ML20244B785

115-kV Capacitor Bank Design Rept

ML20244B785
Person / Time
Site:	Maine Yankee
Issue date:	02/28/1989
From:	Babin M, Baxter F Maine Yankee
To:
Shared Package
ML20244B773	List: ML20244B771 ML20244B785
References
YAEC-1666, NUDOCS 8904190408
Download: ML20244B785 (23)

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115 KV CAPACITOR BANK DESIGN REPORT-t February-1989 Michael J. Babin, renior Electrical Engineer 7244R

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Senior Electrical Engineer Reviewed By:

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Lead Electrical Engineer Yankee Atomic Electric Company Nuclear Services Division 580 Main Street Bolton, Massachusetts 01740 l

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DISCLAIMER OF RESPONSIBILITY 1 (This document.was prepared by Yankee Atomic Electric Company

(" Yankee") . The use of'information contained in this' document-by anyone other than Yankee,; or the Organization for which this document-was prepared under contract', is not authorized and, with respect'to any unauthorized use, neither-Yankee nor its officers, directors, agents, or employees assume any.

obligation,: responsibility, or' liability or make.any warranty or

- representation as to the accuracy or completeness of the material contained

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ABSTRACT Thisireport provides'a detailed description of the 115 kV capacitor

- bank' installed'at Maine Yankee during.the 1988 refueling outage. The, i intentionLisito review the events which brought-.about its. conceptual design 1

-- and'resulted"in'its construction to resolve an outstanding electrical'

.3 - concern. 'The report addresses the design, capabilities,.in-plant changes,- -]

interfaces, functional tests, surveillance requirements, an'd periodic d testing. Thel capacitor . bank' ensures the continued availability of the plant's two off-site' reserve' power sources.

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TABLE OF CONTENTS j Enge

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4 DISCLAIMER OF RESPONSIBILITY...................................... iii ABSTRACT......................................................... iv i LIST OF FIGURES.................................................. vi AC KN 0W LEDG EM ENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vil i I

1.0 INTRODUCTION

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2.0 B A C K G R O UN D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.0 DESIGN BASIS..................................................... 6 I 4.0 INSTALLATION..................................................... 10 5.0 FUNCTIONAL TEST.................................................. 12 6.0 SURVEILLANCE AND PERIODIC TESTING................................ 14

7.0 CONCLUSION

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8.0 REFERENCES

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.1 - One--I.ine' Diagram, Transmission and Utility Interconnections

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in ACKNOWLEDGEMENTS

.The author'and principal' contributors want,to acknowledge the-o

contributions to the success of this project'by.K. Hyyrynen (Yankee Atomic Electric Company). J. Sweeney-(Yankee Atomic; Electric Company), R.lConant-p  :(Central Maine. Power), and J. Begin .(Central Maine Power). Also, the efforts-of the Yankee. Atomic Electric Company Word Processing Center-in preparing this document.are truly appreciated.

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115 KV CAPACITOR BANK DESIGN REPORT  !

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1.0 INTRODUCTION

This report addresses the history and evolution of the 115 kV capacitor bank installation at the Maine Yankee Atomic Power Station. The purpose of the capacitor bank is to restore- the capability of the Section 69 Suroweic 115 kV off-site power line such that either the Surowiec line or the Section 207 Mason 115 kV power line may be relied upon to meet Technical Specification 3.12. The bank is sired at 30.6 MVAR to compensate for reactive VARs over the Section 69 radial feed under worst-case load conditions.

The capacitor bank is installed in the 115 kV Switchyard and includes a circuit breaker to switch the capacitor bank on and of f. Figure 1 is a one-line. diagram showing the location of the capacitor bank on the Central Maine Power (CMP) grid. The controls are self-contained in the Capacitor Bank Control Panel located in the Maine Yankee Main Control Room next to the Electrical Control Board (ECB). The capacitor bank is automatically switched in one step onto the 115 kV Switchyard if Section 207 Mason 115 kV line is out of service and a low voltage condition is detected at the switchyard. The j

automatic control system relieves the responsibility of Maine Yankee operators to energize the capacitor bank. The capacitor bank may be manually switched by Maine Yankee operator action under direction of the CMP System Dispatcher.

The capacitor bank represents an add-on feature to the plant and, thus, has minimal impact on existing systems and structures. The existing electrical systems affected by this installation are the 115 kV Switchyard relay and control equipment, the control circuits for reserve station source circuit breakers 3R and 4R, the de power distribution cabinets 1 and 3, the raceway system, the "RS" annunciator panel, and very minor changes to the front of the ECB.

Upon completion of the installation, functional tests and acceptance tests were performed to verify the adequacy of the design. The functional tests proved that the capacitor bank performed as designed. A program of 7244R L_________-________-__ __ - _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

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" surveillance ~ has be'en' implemented, ; and periodic - testing has been ' planned ' to.

, -ensure continued reliable'~ operation of.the: capacitor bank.-

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, CPIP; has conducted system load studies based on forecasted load growth - 1

.of.the Section 69 line. :The"results indicate that.the capacitor bank will-p-..

4 . provide adequate voltage support for the line for at least the next five years,~with-prospects-for the next te.n' years being-extremely favorable. . Load

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p growth on the line will be evaluated every:two-years.

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On December 14, 1982, the Maine Yankee unit was in the startup mode with both 115 kV Surowiec Line 69 and Mason Line 207 in service and supplying the station auxiliary load of approximately 29 MW. The Section 207 Mason Line was taken out of service at approximately 0800 to refurbish the line. Shortly after the Mason line was isolated, the voltage on the Surowiec line dropped to 109 kV and the 4,160 V bus voltage dropped to 3,750 V. Maine Yankee and CMP j performed corrective action and the Mason line was restored to service and its voltage normalized about 40 minutes after the start of.the event.

The reason for the low voltage occurrence was attributed to increased load growth on the Surowiec line which, in turn, caused greater than expected voltage drop at Maine Yankee. Two recommendations were implemented to correct this situation. CMP reconductored portions of the Surowiec line to improve voltage regulation at the 115 kV Switchyard, and Maine Yankee changed the tap i setting on Station Service Transformer X-14 by 5% to improve voltage levels on the 4.16 kV station auxiliary buses.

Maine Yankee experienced another low voltage incident on July 18, 1986, again while starting up the plant. This time CMP had taken the Section 207 Mason line out of service for routine maintenance, and the station service load was being supplied from the Section 69 Surowiec line. The Shift Operations Supervisor had obtained clearance from the CMP System Dispatcher to start up the first Reactor Coolant Pump (RCP); however, upon starting this RCP, Annunciator Window SS2-2 alarmed to indicate "115 kV Reserve Station Service Low Voltage." Voltage readings at the Maine Yankee ECB indicated that the 115 kV line from Surowiec was between 112-113 kV. The alarm clearef when Section 207 was returned to service a few minutes later. This second incide.at illustrated the need for additional voltage corrective measures because of continued load growth at the Topsham and Bath substations whi:h were located enroute to Maine Yankee.

On December 23, 1987, in a letter to the NRC entitled, " Auxiliary Power Systems Voltage Study," Maine Yankee informed the NRC staff of its decision to I install a capacitor bank in the 115 kV Switchyard to remer "... the low l

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voltage' condition at thit:plantithat'could occur,if the:Surowie'c 115 kV.line,-

Lun' der peak load, conditions,'was being utilized to provide the plant's,-

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• supply, requirements.":' Pursuant to this conclusion, = Maine .

Yankee proposed'a. modification to Technical Specification 3.12,L" Station ~

Service Power," which placed' restrictions on.the.use of'the 115 kV Surowiec

>transmis'alonLline until'the capacitor bank was installed and declared

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3.0 DESIGN BASIS

.3.1 Siming of Capacitor Bank Meine Yankee ' authorized CMP to design and install a capacitor bank in -

the 115 kV Switchyard. CMP sized the capacitor bank to compensate for the worst-case load over the Section 69 radial feeder to achieve near unity power factor correction. As a prerequisite for sizing the capacitor bank, CMP developed a load flow study for Section 69 and included updated loading values on the Surowiec 11ne. Maine Yankee's worst-case loading was obtained from Calculation MYC-430 Revision 1, " Auxiliary Power System Voltage Study," which reflected the results of the CMP load flow study.

CMP commissioned two independent studies to examine the effect of capacitor bank switching on the system. The first study by McGraw-Edison Power Systems consisted of-a " Transient Network Analysis Study" (TNA) to evaluate equipment and operating requirements for transient overvoltage conditions. The TNA study provided recommendations for surge arrester ratings on the network and the requirement for a current limiting reactor to limit current outrush during switchyard single line-to-ground faults. The second study by Power Technologies, Inc. (PTI) examined dynamic simulations of the New England Power Pool network on the loss of the Maine Yankee generator and the subsequent switching of auxiliary load and the capacitor bank. The simulations were intended to establish the voltage profiles at the Maine Yankee, Surowiec, and Mason 345 kV and 115 kV buses. Based on the results of )

the load flow and transient analysis studies, CMP confirmed that the 30.6 MVAR size of the bank was satisfactory and caused no unacceptable perturbations.

I 3.2 Controla_anst Protection l The capacitor bank may be operated automatically or manually.

Automatic control is necessary to obtain fast response for low voltage conditions and to relieve dependence by Maine Yankee on the operators or the CMP System Dispatcher in critical situations. The capacitor bank is automatically connected by breaker KR1 to 115 kV Bus 1 when low voltage is sensed on the 115 kV Bus 1 together with Section 207 Mason being out of service.

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Closure of breaker KR1 will be blocked if Section 69 is out of service.

Automatic or manual closure of breaker KR1 will be blocked by a time delay relay if the capacitor bank has been de-energized for less than five minutes.

l This action prevents transient overvoltages from occurring.

Closing and opening signals for breaker KR1 are normally controlled through undervoltage and overvoltage relays, respectively. The undervoltage l relay scheme incorporates a primary relay set for heavy load transfer and a backup relay set for medium-to-heavy load transfer. The undervoltage relays are set to coordinate with the overvoltage relays to minimize capacitor bank breaker switching under all loading conditions that require voltage support.

The primary undervoltage relay is set low with a short time delay to energize the capacitor bank as quickly as possible and yet to preclude transient conditions. The backup undervoltage relay is set for a higher voltage than the primary undervoltage relay and with a longer time delay. The overvoltage relays remove the capacitor bank from the network during periods of light plant load. The primary overvoltage relay is set high for transient voltages and incorporates a small time delay to filter out short spikes or surges on the network. The backup overvoltage relay is set lower than the primary overvoltage relay with a longer time delay to actuate for longer duration transients or steady-state overvoltages.

The above describes the operating philosophy of the automatic mode of switching the capacitor bank onto and off the network. The capacitor bank breaker KR1 may also be operated manually at the Capacitor Bank Control Panel by placing the auto-manual control transfer switch to the manual position and utilizing the KR1 breaker control switch to close or trip the breaker. This action of manual control through the breaker control switch will usually be performed by the Maine Yankee operator as instructed by the CMP System Dispatcher. The auto-manual control transfer switch must be returned to the auto position by Maine Yankee operator action after any breaker KR1 control switch operation. Tne intention of this action is to restore the control system to its automatic or standby mode in the event of a subsequent low voltage condition.

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The capacito'r bank is provided with primary and backup overcurrent and breaker failure relay protection. Differential bus protection is combined with the existing differential protection for Bus 1 Section 69. Loss of individual capacitor cans is detected with an industry standard protection relay by comparing voltages in each phase independently. This relay responds to the loss of a single capacitor can in a given phase by providing an alarm and supplying a signal to trip the capacitor bank circuit breaker KR1 when the loss of two capacitor cans in a given phase occurs.

3.3 Alarm. Annunciation. and Indication Lights i

The capacitor bank system is monitored by both the Station Computer and the Reserve Source annunciator. Alarm points inputting the Station Computer are:

Capacitor Bank Energized Loss of KR1 Control DC Capacitor Bank Overvoltage Trip Loss of DC to Capacitor Bank Relaying Capacitor Dank Trouble Loss of DC to KR1 Breaker Failure Relaying Capacitor Bank Primary Relaying Trip Lors of AC to Bus 1 or Capacitor Bank CVT Capacitor Bank Backup Relaying Trip KR1 Breaker Failure Trip Loss of KR1 Stored Energy The annunciation points on Annunciator Cabinet RS "115 kV Switchyard Annunciation" are:

Loss of DC Control Power for Relaying Breaker Failure Breaker Relay Trip OCB Air Low Pressure 7244R

1 These annunc'intor inputs are grouped with similar inputs provided for the other 115 kV circuit breakers.

l Indication lights are installed on the front of the Capacitor Bank Control Panel to provide status and alarm functions. Breaker KR1 control switch is monitored by indication lights for breaker position on (red) and off (green), low air pressure (white), and discrepancy (amber). Lockout relays for KR1 breaker failure, primary relaying, and backup relaying utilize a white indication light to display protection system readiness and availability of de power. The Type GPS Automatic Control Device for protection of the capacitor bank utilizes lighted indicators to provide status for power availability, first alarm level detection, and lockout level actuation.

3.4 Elant Interfane The capacitor bank installation had very limited impact on existing plant physical and e'.ectrical systems. The Capacitor Bank Control Panel was designed as a freestanding, self-contained assembly because physical modifications to the existing ECB were impractical. Its location was chosen adjacent to the ECB to minimize cable routing from the capacitor bank in the 115 kV Switchyard to control and protective hardware located in the ECB and Main Control Board (MCB).

The new wiring systems were required to interface with the existing control and protection schemes for the existing 115 kV circuit breakers. The affected circuits included breaker trip and close coils, lockout relays, breaker failure, and bus differential protection. Breakers 3R and 4R control circuits were modified and de power supplies were added from de Buses 1 and 3 as a result of the capacitor bank addition. The close circuits for breakers 3R and 4R were blocked and the trip circuits operated by KR1 breaker failure relaying. DC power was required for KR1 trip /close coils and for capacitor bank primary, backup, and breaker failure relaying.

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4.0 INSTALLATION The installation of the capacitor bank and associated equipment was completed in: December 1988. The work areas included the Main Control Room, the 115 kV Switchyard, the Switchgear Room.'and cable duct networks from the Main Control Room to the 115 kV Switchyard. Control cables and power supply conductors were pulled through underground ducts via manholes and handholes-to provide control and power interconnections between the Main Control Room and the 115 kV Switchyard. Selection of cables and separation criteria were consist r.t with the existing plant design. Separation was maintained between primary and backup protective and control circuitry. In addition, independence via separation was established between 125 V de for KR1 breaker control and.120 V ac for Current Transformer (CT) and coupling Capacitor Voltage Transformer (CVT) circuits. The cable pulling and installation were conducted under the guidelines of " Maine Yankee Wire and Cable Installation / Removal Standards," Maine Yankee STD-ELEC-1, Revision 0.

Integrity of fire barrier penetrations was maintained in adherence to Plant Procedure 19.11, " Fire Barrier Penetration Sealing." Close supervision ensured that work quality met all plant requirements.

The Main Control-Room scope of work included the installation of a new freestanding Capacitor Bank Control Panel, interconnections to the ECB and MCB, and mimic board additions to the front of the ECB 115 kV section.

Capacitor bank primary relaying was supplied by DC Distribution Panel DP/P (from de Bus No. 1), Circuit No. 7, located within the MCB, Section A.

Capacitor bank backup relaying and breaker failure relaying were fed from DC Distribution Panel DP/BU (from de Bus No. 3), Circuit Nos. 23 and 25, respectively, located within the ECB. DC power for breaker KR1 close/ trip circuit No. I was supplied from DC Distribution Panel No. 1, Circuit No. 6.

DC power for breaker KR1 trip circuit No. 2 was supplied f rom DC Distribution Panel No. 3, Circuit No. 4. Both de panels are located in the Switchgear Room. Modifications were also reflected on the 115 kV mimic portion of the ECB. These mimic changes illustrated the addition of the capacitor bank to 1

115 kV Bus 1 and provided indication lights which displayed the status of breaker KR1 and were similar to those on the front of the Capacitor Bank i Control Panel.

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The capacitor bank consists of three 22.13 kV groupings of capaci*nr cans.in series'on each phase. Each grouping is composed of 17 capacitor cans for a total of 51 capacitor cans per phase. Thus, the bank contains a' total i of 153 capacitor cans switched in one step. Each capacitor can is rated at 200 kVAR for a total bank value of 30.6 MVAR and is protected by a current limiting fuse to limit and inter.upt fault current when a capacitor can fails. The fuse is designed to disconnect the faulted unit.before internal arcing can cause tank rupture. As one or more capacitors are disconnected through fuse operations, an unbalanced condition may. result where some of the capacitor cans are operating at an undervoltage level while others are operating at.an overvoltage level. As discussed in Section 3.2, the protection system will alarm for the loss of one capacitor can per phase and trip breaker KR1 to remove the capacitor bank from the system with the loss of two capacitor' cans per phase.

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5.0' FUNCTIONAL TESTS U '

Two stages of functional tests were performed to validate the design and performance of the'capaciter bank system. The first was a verification of-component operation and system design, and the second was an integrated, operational system test. -The former checked the wiring installation and equipment response under a series of specific tests and calibrations. The latter provided an acceptance test by examining the system response to~  :)

i capacitor bank switching.

The first stage of testing was initiated after the wiring and equipment connections were complete. The purposes were to examine the new. wiring configuration and to ensure that unaffected control circuits were not disturbed by the new wiring design. The control and protection relays were calibrated in the Capacitor Bank Control Panel. System wiring was checked and compared to the wiring diagratus. Potential and current circuits were tested.

Control and protective circuits were checked for polarity and proper )

functioning. Breaker KR1'was inspected, tested, and commissioned by trip checking the entire system and by disabling the closing circuit through operation of lockout devices. Affected portions of the control circuits for the' existing switchyard breakers were verified. The integrated trip and close contacts for the plant breakers 3R and 4R were also tested. Trip events were then simulated on breaker KR1 by removing individual capacitor can fuses to test the protection system and by creating an overvoltage condition. Upon completion of this component and subsystem functional test program, the installation was ready for acceptance testing.

The objective of the acceptance test was to provide operating test data which would validate the design basis criteria for sizing the capacitor bank.

Since the plan required maximum plant load available, the test was conducted during the startup following refueling with three Reactor Coolant Pumps running. CMP modeled four system configurations to determine steady-state and transient effects of switching the new capacitor bank. Voltage Watt loading, and VAR loading were simultaneously recorded at the Surowiec, Topsham, Bath, 1 Mason, and Maine Yankee substations under various switching conditions.

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1 The system tbsts were conducted successfully in accordance with the l written test procedure. CMP collected and analyzed the data for each system configuration. Evaluation of the results indicated that the test program had gathered sufficient data for analytical review. The principal conclusion of the review was that the capacitor bank operated as designed. The test results verified the design load flow analysis that CMP had conducted under the peak winter load base case. The worst-case voltage rise determined from the functional test data with the addition of the capacitor bank agreed with the design bases' expected value of 8 kV. CMP has concluded their study of test results and issued a System Functional Test Final Report to describe the method of analysis and document the results.

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n 6.0 SURVEILLANCE AND PERIODIC TESTING To assure continued availability of the capacitor bank, daily surveillance and operational testing are required. Under Procedure 1-200-10-1, Maine Yankee performs daily operating checks on the 115 kV substation'to assist CMP's maintenance of this equipment. This procedure has been modified to include circuit breaker KR1 and the capacitor bank. Visual scans are performed on KR1 hydraulic pressure odometer, and bushing oil level. Capacitor cans are viewed for damage or discoloration of the insulator bushir-= and damage, deformation, or leaks in the capacitor tank. In addition, the individual capacitor fuses are examined to determine a blown fuse or problem with the ejector spring mechanism which holds the fuse link leader under tension. If the surveillance checks reveal abnormal conditions on KR1, Maine Yankee will contact the CMP System Dispatcher to determine the operability of the capacitor bank. Any other equipment problem is referred to CMP for corrective action.

Maine Yankee is. planning to perform routine operational testing by energizing the capacitor bank frequently and monitoring the capacitor bank alarms. The Maine Yankee operator will contact the CMP System Dispatcher to obtain permission to energize the capacitor bank. In the testing mode, the normal prerequisite is that both the K207-1 and KBT breakers be closed. The capacitor bank may be tested on Section 69 only if the plant load on Section 69 is large enough to prevent breaker KR1 from tripping on an overvoltage condition. Normal operation of the capacitor bank such as CMP's use for VAR production into the system may constitute a routine operational test.

Since installation, CMP has frequently utilized the capacitor bank for VAR production during winter peak load periods. The capacitor bank has operated successfully and has provided confidence to the Maine Yankee operators and CMP dispatchers as to its reliability.

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7.0 CONCLUSIOR Maine Yankee's undervoltage incidents of December 1982 and July 1986 illustrated a condition which tended to undermine FSAR and Technical Specification commitments. It was determined that voltage support was needed on Section 69 due to system load growth which had occurred since the plant's inception. The decision was reached that the addition of an automatically switched capacitor bank at the Maine Yankee 115 kV Switchyard would provide adequate voltage support under worst-case plant load conditions. To establish the design basis for the capacitor bank, CMP utilized the combined resources of McGraw-Edison's TNA Study and " Auxiliary Power System Voltage Study,"

MYC-430. CMP performed a load flow analysis on Section 69 to size the capacitor bank and predict the dynamic effects on the network. Their findings were reaffirmed through PTI's 345 kV and 115 kV Voltage Profile Report.

CMP initiated the capacitor bank project for Maine Yankee in concert with Yankee Atomic Electric Company (YAEC). CMP performed the protective and control system design, specified and procured the capacitor bank and appurtenances, and, finally, supervised the switchyard installation and testing. YAEC designed'the plant interface and the interconnecting wiring system and coordinated the overall effort. Upon completion of construction, CMP performed a system acceptance test to confirm their design basis. Review of the results from this system acceptance test were satisfactory and supported the expected voltage rise of 8 kV computed from CMP's load flow study for Section 69. As described in the FSAR Section 8.2.3, the installation and operation of the capacitor bank provides assurance that "...

either of the two 115 kV incoming lines are independently capable of supplying the plant auxiliary power requirements."

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8.0 REFERENCES

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1 A. Engineering Design Change Request (EDCR) No. 88-40, " Capacitor Bank for Plant 115 kV Switchyard Installation."

B. " Transient Network Analyzer Study," McGraw-Edison Power Systems, Study No. FU-880B, dated September 9, 1988.

C. " Auxiliary Power System Voltage Study," MYC-430, Revision 1.

D. "345 and 115 kV Voltage Profiles on Loss of Maine Yankee Generator and Switching of Load and Capacitor Bank," Power Technologies, Inc., dated August 23, 1988.

E. " System Functional Test Report - Final Report," Central Maine Power, dated February 3, 1989.

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