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1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National Laboratory, April 7-8, 2015

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Page 1: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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The View from the Other Side:How Transformers affect GIC

D.H. BotelerGeomagnetic Laboratory

Ottawa

Geomagnetic Disturbance Workshop, Idaho National Laboratory, April 7-8, 2015

Page 2: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Factors affecting GIC in Power Systems

Geomagnetic Induction Earth Conductivity Rate of change of magnetic field

System Characteristics Network

Configuration Impedances

The higher the sampling rate the larger the dB/dt value

GIC modelling uses resistances only.

What about inductances?

How does system L/R time constant affect GIC?

Page 3: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Hydro-Quebec HVDC Tests Bolduc et al, 1989

Page 4: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Hydro-Quebec HVDC Tests

Page 5: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Hydro-Quebec HVDC Tests

Page 6: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Later Reports

Dong, 2002

Walling and Khan, 1991

Page 7: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Calculations of growth of GIC

Bolduc et al (1989b)

Page 8: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Page 9: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Page 10: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Bolduc’s formula for time to saturation

( . / )A tf K Vi

I A A A

p+

+ + -

0

2 3

1 0 13 2 1

15 27 160

;

( )/

/ //

p

K RA tf

V X Xp=

+

1 23 2 1 2

1 20 2

8

3

//

/

. pX XVt A

f K R

é ù+ê ú= ê úë û

2 31 220

1 2

0 355

Fraction of steady-state current reached after time, t

As a function of parameter

Gives time

Page 11: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Using Bolduc’s formulas

a) “Backwards” calculation determine T (secs) for specified i/I

b) “Forwards” calculation determine i/I for specified T (secs)

Page 12: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Effective Inductance seen by GIC

Walling, 2013

Page 13: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Effective Inductance seen by GIC

satt

Tq=

tsat

T

Lunsaturated

LsaturatedIndu

ctan

ce

time

Fraction of time in saturation,

Fraction of time not in saturation,

satT t

Tq

-- =1

Page 14: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Effective Inductance seen by GIC

( )

effL L L

q q-= +

1 2

1 1

T

Lunsaturated

Lsaturated

Indu

ctan

ce

dc dc

eff

e i RDi

Dt L

-=

Page 15: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Relation between θ and GIC

( )( ) cosAI t I ftp= 2

UA mag

S

LI I

L=where

Tq

-2

Tq2

sADC

II in

qp

p

æ ö÷ç= ÷ç ÷çè ø2

2

DC

IdtI

T=

ò

sin DC

A

I

Iq p

p-

æ ö÷ç ÷= ç ÷ç ÷çè ø11

Page 16: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Incremental Growth of GIC

dc dc

eff

e i Ri t

L

-D = D

1. Initially, i = 0, Leff = Lunsaturated

2. Calculate current increase, Δi for time interval, Δt

3. For new value of i, calculate fraction of time in saturation, θ

4. Calculate new value of effective inductance, Leff

5. Return to Step 2, etc

sin DC

A

I

Iq p

p-

æ ö÷ç ÷= ç ÷ç ÷çè ø11

( )

effL L L

q q-= +

1 2

1 1

Page 17: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Incremental Growth of GIC

Page 18: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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3-leg 3-phase transformer

Slope L2

Slope L2

Magnetising curve for AC

Magnetising curve for DC

eff saturatedL L=

Inductance is constant

Page 19: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Transformer with delta tertiary

DC current

Flux offset

Current circulating in delta tertiary

“Delta” phase

“Normal” phase

Walling, 2013

Page 20: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Slope L2

Slope L2

Magnetising curve for “normal” phase

Magnetising curve for “Delta” phase

Transformer with delta tertiary

eff saturatedL L=“Delta” phase

“Normal” phase( )

effL L L

q q-= +

1 2

1 1

Page 21: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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Questions? Answers?

Page 22: 1 The View from the Other Side: How Transformers affect GIC D.H. Boteler Geomagnetic Laboratory Ottawa Geomagnetic Disturbance Workshop, Idaho National

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References Bolduc, L., Pelletier, P. and Boisclair, J-G., DC current in AC transmission system near the electrode of the HVDC converter

at DES Cantons substation, Proceedings of the EPRI Conference on Geomagnetically Induced Currents, Burlingame, California, November 8-10, 1989.

Bolduc, L. and Kieffer, P., A recipe for fast simulation of the effect of the DC component of magnetizing steady-state currents in transformers using EMTP, Proceedings of the EPRI Conference on Geomagnetically Induced Currents, Burlingame, California, November 8-10, 1989.

Bolduc, L., Formula to approximate the setting time for the DC component of magnetizing currents in transformers, Proceedings of the EPRI Conference on Geomagnetically Induced Currents, Burlingame, California, November 8-10, 1989.

Bolduc, L., A. Gardreau, and A. Dutil, “Saturation time of transformers under dc excitation,” Elect. Power Syst. Res., vol. 56, pp. 95–102, 2000.

Boteler, D.H., Characteristics of time-varying inductance, IEEE Trans. Magnetics, 30, 172-176, 1994.

Dong, X., Study of power transformer abnormalities and IT applications in power systems, PhD Thesis, Virginia Polytechnic Institute, 2002.

Walling, R.A. and Khan, A.H., Characteristics of Transformer Exciting Current During Geomagnetic Disturbances, IEEE Trans. Power Delivery, Vol. 6, No. 4, October 1991.