Electrical Power Engineering Department

Hijjawi Faculty of Engineering TechnologyHijjawi Faculty of Engineering Technology

Yarmouk University

Irbid, Jordan

Effect of High Frequency Pulses on the Breakdown Voltage and Lifetime of

MW Insulation of Flyback Transformer

Eyad A. Feilat, Ph.D.Eyad A. Feilat, Ph.D.

US-Jordan WorkshopUS-Jordan Workshop

Modern Power Electronics Research and EducationModern Power Electronics Research and Education

December 16-17, 2002, PSUT, Amman, JordanDecember 16-17, 2002, PSUT, Amman, Jordan

Outline

Design Trends in Electrical and Electronics Equipment

Insulation System of Flyback Transformer

Consequences of Miniaturized Design

Statistical Analysis of Failures

Scope of the Research Paper

Accelerated Aging Test System

Experimental Results

Conclusion

Design Trends inElectrical and Electronics Equipment

Reduce Size (Compact Design)

Light Weight

High Reliability (Low Failure Rates)

Reduce Manufacturing Time

Reduce Cost

Design Trends inElectrical and Electronics Equipment

Bobbin-Wound Coils Fine Gauge Magnet Wires Thin Layers of Insulation Encapsulation of HV Coils

Materials with High Thermal Class

High Frequency Switching Technology

DC-DC Converters (Flyback Transformers) DC-AC Inverters (Adjustable Speed Drives)

DC-DC ConverterFlyback Transformer (FBT)

+HVB+

HOT

Fine Gauge Magnet Wires (MW) TV sets and computer monitors.

Pulse Frequencies of FBT

Applicationof

Flyback Transformer

Numberof

Scanning Lines

Horizontal Deflection(Flyback)

Frequencies (kHz)General (60 Hz) 525 15.75General (50 Hz) 625 15.625HDTV (60 Hz) 1125 33.8

TV

HDTV (50 Hz) 1250 31.3Computers various 24~50MonitorsDisplays various 60~90

Insulation System of Encapsulated Coil

Polyester Housing Layer (Polyethylene Terephthelate)

Impregnation Layer (Epoxy)

Heavy Build Enamel (Polyurethane)

Polyester Bobbin (Polyethylene Terephthelate)

Randomly Wound on Bobbins

Bonded with Baked Coatings

Encapsulated with Epoxy

Magnet Wire (MW)

Insulation Material: polyurethane (PUR) Over Coat: Polyamide (Nylon)

NEMA MW-80C, Class F

AWG 41 MW

Insulation Thickness = 6.35 m

Bare Wire Diameter = 71.1 m

Consequences of Miniaturized Design

Random Wound Coils Beginning and End of the Coil may touch one another High Level of Voltage Stress between Turns

High Frequency Switching Very Short Pulse Period Very Short Duty Cycle

High dV/dt Uneven Voltage Distribution Steady Degradation of the MW Enamel High Temperature Rise, typically 100o-200o C

Causes of Insulation Failure

Electrical and Thermal Stresses

Partial Discharge Developed in Random Windings

Localized Dielectric Heating

Microvoids and Impurities in the Epoxy Fill Material

Insulation Degradation

Premature Failure

Statistical Analysis of Failures

Accelerated Life Tests (Accelerated Aging)

High Electrical Stresses

Elevated Temperatures

Combined Electrical and Thermal Stresses

Various Voltage Waveform and Frequencies

Statistical Analysis of Failures

Probability Distribution (Weibull)

Life Model (Single Stress, Multistress)

xx

xf exp),;(1

T

VBBVAAT)L(V, 21

21exp

Scope of the Study

Effect of Rise Time on the Time-to-Failure Effect of Duty Cycle on the Time-to-Failure Evaluation of the Breakdown Voltage Accelerated Life Tests

High Temperature (100o -180o C )

Pulsating Frequency (15-40 kHz)

Positive Polarity

Accelerated Aging System

DTS-1500 A

Computer Air-CirculatingOven

High FrequencyPulse Generator

Typical Pulse Waveform

TV

D

Experimental Results

Lifetime Studies Effect of Duty Cycle

Effect of Rise Time

Effect of Duty Cycle

V = 950 V

f = 15 kHz

T = 100o C

= 200 ns

0

50

100

150

200

250

10 15 20 25 30 35 40 45 50 55

Duty Cycle %

Tim

e-to

-Bre

akdo

wn

(s)

Effect of Rise Time

V = 950 V

f = 15 kHz

T = 100o C

D = 16%

0

50

100

150

200

250

0 50 100 150 200 250

Rise Time (ns)

Tim

e-to

-Bre

akdo

wn

(s)

Experimental Results

Breakdown Voltage StudiesEffect of Temperature

Effect of Frequency

Effect of Temperature on the Breakdown Voltage

D = 16%

=200 ns

800

1000

1200

1400

1600

1800

2000

75 100 125 150 175 200

Temperature (oC)

Vol

tage

(V)

f = 15 kHz

f = 25 kHz

f = 40 kHz

Effect of Frequency on theBreakdown Voltage

800

1000

1200

1400

1600

1800

2000

10 20 30 40 50

Pulsating Frequency (kHz)

Vol

tage

(V)

T=100 C

T=155 C

T=180 C

D = 16%

=200 ns

Experimental Results

Lifetime StudiesEffect of Pulsating VoltageEffect of TemperatureEffect of Frequency

Lifetime CharacteristicsV-t C/C

f=15kHz

10.0

1.0E+8

100.0

1000.0

1.0E+4

1.0E+5

1.0E+6

1.0E+7

1000.0700.0 760.0 820.0 880.0 940.0Voltage (V)

Tim

e (

s)

100o C180o C

155o C

Lifetime CharacteristicsV-t C/C

100.0

1.0E+8

1000.0

1.0E+4

1.0E+5

1.0E+6

1.0E+7

1000.0600.0 680.0 760.0 840.0 920.0Voltage (V)

Tim

e (s

)

15 kHz25 kHz

40 kHz

T=155o C

Lifetime CharacteristicsT-t C/C

f=15kHz

10.0

1.0E+12

100.0

1000.0

1.0E+4

1.0E+5

1.0E+6

1.0E+7

1.0E+8

1.0E+9

1.0E+10

1.0E+11

100.0 1000.0Temperature (K)

Tim

e (

s)

700 V800 V900 V

Lifetime CharacteristicsT-t C/C

V=800 V

1.0E+4

1.0E+12

1.0E+5

1.0E+6

1.0E+7

1.0E+8

1.0E+9

1.0E+10

1.0E+11

100.0 1000.0Temperature (K)

Tim

e (

s)

15 kHz25 kHz40 kHz

Parameters of theElectrical-Thermal Aging Model

f kHz A1 A2 B1 B2

15 0.49 136.2 -0.167 -20846 32.51

25 0.46 16.03 -0.026 14312 -9.22

40 0.53 17.29 -0.028 6412.5 0.027

T

VBBVAAT)L(V, 21

21exp

Conclusion

The longer the duty, the shorter is the insulation Lifetime

The longer the rise time, the longer is the insulation

lifetime

The Breakdown Voltage declines with the increase of both the Frequency and Temperature

The Accelerated Life Tests show that both the Voltage and Temperature are the two main Factors of Insulation Aging or Degradation

Conclusion

Effect of the pulse frequency on the lifetime is indistinct

It changes with temperature and voltage stress

Reason: Change of polarization Space charge Dielectric lossesChange of Breakdown Mechanisms