ML20085F252
| ML20085F252 | |
| Person / Time | |
|---|---|
| Site: | Mcguire, Farley, McGuire, 05000000 |
| Issue date: | 05/19/1983 |
| From: | Toman G FRANKLIN INSTITUTE |
| To: | Shemanski P NRC |
| Shared Package | |
| ML20085F257 | List: |
| References | |
| CON-NRC-03-81-130, CON-NRC-3-81-130 TAC-51000, TER-C5506-417, NUDOCS 8308190033 | |
| Download: ML20085F252 (19) | |
Text
t INTERIM TECHNICAL EVALUATION REPORT EVALUATION OF McGUIRE UNITS 1 AND 2 UNDERVOLTAGE TRIP ATTACHMENT FAILURES 4
s
?
NRC DOCKET NO. 50-369, 50-370 FRC PROJECT C5506 NRC TAC NO. 51000, 51001 FRC ASSIGNMENT 16 j
NRC CONTRACT NO. NRC 03-81 t30 FRC TASK 417 Prepared by Franklin Research Center Author: G. Toman 20th and Race Streets J. Scone Philadelphia, PA 19103 FRC Group Leadr: G. Tome:
Prepared for Nuclear Regulatory Commission Lead NRC Engineer: P. Shawk.1 Washington, D.C. 20555 May 19, 1983 This report was prepared as an account of work sponsored by an agency of the United States Govemment. Neither the United States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or implied, or assumes any legal liacility or responsibility for any third party's use, or the results of suen use, of any information, acca-ratus, product or process disclosed in this report, or represents that its use by such third party would not infringe pnvately owned rights.
XA Copy Has Been Sent to PDR q-1 L
g.3$gGGO3 h
, g
~
l
. Franklin Research Center A Division of The Franklin Insutute The Senestrun Frannan 7enmey. PNaa.. Pe. 19103 (21M 4481000 l
t i
I l
TER-C550 6-417 CCNTENTS Section Title Page 1
INTRODUCTION 1
2 EVALUATION OF THE INTERACTION BETWEI21 THE UVTA AND THE CIRCUIT BREAKER 2
2.1 Discussion of Failures.
2 2.2 Operation of UVTAs on Circuit Breakers.
3 2.3 Measurements of UVTA Output Force and Circuit Breaker Trip Bar Input Focce 4
2.4 Trip Timing of Circuit Breaker Operation by UVTA 5
.3 EVALUATION OF UVTAs AT FRC.
8 3.1 Characterization Measurements.
8 3.1.1 Mechanical Dimensions 8
3.1.2 Forces Developed 9
3.1.3 Discussion of Roller Bearing 10 4
CONCLUSIONS.
15 5
RECCMMENDATIONS.
16 e
66 A
111
..$ Franklin Researen Center
% wNr 1
4
-m=v..
I
TER-C550 6-417 i
1.
INTECCCCTICN This Interim Report contains the " initial *indings of Franxlin Researen Center (FRC) concerning the evaluation of failures of undervoltage trip attachments (UVTA) associated with tiestinghouse DS-416 reactor trip circuit breaket* (BCTB) from McGuire Units 1 and 2.
This is a report of work in progress; thus, the conclusions contained nereitt may change as subsequent evaluation is completed.
The scope of work for this effort includes the evaluation of:
1.
the interaction between the UVTA and the associated circuit breaker,
/
2.
the failure modes (both those recognized by the Licensee and vendor and those determined by FBC during the evaluation, 3.
newly pcoscribed test methodology for determining correct mating between the UVTA and the circuit breaker and for determining the adequacy of critical clearance between components of the UVTA, 4.
modifications made by the vendor to prevent failures, 5.
evaluation of baseline test data taken on McGuire RTC3s.
l l
_ #_4 - ndb Frankan,n. search Center Re ao r
A L
TER-C5506-417 2.
E7ALCATICN CF THE INTERACT!CN BEThT.EN THE UVTA AND THE CIRCUIT BPIAKER To evaluate circuit breaker and UVTA interaction, Mr. G. Toman and Mr. J. Stone of FBC traveled to McGuire Nuclear Station to view the RTC3 installation, to watch a new UVTA and several f ailure-prone UVTAs in operation on a circuit breaker, and to discuss the past failures and corrective action with Duke Power Company personnel.
2.1 DISCUSSICN CF FAILURES The Cuke personnel described the failures that have occurred to date.
The first was attributed to inadequate clearance between the roller bracket and the moving core in the vicinity of the pin that lif ts the operating rod (see Figure 1 for nomenclature and cutaway drawing; see Figure 3 for side view and operating positions of UVTA). The second failure mode involved improper clearance of the UVTA trip tab with respect to the circuit breaker trip pin on the rotating trip bar. The third failure mode involved the retaining clips of the pivot shaf ts that could walk off the shaf t ends, allowing the shaf ts to drop out of the frame and causing the device to jam.
The corrective action recommended by Westinghouse for the third failure mode is most easily addressed. The grooves for the spring clips were found to be too narrow. Westinghouse has now cut the grooves wider so that the clip is completely relaxed when the clip is properly on the shaft, thereby requiring significantly higher forces to cause the clip to move out of the groove.
As the UVTA is now made in the " modified" version, the clips snould deform and break if enough force is exerted.on them to remove them. This amount of force should not occur due to any nos:nal operation of the device.
The manufacturer's corrective action for the second failure mode was to reject devices with less than 0.018 inches clearance between the moving core and the roller bracket arm.
In addition, a minimum clearance of 0.030 inches between the roller bracket and the brass bushing on its pivot pin is also required to prevent the bushing from causing a lateral force that pinches the O f.O Franklin Research Center s ca a.e n. nimia m
l i
TER-C550 6-417 cracxec between the frame and the bushing. This pincning would act as a braxing mechanism and prevent unlatching of the UVTA.
The third failure mode is improper positioning of the trip tab witn tespect to the trip bar colled pin (trip pin). This positioning is critical in two diloctions, in that the UvTA trip tab must be neither too c1cse nor too far from the pin.
l l
The manufacturer's recommended correctit'e action to prevent positioning problems is to measure the clearance between the trip bar pin of the circuit breaker and the trip tab of the CVTA with the circuit breaker closed and latched and the UVTA armad. Duke personnel found that small drill bits held oy a needle-nosed pliers could be used to make this measurement. The drill bit that exactly fit between the pin and the trip tab was then measured and recorded. A minimum of 0.030 inches is required. Westingnouse refers to this clearance as " pre-travel." To assure that the trip tab had adequate remaining travel to cause the circuit breaker latch to trip, the manufacturer. required that a shim be placed between the reset arm bracket and the brass bushing on the roller bracket pivot pin.
If the UVTA can successfully trip the circuit breaker with a 0.070-inch-thick shim in place, the UvTA has adequate trip margin.
(No te: Trip margin is the manufacturer's term. The shim is called a
+.
trip margin gage.)
For this test, Duke personnel used drill bits to determine the trip margin.
2.2 OPERATICN OF UVTAs CN CIRCUIT BREAKERS Following the discussion of failures and corrective measures, FRC rsquested that Duke personnel place three DVTAs on the test circuit breaker (a Catawba DS-416) for observation of operation and performance of the clearance and force tests that are now recommended by Westinghouse. The UVTAs were benught to the McGuire plant by FRC.
They were the McGuire 1A UVTA that had failed to trip during tests, a Catawba' unmodified UVTA (as originally received
~
with the circuit breakers), anda" modified,"newhmanufacturedUvTA.
A fourth device, the McGuire 2B UVTA, pas brought to the McGuire plant; hcwever, it was in the disassemeled state and could not be tested on a circuit breaker.
l
- c--h.' 2 Franklin Research Center
- o m aavn.rr
,,4
t TER-C550 6-417 The first device to be tried on the circuit breaner was une 1A UWA.
The pretravel gap measurement was taken, and then the trip margin gap test was attempted. This required tripping the circuit breaker by deenergizing the UVTA coil. The 1A UVTA coil was deenergized and the UVTA did not unlatch and trip the circuit breaker. Attempts were made to determine the cause of b inding. The moving core was noted to release and move slightly, indicating that the core had not jammed. The device remained latched for 10 minutes or more until it was jarred while attempting to find the cause of binding. The failure to unlatch at the McGuire plant could not be repeated. The testing of 1
the 1A UVTA and the other two UVTAs was completed on the Catawba circuit breaker without further failures to unlatch.
NOTE:
Subsequent to return to Philadelphia, FRC determined that the source of binding of the 1A UVTA was inadequate clearance between the roller bracket and its brass bushing which caused a braking action that prevented rotation. FRC succeeded in having the device remain latched while deenergized;several times. The clear e between the bushing and the coller shaf t was such that failuss to unlatch would be periodic and not continuous.
2.3 MEASUREMENTS OF UVTA OUTPUT FORCE AND CIRCUIT BREAKER TRI? BAR INPUT FORCE Duke personnel demonstrated the methodology for measuring the force required to unlatch the circuit breaker and the output force from the UVTA.
The force required to trip the latch of the circuit breaker is measured by pushing 'on the trip bar pin of the manual tripping mechanism at approximately the same point at which the UVTA would strike its trip bar pin.
A horizontal spring scale is used. The measurements vary from reading to reading since the method is not highly precise. Consistency is attempted and 4
an average of multiple measurements is required.
l The measurement of available output force that can be performed on the McGuire plant circuit breakers is a static pull of the reset lever from the point just in front of the tab that is above the roller bearing when the device is latched (see Figure 2).
Duke personnel perform this test with the UVTA unlatched, causing the trip spring to be in the most relaxed operating
~
state. This reading is conservative with respect '. 2 a reading taken with the i
1 A
-4_.
M Franklin Research Center
- o n e n. er
e s
TER-C550 6-417 trip spring in the latened position and would compensate for the pivot po int frictions that would reduce initial output force slignely. A multiplier of 0.38 must be used to adjust these forces to account for lever arm differences.
Duke personnel also demonstrated the technique for determining UVTA output force on circuit breakers of slightly newer vintage than those of the McGuire plant. This technique was demonstrated on the Catawba DS-416 circuit i
breaker that was brought to the 6tcGuire plant.
For this test, the UVTA is reset and energized, and the circuit breaker contacts are restrained in the closed position. The circuit breaker trip mechanism is released, allowing the trip bar to rotate freely for a limited arc. The UVTA reset arm is also allowed to rest on the coller of the latch. The output force of the UvTA is measured by pulling on the backside of the manual trip, trip bar pin with tne horizontc1 tpring scale. This causes the UVTA trip bar pin to rotate against the WTA's trip tab, causing the UVTA trip spring to wind tighter. The measurement is read when the reset lever just starts to move. The output force measured by this method is less conservative than the force measured by the first method described, since the trip spring is measured at the highest operating force level (most tightly wound position).
Also, the pivotal friction and the friction of the trip bar pin to WTA trip tab interface would cause the measurements to be slightly higher than actually available.
Duke personnel provided the measured values for the McGuire Units 1 and 2 RTCBs. The force required to trip the circuit breaker latches ranges from a low of 0.25 lb to a high of 1.5 lb.
The range of the WTA outputs (after application of the 0.88 multiplier) was from 3.1 to 4.4 lb.
The minimum ratio of the two forces was 2.6.
2.4 TRIP TIMING OF CIRCUIT BREAKER OPERATION BY UVTA FRC requested that Duke personnel provide the timing of opening of the McGuire Units 1 and 2 RTCBs from time of deenergization of the WTA coil until contact opening. The timing charts provided by Duke personnel indicated a maximum allowable time of 0.150 seconds. The actual recorded trip times ranged from 0.065 to 0.080 seconds.
h.TJU Franklin Research Center a ca a w n. r,
DIRECTION TIR-C5506-417 PRODUCING CIRCUIT BREAKER TRIP
=
RE5ET LEVER "A" AND "B" ARE TRIP BAR
\\
SPRING ROLLER BRACKET TRIP TAB
/
I NM
. ~i ~
RCLLER l
ROLLER BRACKET tA s
A
\\
tU)
UPPER FRAME b'
/ /
\\
//
OPERATING R00
/
f MOVING CORE TRIP SPRING O
\\
COIL
\\\\
\\ '
/
% /
\\
N\\
\\
N s
f
/
\\
\\s s
/
g
\\
\\
/
N
/
/
\\
\\
\\
f
/
g\\
\\
\\
\\
/
\\
\\
/
g\\
/
g s \\
\\
\\
/
/
N
\\
\\
f g g\\
.\\
\\
/
N s
s
/
\\
s //
4',
N
/
g#
' /
]
L
/
WASHER y
,/
\\
/
/
j
/
lj STATIONARY CORE
,=
Q 1 a 1 3
~
LL t)
Figure 1.05-416 Undervoltage Attachment Note:
Portion of reset am and roller bracket arm not shown.
The parts not shown cause mechanical resetting of the
- -n device when the circuit breaker opens.
-- 2 [ g Q es,e g n g ter 6_
TER-C550 6-417 STATIC PULL POINT TRIP BAR 1
TRIP TAB
/
~
NN
~
i N
-co; W
'I l/[
l
[
\\
NN N N
/
\\
N
\\
g
\\ \\,
s e
j
\\
\\
s
/
\\
N s
/
\\
s N
g\\s
\\
\\
\\
/
/
\\
\\
/
g\\
/
g s N
\\
\\
f
/
N
\\
\\
f g
s g\\
.\\
\\,
/
s
/
s s yf s\\N N 7
l
/
L s
/
/
/
/
/
\\
/
/
/
l7 NO 2 a
% i L1 il I
Figure 2.05-416 Undervoltage Attachment Note:
Portion of reset arm and roller bracket arm not shown.
The parts not shown cause mechanical resetting of the device when the circuit breaker opens.
2.2 Franklin Research Center
~7~
- w or N r a n -
SR-C550 6-417 l
POLE t'
SHAFT SKR.
h OPEN BKR.
POSITION
\\ CLOSED
\\ POSITION s} In f-s N
- '.'s i-
'4
-8KR. CLOSED.
2 8
U.V. EN ERGlZED
/n+%"~
i s
TRIP BAR 8KR. CLOSED
%,i e
s 3
g -- "
r s "e?'E _ S l
i 4, I J...
ct
)
Figure 3.
Undervoltage Trip Device Operation l
-a-
.; Franklin Research. Center j
A h w n. F in I
n:-
A r
j TIR-C550 6-417 i
1 3.
EVALUATICN CF UVTAs AT FEC Prior to and following the trip to the McGuire plant by FRC personnel, further evaluation of the four UVTAs in the possession of FRC was performed.
The dropout voltage of the UVTAs was determined for each, tendencies to remain on latch after denergization was investigated, dimensional checks were made, and the disassembled device (McGuire 23) was reassembled and tested.
The force balance between the roller bracket spring and the solenoid were determined.
3.1 CHARACTERIZATION MEASUREMENTS The DS-416 UVTA (Figure 1) was carefully measured to determine whether interference between moving parts could inhibit the operation. Mechanical dimensions were measured, and the forces developed by the trip spring, roller bracket spring, and solenoid moving core were determined.
3.1.1 Mecbanical Dimensions The mechanical dimensions were obtained from the disassembled 2B UVTA.
A surface plate was used as a reference plane. A dial indicator mounted on a vernier height gage, a vernier caliper, a 1-inch micrometer, and a 1-to 2-inch micrometer were used to make these measurements.
The measurements obtained for the critical areas are shcwn in Figure 4.
The position shown is for the reset condition where the coller bracket is pressed down against the operating cod. With the rod firmly against the side of the hole in the moving core, the core would clear the sleeve by 0.0086 inches. However, the diameter of the core does vary by 0.010 inches, wnich would reduce the clearance to 0.0036 inches.
As the roller bracket is rotated in an upward direction by the roller bracket spring, the operating rod will be pulled toward the center line of the sleeving; at the extreme, the center line of the rod will be 0.005 inches past j
the center line of the sleeving. This motion did not show any tendency to O
-9 MU Franklin Research Center
- o== a a n. mm,i,
r
- ER-C550 6-417 prevent the core from moving during the full expansion from reset ;cs2. tion to the fully tripped position.
3.1.2 Forces Develoced The forces and/or torques were measured to determine the levels involved that cause the coller bracket to move out from under the reset lever.
Once l
the roller bracket roller is clear of the reset lever, the trip tao can rotate as driven by the trip spring, to drive the roll pin projecting from the trip bar so that the bar will rotate and trip the breaker.
The first spring to be measured was the trip spring.
In the position associated with the untripped condition, the force exerted against the roller was 3 lb (1360 g). Since the force is nearly ccnstant as the roller moves
" under the reset lever, the torque acting on the roller bracket can be evaluated as a function of bracket position. The equation for the. torque is W60) (sh 0) @.6W gram bches, where e is the angle of the T
=
73 roller arm with zero reference found when the roller is directly under the reset lever, thus producing no rotating torque on the roller bracket. The 0.619 inches is the radius arm of the roller frca support bearing.
In the '
untripped position the angle is approximately 6 degrees, thus producing a torque of 87.9 gram inches that add to the coil torque.
The force developed by the coil was measured by pulling directly upward on the operating rod with a spring scale. No other linkages were involved in this measurement. The data obtained at various excitation voltages are plotted in Figure 5.
As noted on the data plot, the force does drop to a reduced level once the core has moved away from the washer separating it from the stationary core. The torque developed by the moving core is expressed as T
= ces (0-1.3 ) (F ) (0.695). This shows that as the moving core leaves g
the untripped position, the torque tends to increase until e reaches a level of 13 degrees, where the torque would be approximately 6% higher. However, as soon as the core moves, the force of the moving core is reduced approximately 30% due to the increased air gap.
M JJ Franklin Reseeren Center
- om e n. r,
,y
o TER-C550 6-417 Another ocaervation related to tne forces developed by the mcving core is that as the core moves down and with ewitation voltage applied, tne core will pull down first on the side closest to the roller bracxet support shaf t.
This cocks the moving core, but when in the final position, the core is straight; in many attempts, it could not force the core to assume a position that would prevent normal trip operation.
The torque developed by the rouer bracket spring (T g) was determined by use of a spring scale with all other linkages disconnected.
The data obtained frca these measurements are plotted in Figure 6.
As the roller bracket rotates bringing the moving core up from the step, the torque is constantly decreasing.
The connined result of these systems is plotted in Figure 6.
The roller torque is not shown. At the time of the trip activation, it was observed th a t, on the units that f ailed to perform as required, the mpving core does move slightly, but the roller arm shows no sign of movement.
3.1.3 Discussion of Ro M er Bearina The rouer element bearing is not symmecrical because the rollers extend to one end of the bearing housing, but only come to about 75% of the distance from the other end. With the rouers directly under the reset lever, the system will trip consistently. When the bearing is reversed on the mounting shaft, the reset lever now applies force at one end of the rollers.
In this configuration, the assembly can be made to fail.
Further confirmation of the effect of increased friction was studied by taking a brass brushing with the same dimensions as the roller bearing and placing it on the bearing shaf t.
The assembly could readily be made to fail.
The maximum torque level for the rolling friction can then be determined from Figure 7.
Since the slope of T is less than that for the T73, de gg rolling friction would have to be less than 310 gram inches at an angle of -6 3
degrees.
~
- h ib Franklin Research Center
%.a w N rre
TER-C550 6-417 aft. Ano mvro Gen.
c-
=u -
,,,,,..sw,Cd.
ct, sed "M
.e sr -
.~
.s,-
I i
i
'1
. (, 90 d
i I
I s
- t
. c, "
r l
4 ;<CW
,.n Il 1W i
J l
mg 1
w-s s m
~
~
ii\\ N N ri sN ens i\\\\\\
l I;
NN
.A N N ' Im
, s.nN s d\\\\\\
!i NNN A\\\\
JL.d N N
!! \\ \\ N l'
NN' NN I
NN N
!\\
\\'
I k NN-1\\\\
kNNT
!N N
/
L NNV l
I
'I l
l
~
, 504 Figure 4.05-416 UVTA in Reset Position (Partial View Showing Critical Measurements) l l
-u_
1 2'") Franklin Research Center 4 % en.r -
1 TER-c550 6-417 my sW
_/
J 7
I f,
/
i e
/
s
/
/
f n I
Imped
/
i 6
/*
/
t I
i f
e s
/
/_
+
i e
u 11 e
e s
/ "
11
/
et-
- ful a
i
/
7' A
/
W5 e
/
_ _ _ Ai l a" i
e
/
N
./
i 2
v Mt 8
/i s' '
/
)
A_-
/
t
_ f LIJ
/
M?
- /e t
t
-% 1
/
s
. o i
C \\t t
e i
.,./-
i e
/
+
4 p.
e s
e j
4;.
i e
N
,/
f F
i /
/
r /
i
.p n
/i i,
f.
. m
'Isertd
./
i t
I i
1
/'
i F
,/
i
, e we 2
<.s..- - -,.,A,!. _.a A v, -
,E M Mehad.
re... s e me s
- c.,.
i.d I
/
e L
R _^.2 3 '
/
e 8
9 0
g 4
A a -
m,a h
u io gu wo n
g__
s l
m-n..
vo ws 2 a n ni mian j
i e
a e
i 1
Figure 5.
Force Developed by Moving Core versus Coil Excitation '/citage
-U-l'nJ' Franklin Research Center J
- w ce h. n.a
a I
TER-C550 6-417 P J1 n
.w s
s s
b N-
- PLUNGER IN FULLY RESET P O,S IT 10 N s
X M
\\
s l
- 2
\\:
A
,' OPERATING e,
, s
_I N.
ANGLE b_ d. +-
x s
1
\\
- 2
~N.
s_
\\
.s.
_w
.s
- a N.
- c
's
.g y
~
~
\\
\\
s X
ad
\\
', D W y
\\.
X
.g.
k X
\\
,filV t
u 1n w
w, ROLLER BRACXET TRAVEL ANGLE s
l Figure 6.
Torque Developed by Roller Bracket Spring versus Angle of Travel of Roller Bracket LN.,
..tj Franidin Researen Center
- o
- a. w n. %,,..
~
- ER-C550 6-417 97
~
lV l'H I
)
e 6
A a
h
- 3 e
v_'
g%
i i
yy i
e 6
i
_7,_
g g
j i
6 e
t e
,f g
% w I
u.-
e i
=
s QP 4
1 a
M
_n J l
ing w
gas
- w 3
1 ode
?
2 i
y e
i 4
i 9
y b
6 6
O f
> 6 y
I i
\\J g
I e
8 e
u AA y
6 g
%7 f
A m_
i A
C
. m wa 6
s D
za.
m f
f T
s t
m
/-
i 1
l 6
- i f
g eC 1
1 m
i.m, I'
a g
w-f z'
m
.. L'" \\,
i Na I.
- =a.
b i
L. 1 -
e %. J
%i
. e C
e-
.\\
uf
, \\-
3
/
i
+
, x
, i.
g=
1
.I 7
t i
,. X.
f.
6 i
4 i
o i
1 t
i e
>==
L f
_M
+
a s.'
a r,
.m o
X I.
4 1 w a
U e
i N
A.
l 4
u f
g, e
s.
I:
\\
I
'N r
-r w
I' A
_w O
i r
x 3
=
l t
i J
\\
D t
I N
t e
Je X-N r
s t
I.
t
\\
U b
I
\\
y f
\\.
O e
1 m
t I*
.\\
m.
M I
=
1
% v w
e T
=
{
a-f 1
l e.
m. s.
L
\\.
L v
v Mb#
M
\\\\
\\
A rawsarr e runi 1
i
.u, x-x
.i.
X 3
x NI 2 /J t'W E f7 I '
f tA
\\
N l
~ -
- i X
i i
.x l
E
\\
l l
t O 1
I 3
~~
l l-
. n f
r t a r
. A
..'20 Franklin Research Center
- cm an a. m r n u.
i
. I
f c-TER-C5506-417 l
4.
CONC!.USICNS The FRC evaluation indicates tnat the failure modes recognized cy Cuxe and Westinghouse personnel (i.e., clearance problems within tne UVTA, clearance problems between the trip bar pin and the UVTA, and pivot shaft spring clip failure) have been corrected. However, evaluation of the overall operation of the UVTA causes FRC to be concerned about the coller bearing on the coller bracket.
The roller bearing is critical to the operation of the device and slight changes in rolling friction rapidly reduce the margin for correct unictching o f th e UVTA.
While failure to unlatch caused by coller bearing friction has not occurred to date, closer evaluation of the potential of such failures is prudent.
Acceptance critaria have been set for critical measurements for the UV A by the manufacturer. UvTA output force, circuit breaker trip force, bushing clearances, and clearances of UVTA with respt t to the circuit breaker trip bar pin all have criterion set.
Testing methodology has been developed for each of these criterion. Baseline tests for determining whether the 3:Guire reactor trip circuit breakers meet the criteria have been performed.
(
I
- ,._.-N..d Franklin Research Center
- c n w n re I
\\_
o e
i l
TER-C5506-417 5.
RECOMMENDATICNS 1.
The baseline tests on the UVTAs and circuit breakers should te repeated periodically and the data ccmpared to caseline data and trended in order to determine degradation.
2.
Life testing of the avTA should be performed to show that the device can successfully operate for the intended lifetime.
3.
Criteria for a replacement interval should be developed for the UvTA so that replacement occurs significantly before the expected end of life. These criteria should be based on the life testing of Recommendation 2.
4.
The roller bracket to coller bearing frictional forces should ce reviewed and evaluated. Potential for failure to operate should be determined, and any significant potential for failure should be eliminated.
Cata available at the time of writing of this report indicated that there is no immediate short-term concern for roller oearing failures and that this evaluation could be performed in conjunction with the life testing program, d
)
em l
)
4w '
d'.} Franklin n. search.,, Center Re
- cm r
l I