NL-13-1004, Response to Request for Additional Information Concerning Degraded Voltage Compensatory Measures
| ML13172A405 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 06/21/2013 |
| From: | Pierce C Southern Nuclear Operating Co, Southern Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NL-13-1004, TAC MF0412, TAC MF0413 | |
| Download: ML13172A405 (19) | |
Text
Charles R. Pierce Southern Nuclear Regulatory Affairs Director Operating Company, Inc.
40 Inverness Center Parkway Post Office Box 1295 Birmingham, Alabama 35201 Tel 205,992.7872 Fax 205,992.7601 June 21, 2013 SOUIHERN'\\
COMPANY Docket Nos.: 50-321 NL-13-1004 50-366 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Edwin t. Hatch Nuclear Plant Response to Request for Additional Information Concerning Degraded Voltage Compensatory Measures Ladies and Gentlemen:
By letter dated December 21,2012, Southern Nuclear Operating Company (SNC), submitted a license action request (LAR) that would revise the Hatch Nuclear Plant (HNP) Operating Licenses to implement modifications that will eliminate the need for manual actions as part of the HNP degraded grid voltage protection scheme (TAC NOS MF0412 and MF0413).
By letter dated April 22, 2013, the NRC provided SNC with a Request for Additional Information (RAI) for acceptance of the requested licensing action. The information concerns compensatory measures that will remain in place until the proposed modifications are completed at the end of the Unit 1 2020 refueling outage. The enclosure provides the response to the NRC request for additional information.
In summary, due to the actual grid voltage history, grid monitoring, and contingency procedures, the proposed modification schedule is justified.
This letter contains no NRC commitments. If you have any questions, please contact Ken McElroy at (205) 992-7369.
U. S. Nuclear Regulatory Commission NL-13-1004 Page 2 Mr. C. R. Pierce states he is the Regulatory Affairs Director of Southern Nuclear Operating Company, is authorized to execute this oath on behalf of Southern Nuclear Operating Company and, to the best of his knowledge and belief, the facts set forth in this letter are true.
Respectfully submitted,
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C. R. Pierce Regulatory Affairs Director Sworn to and SUbSCriLt, ~e; me thia day Of-=~~~........;;.___-" 2013.
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L CTNOtBTY Public My commission expires: (/- 2~ Zo{?;
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Enclosure:
Response to Request for Additional Information Regarding Degraded Voltage Compensatory Measures cc:
Southern Nuclear Operating Company Mr. S. E. Kuczynski, Chairman, President & CEO Mr. D. G. Bost, Executive Vice President & Chief Nuclear Officer Mr. D. R. Madison, Vice President - Hatch Mr. B. L. Ivey, Vice President - Regulatory Affairs Mr. B. J. Adams, Vice President - Fleet Operations RType: CHA02.004 U. S. Nuclear Regulatory Commission Mr. V. M. McCree, Regional Administrator Mr. R. E. Martin, NRR Senior Project Manager - Hatch Mr. E. D. Morris, Senior Resident Inspector - Hatch State of Georgia Mr. J. H. Turner, Environmental Director Protection Division
Enclosure to NL-13-1004 Response to Request for Additional Information Regarding Degraded Voltage Compensatory Measures Hatch Nuclear Plant Response to Request for Additional Information Concerning Degraded Voltage Compensatory Measures Enclosure Response to Request for Additional Information Regarding Degraded Voltage Compensatory Measures
Enclosure to NL-13-1004 Response to Request for Additional Information Regarding Degraded Voltage Compensatory Measures Electrical Engineering NRC RAI #1 In the event of ESF actuation during degraded voltage conditions (voltage between the alarm setpoint of 3825 volts (V) and trip setpoint of 3280V) provide details on:
- a. Equipment/components that may not have adequate voltage to operate.
- b. Equipment that may trip due to automatic protection such as overload relay actuations.
- c. Equipment that may trip but will require manual action to reset the protective device.
- d. Equipment that may degrade and may not be able to perform its required function.
SNC Response The Hatch Nuclear Plant (HNP) switchyard is normally maintained between 101.3% of 230kV and 104.9% of 230kV. Plant procedural controls, voltage monitoring alarms, and grid operator actions have been established to improve voltage and minimize the potential of a degraded voltage event. The last five years of data provided in the response to RAI #2 demonstrate that these actions are effective and result in adequate voltage for a design basis loss of coolant accident. The measures described in the response to RAI #3 provide assurance that grid voltage is maintained at or above the required minimum expected voltage of 101.3% of 230kV. Class 1 E equipment has adequate voltage to operate and respond properly during anticipated operational occurrences (AOOs), such as a turbine trip or generator load rejection combined with a degraded grid voltage approximately two percent below the 101.3 % established minimum. If the degraded grid alarms are received, an abnormal operation procedure provides specific actions to plant operations during degraded voltage conditions. The alarms are credited in the Technical Specifications. The procedure directs operators to start one diesel generator within 30 minutes and load one safety-related bus on each unit.
Plant operators also initiate a one hour to restore required action statement to initiate a plant shutdown if voltage levels are not restored. These actions will be continued until the permanent plant modifications provided in the Licensing Amendment Req uest (LAR) dated December 21, 2012 are completed.
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to NL-1 004 Response to Request for Additional Information Regarding Degraded Voltage Compensatory Measures An evaluation demonstrates Class 1 E equipment will continue to operate adequately at or above degraded grid setpoint and the 230 kV voltage established at a minimum of 101.3 during both normal operation and (AOO). The evaluation also that safety-related equipment will adequate voltage to operate and respond properly during AOOs, such as a turbine trip or generator load rejection combined with a grid voltage approximately two percent below 101.3 established minimum. The AOO events evaluated represented those posing a potential challenge to the electrical system loading with 4160V supplied by the grid and the plant forced to shut down or scram.
type of event may be similar to experienced by domestic nuclear plants during severe weather events or severe grid disturbances.
The SNC response is on evaluating voltages between alarm setpoint and degraded grid relay setting that automatically divisions one and two safety-related buses from the grid.
a) EquipmenVcomponents that may not adequate voltage to operate.
Background
The emergency bus under voltage alarm has a Technical Specification requirement of 3825V.
alarm setpoint for each was chosen based on the plant aligned in normal operating conditions and not during an accident.
The degraded voltage relay (DVR) is an time CV-7 relay with a IJ.L.."ULJ of 88.34% of 4160V (3675V). The Technical Specification value of 3280V (78.8% of 4160V) represents a calibration point for the inverse time curve.
a.1) Voltage review during accident (LOCA) conditions.
During accident (LOCA) conditions, the existing electrical system at Hatch has voltage at the 4160V when the transmission grid is at the minimum expected voltage of 101.3% of 230kV. As voltage is reduced below 101.3% of 230kV, 600V and 208V loads may experience marginal and/or insufficient unlt",I".""
4000V motors continue to have sufficient voltage during continuous operation and motor at DVR voltage of 88.34% of 4160V.
Enclosure to NL-13-1 004 Response to Request for Additional Information Regarding Degraded Voltage Compensatory Measures An extended degraded voltage event is not expected occur of plant procedural controls, voltage monitoring alarms, and established grid actions to improve voltage and the potential of a degraded voltage event. The compensatory measures in the response to RAI provide assurance that grid voltage is maintained at or the required minimum expected voltage. These actions will continued until the permanent plant modifications provided in the Licensing Amendment Request (LAR) dated December 21,2012 are completed a.2) Voltage review during plant transients (AOOs).
4160V emergency voltages and 1 E loads were evaluated below the setpoint during non-LOCA conditions to the adequacy of plant design to plant conditions. The HNP-2 FSAR chapter 15 identifies transient events which include turbine trip, generator load rejection, etc. The review demonstrates the 230kV grid voltage can drop approximately 1-2% below the established minimum voltage of 101 of 230kV and continue to provide adequate voltage to 1 E loads during plant transients.
b} Equipment that may trip due to automatic protection such as overload relay actuations.
analysis to determine if automatic protection will actuate not been for with 4.16 kV bus at the DVR pickup (88.34% of 60V). The extent of work impacts a broad number of components and is the reason for extensive modifications as described in the dated December 21, 2 to improve plant system voltages.
c) Equipment that may trip but will require manual action to reset the protective device A detailed analysis has not developed to evaluate protective devices that may trip at the DVR pickup. Monitoring systems and procedures are in place to insure 4160V voltages not operate in a sustained degraded voltage condition.
the bus voltage to remain at a degraded voltage pick up of of 4160V),
will have to broken.
barriers include responding to emergency bus monitoring 4160V bus and operator to maintain system voltages.
measures minimize potential for protective actuation or loads subject to durations of under
to NL~13~1004 Response to for Additional Information Regarding Degraded Voltage Compensatory Measures d)
Equipment that may degrade and may not able to perform its required function.
Equipment protection is provided over current protective devices and is not to result in equipment or degradation at the minimum expected voltage of 101.3% 230kV. Acceptable operation is
,,1""\\1,0.\\1<:,1"1 for 4kV motors with bus voltages reduced the DVR pickup voltage.
A evaluation not performed on all protective for components at 600V and 208V with 4160V voltages at the DVR pickup. A general overview of what is expected to occur if 4160V voltages reduce to DVR pickup voltage is motors will have a corresponding increase in full load amps. For some applications, the additional current draw from motors can a 12% to 16%
above the motor's full load amps. The increased current is not expected to actuate over current protection motor thermal protection is typically with a margin of 1 or greater above the motor's full load amps. Monitoring systems of 4160V bus voltages and administrative possibility of operation with sustained degraded SNC previously concluded that raising the undervoltage protection trip setpoint to
% (of 4160V safety buses) would result in little margin between trip setpoint at which the buses would separated from offsite power, and the minimum bus voltage that could occur if offsite voltage declined to the lower end its expected duration) on the mi five years.
(101.3 nimum observed of 230 kV).
details (magnitude and at the 230 kV level during the last SNC Response real time voltage for the Hatch 230 kV bus from January 1,2008 to April 2013 (past five years) has been retrieved for ten minute available transmission operation This resulted in 277,601 valid ten minute points. In all cases, the voltage the grid voltage alarm setting requiring plant shutdown (approximately 95% of 230kV during normal operation). The actual 230kV was within the desired 101.3 ~104.9%
230kV range for the vast majority of the time. Two points were less than 101.3%
of 230kV.
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Enclosure to NL-13-1 004 Response to Request for Additional Information Regarding Degraded Voltage Compensatory Measures There were two instances where the recorded 10 minute voltage was below the 101.3 % of 230kV level. The following table provides a summary of these voltage data points < 101.3 %.
DateTime Voltage 230kV voltage 03/16/2008 227.5362 98.93%
01 :40:00 02/18/2013 232.5620 101.11%
04:40:00 NRC RAI #3 Identify the compensatory actions, onsite and offsite, that will be relied upon to support the proper operation of equipment identified in Question 1 above.
SNC Response There are two primary processes used to ensure that voltages for safe shutdown remain above the load requirements.
A. Voltage Projections The first process involves voltage projections for the HNP 230 kV switchyard voltage given various contingencies. The projections evaluate future system contingencies to ensure that the system is designed so that the HNP 230 kV switchyard voltage will not be less than the MEV of 101.3% of 230 kV. This projection process has two basic features:
- 1. Annually, prior to the summer peak loading conditions, Southern Company Transmission Planning studies steady state load flow cases (i.e. system configurations) to verify the MEV can be maintained at HNP for the current year and the subsequent 5-6 years.
To provide a conservative analysis, the following assumptions are included for each case:
- The Southern Control Area is at summer peak loading.
- Generation is dispatched as expected for each load condition.
Local area generation that could significantly support the HNP 230 kV bus is modeled off-line.
- The full expected load is supplied to the Florida Interchange.
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Enclosure to NL-13-1004 Response to Request for Additional Information Regarding Degraded Voltage Compensatory.V *..""", *.J.
study cases include, but are not limited the following system configurations:
- One unit in a LOCA, and other unit tripped Shutdown).
- One unit in a LOCA, and a transmission line out of service.
- One unit in a LOCA, and the 230/500 kV autobank out of service.
- 2. The second feature of this projection process is related to system operations. Grid operators use a time contingency analysis (RTCA) tool based on the state estimator solution using input of the current system loading conditions reflecting actual generation and transmission line operational Grid are by periodic (every 10 minutes) contingency analysis if next contingency (N-1) condition result in a post-contingency 230 kV grid less than the minimum required.
- i.
on the RTCA results, grid operators will immediately all necessary steps to eliminate any unacceptable N-1 condition. If such correction cannot be within a minutes, the operators will notify HNP of condition the time to eliminate contingency.
ii. Any planned transmission or generation system is evaluated prior to the outage to ensure that an unacceptable N-1 condition would not be created by outage.
voltage projection in Transmission and Operations are the primary means to ensure that HNP not experience voltage conditions below the by alerting them to a potentially inadequate voltage condition before it can occur.
stated in A, the predictive tools are intended to avoid operation below the MEV. In addition to those the actual real time voltage is monitored to ensure the tools are providing the intended results. This process involves continuous monitoring of state of Southern Company system and, in particular, the voltage at HNP 230 kV switchyard. The grid have continuous voltage monitoring and alarm features for the HNP kV bus voltage. Plant operators continuous monitoring and alarm features to them jf voltage condjtions are actually degrading.
- 1. The 230 kV switchyard voltage at HNP normally and 104.5%.
operators will notify HNP if the "'"<,YO.,,.,
101.3 % of kV even though the local plant may not experiencing inadequate conditions.
normal on-line operating conditions, the 101 notification level is approximately above level required for operating 1 E loads.
off-line conditions including ADOs (Le. all on the the 101 notification level from 1 to 2.5%
the level required for the operating Class 1 E loads. This provides early detection of any degrading grid conditions.
E1-6
to Request for Additional Information Voltage Measures procedures coordinating operation of bulk power of Southern Company establish the nuclear plants as a high priority for maintaining each nuclear plant's minimum required voltage. If the voltage at HNP's 230 kV switchyard were to the following actions would typically be by grid (II Notify the plant control room.
(II Capacitor banks at the plant or elsewhere on the grid are switched on as (II Shunt reactors are switched off as necessary.
(II Additional resources are placed in '"''fir*...,
(II Transmission elements are switched in or out of service as (II System is reduced if no other remedy is available.
In addition, plant operators monitor the voltages at the 230kV switchyard and 4160V Class 1 E Each of Class 1 E (three/unit) a Degraded Grid Voltage Alarm to a sustained Class 1 E bus under voltage condition.
HNP has an abnormal operation procedure to provide specific to plant operations. Plant procedure 34AB-S 11-00 1-0, Operation with Degraded System Voltage, addresses specific actions during degraded voltage conditions.
actions are delineated for conditions where:
(II The System is one contingency from a degraded grid condition, or (II The Transmission System is in a degraded condition (below 101.3%
of 230 kV), or (II The 4160V degraded voltage occurs on any of the three 1 E 4160V in each unit.
e Plant start one Diesel on each unit for a degraded grid lasting longer than 30 minutes.
(II Plant operators initiate a one hour to restore required action statement to initiate a shutdown if levels are not restored.
indicates "'....,'w,.,"',
the plan by 3 and in June 2014. Explain the delay in planning and modification
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to NL-13-1004 to Request for Additional Information Degraded Voltage Measures clarification, the modification design did not commence in May of 2012.
Modification design is scheduled to commence in July 201 The planning phase was initiated in May 2012. Due to the complexity of this proper planning is to success.
planning efforts will conclude in June 2013, allowing to commence design activities current schedule, Up Auxiliary Transformer (SAT) specifications are currently developed and will completed by December Upon specification completion, SAT bids will be issued in early 4 to approved vendors. This dictates a Purchase Order of approximately October 2014, which is dependent on vender and satisfactory compliance with said specification.
is expected to be in 2015 new will in January 2016.
why the modification work unit one cannot in February 2016, during 1
refueling outage, and completed 1
outage.
This modification has significant on the existing electrical infrastructure.
is increased short circuit capability. Due to this modifications to the existing and switchgear to allow for a current.
are a to nf<:>1tlt'\\n and are currently 1R27 thereby SAT 1"0rno,"O, as an option for 6 Unit 1 outage.
- a. The titles and procedure numbers of the current control onsite and manual actions to degraded voltage conditions for
- c. A list of the manual actions in sequence OR provide a copy of the current of the relevant procedure(s).
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Enclosure to NL-13-1 004 Response to Request for Additional Information Regarding Degraded Voltage Compensatory Measures SNC Response
- a. Titles and procedures The titles and procedure numbers requested are provided below:
Power Coordination Center (PCG) Procedures BPO Nuclear Plant Procedure NUC-001-Nuclear Plant Interface Coordination for Southern Nuclear Operating Company, Version 2 NUC-001 - Nuclear Plant Interface Coordination for Southern Nuclear Operating Company, Version 2.
Georgia Control Center (GCG)
BPO Nuclear Plant Procedures SO-GL-309 - Capacitor Control Philosophy SO-GL-309 - Voltage Control Philosophy BP Voltage Schedules in Southern Balancing Area (SBA)
HNP 34AB-S11-001 Operation with Degraded System Voltage 34AR-652-122 4160V BUS 1 E VOLTAGE LOW 34AR-652-122 4160V BUS 2E VOLTAGE LOW 34AR-652-222 4160V BUS 1 F VOL T AG E LOW 34AR-652-222 4160V BUS 2F VOLTAGE LOW 34AR-652-322 4160V BUS 1G VOLTAGE LOW 34AR-652-322 4160V BUS 2G VOLTAGE LOW 34S0-N40-001 MAIN GENERATOR OPERATION 34S0-N40-001 MAIN GENERATOR OPERATION 34AB-P41-001 LOSS OF PLANT SERVICE WATER 34AB-P41-001 LOSS OF PLANT SERVICE WATER 34AB-R22-003 STATION BLACKOUT 34AB-R22-003 STATION BLACKOUT 34AB-R22-002 LOSS OF 4160V EMERGENCY BUS 34AB-R22-002 LOSS OF 4160V EMERGENCY BUS 34GO-OPS-013 NORMAL PLANT SHUTDOWN 34GO-OPS-013 NORMAL PLANT SHUTDOWN
- b. Entry Conditions for the procedures For the off-site transmission operators, the PCC and GCC procedures are used at all times by the PCC and GCC to maintain voltage of the transmission system in the most efficient way. The PCC is located in Birmingham, AI and the GCC is located in Atlanta, Ga. Both facilities monitor the voltage in the Plant Hatch switchyard. In real-time, Emergency Management System (EMS) and Supervisory Control and Data Acquisition (SCADA) Alarm points are set for minimum and maximum voltage levels at the Hatch switchyard and alert the operator when conditions have caused the voltage to go outside the acceptable range. In addition, the EMS Real Time Contingency Analysis (RTCA) tool (Power E1-9
to NL-1 004 Response to Request for Additional Information Regarding Degraded Voltage Compensatory Measures Network Analysis-PNA) and the Offline Power Network (OPNA) runs approximately every 10 minutes and would alert operator to postulated conditions that would, following an identified next contingency, prompt further action as defined in the procedures. Voltage violation reporting limits are within these two tools for minimum and maximum acceptable voltage levels at the Hatch switchyard and the if conditions could cause the voltage to go outside the acceptable range.
- c. Manual Actions With regard to manual actions, during real-time operation, a condition not included in the contingency analysis (most probably due to an extreme, multi-contingency event) results in a Hatch voltage excursion outside the acceptable voltage range, the PCC GCC operators will receive a Priority 1 EMS SCADA alarm identifying the Hatch bus voltage violation.
During the execution of the RTCA and OPNA tools, PCC GCC will notification if a postulated contingency requires a response to prevent a degraded grid condition. An alarm is received the next contingency by both the and and/or the OPNA tool reports a bus voltage violation in the voltage violation summary.
both real and postulated degraded conditions notifications just following manual actions would occur:
1.
PCC and GCC operators confer on notifications received and, if real, the GCC Operator notifies Hatch plant operators of the (real/postulated) degraded grid condition.
- 2.
The Operator accesses status of reactors, capacitors, generation, and other facilities in area.
The GCC operator determines the most effective course of action to take to mitigate the next contingency alarm, which include any or all of following:
- a. Turn off (if on) 150 MVAR 500kV reactor at Hatch on the Duval line.
Turn on (if off) 117 MVAR shunt at Vidalia.
- h. Turn on (if off) 108MVAR 230kV shunt capacitor at North Tifton.
- i. Turn on other shunt capacitors in area that are off.
- j. Run CTs at McManus.
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Enclosure Response to."u..."",;:" for Additional Information Regarding Compensatory Measures k.Run generation in the area that is available to come online.
I.
any out of service elements to service.
- m. "",",'d,n.'"
amount of power provided to the Florida nTl"n!:\\('1"
- n.
load in the area.
Upon notification a potential for degraded grid operations or through of Main Control annunciation indicating degraded grid conditions, plant operators would abnormal operating procedure. HNP an abnormal procedure to provide specific actions to plant 34AB-S 11-001-0, Operation with Degraded specific actions during degraded are delineated for conditions where:
.....\\I'~folm is one contingency (or event) a or
_"TOlrn is in a degraded grid condition (below 1 01 of 230 kV), or
- The 4160V voltage alarm occurs on any of the three 1E 4160V buses in unit.
- Plant operators manually start one Diesel generator on each unit for a degraded longer than 30 minutes.
- Plant operators initiate a one hour to restore required action statement to initiate a plant shutdown if voltage levels are not restored.
NRC RAI #1 For each action listed in RAI number 6 above, identify the cue that alerts the operator that is e.g., annunciator, alarm, alarm type, condition (identify how condition is monitored), step sequence in the relevant procedure, supervisory System Operator notification, or other.
SNC Response voltage measurement used to and GCC transmission system text (Priority 1) Alarm from the EMS SCADA For a degraded from a postulated contingency condition by RTCA and OPNA, Alarm processing application will issue to the PCC Operator an audible text "New Contingency Violations" Priority 1 alarm for RTCA violations which then directs the PCC and GCC operator to the EMS RTCA Contingency Violation Summary (display 6.40). OPNA only provides a visual cue (Le. no audible) to GCC operators in the "Voltage Violation" report which the operator is required to monitor at least every 20 minutes and actively a
assessment pop-up window.
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Enclosure to Nl-13-1 004 Response to Request for Additional Information Regarding Degraded Voltage Compensatory Measures following provides Room alarms:
34AR-652-1 1 - 4160V BUS 1 E VOLTAGE lOW 34AR-652-1 60V BUS 2E VOLTAGE lOW 34AR-652-222 60V BUS 1 F VOLTAGE lOW 34AR-652-222-2 41 BUS VOLTAGE lOW 34AR-652-322-1 4160V BUS 1G VOLTAGE lOW 34AR-652-322-2 60V 2G VOLTAGE lOW These procedures direct operators to monitor emergency bus voltage conditions and to enter appropriate station operating procedures to mitigate the low voltage condition.
Describe the most likely of events that would a
of Operator to notify HNP of a degraded voltage condition. What corrective and preventive actions were when a similar failure on March 14, 1993?
In 1993 both the PCC utilized a previous version of Since 1993, the current system has alarming capabilities and expanded contingency result displays with RTCA. In addition, the OPNA tool has been added since that time which provides an additional mechanism to detect a degraded voltage condition.
Supplementing the provided by the current and addition of OPNA over what in 1993, both the for the PCC and GCC operators responsible for monitoring the Hatch now include giving annual training on (including communication protocol and expectations) defined in the and the NUC-001 identified in question 6.
As described in SNC Simulator Guide l T-SG-50425, the of the plant operating crew will be to a decrease in the voltage on switchyard voltage and enter the abnormal procedure for degrading voltage. The crew will closely monitor and maintain generator within limitations of the system operation the voltage continues to on 230/500 kV and 4160V crew will address the Technical Specifications for low voltage (3850V) on 4160V buses.
crew will notify GCC GCC to voltage. If cannot maintained above normal minimum (3850V) or when to less than 3825V the crew will initiate a one hour required action 30 minutes transfer the 60V bus on each unit to the Generators (EDG). System will continue to decrease until Emergency 4160V lockout the normal power supplies to allow EDGs to supply the buses.
E1-12
Enclosure to NL-1 1004 Response to Request Additional Information Regarding Degraded Compensatory Measures NRC RAI #9 Discuss time required to perform manual actions (on-site and off-site), listed in RAI number 6 above, versus time available before equipment occurs.
SNC Response Voltage for the 4160V busses corresponding to alarm setpoint is not expected to result in equipment The following provides requested information regarding time frames to perform the manual actions for off-site transmission operators:
- The reactors and capacitors are set to operate automatically if the voltage outside the points.
are also manually to maintain at levels.
turned off and capacitors turned on in a matter of
- CTs at McManus can on-line in ten minutes.
- It could one to several hours to return transmission elements to depending on the reason for them being out of interface load can to an hour and,
- Reducing load in accomplished within minutes in an emergency situation.
Describe any controls or degraded voltage conditions.
needed (on-site and off-site) to respond to SNC Response discussed in questions 6 the is needed by the PCC and operators to provide the information that a degraded condition may occur or is occurring and the EMS is needed to manually take corrective action Reactors capacitors are set to automatic not manual action to Corrective action can taken by in field without EMS. Corrective can be taken by the Hatch control room to operate the reactors and capacitors. Substation controls would to be working to corrective !:.If'1'lfIrIC NRC RAI #11 Is the simulator used for training on degraded voltage Has simulator used to validate the operators' ability to respond to degraded voltage conditions? How do operators receive training on voltage E1-13
Enclosure to NL-13-1004 Response to Request for Additional Information Regarding Degraded Voltage Compensatory Measures SNC Response There currently is no simulator environment for the transmission operator (PCC and GCC) but the study environment can be used to simulate the effectiveness of sequential responses to degraded voltage events.
Plant operators routinely train in the simulator on degraded grid conditions. This training is part of the initial licensed operator and the licensed operator requalification training programs. In the licensed operator requalification training program, degraded grid conditions are incorporated into simulator scenarios and are trained on within the two year requalification cycle.
NRC RAI #12 Has an operating experience (OE) review been done to provide insights regarding the effectiveness of the current manual actions in responding to degraded voltage conditions, including plant-specific condition reports, Licensee Event Reports, INPO reports, and other relevant sources? Provide a summary of any plant-specific operator errors or other relevant OE involving degraded voltage conditions, including corrective and preventive actions taken. The event of March 14, 1993 need not be summarized.
SNC Response An industry operating experience (OE) search has been performed using the key words "degraded grid" and "loss of offsite power". The degraded grid protection scheme at HNP is unique compared to the rest of the industry. The manual system used at HNP is designed to maintain offsite power as the preferred source during dynamic grid transients. The industry systems rely on their DVRs to initiate a disconnect from their grid. Given the differences in the HNP scheme, assessing how HNP would have responded is not easily established.
The degraded grid OE search primarily discussed cases where discrepancies with the degraded grid design or analysis were discovered. A typical example is where calculation errors resulted in a component having inadequate voltage at the degraded grid relay setpoint. Another example is where the relay was actuated during calibration or surveillance activities. Industry experience indicates that degraded grid conditions are extremely rare events. Loss of offsite power events are much more common. The causes of inadequate voltage at Class 1 E loads are most often due to events at the plant itself due to inadequate design of plant electrical systems under grid minimum expected voltage conditions.
Examples include:
- Improper transformer tap settings or failure of Load Tap Changes (LTCs).
- Overloading of transformers due to bus transfers.
Motor Control Center controls and other low voltage systems not designed for the expected grid voltage conditions.
E1 -14
Enclosure to Nl-13-1 004 Response to Request for Additional Information Regarding Degraded Voltage Compensatory Measures lIP Inadequate design for transient voltage conditions such as fault clearing and motor starting.
lIP Errors in electrical protective device settings such as DVRs.
The loss of offsite power search primarily consisted of cases where electrical busses were not degraded but were completely deenergized. In these cases the response by the loss of offsite power relays at HNP is expected to be similar.
There is no history of adverse effects at HNP due to a sustained degraded grid event occurring at HNP. Consequently, there are no relevant operator errors to have occurred.
An INPQ review in 2006 identified the need to enhance abnormal operating procedure 34AB-S11-001-0 with more specific guidance. Specifically, the manual start and tie of an emergency diesel generator within 30 minutes of a degraded grid was added. Also, INPO previously issued Significant Operating Event Report 99-1, loss of Grid. AIlINPO recommendations contained in the SOER have been completed.
Because of the offsite system monitoring and contingency analysis, a sustained degraded grid does not represent the most probable event. A dynamic voltage transient lasting less than 10 minutes is more likely. As a result, the degraded voltage protection at HNP provides adequate protection for this type of event.
The current manual method allows system operators to quickly restore a grid transient to avoid an unnecessary isolation transient to both units, further degradation of the offsite power supply to the plant, and adverse impacts to neighboring utilities when the offsite power is undergoing a temporary voltage excursion and is not in actual jeopardy.
NRC RAI #13 The licensee stated in its letter of June 17, 2011, that the use of manual actions to respond to degraded voltage conditions provides the flexibility to avoid unnecessary automatic disconnect from the preferred offsite power source. Is there any empirical evidence in the last five to seven years of operating experience that any unnecessary automatic disconnects have been avoided?
SNC Response There is no empirical evidence of a dynamic voltage transient in the last five years that would have caused an unnecessary disconnect from the offsite power supply. As stated in the SI\\lC response to RAI #2, the real time bus voltage for the Hatch 230 kV bus from January 1, 2008 to April 25, 2013 (past five years) has been retrieved for each ten minute interval of available transmission operation data. In all cases, the 4160V voltage exceeded the degraded grid voltage alarm setting. As a result of the voltage projections and continuous monitoring described in the SNC response to RAI #2, the grid has been maintained within acceptable values.
E1-15
Enclosure to NL-13-1004 Response to Request for Additional Information Regarding Degraded Voltage Compensatory NRC RAI #14 If both plants are operational, the System Operator cannot restore voltage to normal levels, do the units respond independently to degraded voltage conditions, or is coordination between units required? If coordination is required, how this is done.
No coordination units is required. The units respond independently. The operating crews for each unit would respond as directed by 34AB-S11-001-0 for operating unit.
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