ML17306A819
| ML17306A819 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 06/17/1992 |
| From: | Miller L NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | |
| Shared Package | |
| ML17306A818 | List: |
| References | |
| 50-528-92-15, 50-529-92-15, 50-530-92-15, NUDOCS 9207090214 | |
| Download: ML17306A819 (76) | |
See also: IR 05000528/1992015
Text
~dk
licensee:
~Pal
6
6
U. S.
NUCLEAR REGULATORY COMMISSION
REGION V
SPECIAL INSPECTION REPORT
50-528/92-15,
50-529/92-15,
50-530/92-15
50-528,
50-529,
50-530,
and
6
Arizona Public Service
Company
P. 0.
Box 53999, Station
9012
Phoenix,
Arizona 85072-3999
Palo Verde Nuclear Generating Station
Units 1,2,
and
3
Palo Verde Nuclear Generating
Station
Wintersburg,
e
Ins ection Conducted:
April 4-10,
1992
~T
L. F. Miller, Jr., Chief, Reactor Safety Branch,
Region V, Team Leader
D.
G. Acker, Engineering Inspector,
Region
V
F. Ringwald, Resident
Inspector,
Palo Verde
F.
Gee,
Engineering
Inspector,
Region
V
J.
Sl
an,
Engineering
spector,
Region
V
~kd 6:
ns ection
Summar
er
r.
C
Reactor Safety
Bra ch,
Region
V
Ins ection
on
A ril 4-10
1992
Re ort Nos.
50-528 92-15
50-529 92-15
and
50-530
9 -15
~l<< d:
dp
6
1
6
p ll
f f ll
f ll ll pk
Typ
62-266
reactor trip breaker to open during routine surveillance test,
and failure of
General Electric Type AKR-30 reactor trip breaker to close after routine
maintenance.
During this inspection,
Inspection
Procedure
92700
was used.
9207090214
9206l7
ADOCK 05000528
8
~es its:
General
Conclus
ons
and
S ecifi
'ndin s:
1.
The inspection
concluded that the licensee's
incident investigation
was
thorough,
and clearly defined the mechanical
causes
of failure of both circuit
breakers.
2.
The inspection
found that both types of circuit breakers
had
a combination
of mechanical
misalignments of the breaker
mechanisms.
The inspection
concluded that these
misalignments
had caused
the breakers to fail.
3.
The inspection
found that partially incomplete,
outdated,
and incorrect
maintenance
practices
had
been
used for the circuit breakers.
The inspection
concluded that these
improper practices
had allowed, if not caused,-the
breaker
mechanism misalignments
which were found.
4.
The inspection
found that the initial troubleshooting of these
breakers
was informal.
The inspection
concluded that the breakers
were not preserved
in their failed condition as well as
was possible.
Si nificant Safet
Matters:
The licensee's
apparent failure to implement the latest
vendor information
into the reactor tri.p" breaker maintenance
program,
use of improper lub'ricants
for the reactor trip breakers,
and initially uncontrolled troubleshooting for
these
components,
are indications of significant weakness
in these
programs.
Summar
of Violations and Deviations:
Based
on the results of this inspection
two apparent violations were
identified:
Improper corrective action'or deficiencies
in the reactor trip
breakers,
and failure to implement formal troubleshooting of the Westinghouse
reactor trip breaker
when the failure initially occurred.
0 en
tems
Summar
Two apparent violations were identified.
l
~,
Persons
Contacted
gETAILS
2.
"A. Alan Johnson,
Supervisor,
Compliance
- T. R. Bradish,
Manager,
Compliance
- G. T. Shanker,
Manager, Station Operating
Experience
Department
(SOED)
- S. Juan, Shift Technical Advisor
- D. Smyers,
SED Supervisor,
Systems
Engineering
Department
- T. J. Fitzpatrick, Supervisor,
Maintenance
Standards
- H. W. Riley, Supervisor,
Systems
Engineering
Department
- D. A. Hettick, Supervisor,
Station Operating
Experience
Department
- K. H. Johnson,
Vice President,
Failure Prevention,
Inc.
- C. N. Russo,
Manager, guality Control
- R. N. Prabhakar,
Manager, guality Engineering
The inspectors
also interviewed other licensee
personnel,
including
electricians,
operators,
and engineers
during this inspection.
- Personnel
present
at the exit interview on April 10,
1992.
Chronolo
of the Events
A.
Failure of the Westinghouse
DS-206 Reactor Trip Breaker to. Open
On March 31,
1992, at approximately ll:18
pm (HST), the Palo Verde Unit 3
Channel
C reactor trip breaker
(RTB) failed to open
on demand
from the
control
room during the performance of a routine surveillance test,
36ST-
9SB04,
"PPS Functional
Test - RPS/ESFAS Logic."
In conducting the test,
operators
had attempted to trip the breaker using
a manual
push button in
the control room.
After pushing the trip button, the operators
observed
conflicting control
room indications for the breaker.
Annunciator alarm window 4A7B "REAC SWGR CKT BKR OPEN" was lit, and the
control
room monitors
and alarm printer indicated the Channel
C breaker
was tripped.
The phase current light 1-3 on the control
board
and
on the
Plant Protection
System
(PPS)
panel did not go out.
Plant electricians
measured
the breaker
phase currents,
and concluded that the "A" and
"C"
phases
were still passing current
and the "B" phase'as
open.
The closed
and
open indicating lights were deenergized
for Channel
C at three
locations:
the
PPS panel,
the local breaker
panel
and the Supplementary
Protection Logic Assembly
(SPLA) cabinet, for Channel
C.
At the breaker,
the position flag indicated
an intermediate position.
A second
attempt to open the breaker
again both from the control
room and
locally failed.
The operators
then tripped open the Channel
A RTB, which
was in series with the Channel
C breaker.
This was done to comply with
- Technical Specification 3.3.1 which required the reactor trip breakers
to
be either operable
or open.
Since the Channel
C breaker could not be
opened,
the reactor trip breaker in series with it was opened.
(The
inspectors
concluded this action
was appropriate.)
1
0
fl
The Shift Supervisor
then conferred
by telephone with the duty STA, who
had been asleep
in his-quarters.
The
STA had
no objection to the actions
taken.
Also,
he offered no advice
on how to proceed.
He specifically
did not require quarantining of the Channel
C breaker,
as
he was required
to do by the licensee's
program
(see paragraph
6.B.(3) fo'r additional
detail).
The Unit'3 Operations
Supervisor
was
on site,
and
came to the control
room to assist
the Shift Supervisor.
The Shift Supervisor authorized
informal troubleshooting to proceed,
with the proviso that it would be
videotaped.
The Shift Supervisor
was concerned that the surveillance
interval for 36ST-9SB04 might be exceeded.
He was also concerned that
the expedient of tripping the Channel
A reactor trip breaker in lieu of
the Channel
C breaker
was not in strict conformance with the wording of
Technical Specification 3.3. 1.
The electricians
assigned
to continue
troubleshooting
researched
the licensee's
version of the Westinghouse
technical
manual, called their supervisor at home,
and developed
an-
informal troubleshooting
plan.
They decided to manually charge the
breaker's
closing springs.
After doing this, they attempted to open the
breaker locally and were unsuccessful.
They then attempted to close the
breaker locally with the manual
close pushbutton
at the breaker.
The
closing springs discharged.
The discharging of the closing springs
provided sufficient vibration to open the circuit breaker.
The actual
opening of the breaker
was not videotaped
because
the electrician
operating the camera
had set it down temporarily to assist
his coworker.
Subsequent
to opening the breaker,
the breaker
was cycled open
and closed
eight times..
Then it was
removed from its cubicle,
and replaced with a
spare
breaker.
The breaker which had failed was cycled approximately
100
more times,
according to its cycle counter,
before formal troubleshooting
'was imposed.
This was done
by the electrical
maintenance
department
in
an attempt to repeat the failure.
Throughout the event, the unit remained at
100X power with power to the
control element drive mechanisms
(GEOM) provided via the parallel
path
Channel
B and
D RTBs.
B.
Failures of the General Electric AKR-30 Reactor Trip Breakers to
Close
The General Electric AKR-30 reactor trip breaker
was installed in Unit 3
Channel
A. It was Serial
Number N2689500011.
It had initially been
installed in Unit 1,
Channel
B in April 1985.
In April 1991 it had
been
installed in Unit 3 Channel
A.
On March 10,
1992, during the performance
of 36ST-9SB44,
"RPS Matrix Relays to Reactor Trip Response
Time Test,"
the breaker
was observed to not stay closed (trip free)
once in four
attempts.
A period of informal troubleshooting of the breaker
ensued.
On March ll the breaker operated
normally in the test position, but would
not close
on three consecutive
attempts
when connected
into its cubicle.
The breaker
was removed from its cubicle for further troubleshooting.
Its trip latch was adjusted,
and it closed
two out of three times.
On
3.
March 12, it closed
one out of three times.
The undervoltage
(uv) coil
was observed to be binding in the trip free position,
and
an adjustment
was made.
The breaker
then operated correctly
11 times.
On March 13, it
was reinstalled,
tested satisfactorily,
using 36ST-9SB44 .and declared
On March 25, during performance of 36ST-9SB04,
the breaker
again did not
stay closed.
During addition'al testing
on March 26 and 27, -it tripped
free four out of 15 times that it was attempted to be closed.
Informal
troubleshooting of the breaker continued until the licensee's
incident
investigation
imposed formal troubleshooting controls
on April 2,
1992.
eview of Generic Corres
ondence
The inspectors
reviewed the generic
correspondence
related to the failure of
and General Electric reactor trip breakers to operate.
A.
NRC Generic Letter (GL) 83-28,
"Required Actions Based
on Generic
Implications of Salem
ATWS Events,"
was developed after reactor trip
breakers
at the Salem plant failed to open in 1983.
After extensive
review of reactor trip breakers't all facilities,
some
inadequate
preventive maintenance
of reactor trip breakers for both Westinghouse
and
General Electric circuit breakers
was identified.
Requirements for
reactor trip breaker maintenance
were specified in Enclosure 4.2 to
Reactor Trip System Reliability (Preventive
Maintenance
and
Surveillance
Program for Reactor Trip Breakers)."
As part of its initial
licensing, the licensee's
preventive maintenance
program for reactor trip
breaker maintenance
was reviewed
and approved
by. the
NRC.
B.
Prior to the issuance
of the Generic Letter, the
NRC also issued
Bulletin No. 83-01, "Failure of Reactor Trip Breakers
DB-
50) to Open
on Automatic Trip Signal."
This bulletin requested
the
applicant
(Palo Verde was under construction at the time) to review the
information in the bulletin.
The bulletin provided Westinghouse
Technical Bulletin NSD-TB-74-1 as
an attachment.
This bulletin in turn
recommended
the use of a dry or near-dry. molybdenum disulfide lubricant
for occasional light, sparing lubrication of the front and back -faces. of
the undervoltage
device vertical travelling latch of Westinghouse
DB type
breakers.
The licensee
improperly concluded in an internal
memorandum
dated April 4,
1983 (File No. 83-047-419) that lubrication of all metal
sliding surfaces
in both its
GE and
W reactor trip breakers
was
appropriate
every six months using dry molybdenum disulfide lubricant
(Molykote 321 R).
The inspectors
observed that this was
a large, unjustified extrapolation
of the Westinghouse
NSD-TB-74-1 recommendation.
Moreover, to implement
this decision,
the licensee
deleted the vendor
manual lubrication
recommendations
throughout the licensee
version of the vendor's
manual,
substituting Holykote 321
R as the required lubricant.
Subsequently,
when detailed maintenance
procedures
were implemented,
Molykote 321
R was
specified
as the lubricant to be used.
The inspectors
noted that the
licensee
had modified its vendor manual lubrication requirements,
and
requested
the licensee to inquire about the suitability of Holykote 321
R
as
a lubricant for'he breakers
replacing, the vendor specified Mobil 28
(GE) and Molykote BR2 Plus
(W) lubricants.
In a l'etter dated April 8,
1992, the
Dow Corning Corporation,
current
vendor for the Molykote product line, stated that use of Molykote 321
R
as
a substitute for Molykote BR 2 Plus was inappropriate,
and could lead
to gumming of the system (if applied over
an existing grease),
or
excessive
buildup (if applied too frequently).
Moreover, in a November 7,
1989 letter received
from the
GE Apparatus
Service
Group concerning
two of the licensee's
GE reactor trip breakers
which had
been sent to
GE for refurbishment,
the licensee
was informed:
"Breaker mechanism
was heavily coated with graphite.
This
-'ubricate
is not recommended
by GE for use
on breakers.
Mechanism failure could occur
due to the graphite.
Already
indications of teflon bushing deterioration
were noted."
The inspectors
.concluded that the licensee's
lubricant substitution of
HolyKote 321R for Mobil 28
(GE)
and MolyKote BR2 Plus
(W) based
on
TB 74-1 was erroneous.
=
The inspectors
also concluded that the licensee
had not followed up on
the
1989 report from GE warning of the mislubrication of the breakers.
The failure to revise the
GE and Westinghouse
reactor trip circuit
breaker maintenance
procedures
in response
to the
GE report is part of an
apparent violation (Violation 50-530/92-15-02)
(See
Paragraph
3.D).
The
inspectors
noted that the effect of this substitution
was difficult to
evaluate,
but may have contributed to increased friction of the
breaker
mechanism
which failed to operate.
The inspectors
also noted that the licensee
promptly initiated
a program to properly
lubricate all reactor trip breakers, within two weeks of the event.
C.
NRC Bulletin No. 88-01
On February
5,
1988, the
NRC issued
NRC Bulletin No. 88-01,
"Defects in
Westinghouse Circuit Breakers".
This Bulletin described
a pole shaft
weld failure in the mechanism of Westinghouse
Type DS-416 circuit
breakers
at the McGuire facility.
The Bulletin required frequent
inspection of the pole shaft welds
on all circuit breakers of similar
configuration, including Type DS-206 breakers.
Alternately, the pole
shafts
could be replaced.
The licensee initially performed these
inspections,
but later elected to
replace the pole shafts.
The
C reactor trip breaker which failed to open
had its pole shaft replaced
by APS using the instructions provided in
Westin'ghouse
Technical Bulletin NSID-TB-87-11, "Westinghouse Circuit
Breakers
Type DS/DSL:
on Breaker's
Pole Shaft," dated
December
1,
1987.
This work was performed using Work Order 302396
on July 21,
1989.
The inspectors
noted that the replacement
of the. pole shaft required
disconnection
and reconnection of the insulating links.
Reconnection
of
the links required tightening
an adjusting nut against the threads
on the
end of the insulating link, while preventing rotation of the insulating
link around the threads.
cautioned in TB 87-11 that failure
to prevent rotation of the insulating link could permit the link to rub
against other parts of the mechanism,
causing binding and friction in the
mechanism.
One of the findings of. the licensee's
incident troubleshooting
(see
paragraph
4.B(4)) was that the phase
B insulating link had not been
properly reassembled,
in that it was cocked around its long axis,
and
binding the mechanism to some degree.
However, this error by maintenance
personnel
did not appear to have caused
enough additional
mechanism
friction to prevent operation of the breaker.
As part of their
corrective action for this event,
the licensee
inspected all of the other
reactor trip breakers.
No other breakers
with cocked insulating links
were identified.
The inspectors
concluded that the licensee's
modification of the DS-206 reactor trip breakers
had not been
performed
correctly in this instance.
Also, the inspectors
concluded that the
licensee's
subsequent
corrective action satisfactorily identified and
corrected
the earlier error.
D.
Technical Bulletin NSD-TB-91-06-RO
On October
18,
1991,
issued
TB NSD-TB-91-06-RO,
"DS-206 and
DSL-206 Breakers
Mechanical Friction of Main Contact Assemblies," to
ensure
proper opening of DS-206 circuit breakers.
In the introduction to
this bulletin, Westinghouse
stated:
"If the contact adjustment
procedures
given in the referenced
Instruction Bulletin are not followed, then the potential exists for
the breaker to only partially open due to excessive friction in the
main contact assemblies."
representatives
stated that TB NSD-TB-91-06-RO had
been
developed
in response
to a previous failure of a DS-206 circuit breaker
to open at the Byron nuclear plant.
TB NSD-TB-91-06-RO recommended
removing the brea"b's
reset
spring
and verifying the contacts
parted
using only the~~ning
(main contact)
springs.
had
concluded that.'verifying
a circuit breaker would open with the reset
spring removed would provide margin to ensure, that it would not fail to
open with the spring attached.
The licensee
had not implemented
TB 91-06's
recommendations
at the time
of the inspection.'he
licensee
had concluded that it was inapplicable,
since
no failures of DS-206 circuit breakers
to open
had
been
experienced.
The licensee's
Vice President of .Nuclear Production received this
technical bulletin and
on November 2,
1991,
requested
that the Director
of Site Technical
Support determine if PV used tbis style of circuit
breaker
and determine
what needed to be done.
Independently
on October
30,
1991, the Director of Site Technical
Support
had directed his staff
to determine if this technical bulletin was applicable to Palo Verde.
On November 26,
1992 the site engineering staff issued
memorandum
number
226-01569-JSS
which determined that no
PV action was required.
The inspectors
concluded that the licensee's
failure to take corrective
action to inspect their Westinghouse
reactor trip breakers for proper
adjustment in accordance
with TB 91-06 was
an apparent violation
(Violation 50-530/92-15-02).
Review of Westin house
Breaker Performance
A.
Description of Operation
Two of the four reactor trip circuit breakers
in each Unit at Palo Verde
were Westinghouse
Type DS-206.
Figure
1 shows
DS-206
circuit breaker.
designed
these circuit breakers
to be
installed in low voltage metal
enclosed
switchgear of the drawout type.
These breakers
.were rated for 800 amps.
Figure
2 shows the arrangement
of the principal mechanical
parts of a DS-
206 circuit breaker.
Figure
3 shows the four basic positions of the
circuit breaker mechanical
linkage.
Figures
4 and
5 show the main
and
arcing contacts
and their adjustments.
Appendix A contains
a detailed description of the DS-206 closing
and
opening (tripping) mechanisms.
Briefly, closing springs
operate
mechanical
linkages which drive and hold the main circuit breaker
contacts
closed
and charge the opening springs.
In this closed position,
the moving arcing contacts
wedge -into the stationary device
as
shown in
the top left drawing of Figure 5.
By design,
the opening
(main contact)
spring force is greater
than the gripping force on the wedged arcing
contacts.
The opening
(main contact)
springs
are
shown in Figures
4 and
5.
As shown in Figure 3,
a trip signal rotates
the trip shaft,
piece 7,
and
releases
the trip latch, piece 5.
The trip latch rotates
and removes'll
mechanical
force from the linkage.
As shown in Figures
3 and 5, the
opening springs
extend
(discharge)
and open the'circuit breaker.
The
reset spring,
shown in Figure 2, pulls the linkage to the fully open
position,
once the moving contact assemblies
have
moved free of the
stationary arcing contacts.
B.
Discussion of Test Results
The licensee's
root cause
team developed
a detailed investigative
procedure.
The investigative procedure
attempted to determine
why,DS-206
7
circuit breaker serial
number 02YN140-15 failed to open.
The initial
steps of this procedure did not modify the circuit breaker as-found
conditions.
However,
as noted earlier,
the circuit breaker
had
been
cycled about
100 times since its failure,
due" to informal troubleshooting
by the Electrical Maintenance
Department.
The investigative procedure
contained
steps
recommended
in Westinghouse
Information Bulletin (IB) 33-
790-1G, "Instructions for Low-Voltage Power Circuit Breakers
Types
DS and
DSL;" Westinghouse
Technical Bulletin (TB) NSD-TB-91-06-RO, dated
September
24,
1991,
"DS-206 and DSL-206 Breakers - Mechanical Friction of
Main Contact Assemblies;"
and verbal
recommendations
from Westinghouse
technical
representatives
acting
as part of the root cause
team.
As discussed
in Section 3.B,
TB NSD-TB-91-06-RO was developed to ensure
proper opening of DS-206 circuit breakers.
had concluded
that verifying that
a circuit breaker would open with the reset
spring
removed would provide margin to ensure that it would not fail to open
with the spring attached.
The root cause
team incorporated this method
of checking for proper breaker. opening force into the investigative
procedure.
The licensee
performed
a dry run of the procedure
using
a
training DS-206 circuit breaker.
The inspectors
reviewed the investigative procedure
and found it
adequate.
The licensee
performed the investigative procedure.
The circuit breaker,
would not open with the, reset spring removed.
The inspectors
observed
the work.
The work was well controlled
and documented.
The investigative procedure identified four problems which'impeded
proper
circuit breaker opening.
These
problems were:
opening spring force
adjustment,
arcing contact
wedge dimensions,
lubrication,
and insulating
linkage binding.
The investigation revealed
no problems with the
tripping mechanism.
The following paragraphs
discuss
the opening
problems.
(1)
Opening Spring Force Adjustment
IB 33-790-1G required that the force on the opening
spring
be adjusted
by making the faces of the main stationary
contact fingers
and leading
edge of the vertical stationary contact
bar parallel
on each
phase.
See dimension
B, Figure 5.
TB NSD-TB-91-06-RO contained
an additional
measurement
of opening spring compression
by using the "X" and "Y" dimension
shown
on Figure 5.
This TB indicated proper spring compression
was
achieved
when
X
Y.
The Westinghouse
representative
indicated that
the "X" and
"Y" dimensions
were added
due to the difficulty of
visually determining that the surfaces of dimension
B were parallel.
A locknut on the insulating link provided
a means for adjusting the
"X" and "Y" dimensions
by increasing
or decreasing
the length of the
linkage.
The investigation determined that phases
A and'C were under-parallel
(X<Y) by one nut flat of adjustment.
The nut had
6 flats and
a
pitch of I/32 of an inch.
The inspectors
concluded that the as-found condition would have
compressed
the opening springs less than
recommended
by TB 91-06,
and, thus,
lowered the'pening
force available.
k
Arcing Contact
Wedge Dimensions
IB 33-790-1G required dimensional
checks of the arcing
contact
wedge dimensions
in both the open
and closed positions.
See
dimensions
A and
C, Figure 5.
This IB contained
only a minimum
value of 0.02 inches for dimension
A.
TB NSD-TB-91-RO
added
a maximum of 0.07 inches for dimension
A.
The investigation determined that dimension
A was above the maximum
of 0.07 inches for dimension
A for all- three phases.
The left side
of phase
A was 0.079 inches,
the left side of phase
B was 0.072
inches,
the right side of phase
C was 0.075 inches
and the left side
of phase
C was 0.077 inches.
Dimension
C was within the specified
0.42 plus or minus 0.08 inches but for all three
phases
these
dimensions
were less than 0.39 inches.
The inspectors
concluded that the out of tolerance
dimension
"A"
indicated that the moving arcing contacts
'were gripped with more
force than if the dimension
had
been within the tolerance
specified
by Westinghouse
TB NSD-TB-91-06-RO.
Overcoming this gripping force
required additional
opening spring force.
lubrication
IB 33-790-1G
and Westinghouse
TB NSD;TB-91-RO both
required
use of lubricant Nolykote BR-2 Plus
by Dow Corning on non-
electrical
moving parts.
The IB specified nine locations for
lubrication.
The TB added
two additional lubrication points,
one
requiring
a special
conductive grease.
The licensee
was using
Dow
Corning 321R lubricant in lieu of the BR-2 Plus.
See Section 3.A
for a discussion of the use of this different lubricant.
The investigation originally determined that the nine locations
specified in the information bulletin were lubricated
and the two
locations
added
by TB NSD-TB-9i-RO were not.
Both of the locations
added
by TB NSD-TB-91-RO were
on the moving contact linkage.
Later
disassembly identified what appeared
to be
a small
amount of
lubricant on one of the locations
added
by TB NSD-TB-91-RO.
Based
on the discussion
in Section 3.A, the inspectors
concluded
that the licensee
was using
an inappropriate lubricant.
The
representative
stated that lubrication of the two
locations specified in TB NSD-TB-91-RO would reduce the linkage
friction which opposed
the opening spring force.
9
(4)
Insulating Linkage Binding
A main drive (insulating) link is shown in Figure 3, piece
14.
The investigation determined that the insulating link on phase
B was
rotated
around
an axis along its length,
and binding (See Section
, 3.C above).
Technical Bulletin NSD-91-06-RO required
that the insulating link be firmly held while adjusting
a locknut
for correct opening spring compression.
The inspectors
concluded that this binding contributed to the
frictional forces. opposing
opening spring force.
The inspectors
concluded that this was
a maintenance
error.
After completion of the initial inspection,
the licensee
corrected
the
- insulating linkage binding.
The circuit breaker would still not open
with the reset
spring removed.
However,
approximately
1/16 of an inch
more moving contact travel
was noted.
The licensee
adjusted
the phase
A
and
C locknuts
one flat to make the "X" and "Y" dimensions
equal.
The
circuit breaker would still not open,
but additional
moving contact
travel
was noted.
TB NSD-TB-91-06-RO recommended
obtaining additional force to
open the circuit breaker
by increasing
the "X" dimension
by up to a full
turn on the adjusting locknut.
The investigative action determined that
the circuit breaker would successfully
open without the reset
spring with
an additional
adjustment of one flat (1/6th turn)
on each
phase.
Th'e inspectors
concluded that all four breaker
opening conditions
discussed
above contributed to the actual failure.
The inspectors
noted
that performance of Westinghouse
TB NSD-TB-91-06-RO would have identified
that DS-206 circuit breaker serial
number 02YN140-15 had several
deficiencies
which could have potentially caused it to fail to open
upon
demand.
5.
eview of General Electric Breaker Performance
A.
Description of Operation
Two of the four-reactor trip breakers
in each unit at Palo Verde
were'eneral
Electric Type AKR-30.
General Electric designed
these circuit
breakers to be installed in low voltage metal
enclosed
switchgear of the
drawout type.
The breakers
were rated for 800 amps.
Appendix
B contains
a detailed description of the AKR-30 closing,and
opening (tripping) mechanisms.
Figure
7 shows the arrangement
of the
'rimary
contact positioning mechanism.
Figure 8 shows
a side view of
this mechanism in the closed,
tripped
and reset configurations.
Figure
9
shows the main contact structures.
10
Briefly, closing springs operated
mechanical
linkages which drove and
held the main circuit breaker contacts
closed
and charged the opening
and
main contact springs.
The gear motor, piece
9 in Figure 7, charged
the
closing springs.
A trip signal rotated the trip shaft,
piece
10 in
Figure 7, which released
the trip latch, piece ll in Figure 7, which
allowed contact springs,
Figure 9,
and the opening spring,
piece
15 in
Figure 7, to move the mechanism to the tripped position,
Figure 8.
Small
springs in the mechanism
moved the, mechanism
from the tripped to the
reset position, Figure 8.
B.
Discussion of Test Results
The licensee's'oot
cause
team developed
a detailed investigative
procedure.
The investigative procedure
attempted to determine
why the
AKR-30 circuit breaker,
Serial
Number N2689500011, failed to remain
closed, while preserving the existing circuit breaker adjustments.
The
investigative procedure
contained
checks
recommended
Maintenance
Manual
GEK-64459B "Low-Voltage Power Circuit Breakers
Types
AKR-30/50 and AKRT-50," as well as
GEK-7310,
"Power Circuit Breakers,"
GEI-86134,
"Power Circuit Breakers,"
GEF-4527D,
"Maintenance
Procedures
for GE AKR-30/50 Circuit Breakers with Undervoltage Devices,"
Combustion
Engineering
(CE) letter V-CE-19157 "Arizona Nuclear
Power Project Under
Recommended
Reactor Trip Switchgear" Modifications,
ADP, Infobulletin,
"Maintenance
Procedures
for GE AKR-30/50 Circuit Breakers with
Undervoltage Devices," Service Advice 175 9. 15,
"AKR-30/50 Low Voltage
Power Circuit Breakers with Undervoltage
Devices - Maintenance
Procedures,"
Service Advice 175 9.20,
"Maintenance
and Upgrade of AK-25
Circuit Breakers with Undervoltage Trip Devices
Used
as Reactor Trip
Breakers,"
Service Advice 175 9.3,
"AK15/25/50/75/100
Low Voltage Power
Circuit Breaker with Undervoltage Trip Device,"
and on-site vendor verbal
recommendations.
The licensee
performed
a dry run of the procedure
using
a training AKR-30 circuit breaker prior to implementing it on the breaker
which failed in service.
The inspectors
reviewed the investigative procedure
and found it thorough
and complete.
The licensee
performed the investigative procedure
and additional
troubleshooting
actions
documented
The inspectors
observed
a portion of the work. 'ased
on observation of the work, the
inspectors
concluded that the work was well controlled
and documented.
with one exception
associated
with the manual trip actuation
butto'n
as
described
below.
The licensee's
investigation identified six problems which could have
.
contributed to the failures of the bre'aker to stay closed.
These
'roblems
were:
low undervoltage
device armature to trip paddle
assembly
clearance,
bent flux shift trip device trip rod, low flux shift trip
device trip rod to trip paddle clearance,
low manual trip actuation
button travel, insufficient trip latch adjustment,
and low (but'ithin
tolerance) trip shaft torque.
Other results
which the inspectors
agreed
had minimal impact on the breaker's failure to close included minor trip
11
latch misalignment,
more pronounced
burn marks
on the "A" phase
main
arcing contact than
on phases
"B" and "C," potentially excessive
trip armature to trip paddle clearance,
misalignment of the shunt trip
paddle,
broken "A" phase
axial free play in the trip shaft,
and minor bending of the charge/discharge
indicator arm and drawout
mechanism.
The problems which the inspectors
concluded could have
contributed to the failures of the breaker to close are discussed
further
in the following paragraphs.
(1)
Low Undervoltage
Device Armature to Trip Paddle
Assembly Clearance
No specification .existed for this measurement
in the vendor
technical
manuals
used
by the licensee
nor were any in GEK-64459B.
In a letter from General Electric dated April 16,
1992 (J.
E. Kusky
to J. Bailey),
GE specified
a minimum trip shaft paddle to
armature
clearance
specification of 0.030 inches.
The investigation determined that the
as found clearance
was only
0.011 inches,
and that by restoring this measurement
to 0.030
inches,
the frequency of failures of this breaker to close
was
reduced significantly.
One possible contributor to this low clearance
may have
been the
guidance
i.n GEK-7310 which stated "If the undervoltage
device does
not have positive tripping ability, the adjustment
screw of the trip
paddle
assembly
may be turned in increments of half turns until the
check is successful."
The inspectors
noted that GEK-64459B has the
same guidance
but also contains
several
other measurements
which can
also affect the positive tripping check.
The inspectors
concluded that this low clearance
would have
- increased
the likelihood of the breaker failing to close.
(2)
Bent Flux Shift Trip Device Trip Rod
While no specification existed for the straightness
of the flux
shift trip device trip rod, the inspectors
noted that description of
the flux shift trip device in the technical
manual
depicted
the rod
as straight.
The investigation determined that the flux shift device trip rod was
slightly bent,
showed signs of wear,
and that metal
shavings
were
present
in the area of the flux shift trip device.
Measurements
of
=
the flux shift trip device trip rod to trip paddle were not changed
by varying the orientation of the bent trip rod.
The inspectors
concluded that the bending of the trip rod had little
impact on the breaker failing to close.
12
Low Flux Shift Trip Device Trip Rod to Trip Paddle
Clearance
The vendor technical
manual
used
by the licensee
(GEK-7310)
contained
GEI-86134,
which specified this clearance
to be 0.125
inches +/- 0.015 inches.
GEK-64450B contains the
same guidance.
The investigation determined that the as found clearance
was 0.095
inches.
This was 0.015 inches or 12 percent
below the minimum
specification.
The inspectors
concluded that this low clearance
would have
increased
the likelihood of the breaker failing to close.
Low Manual Trip Actuation Button Travel
The vendor technical
manual
used
by the licensee
did not contain
any
criterion for this measurement.
GEK-64459B also did not contain
any
criterion for this measurement.
Field discussions
with the vendor
representative
identified
a criterion of 0.31 inches
button travel to trip the breaker with the front escutcheon
plate
installed.
The investigation initially measured
the clearance
between
the end
of the manual trip rod and the trip paddle.
The as found tr'ip
button travel
was not documented
in the work order.
A licensee
engineer
on the investigation
team stated that the
as found manual trip actuation button travel
was approximately 0.2 inches.
During
the investigation,
blueing dye was applied to the actuating devices
for the manual trip, flux shifter, positive interlock,
and shunt
trip, to see if these
devices
were contacting their respective trip
paddies.
After breaker operation, all but the positive interlock
did show blueing die transfer,
suggesting
that the manual trip, flux
shift,
and shunt trip devices
were contacting their respective
paddies without intentional actuation.
The inspectors
concluded that if the manual trip button actuator
clearance
had
been low initially, it would have increased
the
likelihood of the breaker failing to close.
Since the as found
measurement
was not recorded,
the inspectors
concluded that the
actual
impact of this actuator clearance
was indeterminate.
The
inspectors further concluded that the blueing die transfer
marks
which were found on the manual trip paddle without action to depress
the manual trip button provided
some evidence of insufficient
clearance for this actuator.
Insufficient Trip Latch Adjustment
The vendor technical
manual in use
by the licensee,
GEK-7310,
specified that the trip latch adjustment
was correct if three
and
one-half turns of the adjustment
screw caused
a closed breaker to
trip.
GEI 64459B had the
same specification.
13
The investigation found the initial trip latch adjustment to be
three
and one-quarter turns.
The licensee
concluded that this was
a
contributory cause of the breaker failing to close.
The as found adjustment
would have caused
the breaker to trip with a
smaller trip shaft rotation than it would have taken
had this
adjustment
been in accordance
with the vendor guidance.
The.
inspectors
concluded that this would have increased
the likelihood
of the breaker failing to close.
(6)
Low Normal Trip Shaft Torque
The vendor technical
manual
used
by the licensee specified
a maximum
trip shaft torque of 1.5 inch-pounds.
This value was measured
and
trended
every six months
as part of the licensee's
preventive
maintenance
program.
The as-found trip shaft torque
was found to be 0.6, 0.49,
and 0.6
inch-pounds
in three successive
measurements.
The inspectors
noted
that the licensee's
trending program
showed that the minimum value
ever observed for 'a General Electric reactor trip breaker at Palo
Verde was 0. 1 inch pounds,
with more than
15 other occasions
when
. the trip shaft torque
was observed to be less
than the value
observed for this affected breaker.
A low as-found trip shaft torque would permit
an inadvertent
impact
on
a trip paddle to result in a breaker trip more easily'han. if the
trip shaft torque were higher.
With no minimum criterion and
frequent observations
of trip shaft torque lower than what was
observed
on this breaker,
the inspectors
did not conclude that the
observed trip shaft torque
was low.
The licensee
and vendor concluded that the root cause of the breaker
tripping was low clearances
between the trip shaft paddies
and the trip
levers of the actuating devices.
After this troubleshooting,
the licensee
reset the breaker to the
specifications of the vendor manuals in use
on site at the time of the
failure.
The breaker
was cycled one hundred times.
Two close attempts
resulted in the breaker
closing
and then immediately tripping.
The
cause for this continued failure was determined
by the licensee to be
insufficient clearance
between the undervoltage trip device trip paddle
adjustment
screw
and the trip shaft clamp.
This clearance
is also the
clearance
between the undervoltage
device. armature
and the trip paddle
assembly.
This clearance
was reset to the vendor's
recommendation
in
their letter of April 16,
1992,
and the breaker operated satisfactorily.
The inspectors
agreed with the licensee's
assessment.
I
14
~
~
~
6.
Review of Reactor r'reaker
aintenance
Pro ram
A.
Review of Reactor Trip Breaker Haintenance
Procedures
DS-206 Circuit Breakers
Procedure
Revision 5, "Maintenance of Westinghouse
Reactor Trip Switchgear," contained the licensee's
procedure for
maintaining Westinghouse
reactor trip circuit breakers.
The
licensee
was accomplishing
Procedure
32HT-9SBOl every six months.
This procedure listed Westinghouse
Instruction Hanual
IB 33-790-1G,
dated
September
1989
as
a developmental
reference.
technical
representative
reported that this was the correct manual
for the licensee's
DS-206 reactor trip circuit breakers.
The inspectors
compared the requirements
and recommendations
in
Hanual
IB 33-790-1G
and other commitments
and standards
with the licensee's
maintenance
procedure.
The inspectors
noted
five differences
between the licensee's
procedure
and the applicable
vendor information in the procedure.
These five differences
were:
1) The licensee
had authorized
use of Dow Corning (Holykote) 321R
lubricant in place of the, Westinghouse
required
Dow Corning Holykote
BR-2 (See Section 3.B), 2) the licensee
was removing the closing
springs
to. accomplish
selected
visual examinations,
3) the licensee
was not measuring trip shaft torque,
4) the licensee
was not
measuring
and adjusting trip latch overlap,
and 5) the licensee
had
not incorporated
the maintenance
recommendations
of Westinghouse
NSD-TB-91-06.
Problem numbers
2,
3 and
4 are discussed
in more
detail in Appendix C.
The licensee
had performed
an evaluation in 1983 that
Dow Corning
(DC) 321R was
an acceptable
lubricant for the undervoltage coil
moving armature,
but had
no evaluation for other moving parts.
321R was
a spray type dry lubricant.
The licensee
contacted
Dow
Corning.
Dow Corning provided
a letter that stated that
DC 321R was
an appropriate lubricant for clean
and dry metal
surfaces
only.
The
letter indicated that
DC 321R would not be effective if sprayed
over
surfaces
previously greased
and could tend to make the grease
ineffective.
The Westinghouse
representative
stated that
lubrication points listed in IB 33-790-1G were factory greased.
Haintenance
records
indicated that the licensee
was applying
DC 321R
to reactor trip breakers.
The inspectors
concluded that the use of DC 321R was not technically
correct for previously greased
surfaces.
The licensee
committed to
use the Westinghouse
recommended
lubricant pending
a more detailed
lubrication review.
TB NSD-TB-91-06 also contained
several
maintenance
instructions
not contained in either Westinghouse
IB 33-790-1G or
15
(2)
The inspectors
concluded that the checks
and adjustments
of TB NSD-
TB-91-06 were valid maintenance
checks
and adjustments
with specific
tests to ensure that breaker
opening force was sufficient.
The
licensee
committed to incorporate
TB NSD-TB-91-06 in a routine
maintenance
procedure.
Based
on the findings discussed
in Appendix
C the inspectors
concluded that:
1)
Dow Corning 321R was not an appropriate
lubricant,
2) removal
and reinstallation of the closing springs
was
unnecessary
and
had, the potential for damaging the circuit breaker,
3) measuring trip shaft torque
was warranted,
4) measuring
and
adjusting trip latch overlap
was warranted,
and 5) incorporating the
instructions of TB-NSD-TB-91-06 was warranted.
The licensee
agreed
to evaluate
these five potential
problems
and incorporate
the
results in maintenance
procedures.
General. Electric AKR-30 Circuit Breakers
Procedure
32MT-9SB02, Revision
1, Preliminary Change Notice Number
6, "Maintenance of General Electric Reactor Trip Switchgear,"
contained the licensee's
procedure for maintaining General
Electric
(GE) AKR-30 reactor trip circuit breakers.
The licensee
was
.
accomplishing
Procedure
'32MT-9SB02 every six months.
This procedure
listed
GE .Maintenance
Manual
GEK-7310C and supplement
GEI-86134
as
developmental
references.
A GE technical
representative
was invited
to Palo Verde by the licensee to assist
in the investigation.
He
stated that GEK-7310C/GEI-86134
was not the latest
GE maintenance
manual for the
GE reactor trip circuit breakers.
The
representative
stated that the latest
GE manual for AKR-30 ci'rcuit
breakers
was
GEK-64459B.
According to the licensee,
GEK-64459B
"Low-Voltage Power Circuit Breakers,
Types AKR-30/50 and AKRT-50,"
had been onsite since January
1990, for use with GE AKR-50 circuit
breakers.
APS had sought definition of the latest guidance for the
- GE AKR-30 circuit breakers
from GE in April 1988.
They received
no
response
and'queried
CE in November
1988.
CE's response
to this
query in January
1989 stated that
CE believed that the licensee
"had
been
informed of all other
known Service Information Letters
and
Advisories concerning"
AKR-30 circuit breakers.
After receipt of
the newer manual
in January
1990, the licensee
took no further
action to determine its applicability.
The inspectors
observed that
the title of GEK-64459B made it appear that this publication applied
to the AKR-30 reactor trip breakers,
and the licensee
recognized
that the newer technical
information for the
breakers
existed,
but the licensee
from January
1990, did not
confirm the applicability of this information to their maintenance
procedures
for
GE reactor trip circuit breakers until this
inspection.
Therefore,
the licensee
had not received specific
guidance
from General Electric to use this manual
at the time of the
breaker failures.
During the inspection the licensee
received
a
letter dated April 16,
1992 (J.
E. Kusky to J. Bailey) which
confirmed that GEK-64459B was the current technical
manual.
16
B.
The,inspectors
compared the requirements
and recommendations
in
GEK-7310C and GEK-64459B with the licensee's
maintenance
procedure.
The inspectors
noted five potential
problems in the procedure.
These five problems were:
1) the licensee
had authorized
use of Dow
Corning (Molykote) 321R lubricant in place of the
GE required
Mobilgrease
28 (see Section 3.B), 2) the licensee
procedure
authorized
removal
and replacement of the
UV trip device after all
mechanical
UV device adjustments
had been
completed without
rechecking
those adjustments,
3) the licensee did not check for
adequate
mechanical
margin for shunt trip device tripping, 4) the
licensee
was not checking buffer alignment,
5) the licensee's
procedure specified
UV device adjustments,
checks,
and acceptance
criteria which were different than GE's latest crIteria contained
in
GE manual
GEK-64459B.
These five problems
are discussed
in more
detail in Appendix C.
Based
on the findings discussed
in Appendix C, the inspectors
concluded that:
1)
Dow Corning 321R was not .an appropriate
lubricant,
2) Procedure
32MT-9SB02 incorrectly
sequenced
work and
could not ensure
proper
UV device mechanical
adjustment,
3)
measuring of shunt trip device mechanical
margin was warranted,
4)
measuring buffer alignment
may be beneficial,
and 5) incorporating
UV device adjustments,
checks,
and acceptance
criteria contained
in
GEK-64459B. was warrante'd.
The licensee
agreed to verify that
Manual
GEK-64459B was the correct manual for GE AKR-30 breakers
and
to incorporate this manual in maintenance
procedures.
The licensee
also agreed to evaluate
the five potential
problems listed above.
Review of Reactor Trip Breaker Maintenance History
The inspectors
reviewed the maintenance
experience,
trending program,
and
preservation
of evidence during troubleshooting for reactor trip breakers
since unit startup.
(1)
Maintenance History
A selection of approximately
1PO corrective maintenance
Work Orders
(WOs) for both Westinghouse
and General Electric breakers
in all
three units were reviewed.
One immediate difficulty noted
was that work orders identified
equipment
by plant location only,
and not also
by equipment serial
number.
This made tracing maintenance
history by breaker very
difficult since breakers
had
been replaced'and
moved
between units.
The licensee
constructed
a time line of breaker serial
number
locations in unit cubicles.
The history was completed
and available
for NRC review seventeen
days after the effort began.
(a)
Reactor Trip Breaker Maintenance History
The most significant repeat corrective maintenance
issue for
reactor trip breakers
was undervoltage
(UV) device
~
~
17
failures.
Two failures occurred in 1987,
and two more occurred
in 1991.
One of these failures
was
a failure of the
UV device
to tr'ip, even after power was removed completely.
The other
three
.UV trip device failures involved
a bent linkage,
a weak
device
and
a failure of the device to meet the 'acceptance
criteria for UV dropout voltage.
representatives
who were
on site to assist troubleshooting
stated that this was
an above average rate of failure.
The remaining maintenance
history did not indicate
any specific
trends or concerns,
and was typical of what the Westinghouse
representatives
had
seen before.
The Westinghouse
representative
indicated that
a linkage could have
been bent
when closing springs
were reattached
following a slow close
test.
(See Appendix C, Paragraph
1 for more discussion of this
possibility)
The inspectors
concluded that the maintenance
history did not
suggest
any specific maintenance
practice or trend that would
impact directly on the failure of the Westinghouse
breaker to trip.
(b)
General Electric Reactor Trip Breaker Maintenance History
The most significant repeat corrective maintenance
issue for
General Electric reactor trip breakers
was
UV device failures.
The inspectors
did not identify as failures the eight
corrective maintenance
work orders for the recognized
generic
failure of General Electric
UV devices to reset after the
breaker
was tripped resulting in subsequent
Trip-Free operation
of the breaker.
APS evaluated this in
EER 86-SB-101
(which
referenced
CE letter V-CE-30333
and
ADP Info Bulletin 83-13)
These
documents
concluded that this was
a known problem with
the breaker which had littl'e impact
on the safety function of
the breaker.
In addition to this known failure mechanism,
three
Work Orders
identified General Electric
UV device failures necessitating
replacement.
Four others
needed
adjustment
more frequently than
the
18 month
UV device replacement interval..
One
WO identified
a General
El'ectric breaker with an
out-of-'pecification
high trip shaft-trip torque measurement
with
corrective action to lubricate the bearings with Dow Corning
Holykote
BR 321.
This was in contrast to General
Electric
Bulletin 9-20 which stated that when high trip shaft torque
was
identified, the bearings
should
be replaced.
The licensee
indicated that this was
a new breaker that
had
new trip shaft
bearings
packed with Hobil 28 grease.
Also, the breaker
had
been sitting in the warehouse for approximately
two years prior
to this out of specification
measurement.
Therefore,
the
licensee
did not consider it appropriate
at the time to replace
II
I
18
the breaker's
bearings.
The inspectors
concluded,
however,
that lubricating these
sealed
bearings with Dow Corning
BR 321
was inappropriate.
The licensee
agreed. with the inspector's
comments.
The remaining maintenance
history did not indicate
any
additional trends or concerns.
The inspectors
noted that the
variety of out of specification conditions identified on the
malfunctioning breakers
may have resulted fr om electricians
adjusting the
UV trip paddle
assembly adjusting
screw
as
indicated in the vendor manual
used
by the licensee,
GEK-7310C.
The inspectors
noted that work orders did not contain
sufficient detail. to document whether or not this adjustment
had
been
made.
The inspectors
concluded that this
UV trip
paddle adjustment
was the only maintenance
practice which might
have affected the failure of this breaker to close.
(2)
Trending Program
A review of the System Engineer trending program revealed
numerous
failures of the
UV trip device to meet the Westinghouse
specified
as
found and
as left dropout voltages.
The Westinghouse
procedure,
"Haintenance of Westinghouse
Reactor Trip Switchgear,"
specified
.a 37.5
75 volt dropout specification.
The System
Engineer for these
breakers
stated that this was not
requirement,
that Westinghouse
device dropout voltage
settings
were not adjustable,
and, therefore,
no action
had
been
taken in response
to those out of specification values.
The licensee
was not trending Westinghouse
reactor trip breaker trip
shaft torque.
At the time of the inspection,
representatives
recommended that trip shaft torque
be measured
and
trended.
The licensee
agreed to evaluate trending trip shaft
V
The inspectors
concluded that no trends
were apparent
in the
maintenance
history to indicate
a deteriorating condition that might
have contributed to the failures observed with the Westinghouse
&
General Electric reactor trip breakers.
(3)
Control of Troubleshooting
Licensee
procedure
"Technical Specification
Component
Condition Record," required the Shift Technical Advisor (STA) to
either initiate a Root Cause of Failure Condition Report/Disposition
Request
or obtain system engineer
concurrence that one is not
needed.
Licensee
procedure
"Equipment Root Cause of
Failure," Paragraph
3.3. 1, required the duty STA to initiate a
formal request to the applicable
department to preserve
evidence for
a failure investigation.
Interviews with the duty STA on Harch 31,
1992 when Unit 3 "C" reactor trip breaker failed to open at ll:18
PH
revealed that the
STA did not come to the control
room or to the
19
switchgear
immediately after the reactor trip breaker failed to
trip.
Rather,
he agreed with the assistant shift supervisor that no
STA support
was needed
during the night.
During the night the
breaker
was racked out, cycled eight times in the test position,
moved to the shop,
and cycled additional times prior to the
development of a formal troubleshooting
plan.
Interviews with the
duty STA for March 31,-1992
and the relieving STA for.April 1,
1992
revealed that neither
STA was
aware of any
STA responsibility for
attempting to preserve
as-found evidence.
The inspectors
concluded
that this represents
poor control of troubleshooting activities
early after the failure occurs.
This is an apparent violation
(Violation 50-530/92-15-01).
The inspectors
noted that, in Inspection
Report 92-10, there
had
been similar failures to control troubleshooting activities.
These
were the failures of:
a General Electric Pagne-Blast
breaker
where
the breaker
was removed from the cabinet
and tested without a
troubleshooting plan,
a containment isolation purge valve where the
valve was adjusted prior to an inspection or a troubleshooting
plan,
a Potter
8 .Brumfield relay which was cycled in the shop prior to
being shipped'o
the vendor for root cause of failure determination,
and
pump turbine control relay which was
discarded
before
any root cause of failure data could
be identified.
The inspectors
reemphasized
the need for control of root cause of
failure data.
The licensee
acknowledged
the inspector's
comments.
7.
Review of Breaker Actuation
S stem
A.
Performance
Requirements
of the Breaker Actuation Circuitry
The inspectors
reviewed the performance
requirements
of the breaker
actuation circuitry.
Two motor-generator
sets
supplied
power to the
control element drive mechanisms
(CEDH).
The power interruption
devices
were the Supplementary
Protection
Logic Assembly
(SPLA)
and two parallel
paths of breakers.
Each of the parallel
paths consisted of a General Electric Type AKR-30 breaker in series
with a Westinghouse
Type DS-206 breaker.
The interruption of power
was designed to occur when either the
SPLA contactors
opened
or
a
break occurred in both parallel
branches.
In the Westinghouse
breaker,
there were three electrical tripping
mechanisms:
the
UV trip, the shunt trip, and the solid state
,
overcurrent trip.
Any one of the three devices
would actuate
the
trip shaft to rotate to trip the breaker
co'ntacts
open.
The design
of the electrical control circuit was to simultaneously
deenergize
the
UV tr'ip coil and energize
the shunt trip coil to actuate
the
'rip
shaft to open the breaker.
Any one of the three trip signals,
the
PPS trip, SPLA trip, or the manual reactor trip push button in
the control
room, could activate the opening of the breaker.
4
20
Auxiliary contacts
on the breaker provided the status of the breaker
position on the local breaker panel,
the
PPS panel,
and the
SPLA
cabinet.
The auxiliary contacts of the breaker also provided one
input to the control -room annunciation
system which actuated
the
window, the three monitor displays,
and the alarm
printer.
The control
room annunciation
system monitored the opening
of an auxiliary contact
(which would be in an open state
when the
breaker
opened).
A mechanical
linkage in the breaker rotated the
auxiliary contacts.
When the mechanical
linkage did not complete
its rotation or was misaligned, it was possible for the closed
position contact to open while the open position contact
was not yet
closed.
The indications provided by the auxiliary contacts
were not
conclusive evidence of breaker position.
Each phase current of the Motor-Generator-output
was monitored
by an
inductive pickup coil.
Any one of the 'three
phases
conducting would
energize
the phase current light on the
PPS panel
and
on the control
board in the control
room.
The phase current light at these
locations was.a direct and positive indication of whether the
breaker
was
open or not.
The inspector
concluded that the breaker
indication and actuation
circuits for the reactor trip breakers
appeared
to perform according
to their intended functions
and did not appear'o
be the cause of
the failure of the Unit 3 Westinghouse
breaker to trip open.
Inspection of Installed
Equipment
The inspector walked down the breaker indications in, the control
room, the Reactor Trip Switchgears
(RTSG's),
and the
SPLA cabinets
in all three units.
Unit
1 plant was in a refueling outage.
The licensee
removed the
reactor trip breaker from Unit
1 Channel
C and put the
breaker in Unit 3 Channel
C for temporary replacement.
Meanwhile,-
a
spare
breaker
from the warehouse
was checked.
The inspectors
observed that the counter reading
on the spare
breaker
was
557 on
April 4,
1992.
The counter reading
on the .Westinghouse
breaker indicated the number
of open-and-close
cycles that each breaker
had undergone.,
During
the walkdown on April 5,
1992, the inspectors
surveyed the counter
reading of the Westinghouse
reactor trip breakers.
The counter
readings of the installed breakers
ranged
from a low reading of 378
to a high reading of 1130.
The Unit
1 Channel
D breaker
had
a low
counter reading of 378.
The Unit
1 Channel
C breaker,
now being
a
temporary replacement for Unit 3 Channel
C breaker,
had
a counter
reading of 834.
The counter readings for Unit 2 Channels
C and
D
were
949 and
925 respectively.
The Unit 3 Channel
D had
a high
counter reading of 1130.
The inspectors
concluded that none of the
circuit breakers
had
been cycled excessively.
21
The inspectors
also observed that
some flags indicated that spring
conditions were not aligned with the windows.
The flag indicating
"Spring Discharged"
on Channel
0 breaker of both Units
2 and
3 was
not aligned with the window and
showed approximately one-fifth of
the yellow portion of the charged condition at the bottom of the
window.
Unit 2 Channel
C showed approximately one-tenth of the
yellow portion at the bottom of the window.
After the walkdown, the
inspectors
attempted to resolve the meanings of these misaligned
flags.
The inspectors
observed
the charging of the closing springs
at the training breaker.
The rotation of the flag was not
a
continuous
but
a snap-action
type of rotation.
The Westinghouse
representative
indicated to the inspectors that the breaker would
trip open
even with the closing spring partially or fully charged if
the trip signal
was present.
The licensee
demonstrated
the ability
of the breaker to trip open
when the closing spring was either
partially or fully charged
on the training breaker.
-The inspector
concluded that the misaligned flag indication. of the spring
condition appeared
to have
no potential significance in causing the
failure of the breaker to trip open.
8.
ev
ew of
eactor Tri 'witch ear
esi
n
e
The inspectors
reviewed the reactor trip system design to understand
the
vendor's
design
approach,
and the reasons
for the circuit breaker
component
selections.
The inspectors
reviewed
an April 4,
1992 letter from Asea
Brown
Boveri '(ABB) Combustion Engineering
(CE) to the licensee providing the
vendor's
overview of the reactor 'trip switchgear history. 'n addition, the
inspectors
discussed
the history with the onsite
CE representative,
and four
cognizant personnel
in CE headquarters.
Figure
10 provides
a schematic of the
CE System
80 standard reactor trip
switchgear
design.
This was the design
used at Palo Verde,
This design
was
completed in the early 1970s
and sold to three other utilities:
Public Power Supply System,
Valley Authority, and Boston Edison.
However, the licensee
was the only System
80 design which was completed,
the
others
being canceled.
A similar modified System
80 design is under
construction in Korea
(Yongwang 3,4) using only Westinghouse
Type DS-206
circuit breakers.
The System
80 design
was
an evolution from the previous
design
(CE 3410 style).
The System 80 design
made
use of air circuit breakers
from two different-
manufacturers:
General Electric (Type AKR-30) and Westinghouse
(Type
DS-. 206).
The control element drive mechanism
(GEOM) motor generator
(MG) sets for this
design
were rated at 601
amps,
an increase
from the previous
CE design
(CE
3410) rating of 515 amps.
The reactor trip breakers within the reactor trip switchgear
are
used to
interrupt power from the output of the
MG to the input of the
CEDN control
system.
The trip function of the breakers
is activated
by the reactor
protection system.
22
However, the previous design
was
a nine breaker design
(Figure ll) using
General Electric AK-2-25 type breakers.
These breakers
were rated at 600
amps.
The
CE 3410 design
CEDM motor generators
had
a design output of 515
amps.
Each breaker only had to interrupt approximately half of this current
to trip the
CEDN motor generator output.
Therefore, to accommodate
the larger current interrupting requirements
of the
new design,
the next larger circuit breaker size available
was chosen.
The
next frame size available from both manufacturers
was 800 amps,
the Type AKR-
30
(GE) and Type DS-206
(W).
CE stated that two different breaker vendors
were chosen to improve protection
against
common
mode failure concerns
should they exist.
This design
was
approved
by the
NRC in a letter to the licensee
dated
February 24,
1987. That
letter stated that:
/
"The Palo Verde design allows online testing of the reactor trip system,
including independent testing of undervoltage
and shunt trip attachments
of the reactor trip breakers,
and meets
the staff position."
The inspectors
were informed by the Westinghouse circuit breaker technical
representative
present for the incident investigation that Westinghouse
did
not use
Type DS-206 circuit breakers
in its reactor trip switchgear designs.
Instead,
a 1600
amp .frame size breaker
(Type
DS 416)
was used.
This breaker
used
a very similar operating
mechanism
which differed principally in the use
of four main contact springs per phase rather than the one used for the DS-206
breaker.
The representative
stated that these four springs
provided'pproximately
three times the opening force of the spring in the DS-206
breaker.
He further stated that it was for this reason that the Westinghouse
Technical Bulletin NSD-TB-91-06-'RO referenced earlier in this report
was not
applicable to
DS 416 reactor trip breakers.
The
CE representatives
stated
that the DS-416 breaker
had not been
used since the DS-206 met all of the
design requirements,
and was from a reputable
breaker manufacturer.
The inspectors
concluded that the licensee's
reactor trip breaker switchgear
design
was
an
NRC approved design.
They noted that the Westinghouse
Type DS-
206 breaker,
used only at Palo Verde and Yongwang,
had
a potential failure
mode which the Type DS-416 breaker
used at many Westinghouse
reactors
was not
susceptible to.
The Yongwang design only used
DS-206 breakers.
The
inspectors
were also informed by the .licensee that the
GE AKR-30 circuit
breakers
were only in use
as reactor trip breakers
at Palo Verde.
9.
E it Int rview
The inspectors
met with the licensee
personnel
identified in paragraph
1 on
April 10,
1992 to summarize the scope
and findings of the report.
The
inspectors
emphasized
the available conclusions
and findings detailed in this
report.
Licensee representatives
acknowledged
the team's findings,
and agreed
to review whether or not the DS-206 breakers
should
be modified to the DS-416
configuration
as part of their long term corrective action program for this
incident.
Appendix A
DS-206 Circuit Breaker Operating Principles
The operating
mechanism of the DS-206 circuit breaker. was
a spring charged
stored
energy type.
It consisted of two major parts,
a spring-charging
mechanism
and
a closing
and opening mechanism.
The following'paragraphs
contain
a brief discussion of the spring-charging
mechanism
and
a more
detailed discussion of the closing
and opening mechanism.-
1.
Spring-Charging
Mechanism
Figure
2 shows that rotation of the motor crank,
piece 24,
pushed the
oscillator arm counterclockwise forcing the oscillator pawl, piece 9, to push
a tooth in the ratchet wheel, piece
10.
.The ratchet
wheel rotated slightly
more than
one tooth and
was captured
by the hold pawl, piece ll.
This process
repeated until the closing springs
were charged.
Figure
6 shows the charging
springs in both the charged
and discharged
positions.
2.
Closing
and Opening Mechanism
The circuit breaker
close
and opening (trip) linkages
can
have four steady
state conditions,
as
shown in Figure 3.
The angular position of the close
cam
in Figure 3a corresponds
to the angular position of the drive plates
and
closing spring crank arms
shown in Figure 6b.
These figures
show the trip
latch in the tripped position.
The trip latch resets
to the latched position
at the end of the spring charging stroke.
Figure 3b shows the lower end of the main drive- link, with the main roller,
swung upward
and toward the left, pushing the trip latch constraining link so
as to rotate the trip latch back to the reset position.
This action will
occur the
same time that the spring charge is completed
and just before the
close
cam stop roller strikes the spring release
latch.
The position of the
cam in Figure 3b corresponds
to the position of the drive plates in Figure 6a,
with spring charged,
breaker
open.
The breaker
mechanism is now ready for closing.
Counterclockwise rotation of
the spring release
latch started
the closing cycle.
This rotation removed the
hold on the close
cam stop roller,
and allowed the force of the closing
springs to rotate the close
cam counterclockwise
and close the breaker.
Figure 3c shows
a circuit breaker in the closed position with closing springs
discharged.
The close
cam has rotated
about
180 degrees
during the closing
cycle.
The breaker
mechanism is now ready for opening (tripping).
The breaker is
tripped open
by counterclockwise rotation of the trip shaft.
The trip shaft
extends
across
the left hand part of the breaker
and is rotated
by a shunt
trip device,
an undervoltage
device,
a device for measuring faults,
and
a
manual device.
In the closed position, the main contact springs
produced
a clockwise twisting
force on the pole shaft.
This force was transmitted
by the center pole lever
downward through the main drive link to the main roller.
The main drive link
at the main roller connects
to the trip latch by the roller constraining link.
The downward force on the main drive link resulted
in a pulling force on the
roller constraining link.
This force tends to rotate the trip latch
counterclockwise,
but the trip latch is kept from rotating by overlap of the
,latch surface
on the trip shaft.
For tripping,
a very small rotation of the
trip shaft releases
the trip latch to rotate counterc]ockwise to the position
shown in Figure 3a.
Figure 3e shows enlarged
views of the trip shaft
and trip
latch tip in the closed
and tripped positions.
The entire linkage collapses
under the force of the main contact springs.
A reset spring,
Figure 2, piece
19, pulls the linkage to the fully open position.
Appendix
B
General Electric AKR-30 Circuit Breaker Operating Principles
The operating
mechanism of the AKR-30 circuit breaker
was of the spring
charged stored energy type.
It consisted of three major parts,
a spring-
"
charging mechanism,
a closing and opening mechanism,
and
a trip shaft
and trip
devices
mechanism.
The following paragraphs
contain
a discussion of these
three
mechanisms,.
1.
Spring-Charging
Mechanism
(See Figure 7)
The spring charging mechanism rotated the top of the camshaft,
piece 4,
backwards
toward the front of the breaker pulling on*closing springs,
piece l.
This was accomplished
by the eccentric output shaft of the gearmotor,
piece 9,
causing the driving pawl, piece,8,
to reciprocate,
pushing the ratchet
wheel
enough past the distance of "one tooth so the holding pawl, piece 6, could
engage
the next tooth holding the ratchet 'wheel, piece 7, against
increasing
spring force.
This action continued until the springs
were charged.
2.
Closing
and Opening Hechanism
(See Figures
7 and 8)
The circuit breaker
mechanism
had three configurations,
tripped, reset,
and
closed,
as
shown in figure 8.
The transition from one configuration to the
next is described.
From a reset configuration, the discharge of the charging springs rotated the
cam, piece 3, until it engaged
the
cam roller.
This force rotated the main
shaft,
piece
13, pushing the insulated coupling, piece
12, forcing the movable
contact
arm into the stationary contact
assembly
which closed the breaker.
Once the breaker
was fully closed,
the spring charging mechanism
charged
the
closing spring which rotated the
cam back to its reset position.
With the breaker closed,
a trip initiator rotated the trip shaft,
item 10,
clockwise
as
seen in figure 8, which allowed the secondary latch,
item 14, to
pivot clockwise allowing the
cam roller, item 5, to collapse
down to the left.
This allowed the main shaft,
item 13, to rotate counter clockwise pulling the
insulated coupling,
item 12,
and the movable contact
arm to move to the right
breaking the circuit with the stationary contacts.
Arcing contacts,
arc
runners
and arc chutes
were present to dissipate
the arc.
With the breaker tripped, the opening springs discharged,
and the opening
springs
charged,
small lever springs
on the secondary latch,
item 14,
and
cam
roller, item 5, reposition the .linkage back to the reset position
as
shown in
figure 8.
3.
Trip Shaft
and Trip Devices
Mechanism
The trip latch was attached to the trip shaft.
This shaft was supported
by
bearings
and had trip paddies
attached
at intervals along the shaft.
The trip
devices released
some force to push the trip paddle to rotate the trip shaft
so the trip latch rotate
away from the secondary latch resulting in an opening
sequence
as described
above.
Each trip device is described
below.
a.
Undervoltage Trip Device
The undervoltage
device
was
a spring loaded 'armature restrained
by an
electromagnet.
When the voltage to the electromagnet
reduced to
approximately
60 percent of rated, voltage,
the spring pulled the armature
up from the coil causing it to engage with a trip paddle
assembly.
The-
trip paddle
assembly
contained
a fixed and
a floating paddle.
The
device armature
pushed
on the floating paddle
and the
'loating paddle would rotate until it engaged
the fixed paddle to rotate
the trip shaft.
An adjusting
screw on the trip paddle
assembly
would
vary the clearance
between
the armature
and the floating paddle.
b.
Shunt Trip Device
The shunt trip device
was
an spring loaded
armature
actuated
by an
electromagnet.
When voltage
was applied to the electromagnet,
the
armature
was pulled by the electromagnet
against
spring force.
This
movement pulled the armature
against
a trip paddle rotating the trip
shaft.
c.
Flux Shift Trip Device
The flux shift trip device
was
a spring loaded plunger held against
spring force by a permanent
magnet.
When
a trip actuation
signal
was
generated,
an opposing magnetic field allowed spring force to overcome
the magnetic force of the permanent
magnet allowing the trip rod to
impact
a trip paddle rotating the trip shaft.
As the breaker
opened,
reset linkage attached to the main shaft 'reset the trip rod for the next
trip signal.
d.
Manual Trip Button
A manual trip button was located
on the front of the breaker.
The button
was attached to a manual trip rod which was held away from a trip paddle
by a spring.
Pressing
the manual trip button overcame
spring for ce
allowing the manual trip rod to push
on the trip paddle rotating the trip
shaft.
e.
Racking Mechanism Interlock
The racking mechanism interlock was
a mechanical link which prevented
the
racking screw cover from being pushed
aside without first depressing
the
manual trip button.
This prevented
the breaker
from being racked either
in or out without first tripping the breaker.
f.
Disconnect Position Interlock
The disconnect position interlock was
a mechanical link which blocked the
racking screw cover in the open-position
when the breaker
was in the
disconnected
position.
This prevented
the breaker
from being closed in
the disconnected
position
as
a result of the racking mechanism interlock.
g.
Positive Interlock
The positive interlock was
a was
a lever on the side of the breaker.
This lever was linked to the trip shaft
and was actuated
by a ramp
cam in
the cubicle to rotate the trip shaft
when the breaker
was moved from the
connected to the test position.
e
0
Appendix
C
Evaluation of Westinghouse
Reactor Trip Breaker Maintenance
Procedure
1.
Closing Spring Removal
During observation of the investigation of the failed breaker discussed
in
Section 3.B of this report, the inspectors
observed
removal
and reinstallation
of the closing springs.
Craft personnel
had
no difficulty removing the
springs but had
some difficulty reinstalling the springs.
'Craft personnel
hammered the springs
back into position using
a screwdriver
and
a hammer.
Craft personnel
applied the screwdriver blade to the end of the closing spring
at
a large angle
and
hammered
the spring back onto its shaft.
The inspectors
noted that
a small slip of the screwdriver blade could result in damage to
circuit breaker mechanical
devices.
0
The inspectors
reviewed
why it was that these
inspections
were being done.
They determined that these inspections
were initiated following a previous
problem with pole shaft weld cracks.
However,
as noted in Section 5.B, all
the DS-206 reactor trip breakers
had
new type pole shafts,
so this inspection
was
no longer necessary.
The inspectors
concluded that removal of the closing springs every
6 months to
inspect for a previously corrected condition was not appropriate
based
on the
potential for circuit breaker
damage.
The inspectors
discussed
this issue
with the Westinghouse
representative.
The Westinghouse
representative
agreed
that the inspection
appeared
to be technically unnecessary
after pole shaft
replacement.
The inspectors
reviewed this item with the licensee.
The
licensee
committed to evaluate this issue
along with other procedure
recommendations
resulting from the root cause
team's findings.
2.
Trip Shaft Torque Measurement
The licensee
was not measuring trip shaft torque for Westinghouse
breakers.
IB 33-790-1G did not contain this check but the
representative
recommended it be accomplished.
Because
the vendor representative
recommended it, and because it was
an
objective measurement
of the breaker's
margin to trip which could provide
an
early indication of degraded
breaker performance,
the inspectors
concluded
that trip shaft torque measurement
was
a valid maintenance
test which was not
being performed
by the licensee.
Licensee representative
committed to evaluate
incorpation of this measurement
into their maintenance
procedures.
3.
Trip Latch Overlap
The licensee
was also not measuring trip latch overlap.
IB 33-
790-1G provided
a procedure to perform this adjustment
but noted that the
procedure
should only be necessary
when parts
were reassembled'fter
dismantling.
Discussion with the Westinghouse
representative
indicated that
now considered this check to be valid for routine maintenance.
The inspectors
noted that
reactor trip circuit breaker
had
previously failed to close
due to the trip latch overlap being out of
adjustment.
In addition, the licensee
found that the trip latch adjustment
on
the failed circuit breaker
was
out= of adjustment
by I/2 turn.
As discussed
in
Section 3.B, subsequent
investigation of the failed breaker indicated that the
trip latch overlap adjustment did not contribute to the failure.
The inspectors
concluded that measuring
the trip latch overlap
was
a valid
check for routine maintenance.
The licensee
agreed to evaluate
including this
check in the maintenance
procedure.
Appendix
D
Evaluation of GE Reactor Trip Breaker Maintenance
Procedure
1.
Lubrication (See Section 3.B)
The licensee
had
a 1983 evaluation that
Dow Corning
(DC) 321R was
an
.
acceptable
lubricant for the undervoltage coil moving armature
but had
no
evaluation for other moving parts.
DC 321R was
a spray type dry lubricant.
The licensee
contacted
Dow Corning.
Dow Corning provided
a letter that stated
that
DC 321R was
an appropriate lubricant for clean
and dry metal
surfaces
only.
The letter indicated that
DC 321R would not be effective if sprayed
over surfaces
previously greased
and could tend make the grease
ineffective.
GE manual
GEK-64459B specified Mobilgrease
28.
The
GE representative
stated
that the breakers
were factory lubricated with a grease.
Maintenance
records
indicated that the licensee
was applying
DC 321R to
GE reactor trip breakers..
The inspectors
concluded that the use of DC 321R was not technically correct
for previously greased
surfaces.
The licensee
committed to perform
a review
of lubrication used in
GE AKR-30 circuit breakers.
2.
Procedure
Sequencing
Procedure
Section 8.6,
"Undervoltage Device Positive Trip Check
and Adjustment," adjusted
and tested
the
UV device mechanical
linkage.
The
next section of the procedure,
Section 8.7, "Verification and Adjustment of UV
Device Setting,"
checked
and adjusted
UV device pick-up and drop-out voltage.
Section 8.7 directed that the
UV device
be removed,
adjusted,
and replaced if
the pick-up voltage
was not correct.
There were
no instructions in Section
8.7 to repeat Section 8.6 if the
UV device were removed.
The inspectors
concluded that this procedure
was inadequate
to ensure
proper
UV trip device mechanical
adjustment
since the
UV device
was potentially
removed from the breaker after its linkage had been adjusted
and tested.
Procedure
Step 8.7. 14 measured
and recorded
the as-found
UV device
drop-out voltage.
However, previous steps
authorized
removal of the
device,
and adjustment of the
UV device pick-up voltage.
The licensee
was
trending the as-found data.
In addition, the as-found trip torque
was taken
after the circuit breaker
had
been cleaned,
lubricated
and cycled
a number of
times.
l
The inspectors
concluded that Procedure
was not clearly measuring
as-found
UV device drop-out voltage or trip shaft torque.
The licensee
agreed
to evaluate
the recording of as-found data. 'ection'5 of this Appendix
discusses
additional
concerns with UV device adjustments
contained in
Procedure
3.
Shunt Trip Check
GE manuals
GEK-64459B and
GEK-7310C provided
a test to ensure
margin existed
in the shunt trip device mechanical
linkage.
These procedures
verified the
shunt trip device would trip the circuit breaker with a I/32 inch restraint.
The shunt trip check procedure
in GEK-64459B also included
an adjustment to
ensure that nuisance tripping did not occur.
These
checks
were not included
in the licensee's
maintenance
procedure.
The inspectors
concluded that the shunt trip check provided
an easy
method to
ensure
margin existed in the shunt trip device tripping mechanism.
The
inspectors
discussed
the benefits of the shunt trip check with the licensee.
The licensee
agreed to evaluate
including this check in a maintenance
procedure.
4.
Buffer Alignment
The buffer in the
GE AKR-30 circuit breakers
had two uses.
It prevented
the
mechanism
from overdriving the contacts
when the circuit breaker closed
and .it
absorbed
the opening energy of the mechanism
when the circuit breaker
opened.
GE manual
GEK-644598 provided instructions to measure
and adjust the buffer
setting.
-This instruction was not contained
in the licensee's
procedure.
The inspectors
concluded that
an improper buffer setting could increase
the
potential, for mechanical failure of the circuit breaker.
The insp'ector
discussed
measurement
of the buffer setting with the licensee.
The'icensee
agreed to.evaluate
including this check in a maintenance
procedure.
5.
UV Trip Device Adjustments
and
Checks
GE manual
GEK-64459B included adjustments
and checks of the
UV trip device
which were not included .in Procedure
In addition, the drop-out
voltage acceptance
criteria specified in GEK-64459B was different than
Procedure
Based
on discussions
with the
GE technical representative
assisting
the
licensee
in the root cause
analysis of the
GE AKR-30 circuit breaker closing
problem, the inspectors
concluded that the adjustments,
checks,
and acceptance
criteria of GEK-64459B were the latest
GE instructions for performance of UV
device maintenance.
The inspectors
concluded that this information should
be
included in the licensee's
maintenance
procedure.
The inspectors
discussed
these
concerns with. the licensee.
The licensee
agreed to verify that
Hanual
GEK-64459B was the correct
manual for GE AKR-30 breakers
and to
incorporate this manual in maintenance
procedures.
WESTINGHOUSE TYPE DS-206 CIRCUIT BREAKER
AMPTECTOR TRIP
AMPTECTOR TRIP TEST
TERMINALACCESS
r <<a~aswaeoee
I
NAMEPLATE
SHUTTER
EMERGENCY-
CHARGING
HANDLE
DRAWOUTUNIT
POSITION INDICATOR
OPENCLOSE
INDICATOR
PADLOCK PLATE
CLOSE BAR
TRIP PLATE
SPRING CHARGE
INDICATOR
FIGURE
1
l
1't
t
WESTINGHOUSE TYPE DS-206 CIRCUIT BREAKER
POWER OPERATED MECHANISM
25
24
23
10
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/.j
12
13
14
15
16
17
Qfs
Q15
1. Shunt Trip Device
2. Trip Shaft
3. Roller Constraining Link
4. Trip Latch
5. Close Cam
6. Stop Roller
7. Spring Release Latch
8. Spring Release Device
9. Oscillator Pawl
10. Ratchet Wheel
11. Hold Pawl
12. Drive Plate
13. Emergency Charge Pawl
14. Oscillator
15. Crank Shaft
16. Emergency Charge Device
17. Crank Arm
18. Closing Spring
19. Reset Spring
20. Closing Spring Anchor
21. Pole Shaft
22. Motor
23. Emergency Charge Handle
24. Motor Crank and Handle
25. Moving Contact Assembly
26. Insulating l.ink
27. Nain Drive Link
FIGURE 2
CLOSE SPRING IS
SHOWN CHARGED
r
WESTINGHOUSE TYPE DS-206 CIRCUIT BREAKER
FOUR BASIC POSITIONS
OF CIRCUIT BREAKER LINKAGE
'6'@
,Or
e.,:0
'O.')
Breaker Open Springs
Dr'scturrged
c) Breaker Closed Springs
Discharged
l
/
'
dJ Breaker Closed Spnngs
Charged
TripLatch Held
Zap Latch Released
eJ Ihp Shaft Latch Details
06
OS
Oig
11
12
1. Stop Roller
2. Close Cam
3. Roller Constraining Link
4. Pivot Pin
6. Trip Latch
6. Trip Shaft Latching Surface
7. Trip Shaft
L Pole Shaft
8. Center Pole Lever
'10. Pole Lever Pin
11. Moving Contact Arm
12. Stationary Arcing Contact
13. Moving Contact Pivot
Pin'4.
Main Drive Link
15. Main Roller
16. Spring Release Latch
17. Insulating LinkAdjusting
Stud end Locknut
18. Insulating Link
19. Mechanism Side Frame
20. Hardened Latch Surfaces
3
2
1
16
11
16
13
\\
19
b) Breaker Open - Springs Charged (Spring Charged
Position Corresponding To This Closing Cam Position
Shownin Fig. 2 J.
FIGURE 3
I ),
WESTINGHOUSE TYPE DS-206 CIRCUIT BREAKER
POLE ASSEMBLY
MOLOEO BASE
STATIONARYARCINQ
CONTACTS
ARCING CONTACT
SPRING
NIAINCONTACT
SPRING
STATIONARYMAIN
CONTACT F INGERS
MOVING
ARCING CONTACTS
MOVINGCONTACT
ASSEMBLY
PIVOT
BLOCK
HINGE SPRING
INSULATING
LINK
INSULATINOLINK
AOJUSTING NUT
ILOWERI
FIGURE 4
WESTINGHOUSE TYPE DS-206 CIRCUIT BREAKER
CONTACT ARRANGEMENT
DIMENSIONA
I .020 MINIMUMBOTH SIDES
I.O7O MAXIMUM
DIMENSION C
c.-
BREAKER CLOSED
0.42 a A)8
BREAKER OPEN
B
THESE FACES
PARALLEL
ARCING
CONTACT
IIII
IIII
Y
X
MAIN
CONTACT
MAIN OPENING
SPRING
BREAKER CLOSED
BREAKER OPEN
FIGURE 5
WESTINGHOUSE TYPE DS-206 CIRCUIT BREAKER
POWER OPERATED SPRING CHARGE DETAILS
0
Qn
11,
10
11
21
28
30
25
29
21
18
20
0
li
sf'r
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I
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II
I'U
ld
a) Spring Charged
Note: Main earn position for this crankshaft position is shotvn in Fig. 3 a
ta(6Is
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10
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b) Spring Discharged
6. Close Cam
B. Crank Shaft
9. Closing Spring
10. Spring End
11. Crank Arm
17. Ratchet Wheel
18. Hold Pawl
19. Oscillator Bushing
20. Oscillator Spring
21. Ratchet Wheel Pin
25. Drive Plate
27. Pawl Lifter
28. Oscillator Pawl
29. Motor Crank Roller
30. Oscillator
FIGURE 6
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GENERAL ELECTRIC TYPE AKR-30 CIRCUIT BREAKER
2
3
l5
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\\,
p
1 ~
2 ~
3 ~
4.
5.
6.
7 ~
l2
9.
10.ll ~
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13.
14 ~
9
15.
Cloeing Spring
Prop
Cam
Camshaft
Cam Roller
Holding Pawl
Ratchet Whee>
Driving Pawl
.
Gearmotor
Trip Shaft
Trip Latch
Insulated Coupling
Main Shaft
Secondary Latch
Opening Spring
4
5
6
7
8
Fig.
7.
(108D8131)
Electrical breaker tnechanism
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MECHANISM
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. TRIPPED
CLOSED
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RESET
2. Prop
3. Cam
4. Camshalt
5. Cam Roller
10. Trip Shalt
11. Trip Latch
12. insulated Coupling
13. Main Shalt
14. Secondary Latch
15. Opening Spring
FIGURE 8
~
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t
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~
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. ARC RUNNER
CONTACT
SPRING
STATIONARYARCING
CONTACT
MOVABLE
CONTACT
S
~ ~ '
STATIONARYMAIN
CONTACT
ARC RUNNER
~ CONTACT
'PRING
STATIONARYARCING
CONTACT
~t
MOVABLE
- CONTACT
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1
44
STATIONARYMAIN
CONTACT
FIG.
9 AKR 30H
800 AMP CONTACT STRUCTURES
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