Western Mining Electric Association San Antonio TX Layer vs. Disk Windings Discussion NOVEMBER 15, SPX Transformer Solutions, Inc.

Transcription

1 Western Mining Electric Association San Antonio TX NOVEMBER 15, 2012

2 PRESENTED BY David L. Harris, PE Customer Technical Executive SPX Transformer Solutions, Inc. Office: Cell: Dave has a BS Electrical Engineering from Clarkson University, Potsdam, New York, and an MS Engineering Management from Milwaukee School of Engineering. He has been in the transformer industry for 43 years in design, development, manufacturing, testing, marketing, sales and management of transformers and load tap changers. Currently, he holds the position of Customer Technical Executive for SPX Transformer Solutions. Dave is a Life Member of the IEEE and is active in the Electric Power Industry as a past chair of several Working Groups and Subcommittees for the IEEE Substations Committee and IEEE Transformers Committee. Dave is an individual member of CIGRE.

3 Agenda Thermal Performance Mechanical Performance Failure Photos Questions 3

4 Rectangular, Layer-Type Transformers 4

5 Transformer Winding Conductors Copper Strip or Foil Bus bar Rectangular wire (MW) Continuously Transposed Cable (CTC) MW CTC 5

6 Winding Types SLL / Layer / Barrel 6

7 Winding Types (cont.) Helical / Screw 7

8 Winding Types (cont.) Continuous Disk Winding Inner cross-over Outer cross-over 8

9 Circular, Layer-Type Transformers 9

10 Power Class Transformer 10

11 Layer Winding Conductor Arrangements 11

12 Layer Winding Thermal Performance Layer Type Windings Very large thermal mass of conductor and insulation between cooling ducts: difficult to calculate and control the hot spot temperatures No radial ducts, some axial ducts, most of them just on ends, not all around 12

13 Thermal Performance Non-directed flow Directed flow Disk Type Windings All turns are in contact with MOVING oil to lower hot spot temperatures 13

14 Thermal Performance IEEE Std C , IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers Exponents used in temperature determination equations: Adobe Acrobat Document C GUIDE TYPICAL TESTED VALUES* TYPE OF COOLING m n m n OA FA Non-Directed FOA or FOW Not Available Directed FOA or FOW Not Available * Based on transformers tested by SPX Transformer Solutions for disk-type transformers. Similar information should be obtained for transformers with layertype windings for thermal evaluation and loading. 14

15 Thermal Performance (cont.) A four-level criterion has been developed to classify risks to transformers, when there is no previous dissolved gas history, for continued operation at various combustible gas levels. The criterion uses both concentrations for separate gases and the total concentration of all combustible gases (see Table 1 on next slide). Condition 1: TDCG below this level indicates the transformer is operating satisfactorily. Any individual combustible gas exceeding specified levels should prompt additional investigation. Condition 2: TDCG within this range indicates greater than normal combustible gas level. Any individual combustible gas exceeding specified levels should prompt additional investigation. Action should be taken to establish a trend. Fault(s) may be present. Condition 3: TDCG within this range indicates a high level of decomposition. Any individual combustible gas exceeding specified levels should prompt additional investigation. Immediate action should be taken to establish a trend. Fault(s) are probably present. Condition 4: TDCG within the range indicates excessive decomposition. Continued operation could result in failure of the transformer. Proceed immediately and with caution. 15

16 Thermal Performance IEEE Std C , IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers Defines various conditions and limits of gases for each condition: TABLE 1 - DISSOLVED GAS CONCENTRATIONS DISSOLVED KEY GAS CONCENTRATION LIMITS (ppm*) STATUS H 2 CH 4 C 2 H 2 C 2 H 4 C 2 H 6 CO CO 2 TDCG CONDITION CONDITION CONDITION CONDITION 4 >1800 >1000 >80 >200 >150 >1400 >10000 >

17 Winding Leakage Flux Plot Finite Element Analysis of Leakage Flux Between Coils Axial locations of HV DETC taps Flux leaks out radially whenever there is an axial spreading out of turns in a coil. 17

18 Ampere Turn Winding Distribution Plot 18

19 LV and TV Winding Turn Spreading 19

20 Short Circuit Winding Mechanical Performance Short circuit forces pulsate at twice system frequency Major and minor pulses gradually become equal as the offset current decays and the fault current becomes symmetrical 20

21 Layer Winding Short Circuit Performance Fig B2 Forces acting on both the HV and LV windings of a simplified rectangular two-winding core-type transformer during through fault conditions. 21

22 Mechanical Performance 22

23 Short Circuit Mechanical Performance Radial Forces Buckling (inner coil) Axial Forces (Applying Left Hand Rule) Radial Forces Hoop Stress (outer coil) Outward Radial Force converted to Tensile Stress Power Class transformers are designed to withstand forces in all directions. 23

24 Axial Forces Applying Left Hand Rule (Br) (I) Current (I) Flux (B) Force (F) (Fa) Length of beam: l = 2 π R OD m -W ks 24

25 Design for Short Circuit Duty Conductor Telescoping Failure Typically a problem for Layer windings Can happen to disk or helical windings Extent of damage to paper insulation will determine how soon a total unit failure will happen 25

26 Circular, Layer-Type Transformers What is the Axial Force during thru-faults? How much axial compression can you put on this unit? 26

27 Failure Photos 27

28 Failure Photos (cont.) 28

29 Failure Photos (cont.) 29

30 Failure Photos (cont.) 30

31 Failure Photos (cont.) 31

32 Failure Photos (cont.) 32

33 Questions? Thank You! 33