0542.”
The Transmission Provider was not able to complete the transient stability analysis portion of the
System Impact Study due to technical issues with the model provided by the Interconnection
Customer. Until a working model is provided by the Customer and the Transmission Provider is
able to verify and analyze the dynamic behavior and the voltage ride through capabilities of the
turbines used by the Interconnection Customer, the study will remain incomplete and the results
will be deemed unacceptable.
The Project is required to operate in the voltage control mode maintaining the voltage at the POI
based on voltage schedule provided by the Transmission Provider.
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1. Description of Project
The Interconnection Customer has proposed interconnecting a wind farm in Carbon County,
Montana, to PacifiCorp existing Frannie – Yellowtail 230 kV line approximately 2.75 miles
north of Frannie Substation. A preliminary electrical single line diagram depicting the Project’s
interconnection at the point of interconnection (POI) substation is shown in Figure 1.
It is proposed to interconnect 120 Gamesa 2.0 G114 wind turbines generators. Power from each
turbine will be stepped up to 34.5 kV from 0.69 kV. A 34.5 kV collection system will bring the
combined power output to the collector substation where the power will be further increased to
230 kV through a 230/34.5 kV transformer.
Figure 1. Preliminary Single Line Diagram
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2. Study Assumptions
The PSS/E version 33.5 program was used to evaluate system stability. In addition, the
following assumptions were used in performing this study.
Study Period: The 2014 Heavy Summer WECC transmission power flow and dynamics data
updated was used for this analysis.
Study Area: The study area was limited to the Project and the surrounding 230 kV and 115kV
transmission system in Wyoming.
The existing commitments on the TOT4A/ 4B Paths were modeled in the study. Also generators
that are senior in the LGI queue and have TSR requests were modeled in the study.
Other Assumptions:
Transient stability simulations are performed out to 10 seconds in order to assess system
damping.
The Gamesa 2.0 MW G114 wind turbine is required to have voltage ride-through
protection capability; therefore, the wind turbine is designed to stay connected to the grid
in the case of severe faults. As shown in Figure 2 the wind turbines are required to have
the voltage ride through capabilities described in NERC standard PRC-024.
The Customer must ensure that the Gamesa 2.0 G114 wind turbines have voltage ride
through capability that conforms to the voltage ride-through time duration curve shown in
Figure 2 of this report.
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Figure 2. Voltage Ride-through Capability
During normal voltage conditions, the voltage control scheme should operate to minimize
the reactive exchange between the Interconnection Customer’s Project and Transmission
Provider system or as directed by the system operator. As per NERC standard VAR-001-
1a, the Transmission Provider will provide a voltage schedule at the Point of
Interconnection.
As the Transmission Provider cannot submit a user written model to WECC for inclusion
in base cases, a standard model from the WECC Approved Dynamic Model Library is
required prior to interconnection. The list of approved generator models is continually
updated and is available on the http://www.WECC.biz website.
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3. Transient Analysis
The Project facility is required to ride through all 3-phase faults with normal clearing or single
line-to-ground faults with delayed clearing for any event that doesn’t disconnect the facility.
The PSS/E version 33 program was used to evaluate the transient stability performance of the
wind turbines and system for different contingencies. The 2014 Heavy Summer WECC case
(14hs1ap.sav) was used for this analysis. Due to technical issues with the Gamesa user-written
dynamic model provided by the Interconnection Customer, the Transmission Provider was not
able to perform any transient stability analysis. The Transmission Provider has discussed the
model issues with the wind turbine manufacturer several times; however these discussions have
not resulted in the resolution of the technical issues seen by the Transmission Provider.
The Transmission Provider before running any contingency in transient stability simulations,
performs a steady state (no-contingency) run after implementing the dynamic model of the
Project. This ensures that the model provided by the Customer is working accurately and the
transmission system initializes without any technical issues. Ideally, as this is a no contingency
run, this should result in straight lines if the MW and MVAr output of the Project or any other
generator on the transmission system is plotted. This is called the “flat run” meaning a simulation
of the steady state system for 10-20 seconds would produce flat lines. When the Transmission
Provider ran the flat run after interconnecting the Project, the MW and MVAr output for the
Project was not a straight line as shown in Figure 3.
Figure 3: No-contingency run after interconnecting Q0542
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These issues were resolved based on changes suggested by the manufacturer. After the flat run
issues were resolved, the Transmission Provider encountered several issues with the voltage
controller model of the turbine that resulted in tripping of the Gamesa wind turbine units due to
high voltage shortly following fault clearing. While this is believed to be a model issue, the
voltage ride through capability could not be confirmed.
Due to these unresolved model issues, the Transmission Provider was not able to complete a full
transient stability analysis including the voltage ride-through capability for the Project and
determine whether interconnecting the Project to the Yellowtail – Frannie line is feasible without
any reliability issues. Hence, the Transmission Provider will not be able to interconnect the
Project until a working model is provided.
4. Conclusions
The following conclusions have been reached through this analysis:
Transmission Provider was unable to perform transient stability analysis for the Project due to
technical issues with the dynamic model provided by the Customer. The Transmission Provider
has worked with the wind turbine manufacturer to resolve the model issue but has not arrived at
a successful resolution as of this writing. The Transmission Provider was not able to perform
detailed transient stability analysis to determine the voltage ride through capabilities of the
Project and also was not able to analyze the reliability impacts of the Project interconnecting to
Yellowtail – Frannie 230 kV line. Hence, the Transmission Provider cannot allow the Project to
interconnect at the POI until a working model is provided and detailed transient stability analysis
is performed.
Simulation results are based on data provided by the Interconnection Customer as well as other
model data available at the time of the study. The results can be used to help determine whether
or not the Project facilities will meet the performance criteria including ride-through
requirements which are identified in the Interconnection Agreement, and, in some cases, may
indicate that additional equipment is required in order to meet these requirements. However,
ultimately it is the Interconnection Customer’s responsibility to meet these requirements during
actual operation on a daily basis and failure to do so can result in loss of interconnection
privileges. Therefore, the results of these simulations should be regarded as informational rather
than definitive, and do not relieve the Interconnection Customer of any performance
responsibilities.
Finally, if the assumptions utilized in this study significantly change, PacifiCorp reserves the
right to perform a re-study. Significant changes include, but are not limited to, development of
new models which may impact performance as well as changes to the base case assumptions for
planned future but as yet uncommitted transmission line and generation facilities.