View
232
Download
4
Category
Preview:
Citation preview
Elimination of Transformer Inrush Currents When
Energizing Unloaded Power Transformers
John H. Brunke
Presentation Outline
Basics of transformer inrush transients Three phase transformer core flux
transients based on model studies New controlled closing strategies Statistical performance
Transformer Core Characteristics
1
2
Current
Flux
Energizing a Transformer
Transformer Inrush Current
Time 0.05 ms/div
4000
0.0
4000
Amperes
Optimal controlled closing
Three Phase Transformers
Core Flux - No residual
Prospective and Dynamic Flux
58.054.050.0 46.042.0
Time ms1
Flux, zero residual0.80
0.0
-0.80
FluxkV
Three phase residual flux
Time 3 ms/div
Core flux with residual flux
Time 6 ms/div
Core flux, EMTP Study 800
0.0
-800Vs
Prospective and Dynamic Flux
58.054.050.046.042.0
Time ms
Flux, residual 0%, -70%, 70%0.80
0.0
-0.80
Flux kVs
ACB
Prospective and Dynamic Flux
Time 6 ms/div
800
0.0
-800Vs
Closing Strategies
Rapid closing strategy – Requires detailed transformer data and
look up table
Delayed Closing strategy – Generalized approach
Three phase strategy – Limited to high residual flux scenarios
Verification - Laboratory Tests Rapid Closing Strategy
Time 20.5 ms/div
A Phase Flux .8000
0.0
-.8000Vs
Time 20.5 ms/div
B Phase Flux .8000
0.0
.8000Vs
Time 20.5 ms/div
C Phase Flux .8000
0.0
-.8000Vs
Time 20.5 ms/div
Neutral Current20
0.0
-20
Amperes
Verification - Laboratory Tests Delayed Closing Strategy
Time 6 ms/div
.8000
0.0
-.8000Vs
Effect of Closing Error
Model Study Results, Peak Inrush Current for a 70% Residual as a Function of Closing Angle
-1000-500
0500
100015002000250030003500
0 5 10 15 20
Closing Time ms
Pea
k In
rush
Cur
rent
A
mpe
res
Prestrike
Time 2 ms/div
800.
400.
0.0
-400.
-800.
kV
Statistical Studies
Benchmarks - linear bias runs with statistical pole span 1000 studies/run
Controlled studies - 200 studies/run 0.5, 1.0, 1.5, 2.0 ms timing error ranges
Statistical Performance
CLOSING TIMESCATTER, 3 SIGMA
LEVEL EXCEEDING2% AMPERES
PERCENTREDUCTION FROMUNCONTROLLED 2%LEVEL
0.5 62 98%1.0 140 95.31.5 350 88.3%2.0 620 79.3Table 5.3. The improvement in performance using controlled closing with a70% residual flux. .
Transformer Model
Effect of Capacitance
Time
Flux
Time
Flux
State of the Art Peak Inrush Current as a Function of Opening
Time
0
200
400
600
800
1000
1200
0 0.2 0.4 0.6 0.8 1
Opening Time over One Power Frequency Cycle
Peak
Inru
sh C
urre
nt
Ampe
res
Model
Moraw
Delayed Performance Peak Inrush Current (2% Probability of occurrence)as a
Function of Closing Time Scatter
0
100
200
300
400
500
600
700
800
0 0.5 1 1.5 2 2.5
Closing Time Scatter (3 sigma) ms
Wor
st Ph
ase P
eak I
nrus
h Cu
rrent
Amp
eres 70,-70,0
0,0,0
0,-70,70
0,70,-70
0,35,-35
70,-40,-30
Three Phase Performance Peak Inrush Current as a Function of Closing Time
Scatter
0
200
400
600
800
1000
1200
0 0.5 1 1.5 2 2.5
Closing Time Scatter (3 sigma) ms
Wor
st P
hase
Pea
k In
rush
Cur
rent
Am
pere
s
0,-70,70%
0,-35,35%
0,-.5,.5
Rapid Closing Performance Peak Inrush Current (2% Probability of occurrence) as a
Function of Closing Time Scatter
0
100
200
300
400
500
600
700
0 0.5 1 1.5 2 2.5
Closing TIme Scatter (3 sigma) ms
Wor
st P
hase
Pea
k In
ruch
Cu
rrent
Am
pere
s
70,0,-70%
0,-70, 70%
Conclusions
It is possible, by considering residual flux together with the appropriate closing strategy, to eliminate transformer inrush currents in most transformer configurations
With consideration of breaker closing scatter, a reduction of typically 90% of worst, can be achieved
Recommended