Martin Stoessl R&D Manager Siemens Transformers Austria - Weiz

Transcription

1 Martin Stoessl R&D Manager Siemens Transformers Austria - Weiz

2 Transformer reliability Ability to perform its required functions under stated conditions for a specified period of time Failure termination of the ability It is often reported as a probability 2

3 Transformer Reliability - based on ANSI C (1986) Definitions: Population: Transformers that have given common specific characteristics Failure: Termination of a transformer to perform its specific functions Failure with forced outage: Failure of a transformer that requires its immediate removal from the system for more than 1 day in conjunction with internal measures Failure Rate FR [%] = (nf / SY) 100 The ration of the number of failures with forced outage of a given population over a given period of time to the number of accumulated service years for all transformers in that period of time Mean Time Between Failures MTBF [years] = 1 / FR Mean Time between failures (MTBF) = 1 / FR (years) N: Number of units in service within evaluation period (floating 10 years) SY: Number of service years accumulated with [N] units in service nf: Number of failures with forced outage of a population within the evolution period 3

4 Transformer Reliability - based on ANSI C (1986) FRe and MTBF as a degree of Reliability: Failure rate and reliability are related in the following way: R = e -λt t... time in year λ failure rate in failures per transformer-years of service (λ=nf/sy) e MTBF is considered to be the reciprocal of failure rate for purpose of estimating reliability: MTB = 1 / λ MTBF and reliability are related in the following way: R = e -t/mtbf Example: Given a constant MTBF of 500 years The reliability R of a transformer surviving t years of service without a failure would be shown as below: λ = t R For a given MTBF of 500 years the probability of a transformer surviving 20 years of service without failure is 96.08% 4

5 CIGRE activities related to Transformer Reliability SC A2 Reliability Advisory Group 2006 Bathtub curve Reliability databases WG A2.37: Reliability Surveys difficult to get reliable data WG A2.43: TR Bushing reliability (Um 72,5 kv) Started in June 2010 Plans to work on topics like post mortem and end of life decision. 5

6 Reliability of main accessories A2 session papers in Paris 2010 showed that accessories cause a significant proportion of the power transformer major failures. new bushing and tap-changer technologies were introduced recently these technologies and their impact on maintenance have to be reviewed Future task of CIGRE Study Committee A2 6

7 Operation conditions Transformer operating of the electrical insulation system Thermal Electrical Ambient Mechanical 7

8 Electrical insulation system transformer insulation life [1] total time between initial state (new) and the final state when due to normal service thermal ageing dielectric short-circuit mechanical movement could result in a high risk of electrical failure [1] IEC Loading guide for oil-immersed power transformers 8

9 Operation conditions Transformer operating of the electrical insulation system Thermal Electrical Ambient Mechanical 9

10 Thermal es and ageing Caused by the heating due to no-load and load losses Chemical Polymerization Depolymerization Physical Diffusion Expansion/contraction 10

11 Thermal ageing retardation Control possibilities Reduce temp. rises by new cooling stage control (overall loss of life optimization) Hot spot factor determination and control Proper material selection Initial moisture content Air sealing Forced cooling Design know how [1] [1] IEC Loading guide for oil-immersed power transformers 11

12 Manufacturer activities Continue verification cooling calculations Interfaces for dynamic calculation Cooling calculation for alternative insulation fluids Repair experience Post mortem analysis Material tests Supplier control 12

13 Operation conditions Transformer operating of the electrical insulation system Thermal Electrical Ambient Mechanical 13

14 Electrical es and ageing Caused by the electrical field and the interaction within the insulation system Increased local temperatures Partial Discharge X-Wax Leakage current Creeping distance Electrical treeing Static electrification could appear 14

15 Electrical ageing retardation Control possibilities Proper material selection Supplier quality control PD free transformers Design and processing know how Calculation possibilities 15

16 Manufacturer activities Continuous adaptation of the transients package to needs of design departments, and to customer Testing and evaluation of new insulation components and materials Basic reproducible test and comparative investigations Optimize technology to ease production and deliver PD-free products 16

17 Operation conditions Transformer operating of the electrical insulation system Thermal Electrical Ambient Mechanical 17

18 Ambient Caused by different ambient es the inner & outer systems of a Transformer could be damaged Humidity High/extreme low ambient temperature Altitude Pollution Wind Earthquake 18

19 Operation conditions Transformer operating of the electrical insulation system Thermal Electrical Ambient Mechanical 19

20 Mechanical Caused by acceleration during Transport Installation Operation inner & outer systems of a Transformer might be damaged 20

21 Operation conditions Transformer operating of the electrical insulation system Thermal Electrical Ambient Mechanical Real case studies shows a combination of es as well as interactions 21

22 Real case study #1 Sealed GSU Transformer Manufactured in 1952 Power: 8 MVA Rating: 115,5 / 5,25 kv Measurement of Degree of Polymerization (DP-value) in 1982 (after 30 years!!!) Phase 1: HV-winding, shielding ring: DP = 884 Phase 2: HV-winding, leads: DP = 902 Phase 3: HV-winding, winding insulation: DP =

23 #1: Actual Investigations 2011 (after around 60 years of operation) HV leads ~ 300 LV leads ~ 100 DP-distribution over winding height DP average =

24 Real case study #2 Sealed GSU Transformer Manufactured in 1966 Power:103 //51,5 / 51,5 MVA Rating:403// 16 / 16 kv Measurement of T1Q: 642 T1R: 449 T1S: 449 T1T: 704 Samples were taken from LV flexible connector Tests were performed according ISO 14453:

25 #2: Refurbishment Result in 2006 Measurement of De-polymerization (DP value) We expect a transformer rest life time of >13 years under the used load conditions for all 4 transformers. This assessment is based on the results of the performed measurements, the fact that the transformers are new sealed and that the insulation oil is purified. 25

26 In order to create a save energy supply worldwide we as power transformer manufacturers design, build and deliver reliable transformers as a fundamental responsibility Thank you for your attention! 26