Free induction heating course · Chapter 2 of 13

Induction Installations

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This chapter of the free Fluxtrol induction heating course walks through induction installations in 43 slides. View the slides below, or skim the outline and slide text.

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Induction Installation Structure

  • Main components of a typical induction installation:
  • Generator: generates high frequency power from utility line frequency power
  • Heat Station: matches induction coil to a generator
  • Handling Mechanisms: load, process and unload parts
  • Cooling System: provides cooling of installation components (generator, heat station and induction coil)
  • Quenching System: provides conditioned quenching media to the part
  • Control and monitor systems: provides control and monitoring process and equipment

Layout of Induction Hardening Installation

  • Quench system Water cooling system Power Generator Heat station Coil Handling Mechanism/ Machine Machine control

Installation with Coil Mounted on Heat Station

  • Operator Controls Induction Coil Pusher Heat Station Courtesy of EFD Induction

Single Platform Installation

  • installation may be:
  • Quench system
  • Mounted on a single platform Machine
  • Distributed
  • Built in line Water cooling system Power supply Heat station Coil Machine control Single Platform Induction installation:
  • Requires less space Easy to install Shorter installation time Less expensive to install Utilities required at single point

Induction Hardening Installation

  • Scanning machine Mains distribution cabinet Frequency Converter Work area:
  • Inductor
  • Quench Cooling and quench system Control system cabinet Example of a single-platform induction hardening installation, EFD Induction

Power Supply Block Diagram

Command Control electronics 3 phase line input AC to DC conversion Rectifier section DC to AC Inverter section Load matching transformer & capacitors Induction coil Heat station HF Generator Power supply must convert alternating line frequency power (50 or 60 Hz)into a controlled High Frequency power. The most effective way to do that is to convert (rectify) line frequency power into DC power and then generate high frequency using solid state Inverter.

Power Flow in Induction Heating Installation

  • f1/f2 50/60 Hz Power Supply Heat Station Induction Coil f1/f2 Active Power, kW Reactive Power, kVA See Glossary and Basics of Induction Heating for more details

Types of Power Supplies

  • Power Supplies convert line power (50/60 Hz) to controlled power at frequency, current and voltage required for proper induction coil operation. They contain frequency converter (generator) and power matching system.
  • Types of frequency converter s:
  • When developed:
  • Motor-Generators the 20’s
  • Vacuum Tube Generators the 20’s
  • Solid State Generators
  • Thyristor Generators
  • Transistor Generators:
  • early 60’s
  • IGBT Generators early 80’s
  • MOSFET Generators mid 90’s Recent developments of solid state power supplies include:
  • Dual Frequency Power Supplies late 90’s
  • Intelligent Power Supplies late 90’s - 2000s

Motor-Generator Sets

  • Obsolete equipment but still used in industry
  • Frequency limited up to 10 kHz
  • Fixed frequency, no ability of load matching by frequency variation
  • Power from 50 – 2500 kW
  • Efficiency - 65 to 85 %
  • Output voltage from 400–1600Volts
  • Rotating parts require maintenance due to wear and tear
  • Big size and weight
  • Difficult to repair

Vacuum Tube Generators

  • Also known as Radio Frequency Oscillators
  • Frequency range from 60 kHz to 400 kHz and higher (highest known frequency used for Induction heating – 27.12 MHz)
  • Low efficiency
  • Very high voltage s (up to 20k V)require special safety precautions
  • Limited life of vacuum tube (several thousands hours)
  • Expensive vacuum tube replacement
  • Easy load matching
  • 50 to 60 %
  • Can provide high Power Pulses with power densities on the part surface above 30 kW/ square inch
  • Can easily operate with loads having low power factor (big reactive power) Welder with vacuum tube oscillator, EMMEDI company

Solid State Generators

  • Any reasonable combination of frequency and power is possible
  • Variable frequency in a range up to 10 times from the same generator with proper changes in heat station
  • Power from 1 kW – 10 MW
  • Output voltage from 200–1600Volts
  • High efficiency
  • Multiple outputs possible
  • Simultaneous dual frequency output possible
  • Advanced controls
  • Easily adaptable to modern automation techniques
  • Light weight and compact size
  • up to 90- 95 % Powersupply 100kW, 10 or 30 kHz Inductoheat Inc.

Modern Solid State Power Supplies

  • Big and Middle Sizes Courtesy of EFD Induction, Inc.

Simultaneous Dual Frequency Power Supplies

  • For contour hardening of gears and other parts of complex geometry, special transistor power supplies were developed that can generate two frequencies simultaneously. Power levels may be programmed independently for each frequency, providing accurate results and high process flexibility.
  • 600 kW induction hardening machine with variable ratio of Middle Frequency power (up to 400 kW) MF and High Frequency power (up to 200 kW), Eldec Induction U.S.A. Inc.
  • Gear hardened by means of Simultaneous Dual Frequency Heating

Intelligent Power Supplies

  • Modern power supplies can deliver almost any combination of power and frequency; they have high efficiency and small size.
  • The main tendency of further development is improvement in flexibility and controls leading to more intelligent machines.
  • Modern induction power supplies can provide:
  • Power generation in a wide range of frequency
  • Autotuning with coil change and coil parameter variation in the process of heating
  • Process programming
  • Control from Master control system of the production line
  • Process monitoring
  • Automatic troubleshooting
  • Remote control and diagnostics including actions from the manufacturer site Development of more advanced and sophisticated control systems may be expected including real-time process optimization and quality

Comparison of Power Supplies

  • Type of PowerSupply Switching device Frequency range Efficiency of power supply % Line frequency None 50/60 Hz 93 - 97 Motor-Generator None 1 kHz –10 kHz 70 – 85 Solid state SCR Thyristors 500 Hz – 25 kHz 87 - 95 Solid state IGBT Transistors 1 kHz – 200 kHz 85 - 92 Solid state MOSFET Transistors 100 kHz – 400 kHz 85 – 92 Vacuum Tube Generator Vacuum tube 66 kHz – 500 kHz 50 - 60 and more

Large Solid State Power Supplies /

  • Application Areas Category Low Frequency (LF) Medium Frequency High (Radio) Frequency (MF) (HF) Frequency Range 50 Hz to 3 kHz 3 kHz to 60 kHz Above 60 kHz Power Range Up to 30 MW Up to 5000 KW Up to 1800 KW Applications Melting Mass Heating Heat Treating Mass Heating Heat Treating Bonding Brazing Tube welding

Large High Frequency Solid State

  • Power Supply Power range:
  • 150 – 1800 kW Frequency range:
  • 100 – 400 kHz MOSFET power supply (welder) for continuous tube welding Courtesy EFD Induction, Inc.

Mid-Sized Solid State Power

  • Supplies / Application Areas Frequency Range 3 kHz – 500 kHz Power Rating 30 KW – 500 KW Applications Induction Hardening Melting Brazing Mass Heating Tube Welding Innovations Protection against environment Intelligent digital control systems Process or coil monitoring Dual output available (Synchronized or Independent)

Small Solid State Power Supplies /

  • Application Areas Frequency Range 20 kHz – 500 kHz Power Rating 1 kW – 25 kW Applications Induction Hardening Induction Brazing Shrink fitting Melting Innovations Air cooled Self tuning Intelligent digital controls Compact and low weight Dual independent output available Portable and handheld units available Use of flexible cables for easy handling

Small Solid State Power Supplies

  • These power supplies are widely used for a variety of applications requiring high frequency and relatively small power such as:
  • Melting
  • Hardening
  • Brazing
  • Soldering
  • Shrink-fitting etc.
  • Generators are typically aircooled while heat stations have water cooling.
  • Individual heat exchangers or chillers become more and more popular 2kW,150-400kHz power generator with heat station and chiller, Ameritherm Inc.

Dual Output Solid State Power Supplies

  • Dual Output Power Supplies can work in one of the following work modes:
  • Alternating duty
  • Utilizing one output at a time
  • Full power available on each output
  • Common inverter and control system Parallel duty
  • Utilizing both outputs at the same time
  • Output power divided by the output transformers
  • Common inverter and control system Twin Output
  • Two outputs with independent operation and controls
  • Common DC but two inverter sections
  • Outputs could be at different frequencies

Dual Output Solid State Power Supply

  • Controls & Meter Display
  • Power 18 / 25 kW
  • Frequency 10-25 kHz
  • Dual Independent Outputs
  • Hand Held Transformer
  • Flexible Cables Induction Coil Transformer Min ac 18TWIN powersupply, EFD

Power Supply Selection Criteria

  • Frequency
  • Power rating
  • Output voltage range
  • Output current range
  • Load matching capabilities
  • Controls
  • Efficiency
  • Reliability
  • Floor space
  • Easy to operate and maintain
  • Initial cost and repair cost
  • Manufacturers experience and reputation

Load Matching

  • Any electrical energy recipient (bulb, motor, heater etc.) can effectively work at certain frequency, voltage and current values.
  • Example of matching device for cellular phone For electronics and appliances, matching is provided by chargers.
  • Charger:
  • For induction coils there are two matching devices:
  • Transformers voltage matching provide
  • Capacitors compensate (reduce or eliminate) the coil reactive power 120 Volts 50/60 Hz Transformer + Rectifier Phone 6 volts DC

Load Matching with Parallel Circuitry

Generators with parallel circuitry produces relatively “high” output voltage and “low” output current Coils require very high current at “low” voltage Transformer reduces generator voltage to required level Capacitor battery is necessary to compensate reactive power of the coil; it reduces generator current to required value due to “parallel resonance” With the proper load matching power supply could deliver maximum available power to the coil at required voltage and current Generator 800 volts Matching Transformer Inductor 50Volts (example) Tuning Capacitor Generator delivers “high” voltage and “low” current Heat Station Coil demands low voltage and very high current

Load Matching with Series Circuitry

Generator produces “low” output voltage and “high” output current Coils typically require even higher current at low voltage Transformer reduces generator voltage and increases current to required level Capacitor battery is necessary to compensate reactive power of the coil; it reduces transformer primary voltage to required generator output value due to “series resonance” With the proper load matching power supply could deliver maximum available power to the coil at required voltage and current Series Capacitor Generator 800 volts Generator delivers “low” voltage and “high” current Matching Transformer Heat Station Inductor 50Volts (example) Coil demands low voltage and very high current

Heat Station

  • Utilized to match induction coil voltage & current to output voltage & current of generator
  • Heat Station may contain:
  • Matching transformer
  • Tuning capacitors
  • Water cooling circuit components
  • Water pressure gauges and switches
  • Water temperature switch and other monitoring and control devices
  • In small solid state power supplies heat station may be housed inside the power unit for compactness, loss reduction in bus/cables and lower cost

Load Matching Transformers

  • Transformer provides voltage matching of generator output and induction coil. It is similar to a gear box in the car
  • In some cases transformers are necessary for safety (isolation transformers). They prevent line or DC voltage appearance in the coil circuit
  • Some multi-turn coils such as mass heating coils, may not require usage of step-down transformers
  • There are cases when step-up transformers must be used (coil voltage is higher than generator voltage)
  • Low and Middle frequency transformers have magnetic circuit made of laminations Magnetic core Primary winding with taps Secondary winding Layout of variable-ratio transformer Primary winding connections Contact plate of a single-turn secondary winding Variable ratio middle frequency transformer, Jackson Transformer Co.

Capacitor Battery

  • I n induction heating applications, capacitors are used to compensate for the reactive power of the induction coil
  • Capacitor batteries are made of individual capacitors connected in parallel, series or series-parallel
  • Capacitor rating s are capacitance (mkF), voltage, frequency, current, kVAr s, number of taps Common contact Tap8 Tap7 Tap6 Tap5 Tap4 Tap3 Tap2 Tap1 Layout of capacitor with variable capacitance
  • Used also to set up the load resonant frequency (see Glossary)
  • Capacitance must be increased to reduce resonant frequency and vice versa
  • Capacitors may be water-cooled, conduction-cooled or air-cooled Water-cooled oil-filled capacitors for induction heating, High Energy Corp.
  • CELEM conduction-cooled capacitors

Load Matching Procedure

For coil matched all three parameters (frequency, current and voltage) must be in rated range of powersupply. Operating frequency must be close to a resonant frequency of the tank circuitry, which can be calculated as F = 0.16/√(LC), kHz with Step Controlled Parameter One Frequency Voltage Tw o Current Power L – coil inductance in mkH C – capacitance in mkF Recommended Value Inside of Rated Frequency Range Actual Value What to do?

  • Low Reduce capacitance High Add capacitance Both Voltage and High Current should be in the same level of value to have high High power Lower transformer ratio* Maximum required Either increase voltage or current Low Increase transformer ratio* * Possibly it would be necessary to repeat Step 1 after changing the transformer ratio

Power Supply Regulation Modes

  • Many modern power supplies can work in different operation modes, keeping constant output voltage, current or power. These parameters may also be programmed in time. Regulation Mode Power Voltage Current Power regulation Set to regulate Variable until maximum limit is reached Variable until maximum limit is reached Voltage regulation Variable until maximum limit is reached Set to regulate Variable until maximum limit is reached Current regulation Variable until maximum limit is reached Variable until maximum limit is reached Set to regulate When voltage or current reaches maximum limit the generator may turn OFF or continue to operate tracking the limited parameter

Power Connections

  • Generator Heat Station Inductor Generator to Heat Station
  • “Sandwich” buss bars for low frequency high power
  • Litz cables for high frequency low power
  • Water cooled flexible cables for low frequency high power
  • Multiple water cooled flexible cables for high power long distance Heat Station to Coil
  • Water cooled copper buss for heat treating applications
  • Water cooled flexible cables for long distance between heat station and coil especially for forging or melting application

Process Control and Monitoring

  • Energy Coil Voltage Coil Current Water T Part Rotation Coil KVA Monitoring Parameters Scan Speed Frequency Part temperature Quench Flow Quench Temperature Cycle Time

Layout of Induction Circuit with Sensors

  • Induction coil with Flux concentrator Ui Uu Ui – Coil Current Signal Uu –Voltage Signal UB – Flux Density Signal UB

Process Monitors

  • Process monitoring is one of important features of modern installations.
  • the most induction There are many types of monitoring systems from relatively simple coil monitors to sophisticated multifunctional devices.
  • Monitors can provide:
  • Measurement of electrical parameters – current, voltage, power
  • Part temperature control
  • Control of part rotation and scan speed, cooling and quenching conditions etc.
  • Process repeatability control detection of faulty conditions Up to 8 critical parameters Simulation - Digital system may control be monitored in real time and
  • Gathering information for data storage and trend analysis Digital control system Use of monitors improves quality control, facilitate troubleshooting, saves time and costs due to reduction of destructive tests Quality Assurance Monitor, Inductoheat Inc.

Part Handling Systems

  • Different mechanisms are used for different part shapes and size and various types of processes For heat treating the following mechanical systems are usually used:
  • scanners
  • lift and rotate
  • conveyers
  • rotary tables robots Part handling systems may be mechanical, pneumatic or hydraulic Control of heat treating machines may be based on relay logics, PLC or PC In modern lines the whole installation must be under the line master control and stronger requirements are set for process monitoring and reliable coil performance Different part handling and control systems require specific coil types and therefore different opportunities for Fluxtrol concentrator application Installation for scan hardening of rolls with maximum diameter 30”, length 30 feet and weight 30,000lbs.,AjaxTOCCO Magnethermic Corp.

Water Cooling and Quenching

  • Power losses in current carrying components generate heat. When losses are high these components must be water cooled. Generators up to 25 kW may be air-cooled with water-cooled heat stations and coils.
  • Insufficient cooling is the main reason of premature component failure.
  • The following general measures are used to provide reliable cooling:
  • Multiple water circuits to ensure sufficient water flow
  • Input and differential pressure control gauges
  • Water flow rate sensors
  • Temperature sensors in water input line and on various watercooled components
  • Induction coils and transformers require clean water with controlled min (to avoid condensation) and max temperature. Water must have low content of minerals or be demineralized (the best!).
  • Some electronic components may require in addition deionized water to prevent current leakage and component erosion due to electrolysis.
  • See manufacturer requirements!
  • Two or even three water and quench systems may be used in one installation. They may be of open or closed loop type.

Typical Closed Loop Water Cooling System

  • Clean water Filter Heat Exchanger Generator Heat Station & Coil Reservoir Cooling Water Pump

Conclusions

  • There are many installations now to choose from:
  • Wide range of combinations “Power – Frequency”
  • Wide range of types and design
  • Choice of installations adapted to a variety of applications
  • Choice of universal installations with good matching ability in wide frequency range Modern power supplies may be:
  • Small in size and weight
  • Very efficient
  • Easy to operate and maintain
  • Adapted to automated systems Flux concentrators on induction coils can improve the installation performance:
  • Reduce coil power demand or increase production rate
  • Reduce installation size and price
  • Improve efficiency of power supply due to reduced coil current demand
  • Reduce external magnetic fields (shielding!) resulting in:
  • Safer environment for operators
  • No interference to computerized control systems
  • No unintended heating of machine components
  • Eliminate “cross-talking” in multi-generator systems

Questions and Answers

  • An induction Process can be defined by a combination of?
  • Power, Time, Frequency In Induction Heating line power is converted from AC to DC and then back to AC for what reason?
  • To achieve controllable output power at desired frequency What are the 3 main types of power supplies?
  • Motor Generator, Vacuum Tube, Solid State What switching devices are used in solid state power supplies?
  • Thyristors and Transistors What types of power supplies can generates two frequencies simultaneously?
  • Dual Frequency and Twin Output The types of power supplies are?
  • Alternating Duty, Parallel Duty, Twin Output Can line or DC voltage appear on the coil if it’s connected to the power supply through a matching transformer?
  • No What are the 2 devices in induction installations used for coil matching?
  • Transformers and Capacitors A Capacitor Battery is required to compensate for coil ….?
  • Reactive Power The components used to match the coil voltage and current to the output voltage and current of the generator are in the …?
  • Heat Station The taps on a transformer in the heat station are used to?
  • Change transformer ratio and adjust output voltage What coil cooling water parameters it is necessary to control?
  • Temperature, pressure, mineral content

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