ML20039A240
| ML20039A240 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 11/28/1979 |
| From: | Anderson T WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20039A230 | List: |
| References | |
| NS-TMA-2167, NUDOCS 8112160402 | |
| Download: ML20039A240 (14) | |
Text
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\\;O.-;.j ATTACHMENT 1
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a ysstinghouse Electric Corporation Power Systems um Paarc1PurcAm315230 November 28, 1979
'yi g S-TMA-2167 i,*.
Ref: 1. NS-TMA-2063
- 2. NS-TMA-2162 Mr. A. T. Schwencer, Chief Operating Reactors Branch No.1 Division of Operating Reactors U.S. Nuclear Regulatory Commission 2920 Ncrfolk Avenue, NW Washington, D.C.
20555
Subject:
Rod Drop Analysis
Dear Mr. Schwencer:
This letter formalizes the material presented on November 19,1979 with respect to Rod Drop Analysis and the Westinghouse (W) commitment for near and long term resolution of open issues.
i-As a result of the previously committed (Reference 1) on-going review, notification (Reference 2) under 10CFR50.59 and 10CFR50.55E was made by W for three newly identified rod drop analysis problem areas.
A meeting iias held in Bethesda on November 19, 1979 between the NRC, W, and affeci.ed utilities-to discuss these' issues.
At this meeting the attiiched slides were presented which outlined the areas of concern.
Enclosed are ten (10)_
proprietary copies of the slides and ten (10) non-proprietary copies.
Also enclosed are one (1) copy of Application for Withholding, AW-79-43 (non-proprietary) and one copy of Affidavit (non-proprietary).
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The proposed interim solution discussed at the November 19, 1979 meeting in-volves a change in plant operating procedures.
The calculated consequences for this event are dependent upon whether the reactor is being operated in an automatic or manual mode.
The concern is limited to reactor operation in the automatic mode.
The analysis in the SARs for the rod drop event with the reactor in a manual mcde remains valid.
This analysis indicates that the C"3 limit is not exceeded.
If a rou drop event occurs when the reactor is in the automatic mode, the reactor control _ system responds to both the reactor..
power drop (mismatch between turbine power and reactor pcuer) and the decrease in the core average temperature and attempts to restore both quantities to their original values.
This restoration of reactor power by the reactor control system may result in some power overshoot depending upon the excore power signal that is used.
Therefore, a simple ar.d straight forward way to
_ prevent power' overshoot is to either operate in manual rod control ar limit the potential overshoot by restricting rod insertion at high power levels.
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NS-TMA-2167 znovember 28, 1979 d
Page 2 4.
Although the manual mode.of reactor operation is safe and results in no
-jI overshoot for rod drop events,.this could potentially have an adverse impact on normal operational plan maneuvers. 'In particular, the ability of the plant to remain on-line following a load rejection event could be compromised.
6 To minimize these effects and to prevent power overshoot for rod drop events, a procedural change while the plant is in automatic mode of operation is proposed as an alternative to requiring manual control.
The proposed change is as follows:
1.
In Manual Mode of reactor control from 0 - 100% reactor power there is no change from current procedures.
2.
In Aute..atic Mcde of reactor control from 0 - 90% reactor power there is no change from current procedures.
3.
In Automatic Mode of reactor control from >90% of reactor power control Bank D must be withdrawn >215 steps.
By implementing these changes, a dropped rod event during automatic rod control will not result in an overshoot above rated themal power.
For power levels
>90%, a dropped rod event will result in a withdrawal demand from the rod control system.
Since differential rod worth of the D Bank while above 215 steps is negligible, the reactivity required for a power overshoot following a rod drop is not available.
For rod drops below 90% power, analysis has been performed to show that the reactor will not overshoot above rated thermal power and thus the DNB design basis is met.
The above procedures result in no overshoot for a dropped rod event, however, the control system is still capable of responding to certain operational maneuvers.
W is currently reviewing a number of analytic and hardware longer term solutions as an eventual alternative to the above interim recommendations.
Recommenoations will be included as part of a topical report submitted to the NRC in mid-1980.
Included in the topical will be a detailed discussion of Il methodology used in rod drop analysis.
In summary, the following points are noted:
1.
The SAR analysis. for 2 and 4-loop plants may not represent the most limiting credible single failure.
Failures in the nuclear power auctioneering of the rod control system of 2 and 4-loop plants may result in plant responses similar to the three loop concerns discussed in March 28, 1979 notification.
2.
For all W plants, which have a negative flux rate trip,.the previously reco.tT;cniied change in the setpoint to 3% in I second may not assure
. plant trip as a consequence of rod drop.
This is due to a reduction of conservatism in the error allowances and the application of a more conservative core physics model than previously ut'ilized.
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November 28, 1979 Page Three 3.
Experience shows that multiple and single-dropped rod events
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. result-in a reactor trip for a W plant if it has the negative flux
. trip. circuit.
4.
For W plants without a negative flux rate trip, the turbine runback and rod stop feature of the control system, which were approved licensing basis at the time of ' review, is adequate to avoid DNB in the dropped rod transient for all plants.
5.
W is committed to provide the NRC with a topical report on this matter Ey i.iid-1980.
6.
The use of the current procedure to assure Dim limits are not exceeded is*an interim solution.
Long term solutions will be addressed as part of.the topical report.
Correspondence with respect to the Westinghouse affidavit or application for i withholding'should reference AW-79-43, and should be addressed to R. A.
Wiesemann, Manager, Regulatory and-Legislative Affairs, Westinghouse Electric Corporation, P. 0. Box 355,,Pittsburgh, Pennsylvania 15230.
Very truly yours, WESTINGHOUSE ELECTRIC CORPORATI0fl F
Aodce_
T. M. Anderson, Manager Nuclear Safety Department MJH:kk Attactnent c
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Westinghouse Water Reactor NuclearCorrrercial
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Box 355 C
PittsburghPennsylvania 15233 Mr. L. M. Mills, Manager Nuclear Regulation and Safety y
TENNESSEE VALLEY AUTHORITY 400. Chestnut Street, Tower II December 2,1981 J
Chattanooga, TN 37401 TVA Contract Nos. 68C60-91934
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Mr. J. A. Raulston Chief Nuclear Engineer TVA-8467 TEN!!ESSEE VALLEY AUTHORITY WAT-D-4706 400 Commerce Avenue, W10 C126 Knoxville, Tennessee 37902 S.0. TVA/ TEN-485 WAT/WBT-485
Dear Messrs. Mills and Raulston:
Ref: 1) WAT-D-4014/7851,ll/28/
2)NS-EPR-2504,8/18/81 1
.i 7 E-'?/2D TENNESSEE VALLEY AUTHORITY SEQUOYAH AND WATTS BAR NUCLEAR PLANTS
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,5 E3I RECEIV UNIT NUMBERS 1 AND 2 F:a K. 5 CIS 1 DEC071981 sECTQ:1 Dropped Rod Analysis y
REGULATORY STAFF Westinghouse had previously identified to you in November 1979 (Reference 1) a concern with recard to certain assumptions employeo in the dropped rod accident safety analysis applicable to your plant.
This concern derived primarily from the potential for an unanalyzed power overshoot while in automa. tic rod control following selected dropped rod events without immediate reactor trip.
The concern applied to all Westinghouse plants with the '6xception of those older plants which are permitted credit for turbine runback to mitigate undesired power increases.
Operating Plants were notified of an Unreviewed Safety Question under 10CFR50.59 and non-operating plants notified of a Significant Deficiency under 10CFR50.55(e).
Westinghouse recommended certain operational restrictions above 90% power (either manual rod control or restricted rod insertion limits) to you as an interim addressment of the concern and also indicated an intent to further evaluate the concern and, thereby, provide final
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disposition of this matter without recourse to operational restrictions.
The NRC was also notified of this matter during the same time period and concurred in our recommended course of action, both interim and longer term.
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'l Westinghouse has now completed its long terd' evaluation, and in August of this I$
year notified the NRC of our conclusion that, based on a considerable-quantity of work, the interim restrictions 'on operation above 90% power could be removed (Reference 2).
A meeting with members of the Core Performance Branch of the NRC staff was held in late August for the purpose of presenting the basis for this conclusion.
It was agreed at the meeting that the Westinghouse methodology
, utilized warranted further evaluation by the staff.
It was also agreed that, based on preliminary review of information to be formally submitted, the staff would be able to issue an interim position which would result in removal of the-operation restrictions and the return to normal operation in automatic rod contr'ol.
We will provide this information by letter to the NRC in November.
The Westinghouse evaluation and methodology applies generically to all affected Westinghouse plants, both operating and under application, with Westinghouse fuel.
We will verify the applicability of the evaluation on a case by case. basis as part of the standard FSAR or reload analysis for both new applications.and future reloads.
Very truly yours,
/rcc WESTINGHOUSE ELECTRIC CORPORATION L. M. Mills, ll
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J. A. Raulston, 3L cc:
R. E. Lyman, IL J. L. Tain, Manager v S. A. Moser, IL Tennessee Valley Authority B. Wade. IL Projects 9
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Westinghouse Water Reactor nmo m oi.r.m
. Electric Corporation Divisions n,, g.,,
m.i.... cia uu.,i, :ma e,n; NovemberIb,1981 TVA-81-523 Ref 1: Ltr #NS-TMA-21G7, attached
- Mr. H. J. Green, Director of Nuclear Power Tennessee Valley Authority 1750 Chesnut Street Tower II Chattanooga, Tennessee 37401 yg
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Dear Mr. Green:
Tennessee Valley Authority Sequoyah Unit 1 R00 DROP ANALYSIS Westinghouse had previously identified to you in November 1979 (Reference 1) a concern with regard to certain assumptions employed in the dropped rod accident safety analysis applicable to your plant.
This-concern derived primarily from the potential for an unanalyzed power overshoot while in automatic rod control following selected dropped rod events without immediate reactor trip.
The concern applied to all Westinghouse plants with the exception of those l
older plants which are permitted credit for turbine runback to mitigate undesired power increases. Operating plants were notified of an Unreviewed Safety Question under 10CFR50.59 and non-operating plants notified of a Significant Deficiency under 10CFR50.55(e).
Westinghouse recommended cer-tain operational restrictions above 90% power (either manual rod control or restricted rod insertion limits) to you as an interim addressment of the concern and also indicated an intent to further evaluate the concern and, thereby, provide final disposition of this matter without recourse to j
operational restrictions.
The NRC was also notified of this matter during the same time period and concurred in our recommended course of' action, both interim and longer term.
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Westinghouse has now-completed its long-term evaluation, and in August of 4, ;
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thisl year notified the NRC of our conclusion that, based on a considerable quantity _ of work, the interim _ restrictions on operation above 90% power could be removed (Reference Letter #NS-EPR-2504, attached). _ A meeting with members of the Core Performance Branch of the NRC staff was held in late August' for the purpose of. presenting the basis for this conclusion.
It was agreed at the-meeting that.the Westinghouse methodology utilized warranted furtherfevaluation by the staff.
It was also agreed that, based on.
preliminary review of information to be. formally submitted, the staff would be able to issue-an interim position which would result -in removal of the operation restrictions and the return to normal operation in automatic rod control.
We will provide this information by letter to the NRC in November.
The Westinghouse evaluation and methodology applies generically to all affected Westinghouse plants, both operating and under. application, with Westinghouse fuel.
We will ~ verify' the applicability of the evaluation on a case by case basis as part of the standard FSAR or reload analysis for both new applications and future reloads.
Very truly yours, C. - M hi perating,ler, Manager ~ Plant Service Southern Region Attachment
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R. U. Mathieson e
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ATTACHMENT 4 CHANNEL CALIBRATION PROCEDURE FOR NEGATIVE RATE TRIP CIRCUITRY
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Page 18 of 25
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'5.0 PERFORMANCE OF WORK - continued j[.
& i 5.2.6 (continued)
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7, 37.
If XR-92-5001 AFI indicates the desired value i0c5% record 9'
on data sheet "as left".
Otherwise the recorder may require y-
, adjustment.
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- 38. Turn TEST SIGNAL pot R301 fully CCW and repeat steps 36 and
+
~37, but use TEST SIGNAL pot R302 and TP302.
N.
39.
- i If the remaining sections of the CAL are not to be completed, go to section 7.
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' 5.2.7 POWER RANGE RATE CIRCUIT NH311 AND BISTABLE RELAY DRIVER NC301 AND NC303 ADJUSTMENTS. To Adjust Power Range Rate.
j circuit NM311 and bistable relay drivers NC301 and NC303 l
located in Power Range A drawer assembly proceed as outlined in this section.
1.
Bypass the Power Range channel being adjusted, as specified in paragraph 5.2.1.
Place OPERATION SELECTOR switch S303 in the NORMAL position.
2.
Decnergize Power Range B drawer by removing the INSTR.
I 1
POWER fuses, 3.
Disconnect high voltage connector plug P3 3 from s
- jack J353.
i 4.
Disconnect DET A and B SIGNAL plugs P351 and P352 from j
jacks J351 and J352, respectively.
5.
Connect a jumper from GND NM311 TP11I to INPUT NH311 TP21!.
6.
Connect a DVM between test points OUTPUT TP3H (+) and GND TP11I (common) on NM311.
7.
Rotate DELAY ADJ control NM311R511 fully counterclockwise.
(Initial calibration only.)
8.
Energize Power Range B drawer by replacing the fuses.
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SQNP IMI-92-PRM-CAL f
P ge 19 of 25 Rev. 5 c
5.0 PERFORMANCE OF WORK - continued h,.
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.5.2.7
'(continued) y f,9. ; Record the "as found" value on data sheet N-41.
If the DVM'does not indicate 0.000 1 0.005 volts d.c., adjust.
+
ZERO ADJ potentiometer R7H until the DVM indication is within tolerance. Record "as left" value on data sheet N-41.
10.
Lock ZERO ADJ potentiometer R7H.
11.
Remove the jumper from TP1 and TP2 on NM311.
12.
Rotate OPERATION SELECTOR switch S303 to the DET A & B position.
I 4
l 13.
Adjust DETECTOR A and B TEST SIGNAL potentiometers R301
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and R302 for 2.083
.005V as read by a DVM connected be-l tween LE7EL TP301 (+) and GND TP305 (common) and LEVEL i
TP302 (+) and GND (common).
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i 14.
Reconnect the DVM between test points OUTPUT TP311 (+) and GND TP11f (common) on NM311 and wait E 30 sec. for the indication to reach a steady state condition. Record "as g
found" on data sheet N-41.
15.
If the DVM indication is not 0.000 1 0.005 volts d.c.
I adjust BALANCE ADJ potentiometer NM311R311 until the f
DVM indication is within tolerance. Record "as left"
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value on data sheet N-41.
16.
Lock BALANCE ADJ potentiometer R31I.
F 17.
Connect the strip chart recorder between test points 'Cla) 1
' TP1 (common) and OUTPUT TP3 (+) on Power Range Rate cir-l I cuit module NM311. Operate strip chart as necessary to obtain the information required in step-18 (2"/sec, recorder set on 10 volts).
18.
Introduce step inputs as described in steps 21 and 23 below.
Record "as found" value on data sheet N-41. Ro-tate DELAY ADJ potentiometer Nt!311R511 until the time I
taken for the output of assembly NM311 to decay to 37% -
of the peak value equals the desired delay time (= 1.3 sec.).
Record "as left" value on data sheet N-41.
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'IMI-92-PRM-CAL Page 20 of 25 j
j Rev. 10 5.0 PERFORMANCE OF WORK - continued
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i 5.2.7 (continued)-
a 19.
After the DELAY ADJ control is set, lock the potdatiometer.
-v, '
NOTE:
If the "As Found" values for the + 25 volt power i
4-.
supplies and the bistabic in question were found in 4
tolerance, Sections 5.2.7.20 through 5.2.7.31 need not be performed. For this case write the "As Found" u
+
data in the "As Left" data space. j 20.
NEGATIVE RATE TRIP setting is 3% of full power. Rotate OPERATION SELECTOR switch to the A & B position.
21.
With DET A TEST SIGNAL potentiometer R301 fully CCW, adjust DET B TEST SIGNAL potentiometer R302 for a voltage reading of 4.167
.005V at TP 306. Adjust DET A TEST SIGNAL potentiometer for a voltage reading of 4.417 i.005V at TP 306.
22.
For initial adjustment only, rotate TRIP ADJ potentiometer l
R4E and LOOP ADJ potentiometer R11E on Negative Rate Trip bistable relay driver NC301 fully CW.
NOTE:
The LOOP ADJ potentiometer R11E should be fully CW and will remain fully,CW.
I 23.
Rotate OPERATION SELECTOR switch S303 from the DET A i
& B position to the DET B position to introduce a negative step signal.
24.
Adjust TRIP ADJ potentiometer NC301R4E CCW in small increments. While holding RATE MODE switch S304 in the RESET position, rotate OPERATION SELECTOR switch S303 from DET A & B to DET B and back to DET A & B positions after each increment until the bistable j
just trips as indicated by NEGATIVE RATE TRIP lamp DS309 momentarily lighting. Allow 15 seconds to elapse each time before switching the OPERATION SELECTOR switch.
Record "as Icft" value on data sheet N-41.
25.
After the trip peint is located, lock TRIP ADJ potentio-meter NC301R4E.
26.
POSITIVE RATE TRIP setting is 5% of full power. Rotate OPERATION SELECTOR switch to the A & B position.
27.
With DET A TEST SIGNAL potentiometer R301 fully CCW, verify the voltage at TP 306 is 4.167 i.005V.
If not, adjust DET B TEST SIGNAL potentiometer R302 until the I
required voltage is obtained. Adjust DET A TEST SIGNAL potentiometer for a voltage reading of 4.583.1.005V i
l at TP306.
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IMI-92-PRM-CAL Page 21 of 25
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p 5.0 PERFORMANCE OF WORK - continued
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5.2.7 (continued) 1 28.
For initial adjustment only, rotate TRIP ADJ potentiometer R4E and LOOP ADJ potentiometer R11E on Positive Rate Trip bistable relay driver NC303 fully CW.
NOTE:
The LOOP ADJ potentiometer R11E should be fully CW and will remain fully CW.
29.
Rotate OPERATION SELECTOR switch S303 from the DET B position to the DET A & B position to introduce a positive step signal.
30.
Adjust TRIP ADJ potentiometer NC303R3E CCW in small increments. While holding RATE MODE switch S304 in the RESET position, rotate OPERATION SELECTOR switch S303 from DET B to DET A & B and back to DET B po-sitions after each increment until the bistable just trips as indicated by POSITIVE RATE TRIP lamp DS308 momentarily lighting. Allow 15 seconds to elapse each time before switching the OPERATION SELECTOR switch. Record "as left" value on data sheet N-41.
31.
After the trip point is located, lock TRIP ADJ potentio-meter NC303R4E.
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- 32. - With DET A TEST SIGNAL potentiometer-R301 fully CCW, verify i
4' the voltage at TP306 is 4.167 i.005V.
If not, adjust DET B TEST SIGNAL potentiometer R302 until the required
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voltage is obtained. Adjust DET A TEST SIGNAL potentiometer for a voltage reading of 4.375
.005V at TP 306.
33.
Rotate OPERATION SELECTOR switch S303 from the DET A & B position to the DET B position.
NEGATIVE RATE TRIP lamp should not light.
i NOTE:
If the lamp lights, the procedure starting from step 12 must be repeated.
l vY 34.
Rotate OPERATION SELECTOR switch S303 to the DET A and B 4'
position and adjust DET A TEST SIGNAL potentiometer for a 1
7" voltage reading of 4.542 i.005V.
Rotate OPERATION SELECTOR SWITCH S303 to the DET B position and reset the 4'
negative rate trip with RATE MODE switch S304.
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Page 22 of 25
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,5.0 ~ PERFORMANCE OF WORK (Cont.)
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-(Cont.)
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After 15 seconds rotate OPERATION SELECTOR switch S303 j
from the DET B position to the DET A & B position.
POSITIVE RATE TRIP lamp should not light.
NOTE:
If the lamp lights, the procedure starting from step 13 must be repeated.
36.
If the remaining sections of the CAL are not to be completed,Lgo to section 7.
I
,.f 5.2.8 BISTABLE RELAY DRIVERS NC302, 304,-305, 306, 307, and NC308 ADJUSTMENTS 4
i 4
NOTE: If the "As Found" values for the + volt power supplies '
1 and the bistables in question were found in tolerance,
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Section 5.2.8 need not be performed. For this case write l
the "As Found" data in the "As Left" data space.
i This paragraph describes the adjustment of bistable relay A
drives NC302, 304, 305, 306, 307, and NC308. The adjustment y
procedure for relay driver NC308 is described in detail, the other relay drivers are adjusted in accordance with data sheets in the same manner as bistable relay driver R-NC308. The adjustment procedure is as follows:
. NOTE:
Before any adjustments are made to the bistable i
relay drivers make sure the adjustment procedures j
for the summing and level amplifier NM310 have been '
completed in accordance with paragraph 5.2.5 i
1.
Bypass the Power Range channel being aligned as speci-fied in paragraph 5.2.1, steps 1 thru 5.
If the plant is at too high a power level, remove the cables as specified in paragraph 5.2.1, steps 6, 7, 8, and 9.
2.
Rotate OPERATION SELECTOR switch S303 to the DET A & B-position.
3.
Connect the DVM between TP306 (+) and TP305 (-).
i 4.
For initial setup, rotate TRIP ADJ potentiometer a4E and LOOP ADJ potentiometer R11E on bistable relay driver
.c NC308 fully clockwise. Following the initial setup the instrument mech should use their own esperience as a guideline.
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INSTRUCTION FOR NIS POWER RANGE CHANNEL FUNCTIONAL TEST i-i
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