AEP-NRC-2015-99, Response to Request for Additional Information Re License Amendment Request to Revise Technical Specification Section 3.8.1, AC Sources - Operating, Surveillance Requirements 3.8.1.10, 3.8.1.11 and 3.8.1.15
ML15308A094 | |
Person / Time | |
---|---|
Site: | Cook ![]() |
Issue date: | 10/30/2015 |
From: | Gebbie J Indiana Michigan Power Co |
To: | Document Control Desk, Office of Nuclear Reactor Regulation |
References | |
AEP-NRC-2015-99 | |
Download: ML15308A094 (30) | |
Text
IND*IA NA Indiana Michigan Power MICHIGAN Cook Nuclear Plant 1POWER 0ne Conk Place Bridgman, MI 49106 A unit ofAmerican Electric Power IndianaMichiganPower.com October 30, 2015 AEP-NRC-201 5-99 10 CFR 50.90 Docket Nos. 50-315 50-316 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Donald C. Cook Nuclear Plant Units 1 and 2 Response to a Request for Additional Information Regarding the License Amendment Request to Revise Technical Specification Section 3.8.1, "AC Sources - Operating," Surveillance Requirements 3.8.1.10, 3.8.1.11, and 3.8.1.15
References:
- 1. Letter from J. P. Gebbie, Indiana Michigan Power Company (I&M), to U. S. Nuclear Regulatory Commission (NRC), "Donald C. Cook Nuclear Plant Unit 1 and Unit 2 Docket Nos. 50-315 and 50-316, License Amendment Request Regarding Technical Specification Section 3.8.1, "AC Sources - Operating," Surveillance Requirements 3.8.1.10, 3.8.1.11, and 3.8.1.15,"
AEP-NRC-2014-70, dated December 17, 2014, Agencywide Documents Access and Management System (ADAMS) Accession No. ML14356A022.
- 2. Letter from A. W. Dietrich, NRC, to L. J. Weber, l&M, "Donald C. Cook Nuclear Plant, Units 1 and 2 - Request for Additional Information Regarding License Amendment Request to Revise Technical Specification 3.8.1 (TAC Nos. MF5436 and MF5437)," dated June 15, 2015, ADAMS Accession No. ML15163A167.
- 3. Letter from J. P. Gebbie, l&M, to NRC, "Donald C. Cook Nuclear Plant Units I and 2 Response to a Request for* Additional Information Regarding the License Amendment Request to Revise Technical Specification Section 3.8.1, "AC Sources - Operating," Surveillance Requirements 3.8.1.10, 3.8.1.11, and 3.8.1.15," AEP-NRC-2015-60, dated July 9, 2015, ADAMS Accession No. ML15195A434.
- 4. Letter from A. W. Dietrich, NRC, to L. J. Weber, I&M, "Donald C. Cook Nuclear Plant, Units I and 2 - Second Request for Additional Information Regarding License Amendment Request to Revise Technical Specification 3.8.1 (TAC Nos. MF5436 and MF5437)," dated October 5, 2015, ADAMS Accession No. ML15267A683.
This letter provides Indiana Michigan Power Company's (I&M), the licensee for Donald C. Cook Nuclear Plant Unit I and Unit 2, response to a Request for Additional Information (RAI) by
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 2 the U. S. Nuclear Regulatory Commission (NRC) regarding a License Amendment Request to modify the notes to Technical Specification (TS) 3.8.1i, "AC Sources -Operating."
By Reference 1, l&M submitted a request to amend the TS to Facility Operating Licenses DPR-58 and DPR-74. l&M proposes to change TS 3.8.1 to allow surveillance testing of the onsite standby emergency diesel generators during modes in which it is currently restricted. By Reference 2, the NRC transmitted RAIs regarding the proposed amendment. Reference 3 provided I&M's response to Reference 2. By Reference 4, the NRC transmitted RAIs regarding the proposed amendment.
This letter provides I&M's response to Reference 4. Enclosure 1 to this letter provides an affirmation statement pertaining to the information contained herein. Enclosure 2 provides l&M's response to the NRC's RAI contained in Reference 4.
Copies of this letter and its enclosures are being transmitted to the Michigan Public Service Commission and Michigan Department of Environmental Quality, in accordance with the requirements of 10 CFR 50.91.
There are no new regulatory commitments made in this letter. Should you have any questions, please contact Mr. Michael K. Scarpello, Regulatory Affairs Manager, at (269) 466-2649.
Sincerely, Joel P. Gebbie Site Vice President JMT/ams
Enclosures:
- 1. Affirmation
- 2. Response to a Request for Additional Information Regarding the License Amendment Request to Revise Technical Specification Section 3.8.1, "AC Sources - Operating,"
Surveillance Requirements 3.8.1.10, 3.8.1.11, and 3.8.1.15 c: A. W. Dietrich, NRC Washington, D.C.
J. T. King - MPSC MDEQ - RMD/RPS NRC Resident Inspector C. D. Pederson, NRC Region Ill A. J. Williamson, AEP Ft. Wayne, w/o enclosures
Enclosure 1Ito AEP-NRC-2015-99 AFFIRMATION I, Joel P. Gebbie, being duly sworn, state that I am Site Vice President of Indiana Michigan Power (I&M), that I am authorized to sign and file this request with the U. S. Nuclear Regulatory Commission on behalf of I&M, and that the statements made and the matters set forth herein pertaining to I&M are true and correct to the best of my knowledge, information, and belief.
Indiana Michigan Power Joel P. Gebbie Site Vice President SWORN TO AND SUBSCRIBED BEFORE ME THSO1*DAY OF Oe.[t)*=" 2015 Notary Public My Commission Expires 10 - /6 -*O/ "*
,., *ANNE M. PALMA
. . ,Notary Public, State of Michigan
- County of Berrien
.; "*' My Commission Expires 10- *6-2017 Acting in the Countyof ia/
Enclosure 2 to AEP-NRC-2015-99 Response to a Request for Additional Information Regarding the License Amendment Request to Revise Technical Specification Section 3.8.1, "AC Sources - Operating,"
Surveillance Requirements 3.8.1.10, 3.8.1.11, and 3.8.1.15 By letter dated December 17, 2014 (Agencywide Documents Access Management System (ADAMS) Accession No. ML14356A022), as supplemented by letter dated July 9, 2015 (ADAMS Accession No. ML15195A434), Indiana Michigan Power Company (I&M), the licensee, requested an amendment to Renewed Facility Operating Licenses DPR-58 and DPR-74 for Donald C. Cook Nuclear Plant (CNP), Units 1 and 2. The proposed amendments would revise the Technical Specifications (TS) 3.8.1, "AC Sources - Operating," to allow testing of the onsite standby emergency diesel generators (EDGs) during modes in which it is currently prohibited.
Specifically, the proposed changes would remove the mode restrictions in the notes of the Surveillance Requirements 3.8.1.10 (EDG single largest load rejection test), 3.8.1.11 (EDG full load rejection test), and 3.8.1.15 (EDG endurance run).
The U.S. Nuclear Regulatory Commission (NRC) Electrical Engineering Branch (EEEB) staff has reviewed the subject submittal and supplement, and has determined that additional information is needed to complete the review, as described in the Second Request for Additional Information (RAI), below. The draft RAI was sent to l&M via electronic mail on September 23, 2015. The NRC staff clarified the draft RAI in a conference call conducted on October 1, 2015. By letter dated October 5, 2015 (ADAMS Accession No. ML15267A683), the NRC transmitted an RAI regarding the December 17, 2014 license amendment request. On October 15, 2015, the NRC conducted a public meeting to discuss I&M's proposed response to the RAI. This enclosure provides I&M's response to the RAl.
EEEB-RAI-5 In response to EEEB-RAI-2c, the licensee addressed the emergency diesel generator (EDG) operation during a loss of offsite power (LOOP) with a loss-of-coolant accident (LOCA) while the EDG is operatingin parallel with the offsite power. The licensee stated:
"When the EDG [emergency diesel generator]is in test mode, the SI [safety injection] or load shed signal will automatically trip the 4 kV [kilovolts] Output Breaker during EDG test mode (these signals are blocked after two seconds, and therefore SI signal is prevented from reopening the breakerif a load shed occurs first, trips the breaker, then the breaker closes to load the EDG and a SI signal is initiatedsome time later)."
- a. Please discuss the events or signals that initiate the load shed signal. If an SI signal also initiates a load shed signal, please clarify the sentence in parentheses in the above statement. Also, please explain the EDG operation during degraded grid voltage conditions while the EDG is being tested in parallel with the offsite power source in Mode 1 or2.
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 2
- b. Please discuss the EDG operation, including timing of vital load loads sequencing, during a LOOP concurrent with LOCA scenario, while the EDG is being tested in parallel with the offsite power source in Mode I or 2. Also, please clarify whether manual action to reset the lockout relay is allowed during a LOOP concurrent with LOCA event in the CNP licensing design basis accident analysis.
- c. Please provide the timeline of tripping and closing of the EDG breaker, and discuss the timing of vital load sequencing for the following scenarios, with the EDG initially in test mode and paralleledwith the offsite source:
(1) LOOP followed by LOCA (2) LOCA followed by LOOP Response to EEEB-RAI-5a See Figure 1 below for a simplified sketch showing the arrangement of EDG, relays and reserve feed to the 4 kilovolt (kV) buses. The sketch reflects drawing OP-1-12001 (Attachment #1) and relay diagram RSC1-4278 (Attachment #2) (The loss of voltage (LOV) relays are 1-27-1-T11A, 27-2-TI1IA, 27-3-TI1IA and the Degraded Grid Relays (DGR) are 1-27-TI1IA-I, 1-27-TI11A-2, 1-27-Ti11A-3).
relays
@RCP Bus 1A Li BOP
--*motors Offsite Power*4k Ti breakers To 600V 1IE Bus 11IB Fi~qure I Simplified One Line Sketch for EDG Connection to Offsite Power Unit I Train B shown, (typical)
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 3 The loss of offsite power (LOOP) signal is generated by the LOV relays on the 4kV safety buses, when the voltage on a bus is less than approximately 78 percent (%) nominal voltage for a duration of two seconds. Each 4kV safety bus is equipped with a set of three undervoltage relays configured in a 2/3 logic. The function of these relays is to generate the LOOP signal upon recognition of the loss of voltage on the safety bus. The LOOP signal actuates a series of auxiliary relays (master load shedding relays) that initiate load shedding and provide a permissive for the closing of the EDG output breakers. The LOOP and load shed is bus specific. The LOOP event will separate the EDG from the safety bus by tripping the output breaker. The EDG output breaker will close after the load shed and emergency loads will be sequenced.
The Safety Iniection (SI) siginal does not initiate load shed: The EDG will start automatically, but will not connect to the 4kV safety buses should an SI signal be generated.
The SI or load shed signal will automatically trip the 4kV Output Breaker during EDG test mode.
When in test mode, the signal for tripping the EDG output breaker is blocked after two seconds to prevent reopeningi the output breaker if the load shed has already occurred and EDG was reconnected to~the buses.
The DGRs do not directly generate a load shed signal. The DGRs are located on the 4kV safety buses T11A (or"T21A for U2) orT.11D (or T21D for U2). The main function of the DGRs is to protect the large motors from a sustained lower voltage condition; therefore, only 4kV safety buses TIlIA and TI11D are provided with this undervoltage protection. The 4kV safety buses, TI1IB and Ti10C, do not feed motor loads; therefOre, the DGRs are not provided on these buses. The DGRs actuate when the voltage on these buses falls below approximately 94% of nominal bus voltage for a duration of two minutes (no concurrent accident signal) or nine seconds (concurrent SI or Steam Generator Lo-Lo signal). The 4kV safety buses (TI1IA, TI1ID, T21A and T21 D) are each equipped with a set of three degraded voltage relays configured in a 2/3 logic. If a degraded voltage condition is detected by this logic, the degraded voltage relays actuate auxiliary relays that in turn initiate tripping of the normal supply circuit breakers to the 4kV safety buses. The resulting loss of voltage to the 4kV safety buses will then be detected by the LOV relays and a LOOP signal and corresponding automatic actions will be generated as described above for the LOV.
Response to EEEB-RAI-5b LOOP concurrent with a LOCA The SI signal will trip the output breaker of the EDG which separates the EDG from the 4kV bus.
The EDG will continue to run unloaded in standby mode. The LOOP event will result in LOV relays actuating after a two-second time delay once the 4kV bus voltage drops below 78% to allow for motor voltage decay. The actuation of LOV relays initiates load shedding and tripping of the main supply breakers to balance of plant (BOP) 4kV buses and Tie breakers to the safety "T" buses. The time delay of two seconds on the LOV relays allows for motor voltage decay and to override any momentary grid transient before the EDG is connected to the bus. After a two-second time delay, the EDG output breakers will close automatically and emergency motors will be sequenced on to the EDG as follows:
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 4 Start timing of Vital loads for LOCA concurrent with LOOP (Seconds)
(NOTE: Time is after the EDG outout breaker closes)
LOOP with Equipment LOOP LOOP with Safety Containment Injection Spray Centrifugal Charging Pump N.A.S. 3.16 3.16 SI Pump N.A.S. 6.65 6.65 Residual Heat Removal (RHR) NAS 05 05 Pump NAS 05 05 Component Cooling Water 31 47 47 (CCW) Pump Essential Service Water (ESW) 6.65 19.49 19.49 Pump Auxiliary Feed Water (AFW) 10.51 24.69 24.69 Pump Containment Spray Pump N.A.S. N.A.S. 30.44 Non-Essential Service Water 1.83.0NAS Pump 14.78_36.80_N.A.S N.A.S = Not Auto Started The manual action to reset the lockout relay is not addressed in the CNP licensing design basis accident analysis in case a LOOP and LOCA event were to occur coincidently. The EDG is declared Inoperable during the surveillance. The plant EDG surveillance procedures direct the operators to open the output breakers if a LOOP event occurs during the test which would also occur automatically once LOV relays actuate. In a LOOP event concurrent with a LOCA, the EDG does not lock out.
Response to EEEB-RAI-5c (1) LOOP followed by LOCA At CNP, the plant auxiliary load buses, Safety and non-Safety, are connected radially to either the reserve auxiliary transformers (RATs) or unit auxiliary transformers (UATs). For offsite power, each RAT feeds (2) 4kV BOP buses that feed large BOP motor loads such as the Reactor Coolant Pumps and Circulating Water Pumps. The 4kV BOP bus then feeds the 4kV Safety Buses which are connected to the EDG via EDG output breakers. See simplified sketch, Figure 1, provided earlier in response (a.).
In the scenario when the EDG is paralleled to the safety bus being supplied from reserve feed concurrent with a LOOP, the EDG remains connected and will continue to supply power to all 4kV buses. The EDG remains connected to the 4kV buses, thus the LOV relays cannot sense the LOOP event at the onset of grid loss. All connected BOP loads, in excess of 15 MVA, served originally by reserve feed, are picked up by the EDG resulting in an overcurrent trip of the EDG (see RSC1-4261 and OP-1-98043 (Attachments #6 and #3, respectively)). The overcurrent
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 5 relay actuation locks out the EDG output breaker (1-51X-T11IA) (Attachment #3) and the EDG differential (1-87X-DGAB) (Attachment #3). During test mode, the overcurrent relays provide a trip function but are bypassed during an emergency condition. The trip function for differential relays remains active in test and emergency modes, see 0P-1-98043 (Attachment#3)). Once the EDG trips on overcurrent, the power to the 4kV buses is completely lost which actuates LOV relays and load shed is initiated. Once the lockouts are manually reset, the EDG will restart and emergency LOOP loads will be sequenced. Since the lock out requires a manual reset, timing will depend upon the operator's response time. Once the EDG is reset, the load sequence timings will take place as follows:
Start timing of Vital LOOP loads (Seconds)
(NOTE: Time is after the Lockout relays are manually reset, and includes 10 seconds for EDG to start and reach required voltage)
Equipment LOOP event Centrifugal Charging Pump N.A.S.
SI Pump N.A.S.
RHR Pump N.A.S.
CCW Pump 13.16 ESW Pump 16.65 AFW Pump 20.51 Containment Spray Pump N.A.S.
Non-Essential Service Water Pump 24.78 Start timing of Vital loads at LOCA after LOOP event (Seconds)
(NOTE: Time is after the SI signal is received)
Equipment LOCA event after LOOP Centrifugal Charging Pump 3.16 SI Pump 6.65 RHR Pump 10.51 CCW Pump Already running for LOOP ESW Pump Already running for LOOP _.
AFW Pump Already running for LOOP Containment Spray Pump. N.A.S.
Non-Essential Service Water Pump Already running for LOOP (2) LOCA (SI) followed by LOOP The SI signal will trip the output breaker of the EDG, separating the EDG from the 4kV bus. The emergency loads will be sequenced to the safety buses which will be powered from offsite power via the RATs including 4kV BOP buses as follows:
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 6 Start timing of Vital loads on the RATs for a LOCA event prior to LOOP (Seconds)
(NOTE: Time is after SI signal is actuated)
Equipment LOCA (SI) sequence Centrifugal Charging Pump 3.16 SI Pump 6.65 RHR Pump 10.51 CCW Pump 14.78 ESW Pump 19.49 AFW Pump 24.69 Containment Spray Pump N.A.S.
Non-Essential Service Water Pump 36.80 If offsite power is lost during the LOCA event, power to the 4kV bus is lost but the EDG continues to operate in standby. The LOV relays will actuate after a two-second time delay once the bus voltage drops below 78% to allow for voltage decay of running motors. The LOV relay actuation initiates load shedding and tripping of the main supply breakers to the BOP 4kV buses and Tie breakers to the safety "T" buses. The time delay of two seconds on the LOV relays allows for motor voltage decay and to override any momentary grid transient before EDG output breakers close. Once the EDG output breakers close, the emergency motors are re-sequenced on to the EDG as follows:
Start timing of Vital loads on the EDG for a LOOP following a LOCA event (Seconds)
(NOTE: Time is after the EDG output breaker closes)
Centrifugal Charging Pump 3.16 SI Pump 6.65 RHR Pump 10.51 CCW Pump 14.78 ESW Pump 19.49 AFW Pump 24.69 Containment Spray Pump N.A.S.
Non-Essential Service Water Pump 36.80 EEEB-RAI-6 In response to EEEB-RAI-3, the licensee stated that the EDG protective relays for generator overcurrent, generator differential, and generator neutral overcurrent remain active in nonemergency conditions.
- a. Please explain the conditions defined as "non-emergency"and "emergency."
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 7
- b. Please provide a single line diagram showing the connection of the protective relays.
Also, please discuss the physical location of the protective relays, including the lockout relay, for the EDG.
Resoonse to EEEB-RAI-6a
Response to EEEB-RAI-6b See marked up OP-1-12001 (Attachment #1) for protective relays on the EDG. The relay diagrams, showing connections and settings, are also included. Since the protective scheme is same for all EDGs, the Single line and Relay diagrams are only provided for the (AB) EDG. The relays for the Train B (AB) EDG are shown in circle 152, 154 and 175 (Attachment #1); see table below for description:
Relay Number on One Line Relay ID Component Name 4KV BUS TI1IA EMERGENCY FEED OVERCURRENT N/A -SiXTilA LOCKOUT HAND RESET RELAY AB EDG OME-150-AB TRIP LOCKOUT HAND RESET N/A 1-87X-DGAB REA AB EDG OME-150-AB PHASE #10OVERCURRENT 1-51-DGAB-1 REA 154 AB EDG OME-150-AB PHASE #30OVERCURRENT I-51-DGAB-3 REA AB EDG OME-150-AB PHASE #1 DIFFERENTIAL 1-87-DGAB-1 REA AB EDG OME-150-AB PHASE #2 DIFFERENTIAL 152 1-87-DGAB-2 REA AB EDG OME-150-AB PHASE #3 DIFFERENTIAL 1-87-DGAB-3 REA 175 1-51N-DGAB AB EDG OME-i50-AB NEUTRAL Relay Diagram Description R5C1-4260 (Attachment #4) DIESEL GENERATOR lAB DIFFERENTIAL RSCl-4262(Attachment #5) NEUTRAL GROUND OVERCURRENT RSC1-4261 (Attachment #6) OVERLOAD PROTECTION All the relays listed above are located in the main control room; the lockout relays are located on the same Station Auxiliaries (SA) Control Panel, SA and protective relays are located on the Auxiliary Relay Panel 1-All.
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 8 EEEB-RAI -7 In response to EEEB-RAI-4, the licensee stated:
"The maximum 3 phase fault contribution from the EDG is 4.1 kA [kilo amperes]. The maximum fault at the T Bus is less than 42kA including the EDG contribution. The symmetrical interrupting rating of the 4 kV switchgear and breakers is 46.9 kA adjusted for the 4.16 kV rating. The maximum fault current, 42 kA calculated with the EDG in parallel does not exceed the fault rating of switch gear and breakers. The fault currents are conservatively estimated based on the low circuit impedances and maximum fault contribution from the system and the motors connected to the bus."
- a. Section 8.4 of the CNP Updated Final Safety Analysis Report states that one EDG supplies power to two 4.16 KV safety buses (e.g., T11A and T11B in Unit 1, Train B).
Please clarify whether the EDG is connected to both 4.16 kV safety buses (e.g., TI l A and TIlI B) during testing of the EDG paralleled with the offsite power source, and during emergency conditions.
- b. Please provide a summary of the short circuit calculations at the T Bus(es) that is (are) connected to the EDG with the EDG in parallel with offsite power.
Response to EEEB-RAI-7a During the eight hour run, the EDG is connected only to the 4.16kV safety bus that has the large motor loads (T11A or D for Unit 1 or T21A or D for Unit 2) when paralleled with the offsite power source. The other bus, (Ti11B or C for Unit 1 or T21 B or C for Unit 2), is briefly paralleled with the EDG at the end of the test. During an emergency, both output breakers to the buses close and the EDG is connected to both.
Resoonse to EEEB-RAI-7b 3-phase Interrupting fault at bus: Bus TIIA Bus TI11A Total 38.2 kA Contribution from:
- EDG-AB 4.0OkA
- Source Bus IA 33.0 kA
- 4kV Motors 1.0 kA
° Non Motors 0.2 kA The short circuit summary details are provided in the attached reports from Electrical Transient Analysis Program (ETAP) (Attachment #7). The symmetrical interrupting rating of the 4kV
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 9 switchgear and breakers is 46.9kA, which is significantly higher than the fault currents during the EDG surveillance, as shown above.
Attachments:
- 1. OP-1-12001 "Main Auxiliary One-Line Diagram Bus "A" & "B" Engineered Safety System"
- 2. RSC1-4278 Relay Diagram "4KV Bus TI1IA Undervoltage Protection"
- 3. OP-I-98043-056 "4KV Diesel Generator lAB A.C.B. Elementary Diagram"
- 4. RSCI-4260 Relay Diagram "Diesel Generator lAB Differential"
- 5. RSC1-4262 Relay Diagram "Neutral Ground Overcurrent"
- 6. RSCI-4261 Relay Diagram "Overload Protection"
- 7. ETAP Short Circuit Output Reports
Attachment 1 to Enclosure 2 to AEP-NRC-201 5-99 OP-1-12001 "Main Auxiliary One-Line Diagram Bus "A" & "B" Engineered Safety System"
Attachment 2 to Enclosure 2 to AEP-NRC-2015-99 RSCl-4278 Relay Diagram "4KV Bus TI11A Undervoltage Protection"
4KV BUS T1 IA 3 PT's 4200/1 20 V 1-27-1-Ti11A 1-27-Ti1iA-i 1-27-2-Ti iA 1-27-Ti11A-2 1-27-3-TI11A 1-27-Ti11A-3 RELAY SETTING PREPARED -REVIEWED APPROVED CALCULATION BY/DATE BY/DATE BY/DATE ID NUMBER 1-27-1-TIllA 1-27-2-Ti11A 1-27-3-Ti11A DO P<96.28 As-found 952 9254 I38'As-left
- 2V
- 7.j
//,,u/'i o~#..*L*70'
/.,.jO]*"
7 *
/*L.
aT 1-E-N-PROT-RLY-003 R. 0, CS-4 1-2-01-02 Calo 1 Rev. 10 ITE-27N TD 2+_ 0.2 sec 1-27-Ti11A-I1 As-found As-left 1-27-TIlA-2 DO 11.2 11-2i/*/ 1-E,-N-PROT-RLY-003 R. 1, CSA 1-27-TI 1A-3 ___113.81 V ++/-0.2V /'*1-2-01-02 Calc 1 Rev. 10 PU < 115.57 V ITE-27N TD 9 + 0.25 sec REVISION DESCR{W11'JON:
Removal of a DIT (DIT-B-02840-05) reference due to the information in the DIT being superseded completely by Calculation 1-2-0 U Mh1"CALC1. No setting changes. Change is driven by GT 2013-19386-18.
Note: The test instruments used for relay calibration shall have reference accuracy values within_+/- 0.2% + 0.1 V.
RELAY DIAGRAM DWG. # RSC1-4278 D.C. COOK PLANT REv. #6 4KV BUS T11A UNDERVOLTAGE PROTECTION UNIT 1
Attachment 3 to Enclosure 2 to AEP-NRC-2015-99 OP-I1-98043-056 "4KV Diesel Generator lAB A.C.B. Elementary Diagram"
Attachment 4 to Enclosure 2 to AEP-NRC-2015-99 RSC1-4260 Relay Diagram "Diesel Generator lAB Differential"
1 DGAB-1 1 DGAB-2 1 DGAB--3 S3 CT'S
>800/5 D.G. TEST RESITOR 4 kV BUS T11A 4 kV BUS T11B LOAD BANK RELAY SETTING PREPARED REVIEWED APPROVED CALCULATION BY/DATE BY/DATE BY/DATE "ID NUMBER 1-87-DGAB-2 /'..,.,/'-"'
'(*- PS-EDGP-005, Rev. 0 a-87-DGAB -3 P. U. =0.2 AMPS -(Y *. -, --0 C.///*//*/
ABB 87M REVISION DESCRIPTION:
No setting changes. Reformatted consistent with PMP-6065-EIC-001, Rev. 0 and revised relay IDs to reflect FDB format in response to CRA 00-03934-01..
RELAY DIAGRAM DWG. # RSC1-4260 D.C. COOK PLANT REV. #2 DIESEL GENERATOR lAB DIFFERENTIAL UNIT 1
Attachment 5 to Enclosure 2 to AEP-NRC-2015-99 RSC1I-4262 Relay Diagram "Neutral Ground Overcurrent"
0 6 of 1-51 N-DGAB 1 CT 300/5 D. G. iAB REVISION DESCRIPTION:
No setting changes. Reformatted consistent with PMiP-6065-EIC-OO1, Rev. 0. Added calculation Id number.
RELAY DIAGRAM DWG. # RSC1-4262 D.C. COOK PLANT REv. #1
- NEUTRAL GROUND OVERCURRENT UNIT 1 to Enclosure 2 to AEP-NRC-2015-99 RSCI -4261 Relay Diagram "Overload Protection"
DIESEL GENERATOR GOVERNOR LOAD SIGNAL BOX RELAY SETTING PREPARED REVIEWED APPROVED CALCULATION BY/DATE BY/DATE BY/DATE ID)NUMBER 1-51-DGAB-1 TAP 6.0 ch 1 4... PS-EDGP-00 ]
1-51-DGAB-3 Time 66 - . fk/J7- ]
@3 XP.U, I o (,(Is 12IAC51AAI101A REVISION DESCRIPTION:
No setting changes. Reformatted consistent with PMP-6065-EIC-00 1, Rev. 0. Added calculation Id number and revised relay L~s to reflect FDB format in response to CRA 00-03934-0 1.
RELAY DIAGRAM DWG. # RSC1-4261 D.C. COOK PLANT R'v'#
OVERLOAD PROTECTION UNIT 1 to Enclosure 2 to AEP-NRC-2015-99 ETAP Short Circuit Output Reports
ETAP Project: 4kV-600V Load Control Page: 49 12.6.5N Location: D.C. Cook Unit 61 Date: 10-13-2015 Contract: 12105-681 SN: AMELECPWR3 Engineer: Gregory J Hinshaw (S&L) Revision: Zmin Study Case: TR5SCLOCAABP Filename: UI1 ETAP RIO Config.: LCSS TR5 AB2 Calculation l-E-N-ELCP-4KV-001 Revision 10 TR5SC-AB (Att AK55)-Unit 1 LOCA Steady State, TR5 Only, 345kV at 104.8%, 132in M5, AB EDG ON 3-phase fault at bus: Bus TIIA Prefault voltage = 4.135 Prefultvolage=
99.40 %4135=
of nominal but kV ( 4.160 kV)
= 98.74 % of base (4.187 kV)
Contribution 112 Cycle 1.5 to 4 Cycle From Bus To Bun %V kA krA Imag. kA Symin. %V kA kA Imag. kA Symmu.
1D ID3 FronmBaa Real Imaginary tReat Magnitude From Bus Real Imaginary tReat Magnitude Bus TtIA Total 0.00 3.195 -47.6t9 t4.9 47.726 0.00 23t6 -38.t29 16.5 38 t99 NOde.TR11AIOV Bus TllA 0.13 0.108 -0.515 4.7 0.526 0.05 0.033 -0.193 5.8 0.1%
Bus tA Bus TIIA 2.78 2.167 -41.095 14.3 41.195 2.23 2.131 -32.936 15.5 33.005 Node. t11PHAHV Bus TI IA 0.00 0.000 0.000 999.9 0.000 0.00 0.000 0.000 999.9 0.000 S INJ PPtS Bus T11A 103.37 0.024 -0.322 13.2 0.322 103.37 0.015 -0.215 13.9 0.215 MDAuxFdPPW Bus TllA 103.37 0.035 -0.408 11.8 0.410 103.37 0.021 -0.273 13.2 0.274 RHR-PPIW Bus T11A 103.37 0.018 0.0244 13.5 0.245 103.37 0.007 -0.098 14.7 0.091 ESSSvcWPPIW Bus TI IA 103.37 0.014 -0310 223 0.310 103.37 0.004 -0.123 28.6 0.123 CntC hrgPP-t W BrsTt1A 103.37 0.021 -0.363 17.7 0.363 103.37 0.008 -0.145 19.2 0.146 CMPCLGPPIW Bus39 103.37 0.016 0.0360 228 0.361 103.37 0.005 -0.143 28.9 0.143 Bus TI1A 0.00 0.016 -0.360 22.8 0.361 0.00 0.005 -0.143 28.9 0.143
'lBus39 NACD Ratio = 0.90
- Indicates a fault current contribution from a three-winding transformer SIndicates a fault current through a tie circuit breaker If"faulted bus is involved in loops formed by protection devices, the short-circuit rontriutions through these PDs will not be reported.
ETAP Project: 4kV-600V Load Control Page: 50 12.6.5N Location: D.C. Cook Unit #1 Date: 10-13-2015 Contract: 12105-681 SN: AMELECPWR3 Engineer: Gregory J Hinshaw (S&L) Reviaion: Znuin Study Case: TR5SCLOCAAB3P Filename: UI ETAP RIO Config.: LCSS TR5 AB2 Calculation I-E-N-ELCP-4KV-001 Revision 10 TR5SC-AB (Att AK55)-Unit I LOCA Steady State, TR5 Only, 345kV at 104.8%, U2 in M5, AB EDG ON 3-phase fault at bus: Bus TIItB Prefault voltage = 4.120 = 99.05 % of nominal but kV ( 4.160 kV)
= 98.40 % of base (4.187 kV)
Contribution 1/2 Cycle 1.5 to 4 Cycle From Bus To Bas %V kA kA Imag* kA Syrom. %V kA kA Imag. kA Syinm.
ID ID From Bus Real Imaginary /Real Magnitude From Bus Real Imaginary /ReaI Magnitude Bus TIIB Total 000 3.417 -46.298 t3.6 46.423 0.00 2465 -37.273 15.1 37.355 Node TRl 1BHV Bus TIttB 0.t0 0 t09 -0.717 6.6 0.726 0.04 0.037 -0.323 8.7 0.325 Bus 1B Bus TIIB 3.71 3.308 -45.580 13.8 45.700 3.01 2428 -36.950 15.2 37.030 NACD Ratio =090
- Indicates a fault curren contribution from a three-winding transformer "Indicates a fault current through a tie circuit breaker If faulted bus is involved in loops formed by protection devices, the short-circuit contributions through these PDs will not be reported.
ETAP Project: 4kV-600V Load Control Page: 51 12.6.5N Location: D.C. Cook Unit #1 Date: 10-13-2015 Contract: 12105-681 SN: AMELECPWR3 Engiee: Gregory J Hinshaw (S&L) Revision: Zmin Study Case: TR5SCLOCAABP Filename: UI ETAP Ri0 Config.: LCSS TR5 AB2 Calculation I-E-N-ELCP-4KV-001 Revision 10 TR5SC-AB (Alt AK55)-Unit I LOCA Steady State, TR5 Only. 345kV at 104.8%, U2 in M5, AB EDG ON 3-phase fault at bus: Bus TIIC Prefault voltage = 4.129 = 99.25 % of nomsinal bus kV (4.160 kV)
=94.83 % of base ( 4.354 kV)
Contribution 1/2 Cycle 1.5 to 4 Cycle Fron Bus To Bus %V kA kA Imag. kA Syroni %V kA kA Iina& kA Syrom.
ID ID Froni Bus Rest Imaginary /Real Magnitude From Bus Real Imaginary /Real Magnitude Bus T11C Total 0.tO 2 945 -38.79t 13.2 38.902 000 2 143 -30.797 14.4 30.871 Node TR I1CHV Bus TI1C 0t12 0.149 -0.700 4.7 0.716 0.05 0062 -0.298 4.8 0.305 Bus 1C Bus TI1C 2.92 2 796 -38.091 13.6 38.193 2.34 2.081 -30.499 14.7 30.570 NACD Ratio = 1.00
- Indicates a fault nrrrest consribution from a three-winding transfonner
- Indicates a fault eturrest through a tie circuit breaker If faulted bus is involved in loops formed by protection devices, the short-cirvuit contributions through these PDs will not be reprorted.
ETAP Project: 4kV-600V Load Control Page: 52 12.6.5N Location: D.C. Cook Unit #61 Date: 10-13-2015 Contract: 12105-681 SN: AMELECPWR3 Engineer: Gregory J Hinshaw (S&L) Revision: Zmin Study Case: TR5SCLOCAABP F~ilename: Ut ETAP Rt0 Config.: LCSS TR.5 AB2 Calculation I-E-N-ELCP-4KV-001 Revision 10 TR5SC-AB (Att AK55)-Unit I LOCA Steady State, TR5 Only, 345kV at 104.8%, U2 in M5, AB EDG ON 3-phase fault at bus: Bus TIID Prefault voltage 44130 = 99.27 % of nominal but kV ( 4.160 kV)
=94.85 %of base(4.354 kV)
Contribution !/2 Cycle 1.5 to 4 Cycle FromnBus To Bus %V kA kA Imag. kA Symm. %V kA kA haag. kA Synto.
ID ID FromrBus Real Imaginusy /Real Magnitude From Baa Real Imaginary /Real Magnitude Bus TttD Total 0.00 2.956 -39.305 13.3 39.4t6 000 2157 -31.195 t4.5 31 269 Node.TRh11DHV Bus TI1D 0.10 0.102 -0O511 5.0 0.521 0.03 0.030 -0.175 5.8 0.178 Bus tD Bus TI1D 3.91 2.734 -36.805 13.5 36.906 3.19 2.069 -30.023 14.5 30.094 Node. t1PHCHV Bus TIID 0.00 0.000 0.000 999.9 0.000 0.00 0.000 0.0030 999.9 0.000 S INJ PPI1N Bus TIID 103.24 0.024 -0.322 13.5 0.322 t03.24 0.015 -0.215 14.1 0.2t5 RH8RPPI E Bus TI1D 103.24 0.018 -0.244 13.9 0.244 103.24 0.007 -0.098 14.9 0.098 CntChrgPP-t E Bus TIID 103.24 0.020 -0.363 17.8 0.363 103.24 0.008 -0.145 t9.3 0.146 ESSSvcWPP1E Bus TllD 103.24 0.010 -0.271 26.7 0.271 t03.24 0.003 -0.109 3t.1 0.109 AUXFWPPE Bus TI1D 99.27 0.033 -0430 13.2 0.431 99.27 0.020 -0.287 14.4 0.288 CMPCLGPPI1E Bus36 t03.24 0.016 -0.360 22.8 0.360 103.24 0.005 -0.143 28.9 0.143 Bus TI1D 0.00 0.016 -0.360 22.8 0.360 0.00 0.005 -0.143 28.9 0.143 SBus36 NACD Ratio 1.00
- Indicates a fauht current contribution front a three-winding transfonner tIndicates a fault current through a tie circuit breaker If faulted bus is involved in loops formed by protection devices, the short-circuit contributions through these PDs will not be reported.
IND*IA NA Indiana Michigan Power MICHIGAN Cook Nuclear Plant 1POWER 0ne Conk Place Bridgman, MI 49106 A unit ofAmerican Electric Power IndianaMichiganPower.com October 30, 2015 AEP-NRC-201 5-99 10 CFR 50.90 Docket Nos. 50-315 50-316 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Donald C. Cook Nuclear Plant Units 1 and 2 Response to a Request for Additional Information Regarding the License Amendment Request to Revise Technical Specification Section 3.8.1, "AC Sources - Operating," Surveillance Requirements 3.8.1.10, 3.8.1.11, and 3.8.1.15
References:
- 1. Letter from J. P. Gebbie, Indiana Michigan Power Company (I&M), to U. S. Nuclear Regulatory Commission (NRC), "Donald C. Cook Nuclear Plant Unit 1 and Unit 2 Docket Nos. 50-315 and 50-316, License Amendment Request Regarding Technical Specification Section 3.8.1, "AC Sources - Operating," Surveillance Requirements 3.8.1.10, 3.8.1.11, and 3.8.1.15,"
AEP-NRC-2014-70, dated December 17, 2014, Agencywide Documents Access and Management System (ADAMS) Accession No. ML14356A022.
- 2. Letter from A. W. Dietrich, NRC, to L. J. Weber, l&M, "Donald C. Cook Nuclear Plant, Units 1 and 2 - Request for Additional Information Regarding License Amendment Request to Revise Technical Specification 3.8.1 (TAC Nos. MF5436 and MF5437)," dated June 15, 2015, ADAMS Accession No. ML15163A167.
- 3. Letter from J. P. Gebbie, l&M, to NRC, "Donald C. Cook Nuclear Plant Units I and 2 Response to a Request for* Additional Information Regarding the License Amendment Request to Revise Technical Specification Section 3.8.1, "AC Sources - Operating," Surveillance Requirements 3.8.1.10, 3.8.1.11, and 3.8.1.15," AEP-NRC-2015-60, dated July 9, 2015, ADAMS Accession No. ML15195A434.
- 4. Letter from A. W. Dietrich, NRC, to L. J. Weber, I&M, "Donald C. Cook Nuclear Plant, Units I and 2 - Second Request for Additional Information Regarding License Amendment Request to Revise Technical Specification 3.8.1 (TAC Nos. MF5436 and MF5437)," dated October 5, 2015, ADAMS Accession No. ML15267A683.
This letter provides Indiana Michigan Power Company's (I&M), the licensee for Donald C. Cook Nuclear Plant Unit I and Unit 2, response to a Request for Additional Information (RAI) by
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 2 the U. S. Nuclear Regulatory Commission (NRC) regarding a License Amendment Request to modify the notes to Technical Specification (TS) 3.8.1i, "AC Sources -Operating."
By Reference 1, l&M submitted a request to amend the TS to Facility Operating Licenses DPR-58 and DPR-74. l&M proposes to change TS 3.8.1 to allow surveillance testing of the onsite standby emergency diesel generators during modes in which it is currently restricted. By Reference 2, the NRC transmitted RAIs regarding the proposed amendment. Reference 3 provided I&M's response to Reference 2. By Reference 4, the NRC transmitted RAIs regarding the proposed amendment.
This letter provides I&M's response to Reference 4. Enclosure 1 to this letter provides an affirmation statement pertaining to the information contained herein. Enclosure 2 provides l&M's response to the NRC's RAI contained in Reference 4.
Copies of this letter and its enclosures are being transmitted to the Michigan Public Service Commission and Michigan Department of Environmental Quality, in accordance with the requirements of 10 CFR 50.91.
There are no new regulatory commitments made in this letter. Should you have any questions, please contact Mr. Michael K. Scarpello, Regulatory Affairs Manager, at (269) 466-2649.
Sincerely, Joel P. Gebbie Site Vice President JMT/ams
Enclosures:
- 1. Affirmation
- 2. Response to a Request for Additional Information Regarding the License Amendment Request to Revise Technical Specification Section 3.8.1, "AC Sources - Operating,"
Surveillance Requirements 3.8.1.10, 3.8.1.11, and 3.8.1.15 c: A. W. Dietrich, NRC Washington, D.C.
J. T. King - MPSC MDEQ - RMD/RPS NRC Resident Inspector C. D. Pederson, NRC Region Ill A. J. Williamson, AEP Ft. Wayne, w/o enclosures
Enclosure 1Ito AEP-NRC-2015-99 AFFIRMATION I, Joel P. Gebbie, being duly sworn, state that I am Site Vice President of Indiana Michigan Power (I&M), that I am authorized to sign and file this request with the U. S. Nuclear Regulatory Commission on behalf of I&M, and that the statements made and the matters set forth herein pertaining to I&M are true and correct to the best of my knowledge, information, and belief.
Indiana Michigan Power Joel P. Gebbie Site Vice President SWORN TO AND SUBSCRIBED BEFORE ME THSO1*DAY OF Oe.[t)*=" 2015 Notary Public My Commission Expires 10 - /6 -*O/ "*
,., *ANNE M. PALMA
. . ,Notary Public, State of Michigan
- County of Berrien
.; "*' My Commission Expires 10- *6-2017 Acting in the Countyof ia/
Enclosure 2 to AEP-NRC-2015-99 Response to a Request for Additional Information Regarding the License Amendment Request to Revise Technical Specification Section 3.8.1, "AC Sources - Operating,"
Surveillance Requirements 3.8.1.10, 3.8.1.11, and 3.8.1.15 By letter dated December 17, 2014 (Agencywide Documents Access Management System (ADAMS) Accession No. ML14356A022), as supplemented by letter dated July 9, 2015 (ADAMS Accession No. ML15195A434), Indiana Michigan Power Company (I&M), the licensee, requested an amendment to Renewed Facility Operating Licenses DPR-58 and DPR-74 for Donald C. Cook Nuclear Plant (CNP), Units 1 and 2. The proposed amendments would revise the Technical Specifications (TS) 3.8.1, "AC Sources - Operating," to allow testing of the onsite standby emergency diesel generators (EDGs) during modes in which it is currently prohibited.
Specifically, the proposed changes would remove the mode restrictions in the notes of the Surveillance Requirements 3.8.1.10 (EDG single largest load rejection test), 3.8.1.11 (EDG full load rejection test), and 3.8.1.15 (EDG endurance run).
The U.S. Nuclear Regulatory Commission (NRC) Electrical Engineering Branch (EEEB) staff has reviewed the subject submittal and supplement, and has determined that additional information is needed to complete the review, as described in the Second Request for Additional Information (RAI), below. The draft RAI was sent to l&M via electronic mail on September 23, 2015. The NRC staff clarified the draft RAI in a conference call conducted on October 1, 2015. By letter dated October 5, 2015 (ADAMS Accession No. ML15267A683), the NRC transmitted an RAI regarding the December 17, 2014 license amendment request. On October 15, 2015, the NRC conducted a public meeting to discuss I&M's proposed response to the RAI. This enclosure provides I&M's response to the RAl.
EEEB-RAI-5 In response to EEEB-RAI-2c, the licensee addressed the emergency diesel generator (EDG) operation during a loss of offsite power (LOOP) with a loss-of-coolant accident (LOCA) while the EDG is operatingin parallel with the offsite power. The licensee stated:
"When the EDG [emergency diesel generator]is in test mode, the SI [safety injection] or load shed signal will automatically trip the 4 kV [kilovolts] Output Breaker during EDG test mode (these signals are blocked after two seconds, and therefore SI signal is prevented from reopening the breakerif a load shed occurs first, trips the breaker, then the breaker closes to load the EDG and a SI signal is initiatedsome time later)."
- a. Please discuss the events or signals that initiate the load shed signal. If an SI signal also initiates a load shed signal, please clarify the sentence in parentheses in the above statement. Also, please explain the EDG operation during degraded grid voltage conditions while the EDG is being tested in parallel with the offsite power source in Mode 1 or2.
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 2
- b. Please discuss the EDG operation, including timing of vital load loads sequencing, during a LOOP concurrent with LOCA scenario, while the EDG is being tested in parallel with the offsite power source in Mode I or 2. Also, please clarify whether manual action to reset the lockout relay is allowed during a LOOP concurrent with LOCA event in the CNP licensing design basis accident analysis.
- c. Please provide the timeline of tripping and closing of the EDG breaker, and discuss the timing of vital load sequencing for the following scenarios, with the EDG initially in test mode and paralleledwith the offsite source:
(1) LOOP followed by LOCA (2) LOCA followed by LOOP Response to EEEB-RAI-5a See Figure 1 below for a simplified sketch showing the arrangement of EDG, relays and reserve feed to the 4 kilovolt (kV) buses. The sketch reflects drawing OP-1-12001 (Attachment #1) and relay diagram RSC1-4278 (Attachment #2) (The loss of voltage (LOV) relays are 1-27-1-T11A, 27-2-TI1IA, 27-3-TI1IA and the Degraded Grid Relays (DGR) are 1-27-TI1IA-I, 1-27-TI11A-2, 1-27-Ti11A-3).
relays
@RCP Bus 1A Li BOP
--*motors Offsite Power*4k Ti breakers To 600V 1IE Bus 11IB Fi~qure I Simplified One Line Sketch for EDG Connection to Offsite Power Unit I Train B shown, (typical)
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 3 The loss of offsite power (LOOP) signal is generated by the LOV relays on the 4kV safety buses, when the voltage on a bus is less than approximately 78 percent (%) nominal voltage for a duration of two seconds. Each 4kV safety bus is equipped with a set of three undervoltage relays configured in a 2/3 logic. The function of these relays is to generate the LOOP signal upon recognition of the loss of voltage on the safety bus. The LOOP signal actuates a series of auxiliary relays (master load shedding relays) that initiate load shedding and provide a permissive for the closing of the EDG output breakers. The LOOP and load shed is bus specific. The LOOP event will separate the EDG from the safety bus by tripping the output breaker. The EDG output breaker will close after the load shed and emergency loads will be sequenced.
The Safety Iniection (SI) siginal does not initiate load shed: The EDG will start automatically, but will not connect to the 4kV safety buses should an SI signal be generated.
The SI or load shed signal will automatically trip the 4kV Output Breaker during EDG test mode.
When in test mode, the signal for tripping the EDG output breaker is blocked after two seconds to prevent reopeningi the output breaker if the load shed has already occurred and EDG was reconnected to~the buses.
The DGRs do not directly generate a load shed signal. The DGRs are located on the 4kV safety buses T11A (or"T21A for U2) orT.11D (or T21D for U2). The main function of the DGRs is to protect the large motors from a sustained lower voltage condition; therefore, only 4kV safety buses TIlIA and TI11D are provided with this undervoltage protection. The 4kV safety buses, TI1IB and Ti10C, do not feed motor loads; therefOre, the DGRs are not provided on these buses. The DGRs actuate when the voltage on these buses falls below approximately 94% of nominal bus voltage for a duration of two minutes (no concurrent accident signal) or nine seconds (concurrent SI or Steam Generator Lo-Lo signal). The 4kV safety buses (TI1IA, TI1ID, T21A and T21 D) are each equipped with a set of three degraded voltage relays configured in a 2/3 logic. If a degraded voltage condition is detected by this logic, the degraded voltage relays actuate auxiliary relays that in turn initiate tripping of the normal supply circuit breakers to the 4kV safety buses. The resulting loss of voltage to the 4kV safety buses will then be detected by the LOV relays and a LOOP signal and corresponding automatic actions will be generated as described above for the LOV.
Response to EEEB-RAI-5b LOOP concurrent with a LOCA The SI signal will trip the output breaker of the EDG which separates the EDG from the 4kV bus.
The EDG will continue to run unloaded in standby mode. The LOOP event will result in LOV relays actuating after a two-second time delay once the 4kV bus voltage drops below 78% to allow for motor voltage decay. The actuation of LOV relays initiates load shedding and tripping of the main supply breakers to balance of plant (BOP) 4kV buses and Tie breakers to the safety "T" buses. The time delay of two seconds on the LOV relays allows for motor voltage decay and to override any momentary grid transient before the EDG is connected to the bus. After a two-second time delay, the EDG output breakers will close automatically and emergency motors will be sequenced on to the EDG as follows:
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 4 Start timing of Vital loads for LOCA concurrent with LOOP (Seconds)
(NOTE: Time is after the EDG outout breaker closes)
LOOP with Equipment LOOP LOOP with Safety Containment Injection Spray Centrifugal Charging Pump N.A.S. 3.16 3.16 SI Pump N.A.S. 6.65 6.65 Residual Heat Removal (RHR) NAS 05 05 Pump NAS 05 05 Component Cooling Water 31 47 47 (CCW) Pump Essential Service Water (ESW) 6.65 19.49 19.49 Pump Auxiliary Feed Water (AFW) 10.51 24.69 24.69 Pump Containment Spray Pump N.A.S. N.A.S. 30.44 Non-Essential Service Water 1.83.0NAS Pump 14.78_36.80_N.A.S N.A.S = Not Auto Started The manual action to reset the lockout relay is not addressed in the CNP licensing design basis accident analysis in case a LOOP and LOCA event were to occur coincidently. The EDG is declared Inoperable during the surveillance. The plant EDG surveillance procedures direct the operators to open the output breakers if a LOOP event occurs during the test which would also occur automatically once LOV relays actuate. In a LOOP event concurrent with a LOCA, the EDG does not lock out.
Response to EEEB-RAI-5c (1) LOOP followed by LOCA At CNP, the plant auxiliary load buses, Safety and non-Safety, are connected radially to either the reserve auxiliary transformers (RATs) or unit auxiliary transformers (UATs). For offsite power, each RAT feeds (2) 4kV BOP buses that feed large BOP motor loads such as the Reactor Coolant Pumps and Circulating Water Pumps. The 4kV BOP bus then feeds the 4kV Safety Buses which are connected to the EDG via EDG output breakers. See simplified sketch, Figure 1, provided earlier in response (a.).
In the scenario when the EDG is paralleled to the safety bus being supplied from reserve feed concurrent with a LOOP, the EDG remains connected and will continue to supply power to all 4kV buses. The EDG remains connected to the 4kV buses, thus the LOV relays cannot sense the LOOP event at the onset of grid loss. All connected BOP loads, in excess of 15 MVA, served originally by reserve feed, are picked up by the EDG resulting in an overcurrent trip of the EDG (see RSC1-4261 and OP-1-98043 (Attachments #6 and #3, respectively)). The overcurrent
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 5 relay actuation locks out the EDG output breaker (1-51X-T11IA) (Attachment #3) and the EDG differential (1-87X-DGAB) (Attachment #3). During test mode, the overcurrent relays provide a trip function but are bypassed during an emergency condition. The trip function for differential relays remains active in test and emergency modes, see 0P-1-98043 (Attachment#3)). Once the EDG trips on overcurrent, the power to the 4kV buses is completely lost which actuates LOV relays and load shed is initiated. Once the lockouts are manually reset, the EDG will restart and emergency LOOP loads will be sequenced. Since the lock out requires a manual reset, timing will depend upon the operator's response time. Once the EDG is reset, the load sequence timings will take place as follows:
Start timing of Vital LOOP loads (Seconds)
(NOTE: Time is after the Lockout relays are manually reset, and includes 10 seconds for EDG to start and reach required voltage)
Equipment LOOP event Centrifugal Charging Pump N.A.S.
SI Pump N.A.S.
RHR Pump N.A.S.
CCW Pump 13.16 ESW Pump 16.65 AFW Pump 20.51 Containment Spray Pump N.A.S.
Non-Essential Service Water Pump 24.78 Start timing of Vital loads at LOCA after LOOP event (Seconds)
(NOTE: Time is after the SI signal is received)
Equipment LOCA event after LOOP Centrifugal Charging Pump 3.16 SI Pump 6.65 RHR Pump 10.51 CCW Pump Already running for LOOP ESW Pump Already running for LOOP _.
AFW Pump Already running for LOOP Containment Spray Pump. N.A.S.
Non-Essential Service Water Pump Already running for LOOP (2) LOCA (SI) followed by LOOP The SI signal will trip the output breaker of the EDG, separating the EDG from the 4kV bus. The emergency loads will be sequenced to the safety buses which will be powered from offsite power via the RATs including 4kV BOP buses as follows:
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 6 Start timing of Vital loads on the RATs for a LOCA event prior to LOOP (Seconds)
(NOTE: Time is after SI signal is actuated)
Equipment LOCA (SI) sequence Centrifugal Charging Pump 3.16 SI Pump 6.65 RHR Pump 10.51 CCW Pump 14.78 ESW Pump 19.49 AFW Pump 24.69 Containment Spray Pump N.A.S.
Non-Essential Service Water Pump 36.80 If offsite power is lost during the LOCA event, power to the 4kV bus is lost but the EDG continues to operate in standby. The LOV relays will actuate after a two-second time delay once the bus voltage drops below 78% to allow for voltage decay of running motors. The LOV relay actuation initiates load shedding and tripping of the main supply breakers to the BOP 4kV buses and Tie breakers to the safety "T" buses. The time delay of two seconds on the LOV relays allows for motor voltage decay and to override any momentary grid transient before EDG output breakers close. Once the EDG output breakers close, the emergency motors are re-sequenced on to the EDG as follows:
Start timing of Vital loads on the EDG for a LOOP following a LOCA event (Seconds)
(NOTE: Time is after the EDG output breaker closes)
Centrifugal Charging Pump 3.16 SI Pump 6.65 RHR Pump 10.51 CCW Pump 14.78 ESW Pump 19.49 AFW Pump 24.69 Containment Spray Pump N.A.S.
Non-Essential Service Water Pump 36.80 EEEB-RAI-6 In response to EEEB-RAI-3, the licensee stated that the EDG protective relays for generator overcurrent, generator differential, and generator neutral overcurrent remain active in nonemergency conditions.
- a. Please explain the conditions defined as "non-emergency"and "emergency."
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 7
- b. Please provide a single line diagram showing the connection of the protective relays.
Also, please discuss the physical location of the protective relays, including the lockout relay, for the EDG.
Resoonse to EEEB-RAI-6a
Response to EEEB-RAI-6b See marked up OP-1-12001 (Attachment #1) for protective relays on the EDG. The relay diagrams, showing connections and settings, are also included. Since the protective scheme is same for all EDGs, the Single line and Relay diagrams are only provided for the (AB) EDG. The relays for the Train B (AB) EDG are shown in circle 152, 154 and 175 (Attachment #1); see table below for description:
Relay Number on One Line Relay ID Component Name 4KV BUS TI1IA EMERGENCY FEED OVERCURRENT N/A -SiXTilA LOCKOUT HAND RESET RELAY AB EDG OME-150-AB TRIP LOCKOUT HAND RESET N/A 1-87X-DGAB REA AB EDG OME-150-AB PHASE #10OVERCURRENT 1-51-DGAB-1 REA 154 AB EDG OME-150-AB PHASE #30OVERCURRENT I-51-DGAB-3 REA AB EDG OME-150-AB PHASE #1 DIFFERENTIAL 1-87-DGAB-1 REA AB EDG OME-150-AB PHASE #2 DIFFERENTIAL 152 1-87-DGAB-2 REA AB EDG OME-150-AB PHASE #3 DIFFERENTIAL 1-87-DGAB-3 REA 175 1-51N-DGAB AB EDG OME-i50-AB NEUTRAL Relay Diagram Description R5C1-4260 (Attachment #4) DIESEL GENERATOR lAB DIFFERENTIAL RSCl-4262(Attachment #5) NEUTRAL GROUND OVERCURRENT RSC1-4261 (Attachment #6) OVERLOAD PROTECTION All the relays listed above are located in the main control room; the lockout relays are located on the same Station Auxiliaries (SA) Control Panel, SA and protective relays are located on the Auxiliary Relay Panel 1-All.
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 8 EEEB-RAI -7 In response to EEEB-RAI-4, the licensee stated:
"The maximum 3 phase fault contribution from the EDG is 4.1 kA [kilo amperes]. The maximum fault at the T Bus is less than 42kA including the EDG contribution. The symmetrical interrupting rating of the 4 kV switchgear and breakers is 46.9 kA adjusted for the 4.16 kV rating. The maximum fault current, 42 kA calculated with the EDG in parallel does not exceed the fault rating of switch gear and breakers. The fault currents are conservatively estimated based on the low circuit impedances and maximum fault contribution from the system and the motors connected to the bus."
- a. Section 8.4 of the CNP Updated Final Safety Analysis Report states that one EDG supplies power to two 4.16 KV safety buses (e.g., T11A and T11B in Unit 1, Train B).
Please clarify whether the EDG is connected to both 4.16 kV safety buses (e.g., TI l A and TIlI B) during testing of the EDG paralleled with the offsite power source, and during emergency conditions.
- b. Please provide a summary of the short circuit calculations at the T Bus(es) that is (are) connected to the EDG with the EDG in parallel with offsite power.
Response to EEEB-RAI-7a During the eight hour run, the EDG is connected only to the 4.16kV safety bus that has the large motor loads (T11A or D for Unit 1 or T21A or D for Unit 2) when paralleled with the offsite power source. The other bus, (Ti11B or C for Unit 1 or T21 B or C for Unit 2), is briefly paralleled with the EDG at the end of the test. During an emergency, both output breakers to the buses close and the EDG is connected to both.
Resoonse to EEEB-RAI-7b 3-phase Interrupting fault at bus: Bus TIIA Bus TI11A Total 38.2 kA Contribution from:
- EDG-AB 4.0OkA
- Source Bus IA 33.0 kA
- 4kV Motors 1.0 kA
° Non Motors 0.2 kA The short circuit summary details are provided in the attached reports from Electrical Transient Analysis Program (ETAP) (Attachment #7). The symmetrical interrupting rating of the 4kV
U. S. Nuclear Regulatory Commission AEP-NRC-201 5-99 Page 9 switchgear and breakers is 46.9kA, which is significantly higher than the fault currents during the EDG surveillance, as shown above.
Attachments:
- 1. OP-1-12001 "Main Auxiliary One-Line Diagram Bus "A" & "B" Engineered Safety System"
- 2. RSC1-4278 Relay Diagram "4KV Bus TI1IA Undervoltage Protection"
- 3. OP-I-98043-056 "4KV Diesel Generator lAB A.C.B. Elementary Diagram"
- 4. RSCI-4260 Relay Diagram "Diesel Generator lAB Differential"
- 5. RSC1-4262 Relay Diagram "Neutral Ground Overcurrent"
- 6. RSCI-4261 Relay Diagram "Overload Protection"
- 7. ETAP Short Circuit Output Reports
Attachment 1 to Enclosure 2 to AEP-NRC-201 5-99 OP-1-12001 "Main Auxiliary One-Line Diagram Bus "A" & "B" Engineered Safety System"
Attachment 2 to Enclosure 2 to AEP-NRC-2015-99 RSCl-4278 Relay Diagram "4KV Bus TI11A Undervoltage Protection"
4KV BUS T1 IA 3 PT's 4200/1 20 V 1-27-1-Ti11A 1-27-Ti1iA-i 1-27-2-Ti iA 1-27-Ti11A-2 1-27-3-TI11A 1-27-Ti11A-3 RELAY SETTING PREPARED -REVIEWED APPROVED CALCULATION BY/DATE BY/DATE BY/DATE ID NUMBER 1-27-1-TIllA 1-27-2-Ti11A 1-27-3-Ti11A DO P<96.28 As-found 952 9254 I38'As-left
- 2V
- 7.j
//,,u/'i o~#..*L*70'
/.,.jO]*"
7 *
/*L.
aT 1-E-N-PROT-RLY-003 R. 0, CS-4 1-2-01-02 Calo 1 Rev. 10 ITE-27N TD 2+_ 0.2 sec 1-27-Ti11A-I1 As-found As-left 1-27-TIlA-2 DO 11.2 11-2i/*/ 1-E,-N-PROT-RLY-003 R. 1, CSA 1-27-TI 1A-3 ___113.81 V ++/-0.2V /'*1-2-01-02 Calc 1 Rev. 10 PU < 115.57 V ITE-27N TD 9 + 0.25 sec REVISION DESCR{W11'JON:
Removal of a DIT (DIT-B-02840-05) reference due to the information in the DIT being superseded completely by Calculation 1-2-0 U Mh1"CALC1. No setting changes. Change is driven by GT 2013-19386-18.
Note: The test instruments used for relay calibration shall have reference accuracy values within_+/- 0.2% + 0.1 V.
RELAY DIAGRAM DWG. # RSC1-4278 D.C. COOK PLANT REv. #6 4KV BUS T11A UNDERVOLTAGE PROTECTION UNIT 1
Attachment 3 to Enclosure 2 to AEP-NRC-2015-99 OP-I1-98043-056 "4KV Diesel Generator lAB A.C.B. Elementary Diagram"
Attachment 4 to Enclosure 2 to AEP-NRC-2015-99 RSC1-4260 Relay Diagram "Diesel Generator lAB Differential"
1 DGAB-1 1 DGAB-2 1 DGAB--3 S3 CT'S
>800/5 D.G. TEST RESITOR 4 kV BUS T11A 4 kV BUS T11B LOAD BANK RELAY SETTING PREPARED REVIEWED APPROVED CALCULATION BY/DATE BY/DATE BY/DATE "ID NUMBER 1-87-DGAB-2 /'..,.,/'-"'
'(*- PS-EDGP-005, Rev. 0 a-87-DGAB -3 P. U. =0.2 AMPS -(Y *. -, --0 C.///*//*/
ABB 87M REVISION DESCRIPTION:
No setting changes. Reformatted consistent with PMP-6065-EIC-001, Rev. 0 and revised relay IDs to reflect FDB format in response to CRA 00-03934-01..
RELAY DIAGRAM DWG. # RSC1-4260 D.C. COOK PLANT REV. #2 DIESEL GENERATOR lAB DIFFERENTIAL UNIT 1
Attachment 5 to Enclosure 2 to AEP-NRC-2015-99 RSC1I-4262 Relay Diagram "Neutral Ground Overcurrent"
0 6 of 1-51 N-DGAB 1 CT 300/5 D. G. iAB REVISION DESCRIPTION:
No setting changes. Reformatted consistent with PMiP-6065-EIC-OO1, Rev. 0. Added calculation Id number.
RELAY DIAGRAM DWG. # RSC1-4262 D.C. COOK PLANT REv. #1
- NEUTRAL GROUND OVERCURRENT UNIT 1 to Enclosure 2 to AEP-NRC-2015-99 RSCI -4261 Relay Diagram "Overload Protection"
DIESEL GENERATOR GOVERNOR LOAD SIGNAL BOX RELAY SETTING PREPARED REVIEWED APPROVED CALCULATION BY/DATE BY/DATE BY/DATE ID)NUMBER 1-51-DGAB-1 TAP 6.0 ch 1 4... PS-EDGP-00 ]
1-51-DGAB-3 Time 66 - . fk/J7- ]
@3 XP.U, I o (,(Is 12IAC51AAI101A REVISION DESCRIPTION:
No setting changes. Reformatted consistent with PMP-6065-EIC-00 1, Rev. 0. Added calculation Id number and revised relay L~s to reflect FDB format in response to CRA 00-03934-0 1.
RELAY DIAGRAM DWG. # RSC1-4261 D.C. COOK PLANT R'v'#
OVERLOAD PROTECTION UNIT 1 to Enclosure 2 to AEP-NRC-2015-99 ETAP Short Circuit Output Reports
ETAP Project: 4kV-600V Load Control Page: 49 12.6.5N Location: D.C. Cook Unit 61 Date: 10-13-2015 Contract: 12105-681 SN: AMELECPWR3 Engineer: Gregory J Hinshaw (S&L) Revision: Zmin Study Case: TR5SCLOCAABP Filename: UI1 ETAP RIO Config.: LCSS TR5 AB2 Calculation l-E-N-ELCP-4KV-001 Revision 10 TR5SC-AB (Att AK55)-Unit 1 LOCA Steady State, TR5 Only, 345kV at 104.8%, 132in M5, AB EDG ON 3-phase fault at bus: Bus TIIA Prefault voltage = 4.135 Prefultvolage=
99.40 %4135=
of nominal but kV ( 4.160 kV)
= 98.74 % of base (4.187 kV)
Contribution 112 Cycle 1.5 to 4 Cycle From Bus To Bun %V kA krA Imag. kA Symin. %V kA kA Imag. kA Symmu.
1D ID3 FronmBaa Real Imaginary tReat Magnitude From Bus Real Imaginary tReat Magnitude Bus TtIA Total 0.00 3.195 -47.6t9 t4.9 47.726 0.00 23t6 -38.t29 16.5 38 t99 NOde.TR11AIOV Bus TllA 0.13 0.108 -0.515 4.7 0.526 0.05 0.033 -0.193 5.8 0.1%
Bus tA Bus TIIA 2.78 2.167 -41.095 14.3 41.195 2.23 2.131 -32.936 15.5 33.005 Node. t11PHAHV Bus TI IA 0.00 0.000 0.000 999.9 0.000 0.00 0.000 0.000 999.9 0.000 S INJ PPtS Bus T11A 103.37 0.024 -0.322 13.2 0.322 103.37 0.015 -0.215 13.9 0.215 MDAuxFdPPW Bus TllA 103.37 0.035 -0.408 11.8 0.410 103.37 0.021 -0.273 13.2 0.274 RHR-PPIW Bus T11A 103.37 0.018 0.0244 13.5 0.245 103.37 0.007 -0.098 14.7 0.091 ESSSvcWPPIW Bus TI IA 103.37 0.014 -0310 223 0.310 103.37 0.004 -0.123 28.6 0.123 CntC hrgPP-t W BrsTt1A 103.37 0.021 -0.363 17.7 0.363 103.37 0.008 -0.145 19.2 0.146 CMPCLGPPIW Bus39 103.37 0.016 0.0360 228 0.361 103.37 0.005 -0.143 28.9 0.143 Bus TI1A 0.00 0.016 -0.360 22.8 0.361 0.00 0.005 -0.143 28.9 0.143
'lBus39 NACD Ratio = 0.90
- Indicates a fault current contribution from a three-winding transformer SIndicates a fault current through a tie circuit breaker If"faulted bus is involved in loops formed by protection devices, the short-circuit rontriutions through these PDs will not be reported.
ETAP Project: 4kV-600V Load Control Page: 50 12.6.5N Location: D.C. Cook Unit #1 Date: 10-13-2015 Contract: 12105-681 SN: AMELECPWR3 Engineer: Gregory J Hinshaw (S&L) Reviaion: Znuin Study Case: TR5SCLOCAAB3P Filename: UI ETAP RIO Config.: LCSS TR5 AB2 Calculation I-E-N-ELCP-4KV-001 Revision 10 TR5SC-AB (Att AK55)-Unit I LOCA Steady State, TR5 Only, 345kV at 104.8%, U2 in M5, AB EDG ON 3-phase fault at bus: Bus TIItB Prefault voltage = 4.120 = 99.05 % of nominal but kV ( 4.160 kV)
= 98.40 % of base (4.187 kV)
Contribution 1/2 Cycle 1.5 to 4 Cycle From Bus To Bas %V kA kA Imag* kA Syrom. %V kA kA Imag. kA Syinm.
ID ID From Bus Real Imaginary /Real Magnitude From Bus Real Imaginary /ReaI Magnitude Bus TIIB Total 000 3.417 -46.298 t3.6 46.423 0.00 2465 -37.273 15.1 37.355 Node TRl 1BHV Bus TIttB 0.t0 0 t09 -0.717 6.6 0.726 0.04 0.037 -0.323 8.7 0.325 Bus 1B Bus TIIB 3.71 3.308 -45.580 13.8 45.700 3.01 2428 -36.950 15.2 37.030 NACD Ratio =090
- Indicates a fault curren contribution from a three-winding transformer "Indicates a fault current through a tie circuit breaker If faulted bus is involved in loops formed by protection devices, the short-circuit contributions through these PDs will not be reported.
ETAP Project: 4kV-600V Load Control Page: 51 12.6.5N Location: D.C. Cook Unit #1 Date: 10-13-2015 Contract: 12105-681 SN: AMELECPWR3 Engiee: Gregory J Hinshaw (S&L) Revision: Zmin Study Case: TR5SCLOCAABP Filename: UI ETAP Ri0 Config.: LCSS TR5 AB2 Calculation I-E-N-ELCP-4KV-001 Revision 10 TR5SC-AB (Alt AK55)-Unit I LOCA Steady State, TR5 Only. 345kV at 104.8%, U2 in M5, AB EDG ON 3-phase fault at bus: Bus TIIC Prefault voltage = 4.129 = 99.25 % of nomsinal bus kV (4.160 kV)
=94.83 % of base ( 4.354 kV)
Contribution 1/2 Cycle 1.5 to 4 Cycle Fron Bus To Bus %V kA kA Imag. kA Syroni %V kA kA Iina& kA Syrom.
ID ID Froni Bus Rest Imaginary /Real Magnitude From Bus Real Imaginary /Real Magnitude Bus T11C Total 0.tO 2 945 -38.79t 13.2 38.902 000 2 143 -30.797 14.4 30.871 Node TR I1CHV Bus TI1C 0t12 0.149 -0.700 4.7 0.716 0.05 0062 -0.298 4.8 0.305 Bus 1C Bus TI1C 2.92 2 796 -38.091 13.6 38.193 2.34 2.081 -30.499 14.7 30.570 NACD Ratio = 1.00
- Indicates a fault nrrrest consribution from a three-winding transfonner
- Indicates a fault eturrest through a tie circuit breaker If faulted bus is involved in loops formed by protection devices, the short-cirvuit contributions through these PDs will not be reprorted.
ETAP Project: 4kV-600V Load Control Page: 52 12.6.5N Location: D.C. Cook Unit #61 Date: 10-13-2015 Contract: 12105-681 SN: AMELECPWR3 Engineer: Gregory J Hinshaw (S&L) Revision: Zmin Study Case: TR5SCLOCAABP F~ilename: Ut ETAP Rt0 Config.: LCSS TR.5 AB2 Calculation I-E-N-ELCP-4KV-001 Revision 10 TR5SC-AB (Att AK55)-Unit I LOCA Steady State, TR5 Only, 345kV at 104.8%, U2 in M5, AB EDG ON 3-phase fault at bus: Bus TIID Prefault voltage 44130 = 99.27 % of nominal but kV ( 4.160 kV)
=94.85 %of base(4.354 kV)
Contribution !/2 Cycle 1.5 to 4 Cycle FromnBus To Bus %V kA kA Imag. kA Symm. %V kA kA haag. kA Synto.
ID ID FromrBus Real Imaginusy /Real Magnitude From Baa Real Imaginary /Real Magnitude Bus TttD Total 0.00 2.956 -39.305 13.3 39.4t6 000 2157 -31.195 t4.5 31 269 Node.TRh11DHV Bus TI1D 0.10 0.102 -0O511 5.0 0.521 0.03 0.030 -0.175 5.8 0.178 Bus tD Bus TI1D 3.91 2.734 -36.805 13.5 36.906 3.19 2.069 -30.023 14.5 30.094 Node. t1PHCHV Bus TIID 0.00 0.000 0.000 999.9 0.000 0.00 0.000 0.0030 999.9 0.000 S INJ PPI1N Bus TIID 103.24 0.024 -0.322 13.5 0.322 t03.24 0.015 -0.215 14.1 0.2t5 RH8RPPI E Bus TI1D 103.24 0.018 -0.244 13.9 0.244 103.24 0.007 -0.098 14.9 0.098 CntChrgPP-t E Bus TIID 103.24 0.020 -0.363 17.8 0.363 103.24 0.008 -0.145 t9.3 0.146 ESSSvcWPP1E Bus TllD 103.24 0.010 -0.271 26.7 0.271 t03.24 0.003 -0.109 3t.1 0.109 AUXFWPPE Bus TI1D 99.27 0.033 -0430 13.2 0.431 99.27 0.020 -0.287 14.4 0.288 CMPCLGPPI1E Bus36 t03.24 0.016 -0.360 22.8 0.360 103.24 0.005 -0.143 28.9 0.143 Bus TI1D 0.00 0.016 -0.360 22.8 0.360 0.00 0.005 -0.143 28.9 0.143 SBus36 NACD Ratio 1.00
- Indicates a fauht current contribution front a three-winding transfonner tIndicates a fault current through a tie circuit breaker If faulted bus is involved in loops formed by protection devices, the short-circuit contributions through these PDs will not be reported.