Toroidal Transformer Electrostatic Shielding for Impulse Test Compliance
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Solution Overview
Problem
Toroidal transformers fail to meet specifications for power distribution systems due to issues with impulse tests, thermal performance, and electromagnetic forces, leading to inefficiencies and potential failures.
Innovation Solution
The implementation of electrostatic shielding in toroidal transformers, where the core is electrically connected to the high-voltage winding, acts as an electrostatic shield, reducing electromagnetic interference and allowing for a gapless construction that minimizes no-load losses and enhances thermal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If toroidal transformers are designed with traditional insulation systems, then manufacturing is simpler, but they fail to pass impulse tests and exhibit unacceptable failure under lightning strikes
Solution Approach 1:
An electrostatic shield is introduced as an intermediary component between the high voltage winding and the core. This shield, connected to ground potential, mediates the electric field distribution during impulse tests, preventing direct breakdown between the high voltage winding and core, thereby enabling the transformer to pass impulse tests while maintaining a manageable insulation system
Solution Approach 2:
The insulation system is segmented into multiple functional zones: the electrostatic shield creates a separate potential zone between the high voltage winding and core, dividing the insulation requirements into manageable sections. This segmentation allows each zone to be optimized independently for impulse test performance
2Loss of energy
If air gaps are present in the core, then assembly is easier, but magnetizing current and no-load losses increase
Solution Approach 1:
The mechanical adjustment mechanism for core gaps is replaced by an electrostatic field-based solution. Instead of mechanically closing gaps to reduce losses, the electrostatic shield compensates for the effects of gaps by controlling electric field distribution, allowing gaps to remain for ease of assembly while minimizing their negative impact on no-load losses
Solution Approach 2:
The electrical parameters of the core assembly are changed by introducing the electrostatic shield, which modifies the electric field distribution and potential gradients. This parameter change allows the system to tolerate larger physical gaps while maintaining acceptable no-load loss levels through electrostatic field management
3Object-affected harmful factors
If the core is electrically floating, then insulation requirements are reduced, but electromagnetic interference increases
Solution Approach 1:
The electrostatic shield performs multiple functions simultaneously: it provides electromagnetic shielding to reduce interference, establishes a controlled potential reference for the floating core, and manages electric field distribution. This multi-functionality allows the core to remain electrically floating with reduced insulation requirements while actively combating electromagnetic interference
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 solution enables toroidal transformers to pass impulse tests, reduce no-load and load losses, and achieve higher flux density, making them suitable for replacing traditional transformers in distribution systems with improved efficiency and reduced material usage.
Implementation Method 1
the core is electrically connected to the high-voltage winding, acts as an electrostatic shield, reducing electromagnetic interference
Implementation Method 2
Toroidal transformers have typically exhibited unacceptable failure when subjected to the 'impulse test'... The transformer includes a core having a laminated metal core wound into a coil forming a plurality of layers
Data Source
AI summary
Toroidal transformers are currently used only in low-voltage applications. There is no published experience for toroidal transformer design at distribution-level voltages. Toroidal transformers are provided with electrostatic shielding to make possible high voltage applications and withstand the impulse test.