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 r H 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 r 87 of max Transformer Flux 0 5 r 0 of max 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 r 87 of max 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 r 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 r 87 of max 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 r 50 of max 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