Transformer With Internal Load For Furnace
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Solution Overview
Problem
Existing power supplies for electrode furnaces are bulky and inefficient due to large transformers and flexible lead connections, which result in high stray inductance, electromagnetic interference, and power losses, especially when operating at higher frequencies.
Innovation Solution
A transformer with an internal load, where the conductive housing acts as a shield and part of the secondary circuit, eliminating flexible leads and reducing inductance, and using a sliding brush contact for high current connections, allowing for efficient magnetic coupling and easy crucible installation/removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If large mains-frequency power supplies with iron core transformers are used to generate high current, then sufficient heating power is achieved, but the system becomes bulky and difficult to integrate
Solution Approach 1:
The patent combines the transformer core, primary winding, secondary winding, and load (crucible assembly) into a single integrated electromagnetic assembly. The secondary winding is formed by the conductive crucible and electrodes themselves, eliminating the need for separate heavy iron core transformers and flexible lead connections. This merging achieves both compact size and sufficient heating power.
Solution Approach 2:
The patent changes the operating frequency from mains-frequency (50-60 Hz) to higher frequency (e.g., 20 kHz or above). This parameter change allows the use of smaller magnetic cores while maintaining the required power output, directly reducing the transformer size and weight while achieving the necessary heating capability.
2Weight of stationary object
If higher frequency switching supplies are used to reduce transformer size, then compactness is achieved, but stray inductance from flexible leads and electrode inductance creates excessive impedance
Solution Approach 1:
The patent eliminates flexible lead connections by making the load (crucible and electrodes) an integral part of the transformer's secondary winding. The conductive crucible and electrodes form the secondary circuit directly coupled to the transformer core, removing the flexible leads that create stray inductance and simplifying the overall device structure.
Solution Approach 2:
The patent extracts and removes the flexible lead wire connections from the system by designing a configuration where the crucible and electrodes are directly magnetically coupled to the transformer core. This extraction eliminates the source of stray inductance and associated impedance problems at high frequencies.
3Ease of operation
If phase controlled chopper is used to regulate output current, then current control is achieved, but voltage disturbances and poor power factor increase apparent power requirements
Solution Approach 1:
The patent uses pulse width modulation (PWM) or similar periodic switching techniques to control the power delivered to the load. By switching the primary winding on and off at high frequency with controlled duty cycle, the system achieves precise current control while maintaining good power factor and minimizing harmonic distortion, avoiding the problems of phase-controlled choppers.
4Ease of operation
If flexible braided straps are used for high current connection, then mechanical flexibility is achieved, but magnetic field interference with nearby devices occurs
Solution Approach 1:
The patent merges the electrical connection function with the structural components. The crucible and electrodes, which are already present in the furnace, serve as both the load and the electrical conductors. This eliminates the need for separate flexible braided straps, thereby eliminating the source of magnetic field interference while maintaining the ability to remove and replace the crucible.
5Power
If braid conductor is used at switching power supply frequencies, then high current connection is achieved, but skin effect and eddy currents cause extreme heating and oxidation
Solution Approach 1:
The patent combines the load (crucible) with the secondary winding, eliminating the need for separate braid conductors. The crucible, being the actual load, directly receives electromagnetic induction heating from the transformer core, avoiding the problematic braid conductor connections that suffer from skin effect and eddy current heating at high frequencies.
Solution Approach 2:
The patent replaces the mechanical electrical connection system (braid conductors physically connecting transformer to load) with a direct electromagnetic induction system. The transformer core magnetically couples energy directly to the conductive crucible without requiring physical electrical connections, eliminating the heating and oxidation problems of high-frequency braid conductors.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design reduces the size, weight, and electromagnetic emissions of the system, minimizes power losses, and enables operation with higher frequency switching supplies, improving power factor and reducing harmonic distortion.
Implementation Method 1
The transformer core and primary winding are surrounded by a conductive housing or shield that forms a single turn secondary winding magnetically coupled to the primary winding
Implementation Method 2
The transformer using an internal load may be used with higher frequency switching supplies
Implementation Method 3
Current is conducted through the crucible using electrode contacts. The current heats the crucible and any sample material therein
Data Source
AI summary
A transformer assembly (300) for use with an internal load (307) includes a transformer core (323) having a primary winding (405). A first electrode (303) and second electrode (319) are used for contacting an internal load (307). A secondary circuit is formed that includes the first electrode (303), the second electrode (319) and conductors (301,313, 317) positioned between the first electrode (303) and second electrode (319). The transformer assembly (300) is arranged so that the conductors (301, 313, 317) surround the primary winding (405), transformer core (323), the first electrode (301) and second electrode (319). The transformer assembly (300) may be used in an electrode furnace or other high current and voltage applications requiring high efficiency in a small package.