20190924Avista to Staff Consultant Reports-0706.pdf

Mr. Ronald Crow May 6, 2007
Executive General Adjuster
McLain Crow & Associates, LLC
26423 Hidden Timber Lane
Katy, TX 77494
Dear Ron:
RE: Interim Report of Findings – Large Power Transformer Failure
Insured: Avista Utilities
Coyote Springs Substation
GSU Transformer #2
Date of Loss: March 23, 2007
Type of Loss: Transformer Gassing
McLain Crow Number: __
The following is a review of the pre-determined failure and interim findings regarding the
Avista Utilities transformer reported loss at the Coyote Springs Substation Generator
Step-up Unit (GSU) #2. The loss involves a 532-13.8-18 kV three winding power
transformer used to transfer electrical power between the generation facility and the
transmission grid. The GSU transformer involved in the incident was manufactured by
Areva (Alstom) in Turkey, 2002, serial number 316322. The GSU unit is rated
213/284/355 MVA on the 532 kV H side, 88/117/147 MVA on the 13.8kV X side and
125/167/208kV on the 18 kV Y tertiary side winding. The generating plant is a
combined cycle unit, having both a gas turbine and a steam turbine portion with
individual outputs to the transformer 18kV and 13.8kV low voltage windings.
INCIDENT
The Coyote Springs GSU #2 transformer was removed from service on Friday, March
23rd, 2007 at 7:05 AM by Avista engineering and field services personnel following
notification of a high gas alarm from the transformer SERVERON monitoring system.
Additional monitoring systems such as the HYDRAN and the protective Buchholz relay
also operated indicating elevated quantities of combustible gasses earlier in the morning.
The gasses reported were Acetylene, Hydrogen, Methane, Ethane and Ethylene. These
gas quantities are tracked by two on-line transformer monitoring devices, namely the
SERVERON and HYDRAN units. The Bucholz relay is a gas trap relay that operates on
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gas bubbles building up in the transformer tank and rising up thru the windings and into
the conservator tank. This device either trips or alarm on operation.
The SERVERON unit is a multi-gas on-line DGA analysis device that continuously
monitors fault gases, moisture and temperature in a transformer. Avista trends the
historic DGA data of the GSU and provided recent readings showing the increase in the
combustible gasses and hydrogen. The concern for continuously elevating gasses is that it
is an indication of internal arcing and possible insulation breakdown, eventually leading
to transformer failure.
On March 23rd, following the GSU removal from service, Avista engineers performed a
series of electrical diagnostic tests including power factor of the coils and bushings, and
core ground. All diagnostic tests appeared to be acceptable with the exception of an
18kV bushing test. On March 27th, Avista engineers performed an internal inspection
(inspection was limited by space) looking for loose or damaged components, indications
of tracking or insulation breakdown. No visual deficiencies were observed.
A review of the historic Dissolved Gas in Oil Analysis (DGA) report provided by Avista
indicated that the unit was operating satisfactorily with no indication of internal or
operating problems. All gasses were well within ANSI and industry acceptable
standards. The trending report from the SERVERON shows the elevation of gasses
occurred quite rapidly. Also with an unknown incident occurring around March 22nd
showing a spike in Ethylene (oil overheating). This spike could be a sampling
irregularity. The 3/23/2007 traces show a rapid rise of Acetylene and other key
combustible gases indicating that some form of abnormal electrical activity (internal
arcing or overheating) had occurred. It is unknown at this time what the cause of the gas
increase was, or if it still remains. Gases of this nature can be formed by insulation
breakdown, core grounds, and loose connections, among others. It should be noted that
the unit did not fail and trip off line; it was removed from service to perform diagnostic
and internal investigations. At this stage,we believe that is necessary to perform more
in-depth investigation, most likely entailing an untanking and core and coil inspection. It
was reported by Avista that the oil had been previously tested for corrosive sulfur
contamination and was determined to be acceptable.
Should the investigation reveal that the unit cannot be repaired in the field; the GSU must
be shipped to repair facility. The factory inspection and rewind costs, if required, would
be in the order of $2,200,000. A new, replacement unit would be in the range of
$4,500,000 plus shipping and installation. Depending of the physical terrain and location
to a rail siding, we believe the disassembly and shipping costs would be in the order of
$800,000 each way, yielding a total estimated “In and Out’ charge of near $1,600,000.
Should you have any questions or require additional information, please call me.
Sincerely,
Edmund F. Feloni, PE
Principal Partner
..........
. . . . . . . . . .
120 Prospect Street
Ballston Spa, NY 12020
Phone [phone]
FAX [phone]
E-mail [e-mail]
CharlesT.Raymond,P.E.
TransformerInspection
Areva GSU
213/284/355 MVA
Areva S/N 316322
Inspectionsperformedon-site
Charles T. Raymond, P.E.
June 25, 2007
2
Background
This transformer was manufactured in Gebze, Turkey in 2002 as a spare for a
duplicate transformer that failed in service and was scrapped after investigation.
This transformer experienced a failure during factory impulse tests, shipping damage
that required factory disassembly and repair at the ESI repair facility in Westminster,
CA, and an insulation failure in service that required return to Gebze, Turkey for
repair.
It subsequently developed evidence of gassing in service as detected by the Severon
gas monitor. Of particular concern were the levels of ethylene and acetylene. These
gases indicated a high probability of insulation degradation.
On site testing and inspections followed to assess the condition of the transformer.
Site Inspections
Mr. Scott Wilson performed on-site tests and made internal inspections after the oil
was removed. I was provided results of the tests and a video of his inspections as well
as his descriptions as conveyed through phone conversations.
The following is a summary of my opinions:
1. The makeup of the combustible gases indicates a high probability of
insulation failure.
2. Based on the history of this transformer and the prior duplicate, operation
of this transformer with these high gas contents is inadvisable.
3. The on-site electrical tests indicated an elevated power factor between the
low voltage windings.
4. The in-tank inspections did not indicate any evidence of a problem that
could be identified and corrected without going through extensive
disassembly in a transformer facility.
5. The transformer, if properly constructed, should have been capable of
performing in the service conditions encountered including operations in
back-feed from the 500kV system. This was investigated in detail
previously by Dr. Degeneff both theoretically and in conjunction with
transients as measured by the Areva transient measuring equipment.
Charles T. Raymond, P.E.
June 25, 2007
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6. The transformer should not be considered operational without a thorough
teardown investigation. This will undoubtedly necessitate a complete
rewind to restore serviceability.
7. Because of the cost of a teardown, investigation, and rewind, replacement
would be a more economical option and should result in a more reliable
transformer.
C.T. Raymond
6/25/07