ML17212A843

Meeting Slides for Pre-submittal Meeting with Tennessee Valley Authority on Unbalanced Voltage License Amendment Request for TVA Nuclear Plants

ML17212A843
Person / Time
Site:	Browns Ferry, Watts Bar, Sequoyah, 07000052
Issue date:	08/01/2017
From:	Schrull E, Womack T Tennessee Valley Authority
To:	Andrew Hon Plant Licensing Branch II
Hon A
References
Download: ML17212A843 (20)

Text

Class 1E Unbalanced Voltage Relay License Amendment Request Tamatha Womack - Corporate Power System Analysis Ed Schrull - Corporate Manager Fleet Licensing August 1, 2017

TVA Unbalanced Voltage Relays Agenda

• Overview

• Initiative Criteria

• Protection Approach / Design Basis

• Setpoint Methodology

• Project Summary

• License Amendment Request Contents and Schedule Class 1E Unbalanced Voltage Relay l 2 License Amendment Request

TVA Unbalanced Voltage Relays Overview TVA studies identified:

• Open phase events can cause unbalanced voltage

• TVAs station auxiliary design and/or transformer configuration prevented all open phase events from degrading the offsite power source (i.e., source will continue to provide adequate capacity and capability to perform its safety function)

• Existing undervoltage protection schemes would not provide protection for all open phase events that could affect safety equipment function.

Class 1E Unbalanced Voltage Relay l 3 License Amendment Request

TVA Unbalanced Voltage Relays Industry Initiative Criteria

• Detection and Alarms

• Must be detected and alarmed in Main Control Room (MCR) unless it does not prevent function

• Without automatic detection, identification of non desirable configuration should occur in a reasonably short period of time

• Automatic detection for transformers in standby mode is not required until loads are transferred to the standby source

• Actuation circuit(s)

• Minimize misoperation or spurious action that could cause separation from an operable GDC-17 source

• Does not result in lower overall plant operation reliability

• Coordination with other transmission system and plant electrical system protection Class 1E Unbalanced Voltage Relay l 4 License Amendment Request

TVA Unbalanced Voltage Relays Industry Initiative Criteria

• Protection actions

• Without accident signal: No adverse effect on function of safety equipment, TS LCOs maintained, safety equipment is not damaged, and shutdown safety not compromised

• With accident signal: Automatic transfer of loads required to mitigate postulated accidents, unless acceptance criteria are met with the open phase, given other plant features Class 1E Unbalanced Voltage Relay l 5 License Amendment Request

TVA Unbalanced Voltage Relays Approach to Protection

• Open Phase Conditions are:

• Loss of one or two phases at a specific location (high side of transformer)

• Event(s) that can cause unbalanced voltage / negative sequence voltage

• TVAs protection scheme

• Consistent with existing undervoltage protection schemes

• Setpoints are based on measurable parameters (i.e., unbalanced voltage

/ negative sequence voltage) not the event, therefore cannot be referred to as open phase protection

• Setpoints are based on maintaining function for connected Class 1E equipment

• Provides protection from any event in the non-Class 1E system (plant or grid) which can cause adverse unbalanced /negative sequence voltages Class 1E Unbalanced Voltage Relay l 6 License Amendment Request

TVA Unbalanced Voltage Relays Design Basis

• Provide 100% protection against loss of safety function due to unbalanced voltages at the safety buses, including upstream open phase events

• Including both in-plant and transformer open phase events

• Utilize existing undervoltage protection circuits

• Existing sensing circuits (Bus PTs)

• Existing logic circuits (trip offsite power)

• Minimal modification costs

• Utilize relays qualified for Class 1E use TVA chose the ABB Type 60Q Phase Unbalance Relay (negative sequence overvoltage) due to experience with similar relays

• Utilize bottom-up setpoint methodology Class 1E Unbalanced Voltage Relay l 7 License Amendment Request

TVA Unbalanced Voltage Relays (Setpoint Methodology)

LOSS OF LIFE Protects against long term motor degradation:

• Setpoint based on ANSI allowable values

• Time delay allows for clearing anticipated ground faults l 8

TVA Unbalanced Voltage Relays (Setpoint Methodology)

EVERYTHING WORKS Protects against loss of safety function on offsite power:

• No motors trip on current (running or starting)

• No motor start failure, including LOCA sequencing

• Time delay based on safety analysis limit for EDG start time l 9

TVA Unbalanced Voltage Relays (Setpoint Methodology)

SURVIVE Protects ability to survive the unbalance and transfer required safety loads to onsite supply:

• No motors trip on current (running or starting)

• Time delay based on survival time @

100% unbalance l 10

TVA Unbalanced Voltage Relays Relay Scheme - Added to Existing Undervoltage Circuits Permissive Voltage Unbalance 1/2 Logic Relays (Type 60)

Class 1E Unbalanced Voltage Relay l 11 License Amendment Request

TVA Unbalanced Voltage Relays Relay Scheme

• Setpoints are Tech Spec values

• • Activation of MCR indication and trip function require NRC approval Class 1E Unbalanced Voltage Relay l 12 License Amendment Request

TVA Unbalanced Voltage Relays Analytical Limits & Setpoints - SQN

• Analytical Limit: Final Setpoints:

Voltage Limits (V) Time Delay (Sec) Voltage Time Delay (S)

Relay Relay Lower Upper Lower Upper (V)

Alarm 1.3 2.95 Alarm 0.9 *1.5 0.3 *3.0 Low Trip 2.96 9.95 Low Trip 1.5 *3.3 4.0 *10.0 High Trip 18.13 3.95 High Trip 3.3 *20.0 3.0 *4.0

• designated analytical limits

• Voltage measured in line-neutral secondary

• To avoid nuisance actuations, the three relays nominal pick-up settings should be as close as possible to the upper limits, accounting for associated errors and tolerances.

• The time delay setpoints for the Low Trip and the High Trip relays must not overlap with the Alarm relay time delay setpoint, accounting for associated errors and tolerances Class 1E Unbalanced Voltage Relay l 13 License Amendment Request

TVA Unbalanced Voltage Relays - Compliance Summary

• Single Failure Criteria - Class 1E protection scheme

• Class 1E qualified protective relays (ABB 60Q) on each train/division

• Permissive 1 out of 2 logic scheme to provide reliability

• Any failure of a component is the Class 1E failure and the second train will remain available, per single failure criteria

• Accident Time Delay - Consistent with degraded/loss of voltage protection

• Setpoints ensure Class 1E equipment will be able to provide their safety function under all anticipated operational occurrences, including a concurrent design basis event

• Time delays ensure the power source is automatically transferred to the onsite power system within the time assumed in the accident analysis Class 1E Unbalanced Voltage Relay l 14 License Amendment Request

TVA Unbalanced Voltage Relays - Compliance Summary

• Unbalanced Voltage TS LCO Action Completion Times and Surveillance Requirements are consistent with existing undervoltage protection

• Loss of Power Diesel Generator Start Instrumentation being modified

• New function provided by the unbalanced voltage relays for initiation of the diesel generators Class 1E Unbalanced Voltage Relay l 15 License Amendment Request

TVA Unbalanced Voltage Relays - Project Summary

• Unbalanced voltage methodology has been validated through calculations and field testing

• Unbalanced voltage relays are already installed or being installed without trip enabled for monitoring

• BFN: 6 boards installed, 2 remain

• SQN: Complete, 4 boards installed

• WBN: 2 boards installed, 2 remain

• Monitoring setpoints are set significantly lower and in such a manner to provide data acquisition and positive actuation Class 1E Unbalanced Voltage Relay l 16 License Amendment Request

TVA Unbalanced Voltage Relays - TS Example Class 1E Unbalanced Voltage Relay l 17 License Amendment Request

TVA Unbalanced Voltage Relays - Fleet Differences

• There are subtle differences in the presentation /

documentation of the information for the Browns Ferry, Sequoyah, and Watts Bar stations in the fleet submittal.

• The unbalanced voltage relay Technical Specifications remain consistent with each stations existing table formats.

Class 1E Unbalanced Voltage Relay l 18 License Amendment Request

TVA Unbalanced Voltage Relays -

LAR Schedule

• TVA Fleet License Amendment Request

• Submit LAR by September 8, 2017

• Request NRC approval by September 28, 2018

• Activate trip function of UVRs by industry initiative deadline of December 31, 2018 Class 1E Unbalanced Voltage Relay l 19 License Amendment Request