Modular Excitation System for Stator Core Testing
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Solution Overview
Problem
High-energy testing of stator cores in electric generators faces challenges due to high-voltage and high-current requirements, which pose safety hazards and are difficult to achieve, especially when the stator core saturates, leading to non-linear relationships between magnetic flux density and excitation current.
Innovation Solution
A modular excitation system comprising multiple excitation modules with AC-power supplies, capacitors, and synchronized windings, where the power supply acts as a current source with high output impedance, and capacitors provide rapid current adjustments to manage saturation effects, allowing for uniform magnetic flux distribution and reduced voltage hazards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-power supply and high-power excitation winding are used to achieve high magnetic flux density (1.0-1.5 Tesla), then the testing effectiveness is improved, but the voltage and current requirements increase to several kV and several kA, creating safety hazards and operational difficulties
Solution Approach 1:
The excitation winding is divided into multiple independent windings (first excitation winding and second excitation winding) that can be controlled separately. Each winding is connected to its own power supply, allowing the system to achieve the required magnetic flux density through coordinated operation of multiple lower-power components rather than a single high-power component, thereby reducing voltage and current safety hazards.
2Reliability
If the excitation current is increased to overcome stator core saturation (B ≥ 1.3 Tesla), then the magnetic flux density can be maintained, but the current increases faster than linearly and becomes practically unattainable due to lack of adequate inductive current source
Solution Approach 1:
The excitation system is segmented into multiple windings with separate power supplies. When the stator core saturates, the additional current requirements can be distributed across multiple power supply units rather than requiring a single massive current source. This modular approach makes it practically attainable to supply the required current even under saturation conditions.
Solution Approach 2:
Multiple excitation windings are combined to produce the total required magnetic flux density. The first and second excitation windings work together, with their currents coordinated through a synchronization unit, to achieve the cumulative effect needed to overcome core saturation without requiring any single component to handle unattainable current levels.
3Stability of the object's composition
If a single excitation winding with symmetric arrangement is used, then the magnetic flux density distribution is more uniform, but the inductive reactive power requirement increases to several MVAr, which cannot be supplied by available power sources
Solution Approach 1:
The single high-power excitation winding is segmented into multiple lower-power windings, each connected to its own power supply. This reduces the reactive power burden on any single power source while maintaining the symmetric arrangement needed for uniform flux distribution through coordinated operation of the segmented windings.
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
The modular system effectively mitigates high-voltage and high-current issues, enabling safe and efficient high-energy testing by synchronizing currents and using capacitors to manage rapid changes in excitation current, thus overcoming the limitations of existing high-energy testing methods.
Implementation Method 1
A high-energy test requires a magnetic flux density of about 1.0 - 1.5 Tesla to be induced in the stator core. The flux density alternates with time in a way similar to the flux density in service.
Implementation Method 2
The above inductive current can, at least in part, be compensated through a capacitor. That capacitor would be connected in parallel to the excitation winding.
Implementation Method 3
The symmetrical arrangement of the excitation winding yields a more uniform distribution of the magnetic flux density through the core.
Implementation Method 4
They may result in significant eddy currents circulating between the faulted sheets. The losses due to such eddy currents may result in iron melting and even in thermal failure of the electrical insulation of adjacent stator bars.
Implementation Method 5
The losses due to such eddy currents may result in iron melting and even in thermal failure of the electrical insulation of adjacent stator bars.
Data Source
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AI summary
An excitation device for high-energy tests of stator cores (5) of electric generators or motors, the excitation device comprises one or more excitation modules, each excitation module comprises an excitation winding (1-4) and a power supply (10-13) and is configured to drive an excitation current through the excitation winding (1-4), the excitation current through each excitation winding (1-4) contributing to the overall excitation of the stator core (5), wherein an excitation module further comprises a capacitor (6-9), and the power supply (10-13) of said excitation module acts as current source at its output.