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