Western Mining Electric Association San Antonio TX Layer ...

1 Western Mining Electric Association San Antonio TX Layer vs. disk Windings Discussion NOVEMBER 15, 2012 SPX Transformer Solutions, Inc. Layer vs. disk Windings Discussion PRESENTED BY David L. Harris, PE Customer technical Executive SPX Transformer Solutions, Inc. Office: 262-521-0166 Cell: 262-617-3039 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.

2 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. Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Thermal Performance Mechanical Performance Failure Photos Questions Agenda 3 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Rectangular, Layer -Type transformers 4 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Transformer Winding Conductors Copper Strip or Foil Bus bar Rectangular wire (MW) Continuously Transposed Cable (CTC) CTC MW 5 Layer vs.

3 disk Windings Discussion SPX Transformer Solutions, Inc. Winding Types SLL / Layer / Barrel 6 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Helical / Screw Winding Types (cont.) 7 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Continuous disk Winding Winding Types (cont.) Inner cross-over Outer cross-over 8 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Circular, Layer -Type transformers 9 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Power Class Transformer 10 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Layer Winding Conductor Arrangements 11 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc.

4 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 Layer Winding Thermal Performance 12 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Thermal Performance Non-directed flow Directed flow disk Type Windings All turns are in contact with MOVING oil to lower hot spot temperatures 13 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Thermal Performance Adobe A crobat DocumentIEEE Std , IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed transformers Exponents used in temperature determination equations: 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 .

5 Similar information should be obtained for transformers with Layer - type windings for thermal evaluation and loading. 14 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. 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.

6 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 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc.

7 Thermal Performance TABLE 1 - DISSOLVED GAS CONCENTRATIONS DISSOLVED KEY GAS CONCENTRATION LIMITS (ppm*) STATUS H2 CH4 C2H2 C2H4 C2H6 CO CO2 TDCG CONDITION 1 100 120 35 50 65 350 2500 720 CONDITION 2 101-700 121-400 36-50 51-100 66-100 351-570 2500-4000 721-1920 CONDITION 3 701-1800 401-1000 51-80 101-200 101-150 571-1400 4001-10000 1921-4630 CONDITION 4 >1800 >1000 >80 >200 >150 >1400 >10000 >4630 IEEE Std , IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed transformers Defines various conditions and limits of gases for each condition: 16 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Winding Leakage Flux Plot Axial locations of HV DETC taps Flux leaks out radially whenever there is an axial spreading out of turns in a coil.

8 Finite Element Analysis of Leakage Flux Between Coils 17 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Ampere Turn Winding Distribution Plot 18 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. LV and TV Winding Turn Spreading 19 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. 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 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. 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.

9 21 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Mechanical Performance 22 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Short Circuit Mechanical Performance Power Class transformers are designed to withstand forces in all directions. Radial Forces Buckling (inner coil) Radial Forces Hoop Stress (outer coil) Outward Radial Force converted to Tensile Stress Axial Forces (Applying Left Hand Rule) 23 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. (I) (Br) (Fa) Axial Forces Applying Left Hand Rule Flux (B) Current (I) Force (F) l = -Wks 2 ROD m Length of beam: 24 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc.

10 Conductor Telescoping Failure Design for Short Circuit Duty 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 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Circular, Layer -Type transformers What is the Axial Force during thru-faults? How much axial compression can you put on this unit? 26 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Failure Photos 27 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Failure Photos (cont.) 28 Layer vs. disk Windings Discussion SPX Transformer Solutions, Inc. Failure Photos (cont.)