Local Area Transmission Plan Final Draft

Transcription

1 Lcal Area Transmissin Plan Final Draft NrthWestern Energy s Electric Transmissin Tw-Year Lcal Area Planning Cycle January 1, 2014 t December 31, 2015 T&D Engineering Electric Transmissin Planning Department Pht: 500 kv Twer by Susan Malee 1 Frmatted: Fnt clr: Red

2 Table f Cntents EXECUTIVE SUMMARY... 5 NWMT TRANSMISSION SYSTEM OVERVIEW... 7 LOCAL TRANSMISSION PLANNING STUDY CYCLE... 9 DATA SHARING AND PLAN COORDINATION GOAL LOAD FORECAST DEVELOPING THE LOAD FORECAST LOAD FORECAST WINTER METHODOLOGY & CRITERIA PLANNING METHODOLOGY STUDY CRITERIA RELIABILITY CRITERIA Steady-State & Pst-Fault Vltage Criteria fr 230 kv & Belw Steady-state & Pst-fault Vltage Criteria fr 500 kv Thermal Ratings General Minimum Equipment Specificatins BASE CASE PLANNING SCENARIOS TECHNICAL STUDY OUTLINE SYSTEM STUDIES AND FINDINGS STATE OF THE SYSTEM STUDY 2014 AND State f the System Summary f Findings 2014 Cases Thermal Issues results f 2014 Cases: Vltage Issues fr 2014 Cases: PROJECTED FUTURE SYSTEM STUDIES 2019, 2024, Prjects included Summary f findings fr Future System Studies Thermal Issues Cases Vltage Issues Cases STABILITY ISSUES PRIORITIZING CRITICAL PROBLEMS & DECISION RULE PRIORITIZING CRITICAL PROBLEMS DECISION RULE UNCERTAINTY AND OTHER SCENARIOS REACTIVE RESOURCE ASSESSMENT AND PLANNING (VAR ASSESSMENT) RESULTS AND MITIGATION Rank #1: Billings Area: Rundup area 50 kv and 69 kv Vltage Supprt (N-0) Rank #2: Billings Area: Lss f 100 kv Clumbus Chrme and ther area facilities Rank #3: Butte Area: Lss f Mill Creek Deer Ldge Mntana Street 100 kv Line r Mill Creek 100 kv bus line fault r lss f Bnner Missula #4 161 kv line and Missula #1 Drummnd Pump 100 kv line

3 Rank #4: Missula/Hamiltn Area: Lss f Missula Hamiltn Heights 161 kv lines (N-2) Rank #5: Billings Area: Lss f Bradview Wicks 230 kv and Bradview Alkali Creek 230 kv lines (N-2) Rank #6: Helena Area: Lst f East Helena Switchyard 100/69 kv Auttransfrmer r 100 kv Bus Fault Rank #7: Bzeman Area: Lss f Ennis Lne Muntain 69 kv Line r Ennis 161 kv Bus 4744 Rank #8: Missula Area: Rattlesnake Substatin 100 kv Bus Fault Rank #9: Great Falls: Lss f Great Falls Switchyard Mntana Refining 100 kv Line Rank #10: Billings: Lss f Shrey Rad Alkali Creek 230 kv line Rank #11: Butte Area: Dilln-Salmn 161/69 kv Auttransfrmers and Bus Faults Rank #12: Bzeman Area: Lss f East Gallatin Substatin 161 kv Bus & 50 kv Bus Rank #13: Billings Area: Lss f Bradview Wicks Lane 230 kv line r Bradview Alkali 230 kv line (N-1) Rank #14: Great Falls: Lss f Great Falls Switchyard Crked Falls 100 kv lines (N-2) 5249 Rank #15: Bzeman Area: Lss f Duck Creek Big Timber Aut Clumbus-Rapelje 161 kv line PREVIOUS PLAN RESULTS UPDATE RECOMMENDATIONS DISTRIBUTION OF NWMT S ELECTRIC TRANSMISSION LOCAL AREA PLAN Figures Figure 1: Mntana Paths... 8 Figure 2: NWMT s Bulk Electric Transmissin System... 9 Figure 3: Study Cycle Crdinatin Figure 4: Balancing Authrity Area Lad Frecast Tables Table 1 Balancing Authrity Area Lad Frecast with DSM included Table 2 Estimated Peak Lad Temperature Sensitivity Table 3 Peak Lad Frecast Table 4 Planning Methdlgy Table 5 Maximum Upper Vltage Criteria Table 6 - Min. Allwable % Vltage at NWMT Unregulated Lad-Serving Bus Table 7 T&S Equipment: General Minimum Specificatins Table 8 Study Scenaris Table 9 Cnsequences Rating Factrs

4 Table 10 - Likelihd Factrs Table 11 - Highest Pririty System Matrix Table 12 Decisin Rule Matrix Table 13 Recmmendatin Summary Table 14 NWMT Ecnmic Cngestin Study Attachments Attachment A: TRANSAC Charter Attachment B: Stakehlder Invlvement Attachment C: Ecnmic Cngestin Studies Attachment D: Public Plicy Lcal Area Plan

5 Executive Summary NrthWestern Energy's (NWMT) biennial lcal transmissin plan fr Mntana is created in cmpliance per Federal Energy Regulatry Cmmissin (FERC) Order 890 and FERC Order 1000 and develped under FERC Order 890 Attachment K prvisins. NWMT s methdlgy, prcess and criteria are used t evaluate the electric transmissin system, ensuring that system reliability is maintained int the future. NWMT fllws the business practice, methdlgy, criteria and prcess utlined in its FERC Order 890 Attachment K filing 1, meets NERC TPL standards, Western Electricity Crdinating Cuncil s (WECC s) Disturbance Perfrmance Table and nne f the cntingencies evaluated during this biennial prcess resulted in cascading frm NWMT s Balancing Authrity Area (BAA) t anther BAA. In NWMT s Tariff, BAA is als referred t as Cntrl Area. Reliability, by definitin, examines the adequacy and security f the electric transmissin system. Cnsistent applicatin f the methdlgy, criteria, and prcess fr all Balancing Authrity Area (BAA) 2 custmers' (i.e., retail, netwrk and pint-t-pint) infrmatin is ensured thrugh the penness and transparency f NWMT s prcess. All custmers are treated n an equal and cmparable basis as NWMT s transmissin system planning prcess is designed t be transparent, pen and understandable. NWMT s methdlgy is intended t define perating cnditins that fail t meet reliability criteria and then identify slutins (e.g., transmissin and nn-transmissin 3 ) that slve the prblem. NWMT has perfrmed a multi-seasnal, multi-year study that was designed t examine the system s reliability under nrmal perating cnditins, and all single and credible multiple utage cnditins. Previus biennial transmissin plan study wrk has created a benchmark fr future biennial studies t be cmpared against. This cmparisn prvides knwledge n hw the system is changing ver time. Given the results, NWMT has designed mitigatin plans that reslve the identified prblems, starting with the mst critical. T ensure that the NWMT s Lcal Transmissin Planning prcess was pen and transparent, a Transmissin Advisry Cmmittee (TRANSAC) was frmed in TRANSAC is an advisry stakehlder cmmittee that meets with NWMT a minimum f fur times a year t prvide input and cmments during the planning stages f NWMT s Lcal Transmissin Plan. Please see Attachment A: TRANSAC Charter fr an utline f TRANSAC s purpse and Attachment B: Stakehlder InvlvementAttachment B: Stakehlder Invlvement fr an utline f TRANSAC s invlvement with the develpment f this plan. This dcument walks thrugh NWMT s effrts t develp a Lcal Transmissin Plan that addresses reliability by examining the adequacy and security f the electric transmissin system while fllwing 1 All Attachment K related dcuments can be fund n NWMT's OASIS website under the Transmissin Planning Attachment K flder. The Attachment K Business Practice Links dcument is the index fr all Attachment K related dcuments. There are tw dcuments that utline hw NWMT cnducts its transmissin planning prcess: 1) ETP Methd Criteria and Prcess Business Practice effective in sectin Q f the Links dcument addresses the FERC Order 890 transparency principle; 2) Attachment K Business Practice effective in sectin P f the Links dcument addresses the nine FERC Order 890 principles. 2 NERC defines a Balancing Authrity Area as: The cllectin f generatin, transmissin, and lads within the metered bundaries f the Balancing Authrity. The Balancing Authrity maintains resurce balance within this area. NERC further defines Balancing Authrity as: The respnsible entity that integrates resurce plans ahead f time, maintains lad-interchange-generatin balance within a Balance Authrity Area, and supprts Intercnnectin frequency in real time. 3 Demand-side resurce, generatin, interruptible lad, etc. 5

6 NWMT's business practices, methdlgy, criteria and prcess. The findings f NWMT s effrts include the fllwing: N majr prblems with the higher vltage bulk electric system (e.g., 230 kv and abve) were bserved under all perating cnditins and scenaris with the exceptin f ne creditable duble cntingency and several single cntingency utages in the Billings area after the shutdwn f a large (150+ MW) thermal generatin plant. Vltage prblems appear in apprximately five years. On the underlying system in the near term, n thermal were bserved under nrmal perating cnditins. Minr lw vltage prblems were nted in the Rundup area under nrmal summer peak lad perating cnditins. Withut planned mitigatin, a limited number f utages may cause additinal vltage and thermal prblems n lwer vltage systems. Heavy lad summer cnditins cntinued t gvern in mst areas. Thermal prblems bserved are bth line and transfrmer capacity related, which can be mitigated thrugh upgrades r peratinal means. As lads grw, transfrmers tend t reach capacity limits befre line segments. As lad grws, substatin-related utages are becming mre critical withut mitigatin. N utages resulted in uncntrlled cascading utside f the NWMT cntrl area. Sme utages can cause cascading under peak lad cnditins within NWMT cntrl area. N transient stability prblems were bserved. With lad grwth ver time and withut mitigatin, thermal lads and related prblems grw and vltages decline. Mitigatin cmpleted since the end f the last planning cycle has fixed, lessened impacts, r deferred previusly identified prblems. Prpsed generatin intercnnectin prjects and accelerated lad grwth in sme lcalized areas (Bzeman) present the greatest uncertainty in future planning scenaris. Hwever, these intercnnectin prjects willshuld carry with them apprpriate mitigatin either thrugh the intercnnectin prcess r the transmissin service prcess t ensure that the existing transmissin system perfrmance is nt negatively impacted. 6

7 NWMT Transmissin System Overview NWMT s lcal transmissin system prvides regulated electric transmissin services t apprximately 350,000 electric custmers. NWMT s electric transmissin system cnsists f apprximately 7,000 miles f transmissin lines and assciated terminal facilities. NWMT is registered with the Nrth American Electric Reliability Crpratin (NERC) as a Balancing Authrity, Planning Authrity 4 and Transmissin Planner 5. Additins t NWMT s system in 2014 include Fairfield Wind and Tw Dt Wind, bth 10 MW facilities. Als NWMT cmpleted the purchase f PPL MT s hydrelectric facilities (frmerly wned by Mntana Pwer Cmpany), which includes 11 dams, representing 633 MW f capacity. Series cmpensatin was increased at Petersn Flats Substatin t increase the suthbund capacity f Path 18 frm 337 MW t 383 MW. In March 2015, the Crette generatin plant in Billings was shut dwn. In September 2015, the Cnfederated Salish Ktenai Tribes f the Flathead Reservatin assumed wnership f the 194 MW Kerr Dam hydrelectric facility. The transmissin system, with vltage levels ranging frm 50,000 t 500,000 4 NERC defines a Planning Authrity as: The respnsible entity that crdinates and integrates transmissin facility and service plans, resurce plans, and prtectin systems. 5 NERC defines a Transmissin Planner as: The entity that develps a lng-term (generally ne year and beynd) plan fr the reliability (adequacy) f the intercnnected bulk electric transmissin systems within its prtin f the Planning Authrity Area. 7

8 vlts, serves an area f 97,540 square miles, which is equivalent t tw-thirds f Mntana. The 500 kv transmissin system is primarily used t mve pwer frm Clstrip in eastern Mntana t the Nrthwest. NWMT s lwer vltage transmissin system is used primarily t serve lcal lad, but als cntributes t the flws n the tie lines cnnected t neighbring utilities NWMT s transmissin system has intercnnectins t six majr transmissin systemsutilities 6 lcated in the Western Electricity Crdinating Cuncil (WECC) area. and ne Direct Current (DC) intercnnectin t a system that cnnects with the Mid-Cntinent Area Pwer Pl (MAPP) regin. Figure 1: Mntana PathsFigure 1: Mntana Paths displays the external paths with the assciated nn-simultaneus maximum path ratings. Figure 1: Mntana Paths 6 Idah Pwer Cmpany, Avista Crpratin, Bnneville Pwer Administratin, Western Area Pwer Administratin, PacifiCrp, and Alberta Electric System Operatr. 8

9 Figure 2: NWMT s Bulk Electric Transmissin System displays the 100 kv and abve bulk electric transmissin system. The clr cding f lines is as fllws: Red: 230 kv Green: 161 kv Blue: 115 kv Yellw/Black: 100 kv Figure 2: NWMT s Bulk Electric Transmissin System Lcal Transmissin Planning Study Cycle Figure 3: Study Cycle CrdinatinFigure 3: Study Cycle Crdinatin utlines the prcess t implement and crdinate the Lcal Transmissin Planning Study Cycle, the Ecnmic Cngestin Study Cycle and TRANSAC invlvement. The Lcal Transmissin Planning Study Cycle is cnducted ver a tw-year perid (8 Quarters utlined n the far left f Figure 3). The yellw highlighted numbers (1 thrugh 9) crdinate t the Ntes area at the bttm and explain the basic activities cvered during the quarters and mnths (grey clumn tward the middle f Figure 3). The tan highlighted letters (a thrugh f) explain the basic activities fr the Ecnmic Cngestin Study Cycle. The remainder f the Figure utlines an example f TRANSAC and Stakehlder Meetings. Fr mre detail n TRANSAC and Ecnmic Studies, please see Attachment A: TRANSAC Charter, Attachment B: Stakehlder InvlvementAttachment B: Stakehlder Invlvement, and 9

10 Attachment C: Ecnmic Cngestin Studies 10

11 Attachment C: Ecnmic Cngestin Studies, and the LTP Cycle and Timeline 7. Study Cycle Crdinatin With TRANSAC and Public Meetings (Subject t Change as needed) UPDATED: 09/10/2015 Lcal System Planning Study Cycle Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Gal & Scenari Definitins Technical Study Decisin Reprting Next Planning Cycle Tentative TRANSAC Meetings Tentative Public Mth Agenda Items - Lcal Transmissin System Study EcStudyAgnda Meetings 1 a c Jan Yr 1 2 Feb Yr 1 Criteria Scenaris Frecast 3 b Mar Yr 1 Cluster & Prir d Apr Yr 1 Criteria Scenaris Uncertain Scnr May Yr 1 DR Attributes Jun Yr 1 Jul Yr 1 Finalize Cases Aug Yr 1 Study Update DR Attributes L&R Template Study Update Sep Yr 1 4 Crdinate Oct Yr 1 Study Results Mitigate Reqmt DR Attributes Results e Nv Yr 1 5 f Dec Yr 1 Finalize Mitigate Uncertainty DR Attributes a c Jan Yr 2 Uncertainty DR Attributes Feb Yr 2 6 b Mar Yr 2 Mitigate Result Finlz Uncertainty DR Attributes Cluster & Prir 7 d Apr Yr 2 May Yr 2 Jun Yr 2 Uncertn Result Decisn Rule L&R Template 8 Jul Yr 2 Study Update Aug Yr 2 Decn Rule Reslt Recmmendatin Sep Yr 2 9 Oct Yr 2 Results e Nv Yr 2 Dcument f Dec Yr 2 NOTES Fr Flw Chart Lcal System Plan Ecnmic Study Request 1 Develp Gal and Scenari Definitin a Receive requests 2 Build Base Cases b Cluster and priritize requests 3 Cnduct technical studies fr the existing system c RFP fr cnsulting services 4 Build mitigatin change cases d Cnduct technical study 5 Cnduct study with mitigatin e Write reprt 6 Develp uncertainty cases f Cnduct results meeting with spnsr 7 Cnduct uncertainty analysis 8 Cnduct decisin rule analysis 9 Reprting Figure 3: Study Cycle Crdinatin Ecnmic Study Cycle Crdinate with next cycle Fall Year 2 Data Sharing and Plan Crdinatin NWMT is an active member f the Nrthern Tier Transmissin Grup (NTTG) and participates in uses the NTTG prcess fr reginal data sharing, planning and cst allcatin, and interreginal crdinatin with adjacent reginal planning entities. NTTG develps a biennial Reginal Transmissin Plan and respnds t requests fr Ecnmic Studies pursuant t FERC Orders 890 and NWMT participates in the intercnnectin-wide planning activities f the WECC Planning Cmmittee and the WECC TEPPC. NWMT participates in the Western Electricity Crdinating Cuncil ( WECC ) Annual Study Prgram and the WECC Transmissin Expansin Planning Plicy Cmmittee (TEPPC) transmissin planning effrt. NWMT prvides its lcal transmissin plan, data and assumptins t WECC cmmittees 8 that are respnsible fr building databases. WECC cmmittees use this data fr database develpment, lad and resurce assessments, perating studies and planning studies. 7 The LTP Cycle and Timeline is psted n MNWMT Oasis website: 8 Fr example: WECC System Review Wrk Grup (SRWG) and WECC Lad and Resurces (LRS) Subcmmittee. 11

12 NWMT's Attachment K, the NTTG Planning Agreement and the NTTG Planning Charter gvern the relatinship between NWMT lcal transmissin planning and the NTTG s reginal transmissin planning and interreginal transmissin planningcrdinatin activities. These dcuments are listed in the Attachment K Business Practice Links Dcument, available n NWMT s OASIS website 9. The FERC 890 principle bligatins, as mdified by FERC Order 1000, which are met by NTTG includes, but are nt limited t, an pen frum t crdinate transmissin plans f its members with thse f ther reginal transmissin grups within the Regin. NTTG s als has a cst allcatin cmmittee that determines reginal cst allcatins fr a reginal prject selected in NTTG s reginal transmissin plan fr purpses f reginal cst allcatinqualifying system additins where agreement n cst allcatin has nt been reached. NWMT actively participates in NTTG s biennial planning prcess by prviding data, technical expertise, and planning staff t develp NTTG s reginal transmissin plan. The NTTG reginal transmissin plan is shared with neighbring reginal entities: Clumbia Grid, WestCnnect and CAISO. Als, the NTTG s biennial reginal transmissin plan is shared with stakehlders, ther reginal planning entities, WECC and state and federal regulatrs. NWMT keeps TRANSAC Stakehlders infrmed f reginal, interreginal, and intercnnectin-wide activities thrugh NWMT's Lcal Area Prcess. This is dne by psting NTTG Stakehlder meeting ntices n NWMT's OASIS, prviding ntices t the Stakehlders, and by prviding reginal, interreginal, and intercnnectin wide updates at TRANSAC meetings. An example f the data and plan crdinatin fr this prcess is shwn in Figure 3: Lcal and Reginal Planning. As the figure shws, data and plan infrmatin is crdinated between the lcal planning prcess, the NTTG reginal planning prcess and the WECC intercnnectin wide planning prcess 10. Gal The gal fr NWMT s Electric Transmissin Tw-Year Lcal Area Planning cycle is t develp a 15- year lcal transmissin system plan that will: Use mdeling scenaris defining current and future lad and resurce cnditins under nrmal and utage cnditins t evaluate transmissin system reliability and priritize prblems fund, and use a decisin rule t identify the best plans fr mitigatin. Cnsider Public Plicy requirements that are driven by lcal, state, r federal law r regulatins. Cnsider transmissin and nn-transmissin alternatives t mitigate system reliability prblems. Crdinate with Reginal and Intercnnectin-wide entities. Crdinate with TRANSAC. Present study results and recmmendatins t stakehlders fr cmment, and t NWMT management fr apprval and inclusin in the 15-year business plan. Reprt management s decisin t TRANSAC. 9 See Sectin 1-A fr Attachment K, and Sectin 2-D fr NTTG Charters and Agreements f the Attachment K Business Practice Links Dcument. 10 See Sectin 2-M Transmissin Planning Guidance Dcument f the Attachment K Business Practice Links Dcument. 12

13 The gal fr NWMT s lcal transmissin system plan was reviewed by all participants in the March 20, 2014, TRANSAC meeting. Lad Frecast Develping the Lad Frecast NWMT develped its peak lad frecasts, cnservatin and demand-respnse data ( lad frecast data ) frm tw surces. First, pursuant t FERC MOD-016, which became effective in June 2007, NWMT btained lad frecasts frm Lad Serving Entities (LSE) within the Balancing Authrity Area (BAA). NWMT btained lad frecast data frm Netwrk Custmers and Pint-t-Pint Custmers pursuant t NWMT s tariff and FERC Order 890, respectively. NWMT asked that these lad frecasts be adjusted fr any MW savings frm custmers cnservatin prgrams. These peak lad frecasts were summed, assuming they were time cincident, t calculate the BAA lad frecast. NWMT s secnd surce was a regressin-based peak lad frecast mdel that NWMT has maintained ver the years. In this regressin-based mdel the lads within NWMT s BAA are metered and tracked s that lads are well-defined. If the LSE and NWMT lad frecast results are significantly different, NWMT attempts t recncile these differences. If NWMT cannt recncile these differences, NWMT chses which frecast t use in the study. NWMT btained lad frecast data fr ten years f mnthly data and annual data extending thrugh a fifteen-year planning hrizn. NWMT used a peak lad frecast that is based n a 50% prbability f being exceeded (i.e., a 1-in- 2 assumptin). The frecast may be adjusted up t a 1-in-10 r a 1-in-20 (i.e., 10% and 5% prbability, respectively) t capture heavy peak lad cnditins. Fr studies within the BAA, 70% f a 1-in-2 peak lad frecast will be used fr light lad (spring and autumn) and 100% f a 1-in-10 peak lad frecast will be used fr heavy lad (summer and winter). The NWMT BAA peak lad frecast reflects demand respnse resurce reductins, cnservatin reductins and ther apprpriate peak lad mdifying surces. Once a BAA lad frecast was develped, this frecast was disaggregated t the lad buses in NWMT s BAA. There are tw types f lad buses: 1) a lad bus where the lad des nt change ver time (e.g., a single, large industrial lad bus), and 2) a lad bus where the lad changes ver time (e.g., residential lad). NWMT used its knwledge f lad characteristics alng with regressin analysis t extraplate the individual lad bus data in time. The lad bus frecasts were summed and cmpared t the BAA lad frecast. If the tw frecasts d nt match, NWMT adjusts the changing lad bus frecasts until the tw frecasts are the same. In develping the Lad Frecast, a number f variables are used: Dependent Lad Independent Ppulatin Large Industrial Lad Winter Heating Degree Day Summer Maximum Temperature Mnth Energy Ptential changes t the Lad Frecast can include linear regressin cefficients and independent variables. Histrical data trends can be used in linear regressin mdel develpment t frecast 13

14 energy and peak lad. Independent variable data dating back t 1990 is als used. NWMT data includes all lads within its BAA and cunts each f the fllwing nly nce: Lad Serving Entities Pint-t-pint Custmers Netwrk Custmers The estimated mdels are then used t frecast annual energy lad and seasnal peak lads by frecasting independent variables int the future. Histrical frecasts are based n expected r average cnditins (i.e. a 1-in-2 assumptin). NWMT uses mnthly lads shaped t results f regressin-based frecasts t develp the nn-peak lad mnths and the mnthly energy lad frecasts. Future frecasts use expected r average cnditins (i.e. a 1-in-2 assumptin) and als a 1- in-10 r a 1-in-20 peak lad. T frecast uncertainties, NWMT uses varius techniques fr frecasting independent variables. Varying ne r mre f these independent variables develps different frecasts: Histrical Temperature: Average f six weather statins in NWMT s BAA. The heating degree days and maximum temperature frecasts are set equal t the histrical average. This represents a 1-in-2 cnditin. Ppulatin Frecast: Ppulatin is frecast based n the U.S. Census frecast fr Mntana (acquired frm the Census and Ecnmic Infrmatin Center in Helena); frecast grwth f 0.74% per year, is expected fr the next 15 years. Large Industrial Lad: The large industrial lad frecast is based n histrical data frm , yielding a frecast grwth rate f 1.24% per year. DSM Frecast: The Demand Side Management frecast is develped by NWMT s Energy Supply grup and is embedded in the regressin-based energy and peak lad frecast results. Lad Frecast Winter The lad frecast presented herein is the Winter frecast (with the energy supply Demand Side Management (DSM) targets embedded). The graphic belw displays the BAA lad frecast assuming nrmal temperature. Average Lad is calculated frm the annual energy frecast. Figure 4: Balancing Authrity Area Lad Frecast 14

15 The fllwing table, Table 1 Balancing Authrity Area Lad Frecast with DSMTable 1 Balancing Authrity Area Lad Frecast with DSM included, presents the data displayed in the abve Figure 4: Balancing Authrity Area Lad Frecast graphic. Table 1 Balancing Authrity Area Lad Frecast with DSM included Actual Frecast Balancing Authrity Area Lad Frecast - w/dsm Peak MW Annual Energy Summer Winter avg MW BAAGR 1.02% 0.78% 0.86% Per Yr

16 16

17 The estimated peak lad sensitivity used in the summer and winter peak mdels is shwn in Table 2 Estimated Peak Lad Temperature SensitivityTable 2 Estimated Peak Lad Temperature Sensitivity. Table 2 Estimated Peak Lad Temperature Sensitivity Seasn MW Change per Degree Frecast Average System Temperature Winter degrees Summer degrees The mnthly peak lad frecast is displayed in Table 3 Peak Lad FrecastTable 3 Peak Lad Frecast. A mnthly shape factr was develped and applied t the winter and summer peak lad frecasts t develp the nn-peak mnth peak frecast. This infrmatin was supplied t WECC and ther entities. Table 3 Peak Lad Frecast Balancing Authrity Area Peak MW - w/dsm Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nv Dec In develping the base cases described in the State f the System Study sectin f this dcument, NWMT used a System Lad, as ppsed t the Balancing Authrity Area lad referred t in the abve tables and graphs. The System Lad is calculated by starting with the Balancing Authrity Area lad and adding r subtracting specific lad cmpnents such as freign-embedded lad (e.g., rural electric cperatives) lads and auxiliary plant lads, which are then reacquired thrugh the base case building prcess via user entry int the planning sftware. 17

18 The System Lad level assumptins (summer/winter) used include: Histrical: 1-in-2 (2014 = 1650/1582 MW) Prpsed: 1-in-10 (2014 = 1673/1615 MW) Scenari: 1-in-20 (2014 = 1679/1624 MW) Scenari: 1-in-50 (2014 = 1687/1635 MW) The 1-in-2 frecast is typical f average lad cnditins, while the 1-in-10 frecast is used in the standard planning base cases t mre aggressively represent pssible peak lad cnditins. The 1-in- 20 r 1-in-50 frecasts may be used in mre heavily laded uncertainty r extreme scenaris. The basic methdlgies fr develping this frecast data include Transmissin, Generatin and Demand Respnse Resurces. Each f these three is described belw: Transmissin: NWMT used the existing transmissin infrastructure as a starting pint. The data was reviewed and updates t the existing transmissin data were included in the base case. If a new transmissin prject were under cnstructin, then it was included in the base case. Future new transmissin additins nt under cnstructin were nt included in the initial base case unless a prir planning study has accepted the prject and NWMT agreed t include it after discussing it with TRANSAC. These prjects may be included in sme f the base and/r uncertainty scenaris and nt thers. Other future new transmissin additins were cnsidered as ne f the mitigatin ptins if transmissin system reliability prblems arse during the study. Generatin: NWMT used the existing generatin infrastructure as a starting pint. The generatin data was reviewed and any updates r changes were included in the base case. Demand Respnse Resurces: The DSM frecast was develped by NWMT s Energy Supply grup and was subtracted frm the regressin-based energy and peak lad frecast results. Methdlgy & Criteria Planning Methdlgy NWMT s Planning Methdlgy, Criteria and Prcess are utlined in NWMT s ETP Methd Criteria and Prcess Business Practice effective The remainder f this sectin summarizes the highlights frm this business practice. Als, fr all f NWMT's Business Practices and Attachment K related dcuments, please refer t Attachment K Business Practice Links. NWMT s methdlgy includes the fur majr steps shwn in Table 4 Planning MethdlgyTable 4 Planning Methdlgy. These steps are 1) Gal and Scenari Definitin, 2) Technical Study, 3) Decisin, and 4) Reprting. NWMT used scenari planning and nt prbabilistic planning fr develping the electric transmissin system plan. Lcal transmissin planning may be cnfined t a specific gegraphic area, such as the Bzeman area, r it may be bradened t examine a specific transmissin line r lines that extend ver a large gegraphic area, such Table 4 Planning Methdlgy 1. Gal & Scenaris 2. Technical Study 3. Decisin 4. Reprting 18

19 as NWMT s BAA. The transmissin lines used in a lcal transmissin planning study may range in size frm 50 kv t 500 kv and may be netwrked r radial. Lcal transmissin planning methdlgy invlves frecasting custmer demand, identifying area reliability prblems, evaluating pssible mitigatin ptins and selecting a slutin that slves the area s transmissin needs. Transmissin planning evaluates the transmissin system reliability up t 15 years in the future. The planning effrt cnsiders transmissin and nn-transmissin alternatives t reslve the reliability prblem fr a specified area. NWMT s methdlgy is flexible and is intended t develp a plan that: Respnds t custmers needs; Is lw cst (e.g., Ttal Present Value Revenue requirement, Rate Impact, etc.); Cnsiders nn-transmissin and transmissin alternatives; Cnsiders public plicy requirements and cnsideratins 11 Assesses future uncertainty and risk; Prmtes NWMT s cmmitment t prtecting the envirnment; Includes input frm the stakehlders and ther interested parties; Prvides adequate return t investrs; Cmplements crprate gals and cmmitments; Meets applicable NERC and WECC Standards and requirements; Meets the Mntana Public Service Cmmissin expectatins; Meets Reginal and Intercnnectin-wide planning requirements; Addresses custmer and stakehlder cncerns in an pen, fair, and nn-discriminatry manner. Satisfies the requirements f applicable FERC and MPSC Orders; and Cnfrms t applicable state and natinal laws and regulatins. NWMT wrked with its Transmissin Advisry Cmmittee (TRANSAC) t establish the gal and t prvide input thrughut the entire Lcal Transmissin System Planning Prcess. See Attachment B: Stakehlder InvlvementAttachment B: Stakehlder Invlvement. Study Criteria System Nrmal and Outage cnditins were mdeled and studied fr adequacy and system security. Segment r element thermal lading >85% f seasnal ratings were nted under these cnditins; thermal lading abve 100% f the seasnal ratings were nted as verlads. Overladed segments were tripped per standard relaying practice (100% - 150% thermal n lines, 125% minimum thermal n transfrmers) t check fr cascading utages except as nted belw per new NERC requirements; 230 kv lines are nt tripped belw 150% thermal per requirements f NERC PRC-023. May apply t path lines r ther system lines and elements deemed critical. 11 Public plicy requirements are established by lcal, state, r federal laws r regulatins, meaning enacted statues (i.e., passed by the legislature and signed by the executive) and regulatins prmulgated by a relevant jurisdictin. Public plicy requirements and cnsideratins are discussed in Attachment D: Public Plicy Lcal Area Plan. 19

20 Vltages utside f NWMT planning criteria were nted (93% and 95% lw vltage limit depending n line vltage; 105% high vltage limit). Lad-serving bus vltages may fall abve r belw the tabled value if cnditins allw a higher/lwer vltage withut harm t NWMT r custmer equipment. Certain equipment ratings may dictate different limits. Existing Overlad Mitigatin Scheme(s) (OMS) r Special Prtectin Scheme(s) (SPS) were cnsidered. Reliability Criteria Electric transmissin reliability is cncerned with the adequacy and security f the electric transmissin system. Adequacy addresses whether r nt there is enugh transmissin, and security is the ability f the transmissin system t withstand cntingencies (i.e., the lss f single r multiple transmissin elements). NWMT internal reliability criteria is a set f technical transmissin reliability measures that have been established fr the safe and reliable peratin f NWMT s transmissin system. The FERC apprved Standards (cnsisting f thse implemented by NERC and WECC) and WECC Standards set minimum perfrmance standards fr vltage excursins and vltage recvery after a credible utage event n the transmissin system. Credible utages are thse mre likely r plausible, and required t be cnsidered by the gverning standards. NWMT uses these criteria in evaluating a change r additin t its electric transmissin equipment and/r a change r additin t lad r generatin. NWMT uses these reliability criteria as needed t fully evaluate the impacts t its electrical system f prpsed lines, generatin r lads. NWMT augments these criteria with ther standards such as, but nt limited t, the American Natinal Standards Institute (ANSI) and Institute f Electrical and Electrnics Engineers (IEEE) standards. NWMT planning ensures that any change that either directly r indirectly affects its transmissin system will nt reduce the reliability t existing custmers t unacceptable levels. The NWMT electric transmissin system must remain dependable at all times s that it may prvide reliable high quality service t custmers. NWMT internal reliability criteria are used fr reliability perfrmance evaluatin f the electric transmissin system. Steady-state implies the cnditin n the transmissin system befre an utage r after an utage and after switching ccurs, regulatrs adjust, reactrs r capacitrs switch, and the electrical system has settled dwn (typically three minutes r less). This latter cnditin is als called pst-fault reliability. NWMT s criteria include a cllectin f ANSI standards as well as past and current practices, that when applied with experienced engineering judgment, lead t a reliable and ecnmical electric transmissin system. These criteria supprt the NERC/WECC Standards and WECC Reliability Criteria (including NERC Transmissin Planning (TPL) Standards and the WECC Disturbance-Perfrmance Table f Allwable Effects n Other Systems) that disallw a blackut, vltage cllapse, r cascading utages unless the initiating disturbance and crrespnding impacts are cnfined t either a lcal netwrk r a radial system. An individual prject r custmer lad may require an enhanced reliability requirement. NWMT plans fr a transmissin system that prvides acceptable vltage levels during system nrmal cnditins and utage cnditins. Areas f the NWMT system that are served by radial transmissin service are excluded frm single cntingency evaluatin, due t ecnmic cnsideratins. 20

21 Steady-State & Pst-Fault Vltage Criteria fr 230 kv & Belw The steady-state vltage criteria listed in the tables belw are based n the assumptin that all switching has taken place, all generatrs and transfrmer Lad Tap Changers (LTCs) have regulated vltages t set values, and capacitrs r reactrs are switched. The basis fr the percent vltages is the designed perating vltage. Table 5 Maximum Upper Vltage Criteria At Unregulated Lad-Serving Bus Upper Operating Limit As shwn in Table 5 Maximum Upper Vltage Vltages 105% CriteriTable 5 Maximum Upper Vltage Criteria, the recmmended upper vltage limit fr a lad-serving bus is 105% unless equipment rating dictates a different limit. Fr example, equipment used n 100 kv systems is typically rated fr a nminal vltage f 102 kv r higher, s 107 kv r 105% f 102 kv nminal is permitted n 100 kv systems. NWMT fllws the limit as utlined in the American Natinal Standards Institute standards (i.e., ANSI C84.1). It is pssible that a lad-serving bus vltage may exceed the table value if cnditins allw a higher vltage withut harm t NWMT r custmer equipment. The allwable minimum percent vltage fr any lad-serving bus that is within a netwrk cnfiguratin is shwn in Minimum Allwable Percent Vltage at NWMT Unregulated Lad-Serving BusMinimum Allwable Percent Vltage at NWMT Unregulated Lad-Serving Bus. It is pssible that a lad-serving bus vltage may fall belw the table value if cnditins allw a lwer vltage withut harm t NWMT r custmer equipment. This table cnsiders FERC/NERC and WECC criteria as applied t the bulk electric system buses (100 kv and abve). This table is als applied n lwer vltage transmissin buses that are nt part f the bulk electric system (50 kv & 69 kv). The minimum allwable percent vltage fr a lad serving bus that is n a radial transmissin system fr an event n the radial line must nly meet the existing system perfrmance (N-0) shwn in Minimum Allwable Percent Vltage at NWMT Unregulated Lad-Serving BusMinimum Allwable Percent Vltage at NWMT Unregulated Lad-Serving Bus. Any unacceptable vltage perfrmance must be mitigated in accrdance with the criteria described belw. The use f a Special Prtectin Scheme (SPS) is evaluated n a case-by-case basis, with n assurance that NWMT will accept r use a SPS. The values in Minimum Allwable Percent Vltage at NWMT Unregulated Lad-Serving BusMinimum Allwable Percent Vltage at NWMT Unregulated Lad-Serving Bus assume that all ther methds t cntrl vltage have been explred (such as capacitrs, reactrs, and line switching, etc.). Under emergency cnditins, bus vltage between 90% and 110% f nminal is permitted fr up t 30 minutes. Table 6 - Min. Allwable % Vltage at NWMT Unregulated Lad-Serving Bus Minimum Allwable Percent Vltage at NWMT Unregulated Lad-Serving Bus Nminal Vltage Existing System (N-0) First Cntingency (N-1) Secnd Cntingency (N- 2) 230 kv and 161 kv 95% 95% 93% 115 kv and 100 kv 95% 93% 90% 69 kv and 50 kv 93% 93% 90% Nte: 1. Percent vltage is measured frm the nminal vltage kv, 69 kv and radial 100 kv segments are nt bulk electric system elements. 21

22 Steady-state & Pst-fault Vltage Criteria fr 500 kv The allwable perating vltage range fr the 500 kv transmissin system is 100% t 110% f nminal, r 500 t 550 kv. This range is different frm ther vltage levels because equipment used n the 500 kv system is nminally rated at 525 kv. These criteria apply t bth steady-state and pstfault cnditins. Thermal Ratings Transmissin cnductr cntinuus summer ratings are based n 25 C (77 F) ambient air at 1.4 mph (2 ft/sec), 50 C cnductr temperature rise, and 75 C (167 F) maximum perating temperature unless cnditins dictate therwise (e.g., sme cnductrs and lines may be specifically designed fr higher perating temperatures). Winter transmissin cnductr cntinuus thermal ratings are 125% f the summer rating, during the winter mnths Nvember February, r any time ambient temperatures are belw 0 C (32 F).This rating is entered as Rate A in the pwer flw base cases. Unacceptable cnductr lading can be mitigated by system imprvements r, in sme cases, a Special Prtectin Scheme (SPS) that changes system cnditins t mitigate the verlad. The use f an SPS t alleviate cnductr verlading is evaluated n a case-by-case basis, with n assurance that NWMT will accept r use an SPS. Emergency ratings fr transmissin cnductrs are develped n a case-by-case basis, and are dependent n cnductr size, line vltage and available grund clearance under elevated cnductr temperature cnditins. Under emergency cnditins fr standard cnductrs (e.g. nt "high temp" cnductrs), cnductr temperatures are limited t 100 C (212 F) r less, and thermal ratings are limited t 125% f the seasnal rating fr up t 30 minutes. Transfrmer ratings are based n the fllwing: Fr standard service cnditins (24-hur average ambient air temperature f 30 C r 86 F, r less), the cntinuus rating is 100% f the highest peratinal nameplate rating. This rating is entered as Rate A in the pwer flw base case. Fr winter service cnditins (Nvember February, r any time 24-hur ambient air temperature is less than 0 C, r 32 F), lading t 125% f the standard service cnditin rating may be allwed. Under emergency perating cnditins, lading t 125% f the standard service cnditin rating may be allwed fr up t 30 minutes during any seasn. Nte this is the same as the winter rating, and under winter cnditins this lad level is permitted cntinuusly. Unacceptable transfrmer lading can be mitigated by transfrmer replacement, system imprvements r, in sme cases, an SPS that changes system cnditins t mitigate the verlad. The use f an SPS t alleviate transfrmer verlading is evaluated n a case-by-case basis, with n assurance that NWMT will accept r use an SPS. General Minimum Equipment Specificatins The general minimum specificatins fr Nrth Western Energy Transmissin and Substatin equipment are listed in Table 7 T&S Equipment: General Minimum SpecificatinsTable 7 T&S Equipment: General Minimum Specificatins. This table als summarizes the MVA r capacity, vltage, current, equipment Basic Impulse Level (BIL), Maximum Cntinuus Over Vltage (MCOV) fr lightning arresters, and interrupt ratings f equipment as applicable and assciated grunding requirements. Vltage criteria fr 500 kv, General Minimum Equipment specificatins, Transmissin Equipment Rating and Lading, Special Prtectin Scheme (SPS) Applicatin, Vltage Ride Thrugh, Harmnics, and Subsynchrnus Resnance are utlined in NWMT s ETP Methd Criteria and Prcess Business Practice which is psted n NWMT s OASIS website. 22

23 Table 7 T&S Equipment: General Minimum Specificatins Transmissin and Substatin Equipment: General Minimum Specificatins Nminal System vltages - kv 230 kv 161 kv 115 kv 100 kv 69 kv 50 kv MVA and Current Ratings *(1) As Req d As Req d As Req d As Req d As Req d As Req d Equipment BIL (kv) *(2) Maximum Design Vltage (kv) *(3) Breaker Interrupt Current (ka) Breaker and Switch Cntinuus Current (A) *(4) Arrester Duty Rating/MCOV (kv) *(5) 172/ /98 90/70 90/70 54/42 39/31.5 Substatin Insulatr Class TR-304 TR-291 TR-286 TR-286 TR-216 TR-214 Transmissin Line BIL, wd (kv) *(6) Transmissin Line BIL, steel (kv) *(7) Ntes: (1) Prject and equipment specific as required t avid thermal verlads (2) 1050 kv BIL is als used n sme 230 kv equipment (3) At least 5% ver nminal (4) 2000 amp equipment is used in sme applicatins (5) Fr effectively grunded systems (6) Insulatr supprt hardware ungrunded (7) Insulatr supprt hardware grunded Base Case Planning Scenaris Base Case Planning Scenaris (Scenaris) are develped based n the gal f the lcal transmissin system plan and t examine different lad, generatin, and dispatch patterns in the future t identify cnditins that stress the transmissin system in planning mdels and simulatins. Public plicy requirements wuld be cnsidered as well. Thrugh simulatins ptential prblems in system adequacy r security are revealed under nrmal r abnrmal system cnditins. Scenaris are determined per the gals f the transmissin plan and lk at a 15-year planning study perid: current year, five years, ten years, and fifteen years int the future. NWMT uses scenari planning and nt prbabilistic planning fr develping the lcal area transmissin plan. NWMT may, hwever, use prbabilistic assessment methds within a defined scenari t evaluate uncertainty. Base case scenaris are used t examine the transmissin system under a variety f future assumptins fr a specific perid f time. The scenari assumptins may include, but are nt limited t, the fllwing: Lad Frecast (e.g., study year) Lad Cnditin t Study (e.g., seasn, peak lad r light lad, etc.) Generatin Available (e.g., generatin additins/changes) 23

24 Generatin Dispatch Cnditins (e.g., hw the generatin is perated) Transmissin System Elements Available (e.g., transmissin element additins/changes) Transmissin System Cnfiguratin (e.g., what elements are ut-f-service) Public Plicy requirements that are driven by lcal, state r federal law r regulatins The fllwing base scenaris have been fund t prduce maximum stress n the lcal r bulk transmissin system, and are used fr planning purpses: Heavy Lad Scenaris: Tw typical heavy lad scenaris tend t stress the lcal area transmissin system. Heavy Winter, maximum lad cnditins (heating with high pwer factr), maximum thermal generatin, median hydr generatin, mderate exprts. Heavy Summer, maximum lad cnditins (irrigatin and cling, lwer pwer factr), high thermal generatin, high hydr generatin, and mderate exprts. Heavy Summer cnditins tend t gvern in lcal area planning scenaris tday. Light Lad Scenaris: Tw typical light lad scenaris tend t stress the bulk r exprt system. Light Spring, light lad cnditins (little heat r cling, n irrigatin), mderate thermal generatin, maximum hydr generatin, and heavy exprts. Light Autumn, light lad cnditins, high thermal generatin, lw t median hydr generatin, and mderate exprts. Light autumn cnditins typically gvern in bulk system planning tday. As a result, 16 base cases were used: fur seasns (heavy summer, heavy winter, light autumn and light spring) fr the present and future ver a 15-year planning hrizn (2014, 2019, 2024 and 2029). All cases were based n a 1-in-10 lad frecast (mdeled lad has a 1-in-10, r 10% chance f being exceeded in actual cnditins). Histrical lad and system perfrmance weigh heavily in scenari develpment, alng with certain assumptins abut the future. Scenari assumptins can include: lad frecasts (grwth), lad cnditin (peak, light), generatin (as available and hw dispatched), transmissin (additins, upgrades, and status, in-service r ut). Additinal scenaris can be develped t cnsider ther cnditins that may stress the system such as: varius cmbinatins f path ladings, time f day variatins in lad and path ladings, and the effects f new paths, generatin, r lad. A sensitivity analysis r study f uncertainty scenaris helps establish risks, csts, r ther ptential impacts f the uncertain future. Uncertainty Scenaris are develped with the knwledge that the future and the assumptins made in scenaris are uncertain. Fr example, the effects f higher r lwer lad frecasts can be cnsidered, as well as differences in generatin dispatch, r the effects f prpsed new generatin r lad. Fr this study perid, different levels f existing r prpsed wind generatin were cnsidered at minimum and maximum levels. Other scenaris were cnsidered. See the Uncertainty and Other Scenari sectin f this dcument. Scenaris are examined in present and future cases fr system adequacy and security under nrmal and utage cnditins. Adequacy refers t the capacity f the system fr future needs, while Security examines the ability f the system t maintain service thrugh system disturbances r utages. The system must be designed and perated t meet reliability criteria and requirements fr vltage levels, thermal capacity, and dynamic stability as established by FERC, NERC, WECC, reginal and lcal requirements under nrmal and utage cnditins. Other criteria such as Vlt-Amperes reactive (VAr) margins may be examined as well. Nrmal perating cnditins that are studied include 24

25 all system elements in their nrmally in-service perating state (referred t as an N-0 cnditin). Outage cnditins that are studied include the lss r fault f ne (N-1) r mre (N-2, etc.) system elements (line, transfrmer, bus). When mdels and simulatins reveal system inadequacies under these study cnditins, mitigatin scenaris are develped t examine the effects and csts f varius slutins t prblems. Slutins culd include, but are nt limited t, new cnstructin (transmissin lines, substatins), generatin (new r dispatch changes), system recnfiguratin, curtailment f nn-firm system transfers r ther slutins (Demand-Side Management (DSM), imprts/exprts, etc.). The base scenaris used fr the current year, utlined in Table 8 Study ScenarisTable 8 Study Scenaris, were used t develp the 5-, 10-, and 15-year scenaris, alng with the lad frecast. Table 8 Study Scenaris Scenari Name/Year Lad Cnditins Demand P F Hydr Gen Heavy Summer Max 0.92 Heavy Winter Max 0.98 Generatin Thermal Gen Wind Median t High High Median Lw t Median Max Median Light Spring Min 0.95 Max Mderate Median Light Autumn Min 0.95 Lw t Median High Median MT-NW Path 8 Mderate Exprt Mderate Exprt Heavy- Max Exprt Heavy- Max Exprt External Paths MT-ID Path 18 Heavy Exprt Mderate Exprt Lw Imprt r Exprt Lw Imprt r Exprt MT-SE Path 80 Mderate Exprt Mdedrate Exprt Lw- Mderate Imprt Lw- Mderate Imprt MATL Path 83 Max lcal area stress expected. Heavy Mderate irrigatin lad and cling lad, lwer pwer Lw Imprt factr. Mderate Lw Exprt Cmments Lcal area stress expected, wrst cnditin in sme areas (Big Sky). Heavy heating lad with high pwer factr. Mderate High Exprt Heavy bulk system stress expected. Lw Imprt r Exprt Heaviest bulk system stress expected. Technical Study Outline The technical study area examines the reliability f NWMT s electric transmissin system that mves pwer arund NWMT s BAA and between the bulk electric transmissin system and the distributin system. NWMT used a sphisticated cmputer mdel (i.e., Siemens PSS E) t simulate generatr utput, electrical flws thrugh the transmissin lines and transfrmers, electrical equipment actin, custmer lads and exprt (r imprt) path flws. The purpse f the technical study is t quantify transmissin system perfrmance by measuring the bus vltage, equipment lading, reactive pwer requirement, system frequency, and ther electrical parameters. NWMT did nt cnduct studies fr every pssible lad and resurce dispatch cmbinatin fr the 8,760 hurs f the year. Instead, nly the lad and resurce dispatch patterns that stressed the transmissin system were evaluated. The reliability f the lcal transmissin system was evaluated with all transmissin lines in-service r with a variety f elements ut-f-service. Fr each cmputer simulatin run, the transmissin system vltage, equipment lading, and ther parameters were measured and cmpared t specific reliability criteria 12. If the reliability criteria were nt met, then apprpriate mitigatin (transmissin and nn-transmissin) was mdeled in the base case database and the cmputer mdel simulatin was run again. This prcess cntinued until the reliability criteria were met. The mitigatin measures culd include enhancements t the transmissin system, generatin develpment, demand resurce develpment r ther alternatives. 12 Federal Energy Regulatry Cmmissin, NERC, WECC r NWMT reliability criteria. 25