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Design and Optimization of Air-Core High Temperature Superconducting (HTS) Pulse Transformer for Series Type Hybrid Circuit Breaker (S-HCB)
Title
Design and Optimization of Air-Core High Temperature Superconducting (HTS) Pulse Transformer for Series Type Hybrid Circuit Breaker (S-HCB)
Creator
Alashi, Mahmoud
Date
2024
Description
DC power has been gaining much attention and traction due to its superior benefits over AC power in terms of better system stability, better...
Show moreDC power has been gaining much attention and traction due to its superior benefits over AC power in terms of better system stability, better transmission efficiency, and compatibility with the modern DC electric loads. However, DC fault protection is a major challenge in DC power systems due to the lack of current zero crossings that are necessary for arcless current interruption. The reported Solid State Circuit Breakers (SSCB) suffer from the high conduction power loss and the cost of the cooling systems of the power switches. The Hybrid Circuit Breakers (HCBs) offer low conduction loss in the normal operation but a slow fault interruption response due to the complex mechanical switching mechanism.Recently, a new class of circuit breakers termed Series Type Hybrid Circuit Breaker (S-HCB) was proposed to achieve a µs-scale fault interruption faster than the fast-acting SSCB with ultra-low power loss in the normal operation like an HCBand minimal cost and weight. The S-HCB uses a series pulse transformer to inject a transient counter pulse voltage (higher than the main DC voltage) to bring the fault current down to zero within 10µs and maintain the fault current at near zero for 250µs until the series mechanical switch opens arclessly. The transformer secondary winding made of High Temperature Superconducting (HTS) material carries the nominal 100A DC current offering ultra-low power loss in the normal operation.This thesis discusses the design and optimization of a unique HTS air-core pulse transformer for the S-HCB operating in the Liquid Nitrogen (LN2) under cryogenic environment. The HTS pulse transformer is a key component playing a fundamental role in the S-HCB operation and therefore must be uniquely designed to meet the system level S-HCB performance within a set of constraints defined by the cryogenic environment conditions. Unlike in the prior-art HTS AC power transformers,the HTS windings of the new pulse transformer carries a DC load current without any concerns on AC power losses. On the other hand, the S-HCB operation imposes several unique requirements on the HTS pulse transformer design, including an exceedingly large pulse current up to a few kA, potentially causing core saturation, loss of superconductivity (quenching) of the HTS winding, or extremely high mechanical stress. The HTS transformer is comprehensively modeled using COMSOL. The FEM model of the transformer is coupled with a power electronic circuit to perform a time domain mixed mode simulation and optimization of S-HCB.A 10kV/150A HTS transformer prototype is built and LCR parameters are extracted and found consistent with the simulated values. The S-HCB with the HTS transformer is experimentally tested up to 7kV/150A to validate the design. Experimental results show a fault current of 150A was forced down to zero within 7µs and remains as a small ripple current for 200µs before a series mechanical switch opens arclessly.
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