mitsubishi sf6 gas circuit breaker type 100 sfmt-40e ... 2004 sacramento... · vermont electric...

Vermont Electric Power Company, Inc.

Mitsubishi SF6 Gas Circuit BreakerType 100 SFMT-40E

Breaker Failure Report

Prepared by:

Jeffery M. WrightManager – Transmission Field Services

April 6, 2004 – 13:08

• VELCO experienced a breaker failure in the Essex FACTS switchyard. The 115 kV SF6 gas circuit breaker is a Mitsubishi 100SMFT-40E.

• Although there were no visible external damages, relay and protection engineers analyzed the relay information and all indications led to an internal failure of the K98 circuit breaker.

EXAMPLE ONLYMitsubishi 100SMFT- 40E Circuit Breaker

Location: Georgia C80 Cap Bank Breaker

DFR analysis indicates the fault lasted nearly 4 cycles with phase 3 volts dropping to .02 p.u.

IBM, the largest manufacturer in Vermont is electrically connected to redundant VELCO 115 kV sources. They are located .7 miles from the Essex substation.

IBM 115 kV phase 3 bus voltage dropped to approximately the same as what VELCO recorded at Essex. Approximately .02 p.u. for nearly 4 cycles.

The power quality interruption cost IBM in excess of $1.5M in lost tooling hours and production.

An internal inspection directed by Mitsubishi technical engineers verified

that an internal fault had indeed occurred.

The breaker was shipped back two days following the failure to Mitsubishi

(Pittsburgh, PA) for a thorough failure analysis.

SF6 arc byproducts

Formal Mitsubishi Response Friday, April 16, 2004 Conference Call

Failure Analysis Report1) Repair Efforts & Flashover Location

The tanks from Breaker SG006800004 were dis-assembled and inspected.The flashover was noted to have occurred at Bushing Assembly #4, center phase, at the moving end.The evidence indicates that the arc struck from the Bushing #4 conductor to the bushing adapter plate.

Fotos are attached.The quantity of arc byproduct powder in the center phase tank was moderate, indicating the flashover

was not severe.Arc byproduct powder was collected and the SF6 which came inside the breaker was also collected, for

possible future analysis.

Breaker components which were damaged or suspected of being damaged were replaced; major replacedcomponents included center phase interrupter, Bushing Assembly #4 (conductor & insulator), all 6

bushing adapter plates, the SF6 gas system, desiccant, and associated hardware, O-rings, etc.The other 2 phases were also disassembled; all major components from these 2 phases were re-used.

All 3 tanks were thoroughly cleaned; all re-used components were thoroughly cleaned.Breaker SG006800004 was re-assembled and re-tested following written instructions.

Breaker SG006800004 was shipped on 4/15/04.2) Investigation into Cause of Flashover

Our investigation indicated that randomly-occurring water was the likely cause of the flashover.Water was detected using our ultrasonic (UT) inspection technique, which can detect water in boltholes

without dis-assembling the breaker.Boltholes in every nozzle were evaluated for presence of water by the ultrasonic method, and every bolt was

removed for visual examination. This gave us an opportunity to visually confirm the ultrasonicindications.

This investigation indicated that water was present randomly, at different levels, in 3 of the 6 bushing nozzles,in boltholes

Bushing Nozzle # 2 (2 of 12 boltholes, very minor … <0.5 mm)Bushing Nozzle # 3 (2 of 12 boltholes, very minor … < 0.5 mm)Bushing Nozzle # 4 (6 of 12 boltholes, minor & moderate levels)

Small traces of a water-and-oil liquid were noted on the undersides of 4 of 6 bushing adapter plates, wherethey mate with the tank nozzles. Foto attached.

Visual observations of removed bolts & boltholes also indicate that some of the water in the boltholes doesevaporate, and is likely absorbed by the desiccant in each tank

The internal inspection conducted

by Mitsubishi uncovered evidence of the internal fault

between the bushing conductor and

bushing adapter plate inside the bushing throat.

Further investigation uncovered water droplets in the breaker bolt holes of four out of six bushing

adapter plates.

Following the failure analysis, the major components damaged were replaced, the breaker was rebuilt,

shipped back to the Essex substation and commissioned by VELCO

technicians on April 21st at 13:24.

Water Droplets Present

Formal Mitsubishi Response Friday April 16, 2004 Conference Call

• Mitsubishi admits knowledge of three other similar failures of the same type of breaker – one in Illinois and two in Nebraska.

• Mitsubishi admits to a known process control problem which was identified and corrected in June 2001, affecting breakers manufactured between 1999-2001.

•The manufacturing process began with pressure washing the cast breaker tanks with water. The tanks were set outside to dry and the failures are attributed to trapped water in internal bolt holes that eventually migrates into the tank providing a point of discharge, ultimately faulting the breaker internally at the point of the water droplets on the tank wall.

• Mitsubishi did not issue a service advisory to all of their customers notifying them of this problem.

• Mitsubishi has since developed a method for detecting the water in the bolt holes using an ultra-sonic method. They agreed to send a crew to Vermont on Monday April 19th to begin testing other subject breakers – yet to be identified.

Mitsubishi Response

Mitsubishi identifies the

subject breakers that VELCO owns.

Out of the thirty (30) 100SFMT-40E type breakers

VELCO owns, seventeen

(17) are potentially

subject to the same

problem. 2001100-SFMT-40SHESG009110001MITSUBISHIC82SANDBAR

2000100-SFMT-40HESG002770001MITSUBISHIK23WILLISTON

1996100-SFMT-40HE970360101MITSUBISHIK43WILLISTON

2002100-SFMT-40HESG013120006MITSUBISHIK34-40WEST RUTLAND



2002100-SFMT-40HESG013120005MITSUBISHIK34WEST RUTLAND


1998100-SFMT-40HE980360401MITSUBISHIC71NORTH RUTLAND

1999100-SFMT-40HE980360101MITSUBISHIC72MIDDLEBURY

2000100-SFMT-40HESG00564002MITSUBISHIC80GEORGIA

2000100-SFMT-40HESG006800002MITSUBISHIC36ESSEX


2000100-SFMT-40HESG006800004MITSUBISHIK98ESSEX






2000100-SFMT-40HESG007100002MITSUBISHIK25 ESSEX

2000100-SFMT-40HESG005640007MITSUBISHIK25-22ESSEX







2002100-SFMT-40HESG013120001MITSUBISHIC92COOLIDGE

2002100-SFMT-40HESG013120008MITSUBISHIC91COOLIDGE

2002100-SFMT-40HESG013120009MITSUBISHIK32COOLIDGE

YEARTYPESERIAL NUMBERMANUFACTURERPOINTSTATION

The Testing Process

•The breaker is removed from service and CT shrouds are removed, exposing

the bushing throats.

•The bushing throat is filed clean, providing a clean surface to apply the

ultra-sonic device to.

• By aligning the test probe directly with the bolt hole behind the test area, the test device indicates a

waveform. A non-distorted waveform indicates a dry

bolt hole, whereas a distorted waveform can be

an indication of a contaminated bolt hole.

Interpretation of test results is done on site by the

technician.

• An inspection can be completed within four hours.

•The bushing throat is filed clean, providing a clean surface to apply the ultra-sonic device to.

• By aligning the test probe directly with the bolt hole behind the test area, the test device indicates a waveform. A non-distorted waveform indicates a dry bolt hole, whereas a

distorted waveform can be an indication of a contaminated bolt hole. Interpretation of test results is done on site by the technician.

The Internal Inspection / Rebuild Process

• If water is suspected in the bushing adapter plate bolt holes,

the breaker is drained of gas, bushings are removed and all

mounting hardware is removed, cleaned and reassembled.

• The rebuild process typically consumes a twelve to fourteen

hour day.

• Four breakers were rebuilt.

• Once the bushing adapter plate is removed, the holes are inspected for water, blown dry and prepped for reassembly.

Mitsubishi Response

•Mitsubishi’s response was

timely.

•The failed breaker was repaired and

returned to VELCO in seven (7) days.

•Inspections followed

immediately afterward.

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321

SFTWTMS

APRIL

BREAKER FAILS

BREAKER SHIPPED TO MEPPI

BREAKER SHIPPED

TO VELCO

FAILURE ANALYSIS

CONF CALL

INSPECTIONS START

Mitsubishi Response

•All work was wrapped up by the end of June.

•MEPPI was very cooperative and worked weekends to accommodate outage requirements.

•Of the seventeen (17) breakers that were ultrasonically inspected, four (4) required internal inspection and cleaning.

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10987654

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SFTWTMS

APRIL

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3130

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8765432

1

SFTWTMS

MAY

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10987654

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SFTWTMS

JULY

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26252423222120

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SFTWTMS

JUNE

FINISHED

VELCO Response

• VELCO has kept all of its owners and IBM informed of the results of the failure analysis report and the progress and results of the testing.

• VELCO has gone forth and publicized the failure on the Doble Engineering Support Group e-mail forum to inform other utilities of the facts related to theVELCO failure.

• VELCO is satisfied with the Mitsubishi inspection process and rebuilds.

• VELCO intends to hold MEPPI accountable for remedying any further problems identified and is currently negotiating the compensation for VELCO labor and materials. VELCO’s labor and material costs exceed $33,000.

mitsubishi sf6 gas circuit breaker type 100 sfmt-40e ... 2004 sacramento... · vermont electric...

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