Sylvain Candolfi

Finite-Element-Based Optimal Design Approach for High-Voltage Pulse Transformers

This paper presents an optimal design methodology of monolithic high voltage pulse transformers based on the direct 2D FEA identification of the electrical equivalent circuit parameters. This method is applied to the preliminary optimal design of the monolithic high voltage pulse transformer for the future CLIC modulators under study at CERN. The feasibility of such a transformer with tight specifications is demonstrated. The predicted performances obtained with the direct 2D FEA optimization process is validated by 3D FEA simulation.

Finite Elements based optimal design approach for high voltage pulse transformers

Summary form only given. High voltage pulse transformers are widely used in klystron modulators. For these topologies, the quality of the modulator output voltage is strongly dependent on the pulse transformer performance. An optimal design process of such transformers is a necessity, particularly when the specifications of the output voltage are tight such as in the case of the CLIC klystron modulator under study at CERN [1]. Using a sufficiently accurate analytical model to optimize a high voltage transformer design will yield the most efficient design process. The accuracy of the design can then be verified with a Finite Element Analysis as a final check. However in the case of high voltage transformers, it can be difficult to obtain an analytical model that is sufficiently accurate particularly due to effects of parasitic capacitance. As such, it would be desirable to find an efficient method to use only Finite Element Analysis to find an optimal design. This paper presents a new design approach for high voltage pulse transformers, based on a FEA dimensioning model only. For each iteration of the non-linear optimization process, the transformer parameters used to compute the objective and constraints functions are directly derived from the 2D FEA dimensioning model. Programming techniques to speed-up the FEA model evaluation for each iteration of the optimization procedure are presented.

Efficient parametric identification method for high voltage pulse transformers

This paper presents a new identification method for a pulse transformer equivalent circuit. It is based on a analytical approximation of the frequency-domain impedance data derived from a no-load test with open-circuited secondary winding and only requires measurements of primary current and voltage without phase data. Compared with time consuming and complex methods based on off-line non-linear identification procedures, this simple method also gives an estimation of the error on the identified parameters. The method is validated on an existing pulse transformer.

Optimization of a Shared Tailrace Channel of Two Pumped-Storage Plants by Physical and Numerical Modeling

Pump and turbine operations lead to head losses in the tailrace channel. Pumping discharge may be limited due to potential air entrainment into the pump shaft when the downstream reservoir is at its lowest level and the head losses are too high. Regarding turbine operations, the limit is given by the maximum level in the Pelton turbine chamber due to high water level in the downstream reservoir and head losses. The rapid starting and stopping of turbines and pumps lead to highly unsteady flow in the tailrace channel system of the two connected hydropower plants. Negative and positive surges may lead to similar consequences as for stationary operations such as sudden air entrainment into the pump shaft and submerging of the Pelton runner under operation. Therefore, flow and head losses test were conducted on a physical model at 1:30 scale together with numerical simulations using FLOW-3D. On-site measurement of the existing power plant allows validating the results. Representative and extreme operational scenarios have been simulated; the main results are discussed and presented.

FEA identification of high order generalized equivalent circuits for MF high voltage transformers

This paper presents a specific methodology to derive high order generalized equivalent circuits from electromagnetic finite element analysis for high voltage medium frequency and pulse transformers by splitting the main windings in an arbitrary number of elementary windings. With this modeling approach, the dynamic model of the transformer over a large bandwidth is improved and the order of the generalized equivalent circuit can be adapted to a specified bandwidth. This efficient tool can be used by the designer to quantify the influence of the local structure of transformers on their dynamic behavior. The influence of different topologies and winding configurations is investigated. Several application examples and an experimental validation are also presented.

Hybrid design optimization of high voltage pulse transformers for Klystron modulators

This paper presents a generic hybrid optimization methodology based on space mapping techniques for the design of various high voltage pulse transformer structures used in klystron modulators. It is using two dimensioning models with different levels of complexity: a coarse model based on 2D FEA less accurate but cheaper to evaluate and a fine 3D FEA model more accurate but time consuming. A specific correction mechanism is applied to align the 2D FEA dimensioning model with the more accurate 3D FEA dimensioning model. With a suitable selection of the correction factors, the convergence of this hybrid optimal design methodology is obtained with a limited number of time consuming 3D FEA simulations. The method is applied to the optimal design of a monolithic high voltage pulse transformer for the CLIC klystron modulator. The influence of the klystron operating voltage on the size of the optimal pulse transformer is evaluated with the proposed design methodology.

Hybrid design optimization of high voltage pulse transformers for klystron modulators

This paper presents a generic hybrid optimization methodology based on space mapping techniques for the design of various high voltage pulse transformer structures used in klystron modulators. It is using two dimensioning models with different levels of complexity: a coarse model based on 2D FEA less accurate but cheaper to evaluate and a fine 3D FEA model more accurate but time consuming. A specific correction mechanism is applied to align the 2D FEA dimensioning model with the more accurate 3D FEA dimensioning model. With a suitable selection of the correction factors, the convergence of this hybrid optimal design methodology is obtained with a limited number of time consuming 3D FEA simulations. The method is applied to the optimal design of a monolithic high voltage pulse transformer for the CLIC klystron modulator. The influence of the klystron operating voltage on the size of the optimal pulse transformer is evaluated with the proposed design methodology.

HV pulse transformer generalized equivalent circuit identification based on detailed mechanical structure

A modeling methodology of high-voltage pulse transformers based on high-order generalized equivalent circuits (HOGECs) identified from 3-D finite-element analysis is applied to a prototype, and experimental validation tests are performed. The identified HOGEC of the prototype is used to investigate the influence of the detailed mechanical structure and the local winding configuration on the pulse transformer operation performance.

Evaluation of insulation systems for the optimal design of high voltage pulse transformers

This paper presents a study for the design of the insulation systems of high voltage pulse transformer based on experimental tests and numerical simulations. Data of high voltage tests on solid and liquid insulation materials are presented and discussed. The understanding of each part of the insulation is supported by electrostatic fields simulations.