20150728AVU to Staff 20 Attachment B.pdf

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Interoffice Memorandum
System Planning
MEMO: SP-2010-07 Rev02
DATE: October 08, 2010
TO: Scott Waples, System Planning file
FROM: Dean Spratt
SUBJECT: Moscow 230 kV Sub – 230/115 kV Autotransformer Capacity Increase

Description of Project
Transmission compliance and operations studies have shown a growing N-1 issue. A thermal overload occurs on the Moscow 230/115 kV 125 MVA autotransformer, for either the loss of the Shawnee 230/115
kV, 250 MVA autotransformer or the loss of the Hatwai 230 kV bus during both summer and winter peak loading. The Moscow/Pullman area is fed by two 230/115 kV autotransformations; one at Shawnee with
a nameplate rating of 250 MVA and the other at Moscow with a nameplate rating of 125 MVA. Figure 1 shows the thermal loading on the Moscow transformer during the loss of the Shawnee autotransformer in the winter of 2009-10.
A second issue is that the existing equipment at Moscow Substation has structural, mechanical, electrical and reliability deficiencies that require extensive modification and/or replacement to be able to effect the
required capacity increase. These issues are detailed in the following section.

System One Line
SHAWNEE
MOSCOW
MOSCCITY
SPULLMAN113.3 KVARMSTRNG
NPULLMAN NMOSCOW
112.3 KV 115.8 KV
112.2 KV
JULIAETT
VIOLA
BRINKENS
POTLAT A113.7 KV
PALOUSE
GARFIELD
TEKOA
114.0 KV
114.0 KV
CHAMBERS
EASCOLFX ROSALIA111.8 KV 113.9 KV
DIAMOND
EWAN
MARENGO
110.9 KV
115.0 KV
SHAWNEE240.9 KV
0.0 MW
MOSCOW237.7 KV
176.4 MW
115.1 KV
STMARIES
110.3 KV115.5 KV
TERRVIEW
HATWAI
1.04N LEWIST 1.05
22.5 Mvar
LEON 1.01
0.99 pu 0.99 pu
0.98 pu
1.00 pu 0.97 pu
MOSCITYT 1.00 pu
0.97 pu
CHMBRSTP 0.97 pu
21.8 MW 2.7 Mvar
92%C
Amps
97%C
MVA 115%C
MV A

Figure 1 – 2009-10 Heavy Winter ~ N-1 Shawnee 230/115 kV autotransformer outage

The goal of this study is to determine the best course of action to correct the identified N-1 overloads,
while meeting expected load growth and maintaining the reliability requirements for the Moscow/Pullman Area.

Staff_PR_020 Attachment B Page 1 of 7
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Relevant Facts and Information
Following are issues and comments that were brought forward in previous meetings regarding this project;
The existing transformer has been in service for 53 years. The Moscow regulating transformer has been in service 36 years with a history of issues corresponding to the LTC.
The spare autotransformer is 35 years old, but was only in-service for 6 years (1978-84) at
Beacon. It has been in storage at Moscow since.
The existing (2) steps of 22.2 MVAr capacitor bank were added in 1980. The capacitor can size is not Avista’s standard size. We typically have five replacement cans available and the lead time is
40 weeks to obtain replacements. They are also the fused style.
The existing 230 kV bus arrangement is single bus, single breaker which requires the loss of a transmission element to maintain or service the 230 kV substation equipment. This also results in
loss of source for bus faults or stuck breaker contingencies.
The existing 230/115 kV, 125 MVA autotransformer is protected on the high side with a circuit switcher. Using circuit breakers is Avista’s standard protection on new installations of 230 kV.
Increasing the 230/115 kV capacity at Moscow will increase the existing 115 kV bus fault duty
beyond its design limits. Substation Design has reviewed the existing design and the 115 kV bus will have to be rebuilt to accommodate the additional capacity.
The control cable insulation is deteriorating with age, which could pose serious operational problems.
The Station equipment is reaching (or surpassed in some cases) the end of its design life. Maintenance (O&M dollars) is also increasing at Moscow due to the station age and replacement parts are becoming difficult to obtain.
Presently, there is no forecasted need to bring another 230 kV line into the Moscow 230 kV substation.
There may be a future need for a third 115 kV line between Moscow and Pullman.
The station should be designed such that 230 kV line or autotransformer outages will not be
required in order to remove breakers from service for maintenance or replacement.
The station should be designed such that 230 kV line or autotransformer outages will not be required in order to replace or upgrade relays. Outages for this are acceptable for short durations
(< 5 days) for testing.
New fiber communication is planned for the Benewah-Moscow-Hatwai section route. This work has not been budgeted and is still in the early planning stage.
Lastly, note our membership in the EEI Spare Transformer Program. At a minimum, Avista needs
to have a working 230/115 kV, 125 MVA autotransformer that we could either have as a standby or take out of service at a moment’s notice. Avista’s obligation is less than 125 MVA, but obviously a 125 MVA autotransformer is what Avista practically has unless we contracted with
others for a smaller unit. Scott Wilson has more details if needed.

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Study Assumptions
Given that the outage of the Shawnee 230/115 kV, 250 MVA autotransformer results in a thermal overload on the Moscow 230/115 kV, 125 MVA autotransformer, the alternatives evaluated will be based on both a 10 year winter and summer peak case.
2008 peak loading on both the Moscow and Shawnee 230/115 kV, autotransformers, totaled 105 MW summer and 179 MW winter. Projected 2018 loading for this study is 135 MW summer and 223 MW
winter, approximately 1.7% and 2.2% annual load growth respectively.
Terreview substation is in service and load has been transferred from neighboring substations. The future Tamarack substation (Northeast Moscow) is not modeled, but normal load growth in the area results in
similar loading in this study.
The remaining sections of the Pullman – Terreview – North Moscow 115 kV transmission line are
assumed to be rebuilt as part of this study. This line work is planned for 2010 and will correct local N-1 line overloads.
Star Points (normally open sections on the 115 kV network) are correct per System Operations Procedure
02 – 115 kV Star Network.
No other transmission reinforcements are planned in this area.

Alternatives Evaluated
The following alternatives were evaluated by the stakeholders to ensure that the best performing option
was selected based on system performance, operability, constructability, and maintainability.
Option A: Do nothing
The existing system exhibits N-1 overloads of up to 114% for the 2010 winter peak. This will increase yearly with a projected 136% thermal overload of the Moscow 230/115 kV, 125 MVA autotransformer by
the 2018 winter peak. Currently, System Operations can manually transfer load to other sources to minimize this overload, but this only brings the N-1 loading down to around 100%. This result is unacceptable based on Avista’s planning standards.
Option B: Rebuild Moscow substation with parallel 125 MVA transformers
This option would require two new 230/115 kV, 125 MVA autotransformers plus maintaining the existing 230/115 kV, 125 MVA spare for Benewah or Moscow and retiring the existing autotransformer. The 230
kV bus would be rebuilt to accommodate the additional autotransformer position, provide standard protection and improve reliability. The 115 kV bus would be rebuilt due to increased fault duty.
Pros
The parallel 230/115 kV 125 MVA autotransformers provide better flexibility for maintenance and
emergencies.
A single autotransformer outage at Moscow has minimal effect on the system.
Cons
This option requires an extra 230 kV and 115 kV bay over the single 250 MVA autotransformer option
First Cost of a 230/115 kV, 75/100/125 MVA autotransformer is approximately $2 million, for a total of $4 million. The first cost of a 230/115 kV, 150/200/250 MVA autotransformer is
approximately $3 million.
Due to the age of the existing autotransformer and spare, two new 125 MVA autotransformers will need to be purchased. This is to maintain a 125 MVA spare.
The 75/100/125 MVA autotransformer requires equipment and crew from a specialized carriers and riggers company and special permits from the State for transport – no gain in portability with the smaller 125 MVA autotransformers.
The 230 kV bus needs to be rebuilt to accommodate the additional transformer position. The 115
kV bus needs to be rebuilt due to increased fault duty.
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The block estimate for this option is $16.6 million. This assumes that the additional cost to build at the existing site matches the cost to build greenfield and that existing 230 kV and 115 kV bus arrangements
will have to be rebuilt.

Option C: Rebuild Moscow 230 kV Substation with a single 250 MVA autotransformer
The single 230/115 kV, 250 MVA autotransformer provides adequate flexibility for maintenance and
emergencies (during autotransformer outages, load has to be carried by Shawnee). The 230 kV bus would be rebuilt to accommodate the additional autotransformer position and improve reliability. The 115 kV bus would be rebuilt due to increased fault duty.
Pros
Less equipment to maintain over the parallel option (only one autotransformer, LTC, hi & lo CB position).
The system 230/115 kV, 250 MVA autotransformer count increases – better justification for an in-
service spare.
The first cost of a 230/115 kV, 150/200/250 MVA autoransformer is approximately $3 million. First Cost of a 230/115 kV, 75/100/125 MVA autoransformer is approximately $2 million, for a total
of $4 million.
Con
A long term loss of either 230/115 kV, 250 MVA autotransformers at Moscow or Shawnee would
leave this area served by only one autotransformer until a replacement was installed. Since there is no 230/115 kV, 250 MVA spare, we would first check for a WECC spare. Avista in time will
have to either maintain a 250 MVA spare transformer or install in-service spares at key locations.
The 230 kV bus needs to be rebuilt to accommodate the additional autotransformer position. The 115 kV bus needs to be rebuilt due to increased fault duty.
A more reliable 115 kV bus arrangement is required due to the credible, long duration loss of the
Moscow 230/115kV autotransformer. This includes main/aux, breaker & half, aux-bus-plus or double breaker double bus arrangements.
The block estimate for this option is $13.7 million. This assumes that the additional cost to build at the
existing site matches the cost to build greenfield and that existing 230 kV and 115 kV bus arrangements will have to be rebuilt.
Other Options:
All other options reviewed required either a new Moscow/Pullman area source, which would be different
than the existing Moscow Substation or installing new lines or rebuilding existing lines. None of these options are detailed here since they do not correct the underlying problem of the Moscow substation
needing to be rebuilt.

Project Selection:
Based on review with all interested parties, option C was chosen as the preferred alternative. First cost,
lower ongoing maintenance, and standardizing on the 230/115 kV, 250 MVA autotransformer were the main contributing factors in this decision. A 230/115 kV, 250 MVA system spare or in-service spares will
be required at some date in the future, so this main detriment carried less weight. Note that adding an on-site, in-service 230/115 kV, 250 MVA autotransformer is also possible, for an additional $ 4.9 million.

Staff_PR_020 Attachment B Page 4 of 7
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Estimate and Schedule
2010 2011 2012 2013 2014 total
Transmission $575,000 $575,000 $1,150,000
Substation $1,500,000 $3,500,000 $4,000,000 $2,400,000 $500,000 $11,900,000
Distribution $25,000 $25,000 $50,000
total $1,500,000 $3,500,000 $4,000,000 $3,000,000 $1,100,000 $13,100,000

Long Range Planning Horizon Analysis:
An additional check was performed to verify this recommended course of action meets the anticipated long term growth. The existing winter peak load in the area was doubled to approximately 360 MW which
represents roughly 32 years of growth. The existing summer peak load in the area was also doubled to approximately 300 MW. The results are as follows;
Both the Shawnee and proposed Moscow 230/115 kV, 250 MVA autotransformers can support
the area load, with the loss of either. The Moscow 230/115 kV, 250 MVA autotransformer would be at 99% during an N-1 at winter peak.
An additional step of 115 kV, 33.5 MVAr would be needed at Moscow and (2) steps of 33.5 MVAr
would be needed at Shawnee for an N-1 of either source.
The Moscow23-MoscowCity 115 kV line section would overload to 109% under N-1 summer peak. Growth and new distribution substation locations would determine if this overload would become an eventuality.
Based on a basic evaluation of long term load growth, the proposed project meets the area load service requirements.

Reactive Support Analysis:
An N-1 and QV analysis was performed on the 10 year out cases to determine if reactive support was required to replace the existing capacitor bank and if so, the total quantity and the maximum step size.
Note that the completion of the Benewah – Shawnee 230 kV line benefits the area for certain contingencies and that the 2008 summer peak total reactive load for the Moscow/Pullman area was 34.3
MVAr.
The worst N-1 voltage issue occurs at the Potlatch 115 kV bus (2019 summer case showed 0.97 pu & winter 0.95 pu voltage) for the loss of the Shawnee 230/115kV 250 MVA autotransformer. For reference,
to bring this voltage to unity, under this winter contingency, requires about 60 MVAr.
The least local reactive margin occurs with injection at the Shawnee 115 kV bus (2019 summer case
showed 122 MVAr & winter 124 MVAr of reactive margin) during the loss of the Shawnee 230/115 kV autotransformer. The second worst local reactive margin occurs with injection at the Moscow 115 kV bus (2019 summer case showed 132 MVAr & winter 138 MVAr of reactive margin) during the loss of the
Moscow 230/115 kV autotransformer.
Lastly, one step of 33.5 MVAr results in a 1.4% increase in voltage with all lines in service and a 3.5%
increase in voltage, during an N-1 of the proposed Moscow 230/115 kV, 250 MVA autotransformer under light load conditions. This is within Avista guidelines.
The study recommends installing (2) steps of 33.5 MVAr, 115 kV capacitor banks at Moscow.

Staff_PR_020 Attachment B Page 5 of 7
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General Discussion:
This project has been an avenue for discussion for many general system considerations. Following are the major points and determinations;
230 kV Substation rebuilds – rebuild in place or greenfield. The estimate is a 20% increase in
labor to rebuild in place and 30% increase in project completion time. The general consensus was that if space is available it is prudent to choose a greenfield site. This is assuming that the rebuild will require equipment replacement down to the ground grid.
230 kV bus arrangement – All Avista 230 kV bus arrangements will be fully built out (two breakers
for every position, including transformers), double breaker, double bus (DBDB). The option of building an interim ring bus for three or four line positions was discussed, but it was determined
that it was more cost effective and reliable to have the complete double breaker arrangement for each bay.
115 kV bus arrangement – System Planning determined that all future 115 kV bus arrangements
will be breaker and a half when practical. Through further discussion, the Main/Aux was determined to be the minimum bus arrangement where required. This conclusion stems from the fact that most of Avista’s existing substations have a single bus configuration, which typically
makes an easier and more economical transition to main/aux.
Communications – the Benewah-Moscow 230 kV line currently has redundant communication paths (Power Line Carrier & Analog Microwave), but the Hatwai-Moscow 230 kV line only has a
single communication path (Analog Microwave). Typically Avista’s 230 kV line protection schemes have redundant communications paths for transfer trip. Dynamic studies indicate that
the system remains stable for faults (delayed clearing) on the Hatwai-Moscow 230 kV line, when this single communication path is off line, therefore upgrading to a single channel of Digital Microwave will be adequate until communications are improved in the area. Figure 2 shows the
dynamic response for a fault on the Hatwai – Moscow 230 kV line with loss of the single communications path, which results in delayed clearing.

Figure 2 – 2011 High Transfer ~ No transfer trip and delayed clearing for a close in fault at Moscow
on the Hatwai-Moscow 230 kV line.
Note that in this case {ava-10ls1a-11ba1302-woh4129.sav} the WMH (Western Montana Hydro) is at
1670 MW and that the system will go unstable for this fault when the WMH is at 1750 MW.
Staff_PR_020 Attachment B Page 6 of 7
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Figure 2 – Project Diagram and General Information

Distribution:
Scott Kinney, Rick Vermeers, Scott Waples
Garth Brandon, Rich Hydzik, Dave James, Mike Magruder, Randy Spacek, Ken Sweigart 2010 SP Record (SharePoint)
Staff_PR_020 Attachment B Page 7 of 7