Taylor.ppt 2430KB Jun 23 2011 10:31:36 AM

(1)

Transformer Inrush Current

Reduction

(2)

Overview

•

What is Inrush Current?

–

Electromagnetic Phenomenon

–

Magnetic Properties

–

Causes of Inrush

•

Thesis Work

–

Problem Statement

–

Experimental Measurements

–

Pre-fluxing

(3)

Inrush Current

•

Occurs when energizing

transformers

•

5-6 times normal

operating current

•

Stresses insulation

–

Thermal Stress

–

Physical Stress

•

Causes Protection/Power

(4)

Faraday's Law

Magnetic Flux

Density

Magnetic Field

Intensity

Vp Np

d

t



d



B



Acore

H

Np IP



MPL

(5)

Magnetic Hysteresis

B



₀





r



H

Source: http://hyperphysics.phy-astr.gsu.edu/Hbase/Solids/hyst.html

(6)

Normal Transformer Operation

(7)

Inrush Current Causes

•

Based on two main factors:

–

Residual Flux

–

Energizing (or Switching) Instant

•

Ideally switch when prospective flux equals residual

flux

(8)

Inrush – Incorrect Switching Time

(9)

No Inrush – Proper Switching Time

(10)

Ideal Single Phase Switching – Demagnetized Case

0.01 0 0.01 0.02 0.03 0.04

1 0.5 0.5 1

System Voltage

Winding Voltage - Demagnetized Case

Time (s) Vo lt ag e (p u)

0.01 0 0.01 0.02 0.03 0.04

1 0.5 0.5 1

Prospective Flux

Transformer Flux - Demagnetized Case

Time (s) F lu x (p u)

0.01 0 0.01 0.02 0.03 0.04

1 0.5 0.5 1 Residual Flux Prospective Flux

0.01 0 0.01 0.02 0.03 0.04

1 0.5 0.5 1 Winding Voltage System Voltage

0.01 0 0.01 0.02 0.03 0.04

1 0.5 0.5 1 Transient Flux Prospective Flux

(11)

Ideal Single Phase Switching – Demagnetized Case 2

0.01 0 0.01 0.02 0.03 0.04

1.5 1 0.5 0.5 1 Transient Flux Prospective Flux

0.01 0 0.01 0.02 0.03 0.04

(12)

Ideal Single Phase Switching – Magnetized Case

0.01 0 0.01 0.02 0.03 0.04

1 0.5 0.5 1 Transient Flux Prospective Flux

Transformer Flux - Magnetized Case

0.01 0 0.01 0.02 0.03 0.04

Winding Voltage - Magnetized Case

0.01 0 0.01 0.02 0.03 0.04

2 1 1

Transient Flux Prospective Flux

0.01 0 0.01 0.02 0.03 0.04

(13)

Worst Case Single Phase Switching

0.01

 0 0.01 0.02 0.03 0.04 1  1 2 3 Transient Flux Prospective Flux

Time (s) F lu x (p u) 0.01

 0 0.01 0.02 0.03 0.04

1  0.5  0.5 1 Winding Voltage System Voltage

(14)

0.01 0.005 0 0.005 0.01 0.015

1 0.5 0.5 1

Winding Voltage - Phase A System Voltage - Phase A Winding Voltage - Phase B System Voltage - Phase B Winding Voltage - Phase C System Voltage - Phase C

Winding Voltage Time (s) Vo lt ag e (p u)

0.01 0.005 0 0.005 0.01 0.015

1 0.5 0.5 1

Transient Flux - A Phase Prospective Flux - A Phase Transient Flux - B Phase Prospective Flux - B Phase Transient Flux - C Phase Prospective Flux - C Phase

Transformer Flux Time (s) F lu x (p u)

Ideal Three Phase, Three Pole Switching

Φ

_r

=87% of Φ

_max

(15)

Problem Statement

•

Set Residual Flux in Single-Phase Transformer

–

‘Pre-fluxing’

–

Set as high as possible

•

Controlled Energization

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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

(17)

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Experimental Hysteresis

Measurements

•

Nominal Winding Voltage - 25 V

•

Sequence of plots

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Hysteresis Loop Family

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Tertiary Winding at 8.5 Vrms

Flux

(21)

Tertiary Winding at 17 Vrms

Flux

(22)

Tertiary Winding at 19.5 Vrms

Flux

(23)

Tertiary Winding at Rated 25 Vrms

Flux

Magnetizing Current

B

r_max

= 0.95 T

(24)

Inrush Current – Demagnetized

Case

•

Case 1: Unloaded Steady-State Operation

•

Case 2: Proper Switching – No Inrush

•

Case 3: Worst Case Switching – Maximum

(25)

Unloaded Steady-State Operation (230 V Winding)

Voltage

(26)

Demagnetized – Proper Switching Time (~90 deg)

Voltage

(27)

Demagnetized – Proper Switching Time (~90 deg)

Voltage

(28)

Demagnetized – Improper Switching Time (0 deg)

Voltage

(29)

Voltage

(30)

Voltage

(31)

Prefluxing

•

Send a pulse of energy to the transformer

•

Circuit Used

–

Series capacitor and diode

(32)

(33)

Pre-Flux 9 mWb (75% of Φ

r_max

)

Flux

Voltage

(34)

Pre-fluxed – Proper Switching Time (124 deg)

Voltage

(35)

Voltage

(36)

Future Work

•

Sensitivity Testing

–

Non-Ideal Pre-Fluxing

–

Non-Ideal Switching

(37)

0.01 0.005 0 0.005 0.01 0.015

1 0.5 0.5 1

Winding Voltage - Phase A System Voltage - Phase A Winding Voltage - Phase B System Voltage - Phase B Winding Voltage - Phase C System Voltage - Phase C

Winding Voltage Time (s) Vo lt ag e (p u)

0.01 0.005 0 0.005 0.01 0.015

1 0.5 0.5 1

Transient Flux - A Phase Prospective Flux - A Phase Transient Flux - B Phase Prospective Flux - B Phase Transient Flux - C Phase Prospective Flux - C Phase

Transformer Flux Time (s) F lu x (p u)

Ideal Three Phase, Three Pole Switching

Φ

_r

=87% of Φ

_max

(38)

Non-Ideal Pre-Fluxing

0.01 0 0.01 0.02 0.03 0.04

2 1 1

Flux - 3 Phase Case (190 deg)

0.01 0 0.01 0.02 0.03 0.04

Winding Voltage - 3 Phase Case (190 Deg)

0.01 0 0.01 0.02 0.03 0.04

2 1 1

Flux - 3 Phase Case (210 deg)

0.01 0 0.01 0.02 0.03 0.04

Winding Voltage - 3 Phase Case (210 Deg)

Non-Ideal Pre-Fluxing/

Switching

(39)

Non-Ideal Switching– Demagnetized (114°, 24° error)

Voltage

(40)

Voltage

(41)

Future Work (Con’t)

•

Device Sizing

(42)