Optimal Design of Internal

Induction Coils

Dr. Valentin Nemkov

Eng. Robert Goldstein

Dr. Vladimir Bukanin

Types of Inductors for Internal

Surface Heating (ID Coils)

• Inductor with Central Rod

• Hairpin

• Single Turn Cylindrical

• Multi-Turn Cylindrical

Inductor

with

Central Rod

Hairpin

Inductor

Multi-Turn

Cylindrical

Single-Turn

Cylindrical

Equivalent Magnetic Circuit

Pipe ID Heating

Lw = 5.6 cm Lw = 3.0 cm

Case Study Conditions

• Pipe – Non-magnetic Stainless Steel

– ID = 5.6 cm, OD = 6.9 cm, length = 3.0 cm (short) or 5.6 cm (long)

• Coil – 4 turns 6.4 cm square copper tubing

– Concentrator Fluxtrol 50 vs. Air

• CS Program Flux 2D – Does Not Include Return Leg

• Frequency 10 kHz

Results of Study

Part length Core Pole U I ΔPc Psteel Ptotal η cosφ S

55.9 mm y y 33.6 900 1685 8837 10522 84.0% 0.348 30240

55.9 mm y n 32.3 1190 2512 8878 11390 77.9% 0.296 38437

55.9 mm n n 32.9 2000 4168 9285 13453 69.0% 0.204 65800

30 mm y y 30.9 790 1242 8126 9368 86.7% 0.384 24411

30 mm n n 30.2 1760 3179 8282 11461 72.3% 0.216 53152

Results do not consider return leg

Case Study of Magnetic Core Design

• Pipe

– Non-magnetic Stainless Steel

• Coil

– 4 turns 6.4 cm square copper tubing

– Concentrator Fluxtrol 50 vs. Air

• CS Program ELTA – Takes into account whole circuitry

• Frequency 10 kHz

Influence of Return Leg

Case Core Core Uind Iind Pind η cosφ Sind Ugen

Gap (mm) (V) (A) (kW) (kVA) (V)

1 No NA 132 1350 34 55% 0.19 178 480

2 Yes 0 220 568 25.4 77% 0.22 125 760

3 Yes 1 138 570 25.4 77% 0.36 78 460

Coil Head Voltage 85 V for All Cases

Conclusions • Magnetic Flux Controllers Drastically Improve ID

Coil Performance

• Magnetic Flux Controller Should Consist of a Core and Poles for Optimal Performance

• Losses in Return Leg are Usually Small

• Voltage Drop due to Return Leg May Be High

• Proper Design of Magnetic Core Essential for Optimal Performance

• ID Coil Parameters May Be Found Quickly and Accurately Using ELTA Program