Failure of OIP vs. RIP Bushings - Doble Engineering Company · PDF filePower factor problems typically won’t occur in bushings on an In Service transformer • Weather ... • Condenser

©2017 Doble Engineering Company. All Rights Reserved.

USING LABORATORY AND ON‐LINE DGA MONITORING TO KEEP A GSU OPERATIONAL DURING A CRITICAL SERVICE PERIOD

Pam Bahr and Jon Christensen

Intermountain Power Service Corporation

Paul Griffin and Lance Lewand

Doble Engineering Company


Confidential Notice

Doble Engineering (Doble) hereby grants the recipient (you) the right to retain thispresentation and materials included within (the Presentation) for private reference. Noother rights, title, or interest, including, but not limited to, the rights to copy, make use of,distribute, transmit, display or perform in public (or to third parties), edit, translate, orreformat any portion of the Presentation are hereby or otherwise granted and shallremain expressly reserved by Doble. You acknowledge and agree that such limitedlicense is expressly conditioned upon your acceptance of the terms herein. You furtheragree that, in the event of your breach, Doble will suffer irreparable damage and injuryfor which there is no adequate remedy at law. As such, Doble, in addition to any otherrights and remedies available, shall be entitled to seek injunction by a tribunal ofcompetent jurisdiction restricting you from committing or continuing any breach of theseterms.

©2017 Doble Engineering Company. All Rights Reserved. 3

OwnerIntermountain Power Agency

Operating AgentLADWP

OperatorIntermountain Power Service Corp.

• Construction began 1982

• Unit 1 Commercial Operation 1986

• Unit 2 Commercial Operation 1987

Intermountain Power Project


• Intermountain Generating Station

(two 950 MW units)

• 345 kV AC Switchyard

• 500 kV DC Converter Station

• Transmission Systems

(AC & DC)

Intermountain Power Project


Intermountain Power Project Transmission


General Electric Transformer

6

• Vintage 1982

• Voltage class 345 – 26 kV

• Power class 865/969 MVA

• Application: Generator Step‐up transformer

• 55/65°C rise rating

• Forced oil Forced air cooling (OFAF)


• Document strategy for leaving transformer with load sensitive problem in service

• Case involving more than 1 fault type

• Use on‐line DGA monitoring to manage the problem

• Laboratory testing confirmed on‐line DGA results

• Transformer in otherwise good condition – reasonably dry, paper aging at a low to normal rate

• Acoustic monitoring used for fault confirmation and location

Case Study

7


• Bare metal or paper‐wrapped conductor fault

– Generation rate of carbon oxide gases

– Ratio of carbon oxide gases

– Amount and rate of generation of 2‐furfural

– Ethylene/ethane ratio

Possible Sources of Gassing Behavior

8


• Normal for many years

• Excessive gassing associated with Shields 2013

• Second Event – 2014

– Shields again?

– Something new?

• Generation rate TCG increasing

Total Combustible Gas (TCG) Generation

9


• Two connections per shield

• Connections loose

• Carbonized oil between bolts and washers

• Replaced with larger washers

• Tightened loose bolts

First Problem with Shields Stating in 2012

10

60 flexible copper straps, 2 bolted connections each – approximately 30% loose


Overheating and pitting of plate resulting from poor connection

Second Problem: Lower Connection Plate of Shield

11


• Stable for long period of time

• Two issues developed

Generation of Combustible Gases

12


• Initial shield issue in 2012 and again in 2013

• Corrective actions take

• Issue again in 2014

• Gassing patterns similar

13


• Methane, Ethane, and Ethylene

• Ethylene/ethane ratio <4:1

• Typical paper wrapped conductor fault

• Typical of unintentional core ground

Generation of Hydrocarbon Gases

14


• Generation rate of total combustible gases >100 ppm/day

• Rate of increase in total combustible gas was increasing suggesting rapid deterioration of condition

• Issue could be with the magnetic circuit

• Issue could be paper wrapped conductor fault

• Unlikely to make it to planned outage

• Determine if the problem was load dependent by reducing load and using generation rate of gases as indicator

Excessive Rate of Gas Generation

15


Generation Rate Load Dependent

16

Reduced Load


• Gassing rate reduced to reasonable level

• None of the individual combustible gases started increasing significantly

• No acetylene detected

• Acoustic monitoring did not detect significant problem

Leave in Service

17


• Indicated fault might be on the LV side near the bottom

• Recommendation to check the low voltage side for the following possible problems: – Tank wall shields

– LV leads and bus connections

– Neutral leads and connections

– Bottom end frame shields (if present)

• Problem was found on the LV side but closer to the top

Acoustic Location

18


• Normal ratio CO2/CO

• Normal amounts Carbon oxides

• Generation rate increase during fault conditions

Carbon Oxide Gases

19


Second Problem Low Voltage Lead Crimp Connection

20


• Managed to remain in service as long as possible

• Not many strands left

Just in Time

21


Repaired: New Bolted Connection, New Insulation

22


• Solid insulation holds about 1/3 of its weight in oil

• Gases retained in oil in solid insulation takes about 3 months to equilibrate with bulk oil

• After 3 months stable gassing

• Repairs corrective

Continued DGA Post Repair

23


• Large oil volume transformer, sealed conservator

• Gases permeate membrane slowly

• Dissolved gases in oil will tend to change in step‐wise increase or very slow decreases

• Oxygen can vary more due to amount in air

Variation in DGA Results from Monitor

24

0

10

20

30

40

50

60

70

80

0

200

400

600

800

1000

1200

1400

1600

H2

O2

CH4

CO2

C2H4

TDCG

THC

Top Oil


Complete History of DGA Results

25


• Possible to manage load related faults for window of time

• More than one fault can take place at the same time

– Examine the relative composition of gases

– Examine ethylene/ethane ratio to evaluate if paper‐wrapped conductor fault

– Determine the rate of total combustible gas generation and examine slow of gassing curve for accelerated gassing profile

• It would appear that some of the gassing associated with the shield problem might have been from the low voltage lead crimp area

• It is possible that the 3rd problem was created in repairing the 2nd

• DGA accurate in indicating urgent response needed

Conclusions

26


• On‐line DGA monitoring used to manage retaining transformer in service for small window of time

• Allowed for field repair before destructive failure that might have required transformer replacement

• DGA results shows problem has been corrected

Conclusions

27

Documents

Failure of OIP vs. RIP Bushings - Doble Engineering Company · PDF filePower factor problems typically won’t occur in bushings on an In Service transformer • Weather ... • Condenser