Taylor.ppt 2430KB Jun 23 2011 10:31:36 AM
Transformer Inrush Current
Reduction
Doug Taylor
January 29, 2009
Overview
• What is Inrush Current?
– Electromagnetic Phenomenon
– Magnetic Properties
– Causes of Inrush
• Thesis Work
– Problem Statement
– Experimental Measurements
– Pre-fluxing
– Future Work
Inrush Current
• Occurs when energizing
transformers
• 5-6 times normal
operating current
• Stresses insulation
– Thermal Stress
– Physical Stress
• Causes Protection/Power
Quality Issues
Source: Wikipedia
Faraday's Law
Vp
d
Np
dt
Magnetic Flux
Density
Magnetic Field
Intensity
Np IP
B
A core
H
MPL
Magnetic Hysteresis
Source: http://hyperphysics.phy-astr.gsu.edu/Hbase/Solids/hyst.html
Magnetic Permeability
B
0 rH
Normal Transformer Operation
Source: ABB App. Guide
Inrush Current Causes
• Based on two main factors:
– Residual Flux
– Energizing (or Switching) Instant
• Ideally switch when prospective flux equals residual
flux
• Deviations from this instant result in inrush current
Inrush – Incorrect Switching Time
Source: ABB App. Guide
No Inrush – Proper Switching Time
Source: ABB App. Guide
Ideal Single Phase Switching – Demagnetized Case
Transformer Flux - Demagnetized Case
1
Flux (pu)
0.5
0.01
0
0.01
0.02
0.03
0.04
0.5
1
Time (s)
Prospective
Transient
Flux
Flux
Residual Flux
Prospective Flux
Winding Voltage - Demagnetized Case
1
Voltage (pu)
0.5
0.01
0
0.01
0.02
0.5
1
Time (s)
System VVoltage
Winding
oltage
System Voltage
0.03
0.04
Ideal Single Phase Switching – Demagnetized Case 2
Transformer Flux - Demagnetized Case
1
Flux (pu)
0.5
0.01
0
0.01
0.02
0.03
0.04
0.5
1
1.5
Time (s)
Transient Flux
Prospective Flux
Winding Voltage - Demagnetized Case
1
Voltage (pu)
0.5
0.01
0
0.01
0.02
0.5
1
Time (s)
Winding Voltage
System Voltage
0.03
0.04
Ideal Single Phase Switching – Magnetized Case
Transformer Flux - Magnetized Case
1
Transformer Flux - Magnetized Case
1
0.01
0
0.01
0.02
0.03
0.04
Flux (pu)
Flux (pu)
0.5
0.01
0
0.01
0.02
0.03
0.04
1
0.5
2
1
Time (s)
Time (s)
Transient Flux
Prospective Flux
Transient Flux
Prospective Flux
Winding Voltage - Magnetized Case
Winding Voltage - Magnetized Case
1
1
0.01
0.5
0
0.01
0.02
0.03
0.04
Voltage (pu)
Voltage (pu)
0.5
0.01
0
0.5
0.5
1
1
Time (s)
Winding Voltage
System Voltage
0.01
0.02
Time (s)
Winding Voltage
System Voltage
0.03
0.04
Worst Case Single Phase Switching
Transformer Flux - Magnetized Case
3
Flux (pu)
2
1
0.01
0
0.01
0.02
0.03
0.04
1
Time (s)
Transient Flux
Prospective Flux
Winding Voltage - Magnetized Case
1
Voltage (pu)
0.5
0.01
0
0.01
0.02
0.5
1
Time (s)
Winding Voltage
System Voltage
0.03
0.04
Ideal Three Phase, Three Pole Switching
1
Winding Voltage
Φr=87% of Φmax
Transformer Flux
0.5
Φr=0% of Φmax
0.01
0.005
0
0.005
0.5
0.015
0.01
0.005
0
0.005
0.5
1
Time (s)
Winding Voltage - Phase A
System Voltage - Phase A
Winding Voltage - Phase B
System Voltage - Phase B
Winding Voltage - Phase C
System Voltage - Phase C
0.01
Flux (pu)
Voltage (pu)
0.5
1
Φr=-87% of Φmax
1
Time (s)
Transient Flux - A Phase
Prospective Flux - A Phase
Transient Flux - B Phase
Prospective Flux - B Phase
Transient Flux - C Phase
Prospective Flux - C Phase
0.01
0.015
Problem Statement
• Set Residual Flux in Single-Phase Transformer
– ‘Pre-fluxing’
– Set as high as possible
• Controlled Energization
– Precise switching
Experimental Setup
• 55 kVA Transfomer
– Primary/Secondary
Winding – 230 V
– Tertiary Winding – 25 V
• LabVIEW
– Computer-based
Measurement Software
– Measure Flux
• Precision Switch
– Allows Controlled
Energization
LabVIEW
Experimental Hysteresis
Measurements
• Nominal Winding Voltage - 25 V
• Sequence of plots
– 8.5 V Applied
– 17 V Applied
– 19.5 V Applied
– 25 V Applied
Hysteresis Loop Family
Nominal Operation
Source: Wikipedia
Tertiary Winding at 8.5 Vrms
Voltage
Flux
Magnetizing Current
Tertiary Winding at 17 Vrms
Voltage
Flux
Magnetizing Current
Tertiary Winding at 19.5 Vrms
Voltage
Flux
Magnetizing Current
Tertiary Winding at Rated 25 Vrms
Voltage
Br_max = 0.95 T
Flux
Magnetizing Current
Inrush Current – Demagnetized
Case
• Case 1: Unloaded Steady-State Operation
• Case 2: Proper Switching – No Inrush
• Case 3: Worst Case Switching – Maximum
Inrush
Unloaded Steady-State Operation (230 V Winding)
Voltage
Magnetizing Current
Demagnetized – Proper Switching Time (~90 deg)
Voltage
Magnetizing Current
Demagnetized – Proper Switching Time (~90 deg)
Voltage
Magnetizing Current
Demagnetized – Improper Switching Time (0 deg)
Voltage
Magnetizing Current
Demagnetized – Improper Switching Time (0 deg)
Voltage
Magnetizing Current
Demagnetized – Improper Switching Time (0 deg)
Voltage
Magnetizing Current
Prefluxing
• Send a pulse of energy to the transformer
• Circuit Used
– Series capacitor and diode
• Fairly Simple
• Effective
Series Capacitor & Diode
Pre-Flux 9 mWb (75% of Φr_max)
Voltage
Flux
Magnetizing Current
Pre-fluxed – Proper Switching Time (124 deg)
Voltage
Magnetizing Current
Pre-fluxed – Proper Switching Time (124 deg)
Voltage
Magnetizing Current
Future Work
• Sensitivity Testing
– Non-Ideal Pre-Fluxing
– Non-Ideal Switching
– Keep Inrush To 1.5-2 p.u.
– Increase Device Practicality
Ideal Three Phase, Three Pole Switching
1
Winding Voltage
Φr=87% of Φmax
0.01
0.005
Transformer Flux
0.5
0
0.005
0.01
0.015
Flux (pu)
Voltage (pu)
0.5
1
0.01
0.005
0
0.005
210 Deg
0.5
0.5
1
1
Time (s)
Winding Voltage - Phase A
System Voltage - Phase A
Winding Voltage - Phase B
System Voltage - Phase B
Winding Voltage - Phase C
System Voltage - Phase C
Time (s)
Transient Flux - A Phase
Prospective Flux - A Phase
Transient Flux - B Phase
Prospective Flux - B Phase
Transient Flux - C Phase
Prospective Flux - C Phase
0.01
0.015
Non-Ideal Pre-Fluxing
Flux - 3 Phase Case (210 deg)
Flux - 3 Phase Case (190 deg)
1
0.01
0
0.01
0.02
0.03
1
0.04
Flux (pu)
Flux (pu)
Φr=50% of Φmax
Non-Ideal Pre-Fluxing/
Switching
0.01
0
1
1
2
2
Time (s)
0.03
0.04
Transient Flux
Prospective Flux
Winding Voltage - 3 Phase Case (210 Deg)
Winding Voltage - 3 Phase Case (190 Deg)
1
1
0.5
0
0.01
0.02
0.03
0.04
Voltage (pu)
0.5
Voltage (pu)
0.02
Time (s)
Transient Flux
Prospective Flux
0.01
0.01
0.01
0
0.5
0.5
1
1
Time (s)
Winding Voltage
System Voltage
0.01
0.02
Time (s)
Winding Voltage
System Voltage
0.03
0.04
Non-Ideal Switching– Demagnetized (114°, 24° error)
Voltage
Magnetizing Current
Pre-fluxed – Proper Switching Time (124 deg)
Voltage
Magnetizing Current
Future Work (Con’t)
• Device Sizing
– Dependent upon Transformer Size
Questions?
Reduction
Doug Taylor
January 29, 2009
Overview
• What is Inrush Current?
– Electromagnetic Phenomenon
– Magnetic Properties
– Causes of Inrush
• Thesis Work
– Problem Statement
– Experimental Measurements
– Pre-fluxing
– Future Work
Inrush Current
• Occurs when energizing
transformers
• 5-6 times normal
operating current
• Stresses insulation
– Thermal Stress
– Physical Stress
• Causes Protection/Power
Quality Issues
Source: Wikipedia
Faraday's Law
Vp
d
Np
dt
Magnetic Flux
Density
Magnetic Field
Intensity
Np IP
B
A core
H
MPL
Magnetic Hysteresis
Source: http://hyperphysics.phy-astr.gsu.edu/Hbase/Solids/hyst.html
Magnetic Permeability
B
0 rH
Normal Transformer Operation
Source: ABB App. Guide
Inrush Current Causes
• Based on two main factors:
– Residual Flux
– Energizing (or Switching) Instant
• Ideally switch when prospective flux equals residual
flux
• Deviations from this instant result in inrush current
Inrush – Incorrect Switching Time
Source: ABB App. Guide
No Inrush – Proper Switching Time
Source: ABB App. Guide
Ideal Single Phase Switching – Demagnetized Case
Transformer Flux - Demagnetized Case
1
Flux (pu)
0.5
0.01
0
0.01
0.02
0.03
0.04
0.5
1
Time (s)
Prospective
Transient
Flux
Flux
Residual Flux
Prospective Flux
Winding Voltage - Demagnetized Case
1
Voltage (pu)
0.5
0.01
0
0.01
0.02
0.5
1
Time (s)
System VVoltage
Winding
oltage
System Voltage
0.03
0.04
Ideal Single Phase Switching – Demagnetized Case 2
Transformer Flux - Demagnetized Case
1
Flux (pu)
0.5
0.01
0
0.01
0.02
0.03
0.04
0.5
1
1.5
Time (s)
Transient Flux
Prospective Flux
Winding Voltage - Demagnetized Case
1
Voltage (pu)
0.5
0.01
0
0.01
0.02
0.5
1
Time (s)
Winding Voltage
System Voltage
0.03
0.04
Ideal Single Phase Switching – Magnetized Case
Transformer Flux - Magnetized Case
1
Transformer Flux - Magnetized Case
1
0.01
0
0.01
0.02
0.03
0.04
Flux (pu)
Flux (pu)
0.5
0.01
0
0.01
0.02
0.03
0.04
1
0.5
2
1
Time (s)
Time (s)
Transient Flux
Prospective Flux
Transient Flux
Prospective Flux
Winding Voltage - Magnetized Case
Winding Voltage - Magnetized Case
1
1
0.01
0.5
0
0.01
0.02
0.03
0.04
Voltage (pu)
Voltage (pu)
0.5
0.01
0
0.5
0.5
1
1
Time (s)
Winding Voltage
System Voltage
0.01
0.02
Time (s)
Winding Voltage
System Voltage
0.03
0.04
Worst Case Single Phase Switching
Transformer Flux - Magnetized Case
3
Flux (pu)
2
1
0.01
0
0.01
0.02
0.03
0.04
1
Time (s)
Transient Flux
Prospective Flux
Winding Voltage - Magnetized Case
1
Voltage (pu)
0.5
0.01
0
0.01
0.02
0.5
1
Time (s)
Winding Voltage
System Voltage
0.03
0.04
Ideal Three Phase, Three Pole Switching
1
Winding Voltage
Φr=87% of Φmax
Transformer Flux
0.5
Φr=0% of Φmax
0.01
0.005
0
0.005
0.5
0.015
0.01
0.005
0
0.005
0.5
1
Time (s)
Winding Voltage - Phase A
System Voltage - Phase A
Winding Voltage - Phase B
System Voltage - Phase B
Winding Voltage - Phase C
System Voltage - Phase C
0.01
Flux (pu)
Voltage (pu)
0.5
1
Φr=-87% of Φmax
1
Time (s)
Transient Flux - A Phase
Prospective Flux - A Phase
Transient Flux - B Phase
Prospective Flux - B Phase
Transient Flux - C Phase
Prospective Flux - C Phase
0.01
0.015
Problem Statement
• Set Residual Flux in Single-Phase Transformer
– ‘Pre-fluxing’
– Set as high as possible
• Controlled Energization
– Precise switching
Experimental Setup
• 55 kVA Transfomer
– Primary/Secondary
Winding – 230 V
– Tertiary Winding – 25 V
• LabVIEW
– Computer-based
Measurement Software
– Measure Flux
• Precision Switch
– Allows Controlled
Energization
LabVIEW
Experimental Hysteresis
Measurements
• Nominal Winding Voltage - 25 V
• Sequence of plots
– 8.5 V Applied
– 17 V Applied
– 19.5 V Applied
– 25 V Applied
Hysteresis Loop Family
Nominal Operation
Source: Wikipedia
Tertiary Winding at 8.5 Vrms
Voltage
Flux
Magnetizing Current
Tertiary Winding at 17 Vrms
Voltage
Flux
Magnetizing Current
Tertiary Winding at 19.5 Vrms
Voltage
Flux
Magnetizing Current
Tertiary Winding at Rated 25 Vrms
Voltage
Br_max = 0.95 T
Flux
Magnetizing Current
Inrush Current – Demagnetized
Case
• Case 1: Unloaded Steady-State Operation
• Case 2: Proper Switching – No Inrush
• Case 3: Worst Case Switching – Maximum
Inrush
Unloaded Steady-State Operation (230 V Winding)
Voltage
Magnetizing Current
Demagnetized – Proper Switching Time (~90 deg)
Voltage
Magnetizing Current
Demagnetized – Proper Switching Time (~90 deg)
Voltage
Magnetizing Current
Demagnetized – Improper Switching Time (0 deg)
Voltage
Magnetizing Current
Demagnetized – Improper Switching Time (0 deg)
Voltage
Magnetizing Current
Demagnetized – Improper Switching Time (0 deg)
Voltage
Magnetizing Current
Prefluxing
• Send a pulse of energy to the transformer
• Circuit Used
– Series capacitor and diode
• Fairly Simple
• Effective
Series Capacitor & Diode
Pre-Flux 9 mWb (75% of Φr_max)
Voltage
Flux
Magnetizing Current
Pre-fluxed – Proper Switching Time (124 deg)
Voltage
Magnetizing Current
Pre-fluxed – Proper Switching Time (124 deg)
Voltage
Magnetizing Current
Future Work
• Sensitivity Testing
– Non-Ideal Pre-Fluxing
– Non-Ideal Switching
– Keep Inrush To 1.5-2 p.u.
– Increase Device Practicality
Ideal Three Phase, Three Pole Switching
1
Winding Voltage
Φr=87% of Φmax
0.01
0.005
Transformer Flux
0.5
0
0.005
0.01
0.015
Flux (pu)
Voltage (pu)
0.5
1
0.01
0.005
0
0.005
210 Deg
0.5
0.5
1
1
Time (s)
Winding Voltage - Phase A
System Voltage - Phase A
Winding Voltage - Phase B
System Voltage - Phase B
Winding Voltage - Phase C
System Voltage - Phase C
Time (s)
Transient Flux - A Phase
Prospective Flux - A Phase
Transient Flux - B Phase
Prospective Flux - B Phase
Transient Flux - C Phase
Prospective Flux - C Phase
0.01
0.015
Non-Ideal Pre-Fluxing
Flux - 3 Phase Case (210 deg)
Flux - 3 Phase Case (190 deg)
1
0.01
0
0.01
0.02
0.03
1
0.04
Flux (pu)
Flux (pu)
Φr=50% of Φmax
Non-Ideal Pre-Fluxing/
Switching
0.01
0
1
1
2
2
Time (s)
0.03
0.04
Transient Flux
Prospective Flux
Winding Voltage - 3 Phase Case (210 Deg)
Winding Voltage - 3 Phase Case (190 Deg)
1
1
0.5
0
0.01
0.02
0.03
0.04
Voltage (pu)
0.5
Voltage (pu)
0.02
Time (s)
Transient Flux
Prospective Flux
0.01
0.01
0.01
0
0.5
0.5
1
1
Time (s)
Winding Voltage
System Voltage
0.01
0.02
Time (s)
Winding Voltage
System Voltage
0.03
0.04
Non-Ideal Switching– Demagnetized (114°, 24° error)
Voltage
Magnetizing Current
Pre-fluxed – Proper Switching Time (124 deg)
Voltage
Magnetizing Current
Future Work (Con’t)
• Device Sizing
– Dependent upon Transformer Size
Questions?