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Field Experience & Reliability Tests for the New EasyDry Condenser Bushing

LUKAS MUGGLI

© ABBSlide 1September 8, 2015

T. Schütte, ABB Schweiz Ltd, High Voltage Components, Bushings, 2015-10-19

INMR2015 - MunichField experience and reliability tests for the new EasyDry condenser bushing


INMR2015 - Munich

Why do you care about bushings?

How does an EasyDry bushing look like?

Which ageing mechanisms do apply to EasyDry bushings?

How does an EasyDry bushing perform?

RIS Technology – applied to ABB EasyDry Bushings


Bushings contribute for 3% of the total costs of a transformer, but…

… their failure is one of the three main causes for a transformer failure

… are responsible for up to 40% of transformer fires - in case of OIP bushings


Source: S. Tenbohlen et al., «Transformer Reliability Survey: Interim Report», Electra No. 261, pp. 46-49, April 2012



1. Safety of people and equipment

2. Availability of equipment and assets:

Reliability

Long-life cycle

Safe to store

Customer needs

AGEING


Ageing mechanisms in an EasyDry bushing

Ageing of a component depends heavily on the load and on the conditions on site

The three main contributors for ageing of a dry bushing:

Thermo oxidation is the main ageing mechanism for the insulation

Perform a ‘Thermal ageing test’

Multi cycle load due to mechanical impacts or temperature changes

Perform a ‘Multi bending test’

Humidity uptake of insulation material

Perform a ‘Boiling water test’


How does an EasyDry bushing look like?EasyDry Cross-Section

Copper terminal (air side)

Silicone insulator

Condenser core

Mounting flangeMeasuring tap

Current transformer extension, if required

Clamp to fix terminal

Oil side shield


Wind on air side connection leads to permanent mechanical forces on the bushing

Changes in current load of bushing and changes of outside temperature leads to thermal expansion and contraction of the bushing

Small, but steady mechanical impacts on the bushing over the entire lifetime

Reliability tests for EasyDry condenser bushingsMulti bending test – Why?


Most severe test – in addition to standard requirements: This test was performed in collaboration with a utility (Westnetz, according to the RWE standard)

This test included 3 temperature cycles between -30°C and +40°C

The bushing was bent 25’000 times in x- and y-direction with 60% of the cantilever load according to IEC 60137 during the temperature cycles

Reliability tests for EasyDry condenser bushingsMulti bending test – Test procedure


Following the thermo-mechanical pre-stress, a complete type test according IEC 60137 was performed and the bushing successfully passed it

An additional peeling test was performed by cutting into the insulation. The results showed no delamination between the silicone and the epoxy condenser core - even after these extreme tests

Reliability tests for EasyDry condenser bushingsMulti bending test – Results


Humidity ingress of the condenser core during storage or installation leads to an increased power factor

Humidity on the interface between outdoor insulator and condenser core might lead to treeing and finally to flashover

Humidity inside of the bushing is dangerous and can cause fatal break downs

Reliability tests for EasyDry condenser bushingsBoiling water test – Why?


Humidity ingress can be measured with tanδ measurements

So far, no type test is defined by IEC for direct molded bushings for testing the interface between silicone insulator and condenser core

Yet, IEC specifies a type test for surge arresters (IEC 60099)

The bushing was mechanically and thermally pre-stressed according toIEC 60099:

4 bending cycles per 90°(for 24h with 1400N)

Temperature cycles btw. -40°C and +60°C

Reliability tests for EasyDry condenser bushingsBoiling water test – Test procedure


Most severe test No. 2 – in addition to standard requirements: The bushings were actually boiled for 42 hours in deionized water containing 1 kg/m3 NaCl (salt)

After this extreme boiling test, the bushings have (again) passed a complete type test acc. IEC 60137

After cutting the silicone and performing a peeling test for testing purposes we could not find any delamination between the silicone and the epoxy condenser core

Reliability tests for EasyDry condenser bushingsBoiling water test – Results


Ageing of insulation material may limit the lifetime of a bushing due to occurrence of partial discharges or increased tanδ

Thermo-oxidation is the main ageing process of epoxy insulation within a dry-type condenser bushing

Reliability tests for EasyDry condenser bushingsThermal ageing tests – Why?


Material samples aged at different temperatures (btw. 160 = T1 and 240°C = T5)

After defined periods, samples were tested (diagnostic property)

Time till diagnostic property drops to 50% of initial value is determined using linear regression

Determined lifetimes τ50% are plotted against temperature T

Temperature resulting in defined lifetime (typically 20’000h) is determined

Reliability tests for EasyDry condenser bushingsThermal ageing tests – Test procedure


The comparison between RIP and RIS revealed that RIS material showed a slower ageing process than RIP material. Yet, this is just a comparison between the two materials. A final answer about lifetime cannot be given at this time.

Although the tests are of comparative nature, they show that the expected life time should exceed that of RIP material 30 years lifetime in service expected

Reliability tests for EasyDry condenser bushingsThermal ageing tests – Results

Time [h]

Time [h]


- International transmission

- 132kV, 230kV, 300kV DC

- National transmission

- 132kV, 275kV, 500kV DC

- Local Distribution

-11, 22, 33kV

RIS Bushing Field Performance – Malaysian ExperienceAbout TNB Malaysia

Owner of Malaysian grid network from 500kV to 11kV


RIS Bushing Field Performance – Malaysian Experience

The assessment of risks and gathering knowledge on new technologyperformance and reliability in a tropical climatic environment

Shorter lead time, faster manufacturing duration

Ease of storage, no special requirement i,e protective cover etc

What interest TNB to embark on this project….



Project Commencement Date : April 2013

Pilot Installation Date : Apr 2014

Pilot Completion Date : Dec 2014

Summary of Project

8 months duration



Max Ambient 24-40 deg C

Average Humidity 70-90%

Rainfall 4000mm per year

High Average isokeraunic level 300 light.days/year

Why Malaysia ? - Geographical Information


• Manufactured in 1999

• Manufacturer Wilson, Australia

• 60/90MVA full transformer

• 132/33kV Load Transformer

• ONAN/ONAF (Cooling)

• Fitted with 145kV GOB ABB Sweden OIP Bushings

Easy Dry RIS Bushing

Um=145kV, 650kVp BIL, 1250A

RIS Bushing Field Performance – Malaysian ExperiencePilot Transformer


RIS Bushing Field Performance – Malaysian ExperienceFactory Routine Test

Partial Discharge Test

Dielectric Dissipation & Capacitance

@167kV (2Uo) < 2.0 pC

Parameter Before Dielectric After Dielectric

DielectricDissipation

Factor

0.243% 0.241%

Capacitance 220pF 220pF


Service Performance ResultsCapacitance and Voltage Monitoring

No permanent change or capacitance more than allowable +-3%

12 3

1 2 3UL +3%

LL -3%


Service Performance ResultsInfrared Scanning

47.6C

19.6K

46.7C

18.7K

46.9C

18.9K

The max difference between phases approx 0.7K@38MW

85.9K84.9K89.0K

The limits between adjacent bushing werebelow of max limit < 20K

38MW

Full Load 81MW


Service Performance ResultsCapacitance & Dissipation Factor Measurement

Offline Dissipation Factor & Capacitance did noexceed the agreed tolerances, indicating that therewas no significant change in insulation structure orpresence of contaminants that can influence theresults.



Based on findings and conclusion based on trial project evaluation, the project team concluded that the RIS bushing technology was proven reliable and showed excellent performance in the field

Conclusion


Summary

Main ageing mechanisms for EasyDry bushings are:

Mechanical bending

Humidity ingress

Thermo oxidation of insulation material

All performed tests have shown equal or better results when compared with the existing RIP technology

RIS used for EasyDry bushings is a maturing technology for dry-type bushings

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