© ABB Group April 19, 2023 | Slide 1

Leak InductanceExplanation – your ref J1065

Pontus Sundqvist, Senior enginner 2012-08-22

Content

General information about leakage inductance

Calculation of leakage inductance our ref 12Q1686204

© ABB Group April 19, 2023 | Slide 2

Order Data Sheet

This is only applicable to coarse/fine connection

IEC 60214-02 Tap-Changer Application Guide

Normal Switching Conditions

Small L

Only one loop connected

Normal Switching Conditions

Small L

Only one loop connected

Continued operation

All loops in fine winding connected

Large L

All loops from both coarse and fine winding connected

Switching Conditions at Mid Point (Coarse/Fine)

Critical breaking, going from coarse to fine.

Critical breaking, going from fine to coarse winding

Fine

Coarse

Continued operation at mid point

Switching Conditions at Mid Point (Coarse/Fine)

Leak Inductance

The leak inductance can be :

Calculated with simple calculation (Only for radiell placed

windings)

Calculated with FEM program (ABB) (radiell or axiell placed

windings)

Required Indata for FEM Calculations

I1

N1

t12 t2t1

I2

N2

DW2

DW1

DW3

I3

N3

I4

N4

t23

For accurate estimates of the reactance a FEM calculation must be done

© ABB Group April 19, 2023 | Slide 11

Coarse- fine LV- fine Coarse- LV

FEM Calculation Axial Windings, part 1

HV

Coarse

Fine

LV

HV

© ABB Group April 19, 2023 | Slide 12

LV- HV Coarse- HVFine - HV

FEM Calculation Axial Windings, part 2

Further Calculations

© ABB Group April 19, 2023 | Slide 13

Coarse- fine LV- fine Coarse- LV LV- HV Coarse- HVFine - HV

Results from field calculation used in further calculation to establish severity at breaking

© ABB Group April 19, 2023 | Slide 14

Determination of the recovery voltage

i2ci i1ci

ugci

Hg breaking Rf closing Rg breaking Hf closing

Calculation of leakage inductance our ref 12Q1686204

© ABB Group April 19, 2023 | Slide 15

This window was drawn in ABB FEM program

Window of one phase in FEM program

© ABB Group April 19, 2023 | Slide 16

Made following assumptions:

HV = 883 turns

Coarse 91 turns

Fine 84 turns.

Result:

Recovery voltage appox 6 kV more than 10 times above our limits.

6 kV equals approx 18mH

Result

© ABB Group April 19, 2023 | Slide 17

Recovery voltage appox 6 kV more than 10 times above our limits.

6 kV equals approx 18mH.

In ordering data mentioned 2.15 mH compared to my calculated 18 mH.

18 mH is a normal value for axiell disposed windings (can be from approx 5 mH and higher)

For radiell disposed windings the leakage inductance normal is not higher than 5 mH.

Why such big difference?

Some transformer manufactures use the formula mentioned in a book written ny a competitor to ABB which looks like this:

© ABB Group April 19, 2023 | Slide 18

This fomula is only valid radiell disposed windings not axiell.

This could explain the big difference, I don´t know.

© ABB Group April 19, 2023 | Slide 19