Confidential and Proprietary Information of Fluxtrol, Inc. Auburn Hills, MI

Simulation of Induction System for Brazing of Squirrel Cage Rotor

Dr. Valentin Nemkov(1), Dr. Valentin Vologdin(2)

Dr. Vl. Vologdin Jr. (2), Kevin Kreter(1) (1)Fluxtrol, Inc., USA; (2)Freal, Ltd., Russia

Padua, Italy, May 21-24, 2013

Specs and System Description • Copper ring must be heated up to temperature 800-850 C• Single-turn coil has П-shaped concentrator made of Fluxtrol LRM • Concentrator is attached to the coil with a thermally conductive

glue, k = 0.01 W/cmK• Ceramic fiber insulation pad between the coil and ring has

thermal conductivity k = 0.002 W/cmK; thickness of pad is 2 mm• Motor bars are substituted for a tube filling the whole groove;

thermal conductivity and heat capacity of the tube reduced by space factor g = 0.42

• Simulation was made at a constant coil voltage corresponding to mean power equal to 50 or 75 kW during the heating time

• Program Flux 2D has been used for simulation

Brazing Setup and Joint Cross-section

№ Rotor type

D1,

mmD25, mm D21, mm D22, mm D23, mm D24, mm h, mm H2, mm

1 АDТ-3 170 151 155 211 165 206 14 348

2 DТА-1 242 223 222 298 243 294 20 500

Case 1

Temperature at Braze Joint

0 50 100 150 2000

100

200

300

400

500

600

700

800

900

3 kHz

50 kHz

Time (s)

Temperature(C)

Case 1, 50 kW

Study was made for two rotor sizes (case 1 and case 2), two levels of frequency (3 kHz and 50 kHz) and two levels of power (50 and 75 kW)

Braze Thermal Profile

Case 1, 50 kHz, 50 kW

• Ii = 6300 A• Ui = 21 V• Coil losses: 23.6 kW• Ring: 26.2 kW• Fluxtrol: 0.2 kW• t = 205 seconds

Rotor Cool Down

0 200 400 600 800 1000 1200 1400 1600 1800 20000

100

200

300

400

500

600

700

800

900

Case 1 - 50 kHz

Case 1 - 3 kHz

Case 2 - 50 kHz

Case 2 - 3 kHz

Time (s)

75 kW 50 kW

Temperature at braze joint

Temperature curves show that heat losses in bars are very high and thermal efficiency at 75 kW at the end of heating is less than 50%

Coil Thermal Profile at the End of the Process

Case 1, 50 kW

Frequency 50 kHz, Tmax = 160 0CFrequency 3 kHz, Tmax = 150 0C

Braze Thermal Profiles

Case 2, 50 kHz, 75 kWCase 2, 3 kHz, 75 kW

Temperature profiles are almost the same for 3 kHz and 50 kHz

0 50 100 150 200 250 3000

100

200

300

400

500

600

700

800

900

1000

3 kHz50 kHz

Time (s)

Temperature(C)

Temperature at Braze Joint

Case 2, 75 kW

Coil Thermal Profile at the End of the Process

Case 2, 50 kHz, 75 kWTmax = 200 0C

Case 2, 3 kHz, 75 kWTmax = 190 0C

Tmax of concentrator is close to upper limit for Fluxtrol material and must be kept under control by material selection, concentrator design and proper manufacturing.

Intensive coil cooling is required

Simulated and Experimental Process Parameters

Rotor type

Power, kW Frequency kHz Time sec NotePtotal Pcoil Pring Pмagn

АТD-3Case 1

50 22.8 26.7 0.5 50 185 Model (Case 1)

50 - - - 54 170 Experiment

50 23.6 26.2 0.2 3 205 Model (Case 1)

DТА-1Case 2

50 21.6 28.1 0.3 50 925 Model (Case 2)

50 - - - 46 930 Experiment

75 34 40.6 0.4 50 310 Model (Case 2)

75 35 39.8 0.2 3 335 Model (Case 2)

0 50 100 150 200 250 3000

50

100

150

200

250

300

3 kHz50 kHz

Time (s)

Axial Force on Ring

(N)

Electrodynamic Forces on Ring

75 kW

Forces are rather high especially at 3 kHz. They can cause vibration and noise

End of Test Brazing Process

Operator controls brazing quality and adds solder when required

Red spot in the circle shows a point of the temperature control using laser aiming

Conclusions• 2D simulation gives accurate enough results despite several assumptions

• Frequency variation in the wide range from 3 to 50 kHz does not influence the process efficiency and temperature distribution much

• The use of frequency below 8 kHz may be limited by forces and noise

• The use of the higher range of frequency may be limited by high coil voltage and elevated temperature of SMC concentrator

• Optimal frequency for the studied rotors is in a range of 10-30 kHz

• Process is sensitive to a minimum power level. Brazing of rotor no. 2 at 50 kW is marginal. Heating time is almost triple compared to 75 kW

• Simulation and experiments showed that SMC concentrators may be effectively used in rotor brazing

• Computer simulation may be used as a powerful tool for design of rotor brazing processes

Thank you!

I Protest against Induction Brazing of My Cage!