SBK-L-20057, Response to Request for Additional Information Regarding Degraded Voltage Time Delay Setpoint License Amendment Request

Response to Request for Additional Information Regarding Degraded Voltage Time Delay Setpoint License Amendment Request

ML20142A204
Person / Time
Site:	Seabrook
Issue date:	05/20/2020
From:	Mccartney E NextEra Energy Seabrook
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
SBK-L-20057
Download: ML20142A204 (14)

Text

May 20, 2020 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Seabrook Station Docket No. 50-443 Seabrook Station NEXTera ENERGY~

SEABROOK 10 CFR 50.90 SBK-L-20057 Response to Request for Additional Information Regarding Degraded Voltage Time Delay Setpoint License Amendment Request

References:

1.

NextEra Energy Seabrook, LLC letter SBK-L-20001, "License Amendment Request 19-03, Application to Revise Degraded Voltage Time Delay Setpoint", January 24, 2020 (ML20027A239).

2.

NRC Request for Additional Information Regarding Degraded Voltage Time Delay Setpoint, April 23, 2020 (ML20114E159)

In Reference 1, NextEra Energy Seabrook, LLC (NextEra Energy Seabrook) submitted License Amendment Request (LAR) 19-03, requesting an amendment to the license for NextEra Energy Seabrook to revise the degraded voltage time delay set point for Seabrook Station, Unit No. 1. Specifically, the LAR would decrease the trip setpoint and allowable value for the 4.16 kV Bus 5 and Bus 6 degraded voltage time delays listed in Technical Specifications (TS) Table 3.3-4.

In Reference 2, the NRC requested additional information to complete the review of NextEra Energy Seabrook LAR 19-03.

The enclosure provides NextEra Energy Seabrook's response to the NRC's Request for Additional Information (RAI).

NextEra Energy Seabrook, LLC, P.O. Box 300, Lafayette Road, Seabrook, NH 03874

SBK-L-20057 Page 1 of 7 U.S. Nuclear Regulatory Commission SBK-L-20057/Page 2 This response does not alter the conclusion in Reference 1 that the change does not involve a significant hazards consideration pursuant to 10 CFR 50.92, and there are no significant environmental impacts associated with this change.

No new or revised commitments are included in this letter.

If you have any questions regarding this correspondence, please contact Mr. Kenneth Browne, Safety Assurance and Learning Site Director, at (603) 773-7932.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on May 20, 2020.

Sincerely, NextEra Energy Seabrook, LLC Enclosure cc:

NRC Region I Administrator NRC Project Manager NRC Senior Resident Inspector Director Homeland Security and Emergency Management New Hampshire Department of Safety Division of Homeland Security and Emergency Management Bureau of Emergency Management 33 Hazen Drive Concord, NH 03305 Katharine Cederberg, Lead Nuclear Planner The Commonwealth of Massachusetts Emergency Management Agency 400 Worcester Road Framingham, MA 01702-5399 to SBK-L-20057 Response to Request for Additional Information Regarding Degraded Voltage Time Delay Setpoint License Amendment Request

SBK-L-20057 Page 1 of 7 By letter dated January 24, 2020 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20027A239), NextEra Energy Seabrook, LLC (NextEra, the licensee) submitted a license amendment request (LAR) to revise the degraded voltage time delay setpoint for Seabrook Station, Unit No. 1. Specifically, the LAR would decrease the trip setpoint and allowable value for the 4.16 kV Bus 5 and Bus 6 degraded voltage time delays listed in Technical Specifications (TS) Table 3.3-4.

The NRC staff has identified the need for additional information to complete their review of the LAR.

Responses to these requests for additional information (RAls) are provided below.

RAl#1 Page 2 of the LAR Enclosure states, "Engineering Change (EC) 293173 - Replacement TOL Heaters [Thermal Over Load Relays] for Block Start MOVs [Motor Operated Valves], revised TOL heater sizing for the block start MOVs. That EC approves replacing the TOL heaters for the MOVs that operate on an SI [Safety Injection] signal with resized TOL heaters of a larger size."

Provide a detailed summary of the relevant calculation information that determined the resizing of the TOL heaters with a larger size for the MO Vs that operate on an SI signal was acceptable.

NextEra Energy Seabrook Response #1 Regulatory Guide RG 1.106, Thermal Overload Protection for Electric Motors on Motor-Operated Valves, provides guidance for sizing thermal overloads, and references IEEE 741-2007, Criteria for the Protection of Class 1 E Power Systems and Equipment in Nuclear Power Generating Stations, as providing a methodology for MOV TOL sizing.

Annex B of IEEE 741-2007 (2017) describes the use of the 12t methodology for TOL sizing.

The existing Seabrook Station TOL sizing methodology is established in calculation 9763-3-ED-00-28-F "Motor Control Circuit Protection". This methodology states:

TOL trip point is then determined such that:

A) When carrying full load current (FLA) multiplied by the service factor (SF),

the TOL will not trip in a time period less than three times the stroking time of the MOV.

B) When carrying locked rotor current (LRA), the TOL should trip in a time within the motor's limiting time for carrying LRA.

SBK-L-20057 Page 2 of7 If it is not possible to achieve both A and B due to the TOL characteristics, then Criterion B can be relaxed. Criterion A will not be compromised for any reason. This is consistent with the requirements of R.G. 1.106 Rev. 1.

IEEE 741-2007 (2017) Annex B recommends using the i2t methodology for selection of TOL relays. Seabrook Calculation 9763-3-ED-00-28-F is revised in order to use the i2t methodology for the block start MOV TOLs. The TOL sizing methodology for the block start MOVs in 9763-3-ED-00-28-F, Motor Control Circuit Protection, was revised by the station under 1 OCFR50.59 to include the following additional criteria:

C) When carrying LRA applicable to the degraded voltage condition, the TOL shall not trip in less than the maximum time for grid separation due to degraded voltage.

D) After carrying locked rotor current applicable to the degraded voltage condition for the time interval described in C) above, the thermal overload relay shall not trip for a time period less than three times the MOV stroking time while carrying full load current (FLA) times the service factor.

If it is not possible to achieve criteria A through D due to TOL characteristics, Criterion B can be relaxed. Criteria A, C and D will not be compromised for any reason.

Block start TOL sizing is evaluated as follows in Calculation 9763-3-ED-00-28-F to determine criteria A through D are met:

The minimum multiple of LRA at minimum trip time (Z) is determined at 7 seconds using the time-current curve for the TOL.

The desired heater amps (DHA) is calculated: LRA I (Z x 1.25) = DHA The TOL heater size is selected with DHA within minimum and maximum current range of TOL, and the actual heater trip current (Y) is calculated: Minimum Heater Current x 1.25 = y LRA in multiples of actual heater trip current is calculated: LRA I Y The LRA in multiples of actual heater trip current is then compared to the time current curve for the TOL, and the actual LRA minimum and maximum trip times are determined.

The actual LRA maximum trip time is compared to criterion B to determine if the TOL size chosen meets this criterion.

The actual LRA minimum trip time is compared to criterion C to determine if the TOL size chosen meets this criterion.

The FLA in multiples of actual heater trip current is calculated: FLA x SF I Y

SBK-L-20057 Page 3of7 The FLA in multiples of actual heater trip current is then compared to the time current curve for the TOL, and the actual FLA trip time is determined.

The actual FLA trip time is compared to Criterion A to determine if the TOL size chosen meets this criterion.

The completion of above steps determines that Criteria A, B and C are met. To ensure criterion D the following additional steps are completed.

The total stroke series duration is determined for the valve. This includes the sum of time to disconnect from the grid, inrush and three times the valve full stroke time.

From TOL minimum curve the multiple of actual heater trip current is determined at total stroke time duration.

TOL Trip current at total stroke time duration is determined by multiplying the multiplier from the step above and actual heater trip current.

The TOL trip value i2t is calculated by multiplying the TOL trip current squared by the valve total stroke series duration.

The grid disconnect time i2t is calculated by multiplying the LRA at 90% voltage squared by 7 seconds.

The valve stroke i2t is calculated by adding the LRA squared multiplied by 1 second with the FLA squared multiplied by 3 times the valve stroke time.

The total i2t is calculated by adding the valve stroke i2t and the grid disconnect i2t.

The total i2t is then compared to the TOL trip i2t value to determine if the TOL size chosen meets the acceptance criterion D.

Reference Attachment 1 for Seabrook Calculation 9763-3-ED-00-28-F worksheets to perform this calculation. Includes both work sheets - one for Criteria A, B, and C (sheet 25A of calc-28) and the second one for criterion D.

RAl#2 Page 4 of the LAR Enclosure states, "In addition, that design change approved replacing the 4.16 kV Bus 5 and 6 degraded voltage time delay relays, and decreasing the setpoint from a nominal 10 seconds (10.96 seconds allowable value) to 6 seconds (6.72 seconds allowable value)."

Provide a detailed summary of the relevant calculation information that determined decreasing the setpoint of the 4. 16 kV Bus 5 and 6 degraded voltage time delay relays

SBK-L-20057 Page 4 of7 from a nominal 10 seconds (10.96 seconds allowable value) to 6 seconds (6. 72 seconds allowable value) was acceptable.

NextEra Energy Seabrook Response #2 The degraded voltage time delay was established using the following criteria:

The time delay, including margin, shall not exceed the maximum time delay assumed in the final safety analysis (FSAR) accident analyses:

The time delay is established to ensure that the allowable time delay, including margin, shall not exceed the maximum time delay that is assumed in the final safety analysis report (FSAR) accident analyses. As described in Seabrook UFSAR Section 6.3.3.4, the total response time for the Safety Injection Signal with a loss of offsite power is 30 seconds. The "S" Signal reaches the pumps and valves in 2 seconds. Ten seconds later the Diesel Generator Breaker is closed and the Charging System Pumps start.

The remaining engineered safety features actuation system (ESFAS) loads are sequenced onto the safety bus thereafter.

The Diesel start and loading time of 12 seconds was the original bounding assumption for the original selection of the degraded voltage time delay relay setting of 10 seconds.

Reducing the degraded voltage time delay relay setting to 6 seconds is conservative with respect to ESFAS accident analysis time response as it is bounded by the original 10 second start time for the emergency diesels.

The time delay shall be of limited duration to prevent damage to valve actuator motors operating at locked rotor current (LRA) due to a degraded voltage condition:

According to Limitorque Bulletin LM-77, the thermal overload should be selected to ensure the motor will trip the overload device while at locked rotor current within 10 seconds for AC motors. This establishes the upper bounding limit on the degraded voltage time delay setting in order to prevent damage to the valve motors. By reducing the degraded voltage time delay relay setpoint from nominal 10 seconds to 6 seconds, the valve motors would not be subjected to locked rotor current for greater than 6.91 seconds (see RAI #3 response for details). Therefore, they would not be damaged due to a locked rotor condition following an SI during a degraded voltage event before the emergency bus is disconnected from offsite power and re-powered from the emergency diesel generator.

The time delay shall be of sufficient duration to prevent disconnection from the preferred power source during grid transients and 4 kV motor starts:

The degraded voltage time delay value was selected to ensure large motors can start following the SI. The 4 kV motors that start on a SI signal are listed in Table 8.4-1 in Calculation 9763-3-ED-00-02-F, Voltage Regulation Study. This table includes CS-P-

SBK-L-20057 Page 5of7 2A/B, Sl-P-6A/B, RH-P-8A/B, and FW-P-378. Motor data sheets were reviewed to ensure these motors would start in less than the 5.28 second minimum degraded voltage time delay (see RAI #3 response for details). The start times for these motors at a degraded voltage are as follows:

Sl-P-6A/B: 4.5s at 70%V CS-P-2A/B: 3.9s at 70%V RH-P-8A/B: 2.3s at 80%V FW-P-378: 3.4s at 80%V 9763-3-ED-00-23-F, Medium Voltage Protective Relay Coordination & Miscellaneous Relay Set points, was reviewed to determine if existing protective relay settings are adequate to ensure 4 kV motors will not trip when starting at the loss of voltage relay allowable value of 2908V (72.7% rated motor voltage). Seabrook documents FP52504 and FP52508 show the motor acceleration curves for the SI pump motors and CS pump motors at 70% rated voltage. Comparison of these curves with the trip curves in 9763 ED-00-23-F shows that these motors will not trip when starting at 70% rated voltage.

9763-3-ED-00-23-F shows the motor acceleration curves for the RH pump motors and EFW pump motor at 80% voltage. While motor acceleration curves are not available to show motor starting at 70% voltage, a qualitative review of 9763-3-ED-00-23-F shows that there is sufficient margin to ensure that these motors will not trip when starting at 2908V.

Block start MOV TOLs shall not trip in the event of an accident signal coincident with a degraded voltage condition:

As discussed in the response to RAI #1, the TOLs for block start MOVs are sized to ensure that when carrying LRA they will not trip in less than 7 seconds. Therefore, the degraded voltage time delay relay setpoint, including tolerances, must be less than 7 seconds. This will ensure availability of the block start MOVs to perform their safety function following disconnection from the preferred offsite power source, and subsequent connection to the emergency diesel generators.

RAl#3 Page 6 of the LAR Enclosure states, "By reducing the degraded voltage time delay relay setpoint from nominal 10 seconds to 6 seconds, the valve motors would not be subjected to locked rotor current for greater than 6.91 seconds (6.72 seconds allowable value+ 0.067 second delay for the under voltage relay+ 0.04 second for the emergency power sequencer+ 0.083 second breaker interrupting time). Therefore, they would not be damaged following an SI during a degraded voltage condition before they are powered from the diesel generator."

Provide a detailed summary of the relevant calculation information that determined the above time values are acceptable, unless this information is included as a part of the calculation information requested in RAls # 1, 2 above.

SBK-L-20057 Page 6 of7 NextEra Energy Seabrook Response #3 Based on the RAI #2 response, the degraded voltage time delay relay pickup time must be greater than 4.5 seconds, and less than 7 seconds. Therefore, a setpoint of 6 seconds was chosen. To ensure relay pickup time, including tolerances, will occur between 4.5 and 7 seconds, the relay allowable value is calculated as follows in Seabrook Calculation SBC-128, Technical Specifications - Set points and Allowable Values:

The Relay Adjustable Range is 1.5 to 15 Seconds The relay setpoint is 6.0 Seconds RA= Relay Accuracy of 5% (Reference Seabrook Document FP31123, 5 kV Metal Clad Switchgear Instruction Manual)

RA= 0.30 Seconds RD = Relay Drift is assumed to equal 3% span (Consistent with original design).

RD= 0.41 Seconds MTE =Measurement and Test Equipment Accuracy (Assumed)

MTE = 0.01 Seconds Therefore, the relay Allowable value (maximum time delay) was determined to be the arithmetic sum of the above terms resulting in an Allowable value of 6.72 seconds.

The maximum under voltage relay response time is< 3 cycles (0.05 second) per the manufacturer's data (Reference Seabrook Document FP31123, 5 kV Metal Clad Switchgear Instruction Manual). Based on discussions with the manufacturer, a response time of 1 cycle longer than specified can be expected due to variation in field test equipment. The value of< 4 cycles (0.067 seconds) has been conservatively chosen as the design value. Therefore, the maximum time that the actuation of the degraded voltage protection scheme would be blocked assuming the degraded voltage setpoint has been reached coincident with a safety injection signal would be:

Time= 6.72 + 0.067 Time= 6.787 Seconds.

This time (6.787 seconds), plus the time of the emergency power sequencer (0.040 second, Reference Seabrook Document SBP 86-1050 Memo from B. Beuchel to J.

DeVincentis "Diesel Generator Start Time Extension"), plus the circuit breaker interrupting time (0.083 second, Reference Seabrook Document FP30885, 5 kV Switchgear 1200 & 2000 A Circuit Breaker Certification) equals 6.91 seconds. This is the maximum time the buses would be subjected to degraded voltage conditions

SBK-L-20057 Page 7 of7 coincident with a safety injection signal, which is less than the value of 7 seconds used for sizing the block start MOV TOL heaters.

The allowable value combined with the response time of the degraded voltage relay ensures that the degraded voltage protection scheme actuates before the thermal overload protection would be expected to actuate due to locked rotor during an SI coincident with a degraded voltage condition.

Similarly, the minimum time that the time delay relay would be expected to operate would be the nominal trip setpoint less 0.72 seconds or:

Minimum Relay Pickup time= 6.0 - 0.72 Minimum Relay Pickup time = 5.28 Seconds This meets the requirement of greater than 4.5 seconds.

Based on the above discussion, a nominal 6 second time delay is acceptable in order to ensure adequate time is available for blocking actuation of the degraded voltage protection scheme during motor starting and transient voltage conditions. The selected time delay settings ensure adequate motor protection and prevents any Class 1 E load becoming unavailable due to its protective devices trip such that it cannot be automatically transferred successfully to the onsite supply.

SBK-L-20057, Attachment 1 Page 1of4 - Seabrook Calculation 9763-3-ED-00-28-F, Motor Control Circuit Protection, TOL sizing worksheets Calculation No. 9763-3-ED-00-28-F Sheet 25A Worksheet-Block Start Calc-28 MOV Protection Sizing Valve Tag#: ____ _

MCC-Circuit Node#

Calc-28 Sht.

Input Data:

l-NHY-310231, Sh. __

NP= FLA= __ A Test current Ref.

TC*= Test Current= --- A" '

AR Ifno TC, use FLA= 1.25 x NP= 1.25 x

=

A LRA=

A If TC available, determine FLA using one of following three options :

Running time = __ s l.3NP = 1.3 x

=

A [Design Basis IV.(2)]

(1-NHY-250000)

If TC> l.3NP, then FLA= TC = __ A Service factor = SF = --

IfTC:'.SNP, thenFLA=NPx 1.1= __ x1.1 = __ A

• use larger of open or close test IfNP<TC<l.3NP, then FLA= TC x 1.1 = __ x 1.1 = __ A current Size/Type Controller-Design Bases 1.(1)&(2)

Size -- FVR Starter Circuit Breaker Frame Size, Design Basis 1.(3)

-- A DIT = Desired instantaneous trip setting 12 x FLA=

A Design Basis 1.(5) 2x LRA=

A Use larger Select trip coil rated to carry FLA x SF See App. A, sheet 1; Design Basis 1.(4)

A Coil Select adjustable trip setting::=:: DIT [do not use lo/hi]

See App. A, Sheet 1; Design Basis 1.(5)

Set@

(

A trip)

Minimum Multiple of LRA at Minimum Trip Time See Sh. 17, Figure IA at 7 Seconds: (Z) (Gould)

Z = 3.8 Multiples (Gould)

See Sh. 18, Figure 1B at 7 Seconds: (Z) (G.E)

Z = 7.6 Multiples (G.E.)

DHA=Desired heater amps = LRA I (Z x 1.25)

Design Basis IV.(l)(C)

DHA=

I (Z x 1.25) =

A Select heater size with DHA within MINIMAX current range. See appendices A and Al.

G30T (Gould) CR123C (G.E.)

Heater MINIMAX current Range

(

)

Y = Actual heater trip current = (MIN x 1.25)

Y=

x 1.25 =

A LRA in multiples of actual heater trip current [round to two places]

Multiples = LRA/Y = __ I

=

Actual LRA trip time (see Sheet 17 (Gould) 18 (G.E.), max curve) s; Criteria met: Yes or No Criteria: trip time.:::;10 s: Design Basis IV.(l)(B)

Justify no:

Actual LRA trip time (see Sheet 17 (Gould) 18 (G.E.), max curve)

--- s; Criteria met: Yes -

or No -

Criteria: trip time :'.::7 s: Design Basis IV.(l)(C)

(FLA x SF) in multiples of actual heater trip current:

(FLA x SF) /Y Multiples= L__ x __)I __ = __

Actual (FLA x SF) trip time (see Sheet 17 (Gould), 18 (G.E.) min s*

3x

=

s curve) Criteria: trip time :'.::3 x running time Design Basis IV.(l)A)

Criteria met: Yes or No Justify no:

SBK-L-20057, Attachment 1 Page 2of4 Calculation No. 9763-3-ED-00-28-F, Rev.

Appendix F Sheet Structure or System: Electrical Distribution

Subject:

BLOCK START MOV I2t Calculation Safety (Using Field Tested FLA)

Input Data Valve Actuator Type TOL Size Used Range TOL Trip Current (Tripl)

DVR Grid Disconnect Time Max. (GDtrn)

Locked Rotor Time Without Lost Motion (LRTnlm)

Full Stroke Time (PST)

Locked Rotor Current (LRA)

MCC to

TOLminI x 1.25

Locked Rotor Current during Degraded Voltage (LRAt, 90% LRA)

Full Load Current (FLA)

Service Factor (SF)

Calculation FLA x SF (FLAsf)

Total Stroke Series Duration (Tdur)

Multiplier from Figure 1B Min Curve at Tdur (Mult)

Trip Current at Trip Time Tdur (Titd)

Trip I2t Value Trip I2t (TI2t) = Titd2 x Tdur Grid Disconnect Time Max. I2t (TDI2t)

= LRAt2 x GDtrn = LRAt x LRAt x GDtrn Stroke I2t Value without Lost Motion (SIT2nlm)

Inrush I2t (II2tnlm) = LRA2 x LRTnlm Stroke I2t (SI2tnlm)= FLAsfl x 3 x PST Sum I2t (SIT2nlm)

Total I2t (TotI2t)

Acceptable?

TDI2t + SIT2nlm

TI2t > TotI2t = Yes Node Amp.

Amp.

Sec.

Sec.

Sec.

Amp.

Amp.

Amp.

Amp.

Sec.

Amp.

A2sec A2sec A2sec A2sec

SBK-L-20057, Attachment 1 Page 3of4 Cumulative 12t Calculation Methodology:

Block Start MOVs Calculation 9763-3-ED-00-28-F Appendix G Required input data and calculated results are listed below in the order that they appear on the TOL sizing worksheet on the previous page. These data items and the calculated results have been assigned variable names in the TOL sizing worksheet. Those names are shown here to promote easy comparison between the descriptions here and the form inputs. Other data is entered on the TOL sizing worksheet informationally, but only values used in calculations and calculation results are named and addressed here. The active inputs, calculated point formulae, and justifications follow.

TOL Heater Minimum Current (TOLminl)

Enter the lower current value for the heater size being evaluated for both Gould and G.E.

Heaters as published in Appendices A or A 1 of this calculation.

TOL Trip Current (Tripi) (Calculated)

=1.25 x TOLminl for both Gould and G.E. per manufacturer specifications.

DVR Grid Disconnect Time Max. (GDtm)

A 7 second duration is used which conservatively envelopes the 6.91 second value from calculation SBC-128-CALC.

Locked Rotor Time Without Lost Motion (LRTnlm)

A bounding value of 1 second is provided in IEEE Std. 741-2017, Annex 8. Neither Seabrook nor the fleet MOV engineer has test data to support a less conservative number.

Therefore, enter "1" for Limitorque actuators (currently only Limitorque actuators block start).

If a Rotork actuator requires block start evaluation in the future, Rotork correspondence titled "LN0196 - Inrush current for a 11NA1 actuator is under 100 milliseconds", attached to this appendix, supports 100 ms. 200 ms should be applied for conservatism.

Full Stroke Time (FST)

This is the MOV stroke time as tabulated per motor control center (MCC) node ID in this calculation. This should also match the upper value reflected in drawing 1-NHY-250000.

Locked Rotor Current (LRA)

Enter locked rotor current value as documented for the MOV's MCC node ID in this calculation.

Locked Rotor Current during Degraded Voltage (LRAt) (Calculated)

MOV motors behave as constant impedance devices within a range of voltages above and below rated voltage. For the block start case, voltage during the locked rotor duration is well below 90% voltage, and likely outside the region of constant impedance response. 90% voltage is within the high confidence region of constant impedance response, and is conservatively assumed for this purpose, therefore LRAt = 90% x LRA.

Full Load Current (FLA)

Enter full load current value as documented for the MOV's MCC node ID in this calculation.

SBK-L-20057, Attachment 1 Page 4of4 Service Factor (SF)

Enter service factor value as documented for the MOV's MCC node ID in this calculation, usually 1.0 for MOVs.

FLA x SF (FLAsf) (Calculated)

Per UFSAR criterion 8.3.1.1.g.2.2(a) and Calculation design basis IV(1)(A), =FLA x SF Total Stroke Series Duration (Tdur) (Calculated)

Sum of stalled locked rotor, inrush, and stroking times, Tdur = GDtm + LRTnlm + 3

• FST Multiplier from TOL Min Curve at Tdur (Mult)

From the appropriate (Gould or G.E.) TOL curve, Figure 1A (Gould) or Figure 1 B (G.E.)

of this calculation, find the value of Tdur on the vertical (time) axis. Plot a line to the right to the lower trip curve, then down to the multiplier value. Enter this multiplier.

Trip Current at Trip Time Tdur (Tltd) (Calculated)

TOL trip curves are presented in multiples of trip current. To get actual current multiply the multiplier by the TOL trip current. =Tripi x Mult Trip 12t Value (Tl2t) (Calculated)

Current squared multiplied by time, = Tltd2 x Tdur DVR Grid Disconnect Time Max. 12t (TDl2t) (Calculated)

Locked Rotor Current during Degraded Voltage (LRAt) squared multiplied by DVR Grid Disconnect Time Max. (GDtm). = LRAt2 x GDtm Inrush 12t without Lost Motion (112tnlm) (Calculated)

Locked Rotor Current (LRA) squared times Locked Rotor Time Without Lost Motion (LRTnlm), = LRA2 x LRTlm Stroke 12t without Lost Motion (Sl2tnlm) (Calculated)

Full Load current x service factor (FLAsf) squared times 3 times Full Stroke Time (FST),

= FLAsf2 x 3 x FST Stroke 12t Value without Lost Motion (SIT2nlm) (Calculated)

Sum of 12t contributors for a stroke with no lost motion. =112tnlm + Sl2tnlm Total 12t (Totl2t) (Calculated)

Sum of all 12t contributors = TDl2t + SIT2nlm Acceptable? (Calculated)

If Trip 12t Value (Tl2t) >Total 12t (Totl2t) Yes, Otherwise No. If no, increment heater size and try again.