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POWER TRANSFORMERS:Saturation Compensation Modeling,

Simulation, and Experiments

John Thomas, Dr. David CopeEngineering Matters, Inc.

23 Farwell StreetNewton, MA 02460

www.engineeringmatters.com

14 October 2003

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Engineering Matters®

Short Form Resume

• Incorporated 1998• Woman-Owned Small Business• Won several Phase I and Phase II SBIRs• Electromechanical Focus

– Specialty motors, robotics, electromagnetic signature control and analysis

• Direct drive force feedback joysticks– Several patents received– Three high-performance versions available

• Ansoft user since 1984.

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Engineering Matters®

Design & Analysis Expertise

• Electromagnetics– Motors– Actuators– Sensors

• Electrical design– Power

– Analog and digital design

• Systems integration

• Mechanical design– Prototype– Design for

Manufacturing

• Software design– Firmware– GUI/API– Computer interfacing

• Control design.

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Power Transformer Saturation Progression

• Large scale common mode transformer currents, through a series of physical interactions, cause many deleterious effects. In some notable cases, these effects have led to total system collapse.

SMD

ESP

EMP

GICσ

Harmonics

B

H

VAR

HEATSMD = Solar Magnetic DisturbanceEMP = Electromagnetic PulseESD = Earth Surface PotentialGIC = Ground-Induced CurrentsVAR = Volts-Amps Reactive

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Reasons for interest in transformer saturation

• Transformer DC current causes half-cycle saturation, generation of harmonics, over-heating, increased audible noise, and mechanical stress.

• Results in decreased transformer life.

φ(t)B(H)

H

Imag

t

t

t1 t2 t3

t4 t5 t6

t1

t2

t3

t4

t5

t6

DC FluxOffset

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Ground-Induced Currents (GIC) Two Causes:

• Solar Coronal Mass Ejections (CME) affect utility operations– Generates an Earth-surface

potential (1-10 V/km)– Drives a quasi-DC ground

current (10-100A DC)– Duration 2-4 hours.

• HEMP effects are more intense than CME effects– 10X voltage (10-100 V/km)– 10X current (~1000A DC)– 10-15 minutes/burst.

Image credit: NASA

II

I

I/3 I/3

I/3

I/3 I/3

I/3

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Solar Magnetic Disturbances

• Solar magnetic disturbances (SMD) emit coronal mass ejections (CME) that interact with the earth’s magnetic field.

Image credit: NASA

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SMDs follow the 11 Year Sunspot Cycle

Measurementperiod

March 2003

Image credit: Meteorological Satellite Applications Branch, Air Force Weather Agency.

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Overall Electrical Schematic for GIC Compensation

Phase ALoad

Phase BLoad

Phase CLoad

GIC Compensation

GIC Compensation

Tertiary Winding

Tertiary Winding

Tertiary Winding

SinglePhaseXFMR

GICCompensation

Transmission Line

Earth ground

Y-Y XFMR

GSU XFMR

60 Hz Filter

3φ Generator

a b c

SourceEnergyStorage

SinglePhaseXFMR

SinglePhaseXFMRGIC injection

(simulated)

GIC injection(simulated)

GIC injection(simulated)

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Ansoft Maxwell® & Simplorer®

Modeling

• Three cases: (1) No GIC (before), (2) GIC (during), (3) GIC with compensation (after)

• Maxwell 2D nonlinear Model

• Simplorer Model– Block diagram &

circuit simulation– Post processing

analysis.

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Maxwell-Simplorer LinkagesNonlinear Transformer Model

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Simplorer Block Diagram Functionality of three circuits

(PLL, time delay switch, op-amps)

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Simplorer Results: Saturation Compensation Control

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Simplorer Results: Closed-loop Error Signal & Correction Current

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Simplorer Results:Post-processing FFT

Before GIC I2n~0

During GIC, large I2n

After GIC with Compensation I2n~0

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Maxwell 2D Results:Transformer |B| plots

Before GIC During GIC

Compensation

After GIC with

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Sub-scale Mock-up Demo Unit

• Sub-scale demonstration unit built & tested

• Experimental measurements compared with simulation results

GeneratorGSU XFMR

Ste

p-do

wn

XF

MR

Load

CompensationCircuits

TransmissionLines

GICInjection

Filter

Filter

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Sub-scale Unit Measurements: Error Signal & Compensation Current

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Sub-scale Unit Measurements:Primary currents for three cases

Before GIC

During GIC

After GIC with Compensation

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Sub-scale Unit Measurements:FFT Harmonic Amplitudes

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Transformer Saturation Compensation Summary

• Natural & man-made events can cause transformer saturation which threatens power electric system stability and reliability

• Regained transformer stability by automated measurement and compensation

• Achieved very good comparison between simulations and experiments

• Future work will extend SMPS capabilities to higher power and voltage. More modeling and simulation are needed.

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Additional Projects of Interest (designed with Maxwell® 3D)

• Force Feedback Joystick (Direct drive, wide bandwidth, very rugged)

• MEMS OXC actuator

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Robotic Design and System Integration—Power Electronics, Vehicle design, Test Plan; RC, Motor

and Battery selection

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Acknowledgements

The GIC-compensation project was developed with funding from the United States Army Space & Missile Defense Command Contract numbers DASG60-01-C-0017 and DASG60-02-C-0066.

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Unconventional Alternative Power Applications

• Geothermal• Wave-action• Human-effort

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Bill Powell working out in Icelandic geothermal pool

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References

• Introduction to Geomagnetic Fields, Wallace Campbell, Cambridge University Press, NY, 1997.

• “Geomagnetic Storms and Their Impact on Power System,”Kappenman, John, G., IEEE Power Engineering Review, May 1996, p. 5.

• “Comparison of SS-GIC and MHD-EMP-GIC effects on power systems,” Meliopoulos, A.P.S.; Glytsis, E.N.; Cokkinides, G.J.;Rabinowitz, M. Georgia Inst. of Technol., Atlanta, GA, USA Power Delivery, IEEE Transactions on, Pages: 194-207 Jan. 1994 Vol. 9 Issue: 1 ISSN: 0885-8977.

• "Geomagnetically induced Currents during Magnetic Storms", R.Pirjola, Plasma Science, IEEE Transaction on, Vol. 28, No. 6, Dec. 2000, p. 1867.

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Significant Power System Outages (GIC & Other)

• GIC Storms: – February 1986, March

1989, March 1991, November 1991 and May 1992.

• GIC-Utility Events (place, people affected, duration): – North America: April 1940,

Sept. 1989, March 1991, Oct 1991

– Quebec March 1989, 6M, 9 hr. massive outage

• General Outages (place, people affected, duration):– US August 2003, 50M, 16-

20 hr. – London August 2003,

1.5M, 1 hr.– Denmark & Sweden

September 2003, 5M, 4 hr.– Italy September 2003, 57M,

9 hr.

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March 13, 1989 GIC-related ‘Events’

Image credit: Kappenman