Transcript Effect of High Frequency Pulses on the Breakdown Voltage

Electrical Power Engineering Department
Hijjawi 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.
US-Jordan Workshop
Modern Power Electronics Research and Education
December 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 in
Electrical and Electronics Equipment
 Reduce Size (Compact Design)
 Light Weight
 High Reliability (Low Failure Rates)
 Reduce Manufacturing Time
 Reduce Cost
Design Trends in
Electrical 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 Converter
Flyback Transformer (FBT)
B+
+HV
HOT
 Fine Gauge Magnet Wires (MW)

 TV sets and computer monitors.
Pulse Frequencies of FBT
Application
of
Flyback Transformer
General (60 Hz)
General (50 Hz)
TV
HDTV (60 Hz)
HDTV (50 Hz)
Computers
Monitors
Displays
Number
of
Scanning Lines
525
625
1125
1250
various
various
Horizontal Deflection
(Flyback)
Frequencies (kHz)
15.75
15.625
33.8
31.3
24~50
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)
x
f ( x ; ,  )   
  

 1


x
   
exp   
 




Life Model (Single Stress, Multistress)
B1  B2V 

L(V,T)    exp A1  A2V 

T


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-Circulating
Oven
High Frequency
Pulse Generator
Typical Pulse Waveform
D
V
T

Experimental Results

Lifetime Studies

Effect of Duty Cycle

Effect of Rise Time
Effect of Duty Cycle
250
V = 950 V
f = 15 kHz
200
Time-to-Breakdown (s)
T = 100o C
 = 200 ns
150
100
50
0
10
15
20
25
30
35
Duty Cycle %
40
45
50
55
Effect of Rise Time
250
V = 950 V
f = 15 kHz
Time-to-Breakdown (s)
200
T = 100o C
D = 16%
150
100
50
0
0
50
100
150
Rise Time (ns)
200
250
Experimental Results

Breakdown Voltage Studies
Effect
of Temperature
Effect
of Frequency
Effect of Temperature on the
Breakdown Voltage
2000
f = 15 kHz
1800
f = 25 kHz
f = 40 kHz
Voltage (V)
1600
1400
1200
1000
800
75
100
125
150
Temperature (oC)
175
200
D = 16%
 =200 ns
Effect of Frequency on the
Breakdown Voltage
2000
1800
T=100 C
D = 16%
T=155 C
 =200 ns
Voltage (V)
T=180 C
1600
1400
1200
1000
800
10
20
30
40
Pulsating Frequency (kHz)
50
Experimental Results

Lifetime Studies
Effect
of Pulsating Voltage
Effect of Temperature
Effect of Frequency
Lifetime Characteristics
V-t C/C
1.0E+8
155o C
f=15kHz
1.0E+7
180o C
100o C
T i m e (s )
1.0E+6
1.0E+5
1.0E+4
1000.0
100.0
10.0
700.0
760.0
820.0
Voltage (V)
880.0
940.0
1000.0
Lifetime Characteristics
V-t C/C
1.0E+8
25 kHz
T=155o C
15 kHz
1.0E+7
40 kHz
Time (s)
1.0E+6
1.0E+5
1.0E+4
1000.0
100.0
600.0
680.0
760.0
Voltage (V)
840.0
920.0
1000.0
Lifetime Characteristics
T-t C/C
1.0E+12
900 V
1.0E+11
800 V
700 V
f=15kHz
1.0E+10
1.0E+9
T i m e (s )
1.0E+8
1.0E+7
1.0E+6
1.0E+5
1.0E+4
1000.0
100.0
10.0
100.0
1000.0
Temperature (K)
Lifetime Characteristics
T-t C/C
1.0E+12
40 kHz
1.0E+11
V=800 V
25 kHz
15 kHz
1.0E+10
Time (s)
1.0E+9
1.0E+8
1.0E+7
1.0E+6
1.0E+5
1.0E+4
100.0
1000.0
Temperature (K)
Parameters of the
Electrical-Thermal Aging Model
f kHz

A1
A2
B1
B2
15
25
40
0.49
0.46
0.53
136.2
16.03
17.29
-0.167
-0.026
-0.028
-20846
14312
6412.5
32.51
-9.22
0.027
B1  B2V 

L(V,T)    exp A1  A2V 

T


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 losses
Change of Breakdown Mechanisms