Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company or an emerging growth company.  See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Indicate the number of shares outstanding of each of the issuer’s classes of common stock, as of the latest practicable date.

This Form 10-Q is filed by Northern States Power Company, a Wisconsin corporation (NSP-Wisconsin).  NSP-Wisconsin is a wholly owned subsidiary of Xcel Energy Inc.  Xcel Energy Inc. wholly owns the following subsidiaries: Northern States Power Company, a Minnesota corporation (NSP-Minnesota); Southwestern Public Service Company, a New Mexico corporation (SPS); Public Service Company of Colorado, a Colorado corporation (PSCo); and NSP-Wisconsin.  NSP-Minnesota, NSP-Wisconsin, PSCo and SPS are also referred to collectively as utility subsidiaries.  The electric production and transmission system of NSP-Minnesota and NSP-Wisconsin, which is operated on an integrated basis and is managed by NSP-Minnesota, is referred to collectively as the NSP System. Additional information on Xcel Energy Inc. and its subsidiaries (collectively, Xcel Energy) is available on various filings with the Securities and Exchange Commission (SEC).

In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments necessary to present fairly, in accordance with accounting principles generally accepted in the United States of America (GAAP), the financial position of NSP-Wisconsin and its subsidiaries as of Sept. 30, 2017March 31, 2018 and Dec. 31, 2016;2017; the results of its operations, including the components of net income and comprehensive income, for the three and nine months ended Sept. 30, 2017March 31, 2018 and 2016;2017; and its cash flows for the ninethree months ended Sept. 30, 2017March 31, 2018 and 2016.2017. All adjustments are of a normal, recurring nature, except as otherwise disclosed. Management has also evaluated the impact of events occurring after Sept. 30, 2017March 31, 2018 up to the date of issuance of these consolidated financial statements. These statements contain all necessary adjustments and disclosures resulting from that evaluation. The Dec. 31, 20162017 balance sheet information has been derived from the audited 20162017 consolidated financial statements included in the NSP-Wisconsin Annual Report on Form 10-K for the year ended Dec. 31, 2016.2017. These notes to the consolidated financial statements have been prepared pursuant to the rules and regulations of the SEC for Quarterly Reports on Form 10-Q. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP on an annual basis have been condensed or omitted pursuant to such rules and regulations. For further information, refer to the consolidated financial statements and notes thereto, included in the NSP-Wisconsin Annual Report on Form 10-K for the year ended Dec. 31, 2016,2017, filed with the SEC on Feb. 24, 2017.26, 2018. Due to the seasonality of NSP-Wisconsin’s electric and natural gas sales, interim results are not necessarily an appropriate base from which to project annual results.

The significant accounting policies set forth in Note 1 to the consolidated financial statements in the NSP-Wisconsin Annual Report on Form 10-K for the year ended Dec. 31, 2016,2017, appropriately represent, in all material respects, the current status of accounting policies and are incorporated herein by reference.

Except to the extent noted below, Note 6 to the consolidated financial statements included in NSP-Wisconsin’s Annual Report on Form 10-K for the year ended Dec. 31, 20162017 appropriately represents, in all material respects, the current status of other income tax matters, and are incorporated herein by reference.

Federal Audits — NSP-Wisconsin is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. The statute of limitations applicable to Xcel Energy’s 2009 through 2011 and 2012 through 2013 federal income tax returns following extensions, expires in June 2018 and October 2018, respectively.expire as follows:

In 2012, the Internal Revenue Service (IRS) commenced an examination of tax years 2010 and 2011, including athe 2009 carryback claim. The IRS proposed an adjustment to the federal tax loss carryback claims that would resultand in $14 million of income tax expense for the 2009 through 2011 claims, and the 2013 through 2015 claims. In the fourth quarter of 2015 the IRS forwarded the issue to the Office of Appeals (Appeals)(“Appeals”). In the third quarter of 2017 Xcel Energy and Appeals reached an agreement and the benefit related to the agreed upon portions was recognized. NSP-Wisconsin did not accrue any income tax benefit related to this adjustment. As of March 31, 2018, the case has been forwarded to the Joint Committee on Taxation.

In the third quarter of 2015, the IRS commenced an examination of tax years 2012 and 2013. In the third quarter of 2017, the IRS concluded the audit of tax years 2012 and 2013 and proposed an adjustment that would impact Xcel Energy’s net operating loss (NOL) and effective tax rate (ETR). After evaluating the proposed adjustment Xcel Energy filed a protest with the IRS. Xcel Energy anticipates the issue will be forwarded to Appeals. As of Sept. 30, 2017,March 31, 2018, Xcel Energy has recognized its best estimate of income tax expense that will result from a final resolution of this issue; however, the outcome and timing of a resolution is unknown.uncertain.

State Audits — NSP-Wisconsin is a member of the Xcel Energy affiliated group that files consolidated state income tax returns. As of Sept. 30, 2017,March 31, 2018, NSP-Wisconsin’s earliest open tax year that is subject to examination by state taxing authorities under applicable statutes of limitations is 2012. In 2016, the state of Wisconsin began an audit of years 2012 and 2013. As of Sept. 30, 2017,March 31, 2018, Wisconsin had not proposed any material adjustments, and there were no other state income tax audits in progress.

Unrecognized Benefits — The unrecognized tax benefit balance includes permanent tax positions, which if recognized would affect the annual ETR. In addition, the unrecognized tax benefit balance includes temporary tax positions for which the ultimate deductibility is highly certain but for which there is uncertainty about the timing of such deductibility. A change in the period of deductibility would not affect the ETR but would accelerate the payment of cash to the taxing authority to an earlier period.

A reconciliation of the amount of unrecognized tax benefit is as follows:

The unrecognized tax benefit amounts were reduced by the tax benefits associated with NOL and tax credit carryforwards. The amounts of tax benefits associated with NOL and tax credit carryforwards are as follows:

The payable for interest related to unrecognized tax benefits is partially offset by the interest benefit associated with NOL and tax credit carryforwards. The payables for interest related to unrecognized tax benefits at Sept. 30, 2017March 31, 2018 and Dec. 31, 20162017 were not material. No amounts were accrued for penalties related to unrecognized tax benefits as of Sept. 30, 2017March 31, 2018 or Dec. 31, 2016.

In January 2018, the Public Service Commission of Wisconsin (PSCW) issued an order requiring public utilities to apply deferred accounting for the impacts of the TCJA. In March 2018, NSP-Wisconsin filed recommended plans for Wisconsin, which for electric operations included an option for an immediate bill credit for a portion of the tax savings in 2018 and 2019, while deferring the remainder until NSP-Wisconsin’s 2020 electric rate case. For the natural gas operations, NSP-Wisconsin proposed using the TCJA to reduce the unamortized regulatory asset for the Ashland/Northern States Power Lakefront Superfund Site (the Site) clean-up. A PSCW decision on the regulatory treatment of the TCJA is anticipated later in 2018.

In December 2015, an administrative law judge (ALJ) recommendedSeptember 2016, the FERC approveapproved an Administrative Law Judge (ALJ) recommendation that MISO TOs be granted a base ROE of 10.32 percent for the MISO TOs. The ALJ found the existing 12.38 percent ROE to be unjust and unreasonable. The recommended 10.32 percent ROE applied a FERC ROE policy adopted in a June 2014 order (Opinion 531). The FERC approved the ALJ recommended 10.32 percent base ROE using the methodology adopted by FERC in an order issued in September 2016.June 2014 (Opinion 531). This ROE would be applicable for the 15 month15-month refund period from Nov. 12, 2013 to Feb. 11, 2015, and prospectively from the date of the FERC order. The total prospective ROE would be 10.82 percent, including a 50 basis point adder for RTO membership. Various parties requested rehearing of the September 2016 order. The requests are pending FERC action.

Except to the extent noted below and in Note 5 above, the circumstances set forth in Notes 10 and 11 to the consolidated financial statements included in NSP-Wisconsin’s Annual Report on Form 10-K for the year ended Dec. 31, 2016 and in Notes 5 and 6 the consolidated financial statements included in NSP-Wisconsin’s Quarterly Report on Form 10-Q for the quarterly periods ended March 31, 2017 and June 30, 2017, appropriately represent, in all material respects, the current status of commitments and contingent liabilities and are incorporated herein by reference. The following include commitments, contingencies and unresolved contingencies that are material to NSP-Wisconsin’s financial position.

NSP-Wisconsin provides a guarantee for payment of customer loans related to NSP-Wisconsin’s farm rewiring program. NSP-Wisconsin’s exposure under the guarantee is based upon the net liability under the agreement. The guarantee issued by NSP-Wisconsin has a stated maximum amount. The guarantee contains no recourse provisions and requires no collateral. These agreements have expiration dates through 2020.

The following table presents the guarantee issued and outstanding for NSP-Wisconsin:

In 2012, NSP-Wisconsin agreed to remediate the Phase I Project Area (which includes the Upper Bluff and Kreher Park areas of the Site), under a settlement agreement with the United States Environmental Protection Agency (EPA). In January 2017, NSP-Wisconsin agreed to remediate the Phase II Project Area (the Sediments), under a settlement agreement with the EPA.Environmental Protection Agency. The settlement wasagreements were approved by the U.S. District Court for the Western District of Wisconsin. NSP-Wisconsin initiated field activities to perform a full scale wet dredge remedy of the Sediments in 2017 and2017. Under the current plan, NSP-Wisconsin anticipates completion of restoration activities of the Sediments in 2018.2018 with finalization of Phase I Project Area (which includes the Upper Bluff and Kreher Park areas of the Site) construction and restoration activities in early 2019 although April weather may challenge that schedule. Groundwater treatment activities at the Site will continue.

The current remediation cost estimate for the remediation of the entire site (both the Phase I Project Area and the Sediments) is approximately $162.9$172 million, of which approximately $131.8$139 million has been spent. As of Sept. 30, 2017March 31, 2018 and Dec. 31, 2016,2017, NSP-Wisconsin had recorded a total liability of $31.1$33 million and $64.3$30 million, respectively, for the entire site.

NSP-Wisconsin has deferred the unrecovered portion of the estimated Site remediation costs as a regulatory asset. The PSCW has authorized NSP-Wisconsin rate recovery for all remediation costs incurred at the Site. In 2012, the PSCW agreed to allow NSP-Wisconsin to pre-collect certain costs, to amortize costs over a ten-year period and to apply a three percent carrying cost to the unamortized regulatory asset. In MayDecember 2017, the PSCW approved an NSP-Wisconsin filed a natural gas rate case, which included recovery of additional expenses associated with remediating the Site. If approved, theThe annual recovery of MGP clean-up costs would increaseincreased from $12.4$12 million in 2017 to $18.1$18 million in 2018.

NSP-Wisconsin is involved in various litigation matters that are being defended and handled in the ordinary course of business. The assessment of whether a loss is probable or is a reasonable possibility, and whether the loss or a range of loss is estimable, often involves a series of complex judgments about future events. Management maintains accruals for such losses that are probable of being incurred and subject to reasonable estimation. Management is sometimes unable to estimate an amount or range of a reasonably possible loss in certain situations, including but not limited to when (1) the damages sought are indeterminate, (2) the proceedings are in the early stages, or (3) the matters involve novel or unsettled legal theories. In such cases, there is considerable uncertainty regarding the timing or ultimate resolution of such matters, including a possible eventual loss. For current proceedings not specifically reported herein, management does not anticipate that the ultimate liabilities, if any, arising from such current proceedings would have a material effect on NSP-Wisconsin’s financial statements. Unless otherwise required by GAAP, legal fees are expensed as incurred.

e prime, Xcel Energy Inc. and its other affiliates were sued along with several other gas marketing companies. TheThese cases were all consolidated in the U.S. District Court in Nevada. Six of the cases remain active, which includes onea multi-district litigation (MDL) matter consisting of a Colorado class (Breckenridge), a Wisconsin class (Arandell Corp.), a Missouri class, a Kansas class, and two other cases identified as “Sinclair Oil” and “Farmland.” A motionIn March 2017, summary judgment was granted by the MDL judge in favor of Xcel Energy and e prime in the Sinclair Oil and Farmland cases. In November 2017, the U.S District Court in Nevada granted summary judgment against two plaintiffs in the Arandell Corp. case in favor of Xcel Energy and NSP-Wisconsin, leaving only three individual plaintiffs remaining in the litigation. In addition, the plaintiffs’ motions for class certification wasand remand back to originating courts in these cases were denied and plaintiffsin March 2017. Plaintiffs have appealed the rulingsummary judgment motions granted in the Farmland and Sinclair Oil cases and the denial of class certification and remand to the U.S. Court of Appeals for the Ninth Circuit. Motions for summary judgmentCircuit (Ninth Circuit). Oral arguments were granted by the MDL judge in favor of e prime and Xcel Energy in Sinclair Oil and Farmland. Plaintiffs in both cases appealed this decision to the Ninth Circuit. Motions for summary judgment were also filed by defendants, including e prime, in all of the remaining lawsuits. These motions were denied and e prime subsequently filed an appeal in September 2017. Dates for all matters pendingheard before the Ninth Circuit in February 2018. In March 2018, the Ninth Circuit reversed and remanded the summary judgment in the Farmland case. The Farmland defendants subsequently filed a request for further review by the Ninth Circuit. In light of the decision in the Farmland case, the Sinclair plaintiffs have not been scheduled.requested the Ninth Circuit to reverse the grant of summary judgment without hearing. Final rulings on all pending motions and appeals are expected by the end of 2018. Xcel Energy, NSP-Wisconsin and e prime have concluded that a loss is remote.

Letters of Credit — NSP-Wisconsin uses letters of credit, generally with terms of one year, to provide financial guarantees for certain operating obligations. At Sept. 30, 2017March 31, 2018 and Dec. 31, 2016,2017, there were no letters of credit outstanding.

At Sept. 30, 2017,March 31, 2018, NSP-Wisconsin had the following committed credit facility available (in millions of dollars):

All credit facility bank borrowings, outstanding letters of credit and outstanding commercial paper reduce the available capacity under the credit facility. NSP-Wisconsin had no direct advances on the credit facility outstanding at Sept. 30, 2017March 31, 2018 and Dec. 31, 2016.2017.

Other Short-Term Borrowings — The following table presents the notes payable of Clearwater Investments, Inc., a NSP-Wisconsin subsidiary, to Xcel Energy Inc.:

The accounting guidance for fair value measurements and disclosures provides a single definition of fair value and requires certain disclosures about assets and liabilities measured at fair value.  A hierarchical framework for disclosing the observability of the inputs utilized in measuring assets and liabilities at fair value is established by this guidance. The three levels in the hierarchy are as follows:

Specific valuation methods include the following:

Cash equivalents — The fair values of cash equivalents are generally based on cost plus accrued interest; money market funds are measured using quoted net asset values.

Interest rate derivatives — The fair values of interest rate derivatives are based on broker quotes that utilize current market interest rate forecasts.

Commodity derivatives — The methods used to measure the fair value of commodity derivative forwards and options utilize forward prices and volatilities, as well as pricing adjustments for specific delivery locations, and are generally assigned a Level 2 classification.  When contractual settlements extend to periods beyond those readily observable on active exchanges or quoted by brokers, the significance of the use of less observable forecasts of long-term forward prices and volatilities on a valuation is evaluated and may result in Level 3 classification.

NSP-Wisconsin enters into derivative instruments, including forward contracts, futures, swaps and options, for trading purposes and to manage risk in connection with changes in interest rates and utility commodity prices.

At Sept. 30, 2017,March 31, 2018, accumulated other comprehensive loss related to interest rate derivatives included $0.1 million ofimmaterial net losses expected to be reclassified into earnings during the next 12 months as the related hedged interest rate transactions impact earnings, including forecasted amounts for unsettled hedges, as applicable.

The following table details the gross notional amounts of commodity options at Sept. 30, 2017March 31, 2018 and Dec. 31, 2016:2017:

During the three and nine months ended Sept. 30,March 31, 2018 and 2017, changes in the fair value of natural gas commodity derivatives resulted in $0.1 millionimmaterial and $0.2$0.1 million of net losses, respectively, recognized as regulatory assets and liabilities, respectively. For the three and nine months ended Sept. 30, 2016, changes in the fair value of natural gas commodity derivatives resulted in $0.1 million and $0.2 million of net losses recognized as regulatory assets and liabilities, respectively.liabilities. The classification as a regulatory asset or liability is based on commission approved regulatory recovery mechanisms.

NaturalThere were no natural gas commodity derivativesderivative settlement gains or losses ofrecognized and $0.2 million and $0.6 million wereof losses recognized for the ninethree months ended Sept. 30,March 31, 2018 and 2017, and 2016, respectively, and were subject to purchased natural gas cost recovery mechanisms, which result in reclassifications of derivative settlement gains and losses out of income to a regulatory asset or liability, as appropriate. There were no natural gas commodity derivatives settlement gains or losses recognized during the three months ended Sept. 30, 2017 and 2016, respectively.

NSP-Wisconsin had no derivative instruments designated as fair value hedges during the three and nine months ended Sept. 30, 2017March 31, 2018 and 2016.2017. Therefore, no gains or losses from fair value hedges or related hedged transactions were recognized for these periods.

Consideration of Credit Risk and Concentrations — NSP-Wisconsin continuously monitors the creditworthiness of the counterparties to its interest rate derivatives and commodity derivative contracts prior to settlement, and assesses each counterparty’s ability to perform on the transactions set forth in the contracts. Given this assessment, as well as an assessment of the impact of NSP-Wisconsin’s own credit risk when determining the fair value of derivative liabilities, the impact of credit risk was immaterial to the fair value of unsettled commodity derivatives presented in the consolidated balance sheets.

NSP-Wisconsin employs additional credit risk control mechanisms when appropriate, such as letters of credit, parental guarantees, standardized master netting agreements and termination provisions that allow for offsetting of positive and negative exposures. Credit exposure is monitored and, when necessary, the activity with a specific counterparty is limited until credit enhancement is provided.

As of Sept. 30, 2017March 31, 2018 and Dec. 31, 2016,2017, other financial instruments for which the carrying amount did not equal fair value were as follows:

The fair value of NSP-Wisconsin’s long-term debt is estimated based on recent trades and observable spreads from benchmark interest rates for similar securities. The fair value estimates are based on information available to management as of Sept. 30, 2017March 31, 2018 and Dec. 31, 2016,2017, and given the observability of the inputs to these estimates, the fair values presented for long-term debt have been assigned a Level 2.

Other income (expense), net consisted of the following:

Operating results from the regulated electric utility and regulated natural gas utility are each separately and regularly reviewed by NSP-Wisconsin’s chief operating decision maker.  NSP-Wisconsin evaluates performance based on profit or loss generated from the product or service provided.  These segments are managed separately because the revenue streams are dependent upon regulated rate recovery, which is separately determined for each segment.

NSP-Wisconsin has the following reportable segments: regulated electric utility, regulated natural gas utility and all other.

Asset and capital expenditure information is not provided for NSP-Wisconsin’s reportable segments because as an integrated electric and natural gas utility, NSP-Wisconsin operates significant assets that are not dedicated to a specific business segment, and reporting assets and capital expenditures by business segment would require arbitrary and potentially misleading allocations which may not necessarily reflect the assets that would be required for the operation of the business segments on a stand-alone basis.

To report income from operations for regulated electric and regulated natural gas utility segments, the majority of costs are directly assigned to each segment.  However, some costs, such as common depreciation, common operating and maintenance expenses and interest expense are allocated based on cost causation allocators.  A general allocator is used for certain general and administrative expenses, including office supplies, rent, property insurance and general advertising.

In January 2017,2018, contributions of $150.0$150 million were made across four of Xcel Energy’s pension plans, of which $9.0$10.0 million was attributable to NSP-Wisconsin. Xcel Energy does not expect additional pension contributions during 2017.2018.

Changes in accumulated other comprehensive loss, net of tax, for the three and nine months ended Sept. 30,March 31, 2018 and 2017 and 2016 were as follows:

Reclassifications from accumulated other comprehensive loss for the three and nine months ended Sept. 30,March 31, 2018 and 2017 and 2016 were as follows: