Field Experience & Reliability Tests for the New EasyDry Condenser Bushing LUKAS MUGGLI

Field Experience & Reliability Tests for the New EasyDry Condenser Bushing LUKAS MUGGLI

T. Schütte, ABB Schweiz Ltd, High Voltage Components, Bushings, 2015-10-19 INMR2015 - Munich Field experience and reliability tests for the new EasyDry condenser bushing Slide 1

INMR2015 - Munich RIS Technology applied to ABB EasyDry Bushings 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? Slide 2

Why do you care about 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 Slide 3

Why do you care about bushings? Customer needs 1. Safety of people and equipment 2. Availability of equipment and assets: Reliability Long-life cycle Safe to store AGEING Slide 4

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 Slide 5

How does an EasyDry bushing look like? EasyDry Cross-Section Copper terminal (air side) Clamp to fix terminal Condenser core Silicone insulator Mounting flange Measuring tap Current transformer extension, if required Oil side shield Slide 6

Reliability tests for EasyDry condenser bushings Multi bending test Why? 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 Slide 7

Reliability tests for EasyDry condenser bushings Multi bending test Test procedure 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 Slide 8

Reliability tests for EasyDry condenser bushings Multi bending test Results 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 Slide 9

Reliability tests for EasyDry condenser bushings Boiling water test Why? 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 Slide 10

Reliability tests for EasyDry condenser bushings Boiling water test Test procedure 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 prestressed according to IEC 60099: 4 bending cycles per 90 (for 24h with 1400N) Temperature cycles btw. -40 C and +60 C Slide 11

Reliability tests for EasyDry condenser bushings Boiling water test Results Most severe test No. 2 in addition to standard requirements: The bushings were actually boiled for 42 hours in deionized water containing 1 kg/m 3 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 Slide 12

Reliability tests for EasyDry condenser bushings Thermal ageing tests Why? 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 Slide 13

Reliability tests for EasyDry condenser bushings Thermal ageing tests Test procedure 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 τ 50% are plotted against temperature T Temperature resulting in defined lifetime (typically 20 000h) is determined Slide 14

Reliability tests for EasyDry condenser bushings Thermal ageing tests Results 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. Time [h] 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 Time [h] Slide 15

RIS Bushing Field Performance Malaysian Experience About TNB Malaysia Owner of Malaysian grid network from 500kV to 11kV - International transmission - 132kV, 230kV, 300kV DC - National transmission - 132kV, 275kV, 500kV DC - Local Distribution -11, 22, 33kV Slide 16

RIS Bushing Field Performance Malaysian Experience What interest TNB to embark on this project. The assessment of risks and gathering knowledge on new technology performance and reliability in a tropical climatic environment Shorter lead time, faster manufacturing duration Ease of storage, no special requirement i,e protective cover etc Slide 17

RIS Bushing Field Performance Malaysian Experience Summary of Project Project Commencement Date : April 2013 Pilot Installation Date : Apr 2014 Pilot Completion Date : Dec 2014 8 months duration Slide 18

RIS Bushing Field Performance Malaysian Experience Why Malaysia? - Geographical Information Max Ambient 24-40 deg C Average Humidity 70-90% Rainfall 4000mm per year High Average isokeraunic level 300 light.days/year Slide 19

RIS Bushing Field Performance Malaysian Experience Pilot Transformer 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 Slide 20

RIS Bushing Field Performance Malaysian Experience Factory Routine Test Partial Discharge Test @167kV (2Uo) < 2.0 pc Dielectric Dissipation & Capacitance Parameter Before Dielectric After Dielectric Dielectric Dissipation Factor 0.243% 0.241% Capacitance 220pF 220pF Slide 21

Service Performance Results Capacitance and Voltage Monitoring UL +3% 1 2 3 LL -3% 1 2 3 No permanent change or capacitance more than allowable +-3% Slide 22

Service Performance Results Infrared Scanning 89.0K 84.9K 85.9K Full Load 81MW 47.6C 46.7C 46.9C 38MW 19.6K 18.7K 18.9K The max difference between phases approx 0.7K@38MW The limits between adjacent bushing were below of max limit < 20K Slide 23

Service Performance Results Capacitance & Dissipation Factor Measurement Offline Dissipation Factor & Capacitance did no exceed the agreed tolerances, indicating that there was no significant change in insulation structure or presence of contaminants that can influence the results. Slide 24

RIS Bushing Field Performance Malaysian Experience Conclusion 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 Slide 25

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 Slide 26