increasing inductor lifetime by predicting coil copper temperatures presentation

Increasing Inductor Lifetime by

Predicting Coil Copper

Temperatures

Robert Goldstein

www.fluxtrol.com

September 2007, Detroit

Overview

• Demand for Improved Inductor Life

• Failure Modes of Induction Coils

• Extending Inductor Lifetime

• Method for Optimal Inductor Design including Copper Temperature Prediction

• Case Story – Seam Annealing of Large Diameter Pipe

• Conclusions

Demand for Improved Inductor Life

• Increased competition has led to

increased pressure to maximize

manufacturing efficiency and equipment

utilization

• Machine downtime is extremely costly,

especially if it is unplanned

• Inductor failure is one of the leading

causes of machine downtime

Common Failure Modes of

Induction Coils

• Mechanical Damage

• Electrical Break

• Thermal Degradation

Mechanical Damage

• Coil to part impact

– Inaccurate coil set-up

– Improper part installation

– Incoming part defect

• Electrodynamic forces

– Distortion of winding shape

– Elongation of winding (copper creep)

Electrical Break

• Insufficient insulation between turns

– Poor design

– Insulation displaced during shipping/installation

– Wearing of insulation over time

• Process Debris

– Scale from the part

– Magnetic chips from prior machining

Thermal Degradation

• Total overheating of

inductor

– Insufficient water flow

• Local overheating of

inductor component

– Copper cracking due to

thermal ratcheting

(intermittent processes)

– Gradual coil deformation

(continuous processes)

Extending Inductor Lifetime

• Failures due to mechanical damage and

electrical break can be prevented

– Good machine design

– Proper coil manufacturing procedures

– Proper maintenance

• Failures due to thermal degradation more

complicated

Thermal Degradation Prevention

Methods

• Primarily done in response to failures based upon experience

– Increase water flow

– Add booster pumps

– Change water pockets in windings

– Split concentrator into multiple sections

– Change winding design

• Changes made on trial and error basis, no scientific method

Optimal Design Method 1. CS to optimize coil based upon part heating

2. Coil engineering using CAD

3. Hydraulic calculations for cooling circuit

4. Calculation of heat transfer coefficients

5. CS of coil component heating

6. If elevated T exist, return to step 2 to improve cooling circuit

7. If elevated T exists, return to step 1 and change coil design to find compromise between part heating and inductor T

Case Story – Seam Annealing

Case Study Conditions • ¼” Pipe wall thickness

• Feed rate 7.4”/sec

• Frequency 1 kHz

• Power 600 kW

• Maximum temperature – 1200 C

• Equalized temperature – 1000 - 1050 C

• Compare 2 types of flux controller

– Laminations

– Fluxtrol A

Geometry for Simulation of Part

Heating

• Due to symmetry, ½ of system simulated

• Time corresponds to position of the part under the inductor

Pipe

Air

Return Leg

Main Leg

Flux

Controller

Water

Cooling

Part Heating, Laminations Color Shade Results

Quantity : Temperature Deg. Celsius Time (s.) : 4.4 Phase (Deg): 0Scale / Color42.3855 / 115.03716115.03716 / 187.6888187.6888 / 260.34045260.34045 / 332.99213332.99213 / 405.6438405.6438 / 478.29541478.29541 / 550.94708550.94708 / 623.59875623.59875 / 696.25043696.25043 / 768.90204768.90204 / 841.55371841.55371 / 914.20538914.20538 / 986.85699986.85699 / 1.05951E31.05951E3 / 1.13216E31.13216E3 / 1.20481E3

Color Shade ResultsQuantity : Temperature Deg. Celsius Time (s.) : 7.599999 Phase (Deg): 0Scale / Color45.1254 / 108.46457108.46457 / 171.80374171.80374 / 235.14291235.14291 / 298.48209298.48209 / 361.82126361.82126 / 425.16043425.16043 / 488.49957488.49957 / 551.83881551.83881 / 615.17792615.17792 / 678.51715678.51715 / 741.85626741.85626 / 805.1955805.1955 / 868.53461868.53461 / 931.87384931.87384 / 995.21295995.21295 / 1.05855E3

Temperature Exiting Coil Equalized Temperature

Total Coil Current 18,800 A, Total Power 600 KW

Part Heating, Fluxtrol A

Color Shade ResultsQuantity : Temperature Deg. Celsius Time (s.) : 4.4 Phase (Deg): 0Scale / Color41.60269 / 113.62705113.62705 / 185.65143185.65143 / 257.67578257.67578 / 329.70013329.70013 / 401.72449401.72449 / 473.74884473.74884 / 545.77325545.77325 / 617.79761617.79761 / 689.82196689.82196 / 761.84631761.84631 / 833.87067833.87067 / 905.89502905.89502 / 977.91937977.91937 / 1.04994E31.04994E3 / 1.12197E31.12197E3 / 1.19399E3

Color Shade ResultsQuantity : Temperature Deg. Celsius Time (s.) : 7.599999 Phase (Deg): 0Scale / Color44.25912 / 106.98604106.98604 / 169.71295169.71295 / 232.43987232.43987 / 295.16675295.16675 / 357.89368357.89368 / 420.62061420.62061 / 483.34753483.34753 / 546.0744546.0744 / 608.80133608.80133 / 671.52826671.52826 / 734.25513734.25513 / 796.98206796.98206 / 859.70898859.70898 / 922.43591922.43591 / 985.16284985.16284 / 1.04789E3

Temperature Exiting Coil Equalized Temperature

Total Coil Current 20,000 A, Total Power 600 kW

Summary of Heating Simulation

• Temperature distributions produced with Laminations and Fluxtrol A nearly identical

• Power required for both coils the same – 600 kW

• Coil current used in simulation higher for Fluxtrol A than Laminations (20 and 18.8 kA)

– Does not take into account copper keepers and unusable sections near crossovers

Inductor Drawing

Hydraulic Calculations

• Coil has 4 separate water circuits, all identical

• Make calculations for flow rate based upon ΔP from the cooling pump

– Hoses

– Tubing

– Directional/Diameter Changes

• Calculate local water velocities in different sections of the inductor

Heat Transfer Coefficients

• Input losses in different sections of the

water circuit to update water T in different

zones

• Calculate Reynolds and Prandtl numbers

• Calculate Nusselt numbers

• Calculate heat transfer coefficients

Coil Temperature Calculations

• Recalculate currents from heating simulation

to take into account copper keepers and

distance from end loops – 19.9 kA for

laminations, 20.1 kA for Fluxtrol A

• Input losses in concentrator based upon flux

densities in EM simulation

• Install heat transfer coefficients – 14,000 W/m2K main leg, 22,500 W/m2K return leg

Steady State Temperature in Coil

with Laminations Color Shade Results

Quantity : Temperature Deg. Celsius Time (s.) : 0.002E6 Phase (Deg): 0Scale / Color20 / 34.37534.375 / 48.7548.75 / 63.12563.125 / 77.577.5 / 91.87591.875 / 106.25106.25 / 120.625120.625 / 135135 / 149.375149.375 / 163.75163.75 / 178.125178.125 / 192.5192.5 / 206.875206.875 / 221.25221.25 / 235.625235.625 / 250

Temperature scale 20 – 250 C


with Fluxtrol A


Color Shade ResultsQuantity : Temperature Deg. Celsius Time (s.) : 0.002E6 Phase (Deg): 0Scale / Color20 / 34.37534.375 / 48.7548.75 / 63.12563.125 / 77.577.5 / 91.87591.875 / 106.25106.25 / 120.625120.625 / 135135 / 149.375149.375 / 163.75163.75 / 178.125178.125 / 192.5192.5 / 206.875206.875 / 221.25221.25 / 235.625235.625 / 250

Evaluation of Temperatures • Temperatures in inductor with laminations

higher than those on the inductor with Fluxtrol A

• Maximum temperature in both cases in the corner of the copper

• In general, temperatures are all in the safe level and inductor should have good lifetime

• For the sake of study, we’ll increase power 50% for both laminations and Fluxtrol A to see higher temperature dynamics


with Laminations (50% higher P)




with Fluxtrol A (50% higher P)



Temperature Evolution Curves in

Critical Areas (to steady state) Coil Heating Data

0

50

100

150

200

250

0 200 400 600 800 1000

Time (seconds)

Tem

pera

ture

(C

)

Cu Corner A,

HP

Fluxtrol

bottom, HP

Cu Corner

Lams, HP

Lams

Bottom, HP


Critical Areas (first 10 seconds)

Coil Heating Data

0255075

100125150175200225250

0 2 4 6 8 10

Time (seconds)

Tem

pera

ture

(C

)

Cu Corner A,

HP

Fluxtrol

bottom, HP

Cu Corner

Lams, HP

Lams

Bottom, HP

Evaluation of Temperatures

• Temperatures in coil copper are higher with laminations than with Fluxtrol A

• Overall temperature of laminations significantly higher than for Fluxtrol A

• For laminations, maximum in temperature occurs both in the corner of the copper and the edge of the laminations

• In general, temperatures are no longer in the safe level, especially in the laminations

• From the snapshot of the first 10 seconds, it is clear that the heat in the Fluxtrol A is mainly due to conduction from the hot corner of the copper


Critical Areas for Intermittent Heating Intermittent Cycle Comparison

0

50

100

150

200

250

0 50 100 150 200 250 300

Time (s)

Te

mp

era

ture

(C

)

Cu Corner,

Flux A

Fluxtrol A

bottom

Cu Corner

laminations

Lamination

s bottom

10 seconds on, 5 seconds off

Conclusions • Inductor lifetime is an increasingly important

factor in induction heat treating applications

• One of the main failure modes of induction

coils is thermal degradation

• A method for predicting coil temperatures

and optimizing them in terms of lifetime is

presented

• A case story for seam annealing of heavy

walled pipe was presented to demonstrate it

Conclusions Ctd. • The copper temperature on the seam

annealing coil with Fluxtrol A was lower than

with laminations and this effect grew with

higher power levels (6º C regular, 18º C

high power, 40º C smaller ΔT intermittent)

• The overall temperature of Fluxtrol A was

significantly lower than laminations

• Further study should be done with different

coil styles and duty cycles

increasing inductor lifetime by predicting coil copper temperatures presentation

Documents

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cs of coil component

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