Mark Allan Juds

Dynamic stress in magnetic actuator computed by coupled structural and electromagnetic finite elements

Mechanical stress versus time is computed by coupled electromagnetic and structural finite element analyses. The theory of the stress computations, including Maxwell stress tensors, is presented. The method is applied to an actuator driven by a step AC voltage. After verifying the calculated current and motion, the computed stress distribution is shown to depend on the placement of the nonlinear springs moved by the actuator.

AC contactor motion computed with coupled electromagnetic and structural finite elements

An alternating current relay contactor is analyzed using coupled electromagnetic and structural finite elements, The structural finite elements include a nonlinear spring for the relay contact arms. The electromagnetic finite elements include 2D nonlinear elements for the steel laminations and aluminum shading ring, as well as 1D and 0D elements for the voltage-driven coil windings and end-turn inductance. The computed current and motion of the actuator are in good agreement with measurements.

A study of ignition time for materials exposed to DC arcing in PV systems

This study examines the factors that influence the time to first ignition and burn through for materials, found in PV power systems, when exposed to DC arcing. Materials of interest include PV wire insulation, connectors, metal conduits, and insulation. The most important factors for the time to ignition are the power density absorbed and the material threshold. The most important factors for burn through are power density, heat released by polymers, thickness and flame retardant chemistry. Ignition occurs when the arc power and time of exposure are sufficient to produce localized heating that exceeds material thresholds. Data shows that arcs as low as 200 watts, at a radius of 10 mm, will ignite most plastics in 4 seconds. A radiation model is presented to calculate the absorbed power density. Times to the first ignition, re-flash, burn rate and flame retardants are factors in the prediction. The ratio of arc power density to the peak heat release rate of polymers is used in the burn through time prediction. A burn through time vs. arc watt correlation has been established. Burn through time is sensitive to the power density absorbed by the exposed material and includes geometry factors and material thresholds. Radiated power density is driven by arc power density. Arc power is determined by arc current, and arc gap. Ignition time & burn through estimates can be used to establish an AFCI trip curve to reduce the risk of fires due to arcing.

Thermal Management of a Soft Starter: Transient Thermal Impedance Model and Performance Enhancements Using Phase Change Materials

Adverse effects of starting-torque transients and high in-rush currents in induction motors are typically mitigated by employing electronically controlled soft starting voltages through silicon-controlled rectifiers (SCRs). However, the heat dissipation in the soft starter must be carefully managed in the design of motor drives. The objective of this study is both to address the heat dissipation in the soft starter by implementing analytical solutions to the heat diffusion equations inside the soft starter, and to investigate the use of a phase change material (PCM) based heat sink for thermal management of the device. The analytical modeling approach is, however, general, and can be applied to the solution of a range of thermal problems in power electronics. The transient analytical thermal model, based on the thermal quadrupole approach, allows a determination of the transient performance of a soft starter by evaluating the thyristor junction temperature. Predictions from the model are first compared to results obtained using a coupled thermal and electrical model based on a resistance/capacitance network approach. Experimental results obtained with the soft starter connected to a low-voltage 200 hp induction machine are then used to validate the model. Additionally, the performance improvement resulting from the use of a hybrid heat sink (plate fin heat sink immersed in a PCM) is evaluated and compared to a conventional air-cooled heat sink without a PCM under identical conditions.

A Thermal Quadrupole-Based Model for Heat Diffusion in a Multilayered System: Application to Determination of Transient Performance of a Medium-Voltage Soft Starter

Adverse effects of starting-torque transients and high inrush currents in induction motors are typically mitigated by employing electronically controlled soft starting voltages through silicon controlled rectifiers (SCRs). However, the heat dissipation in the soft starter must be carefully managed in the design of motor drives. The objective of this study is to address the heat dissipation in the soft starter by implementing analytical solutions to the heat diffusion equations inside the soft starter. The transient analytical thermal model allows an estimation of the thermal system transfer function from the transient thermal impedance curve, and can be incorporated into a dynamic system model in order to determine the transient performance of a soft starter by evaluating the thyristor junction temperature for different switching time profiles, motor and load combinations, and “ON/OFF” cycles. Predictions from the model are validated by comparing against a coupled thermal and electrical model using a resistance/capacitance network approach.Copyright

Optimized design for three port transformer considering leakage inductance and parasitic capacitance

The power flow capability of high frequency phase-shifted dc-dc converter depends on transformer leakage inductance and switching frequency. The design of multi-port transformer requires optimized volume and losses with required leakage inductance for rated power flow. Use of fast-switching SiC devices also demand low inter-winding parasitic capacitance for reduced common mode current. The work in this paper focuses on loss-volume optimized design of three port high frequency transformer integrating PV and Energy Storage(ES) based on leakage inductance and parasitic capacitance model. Two laboratory prototypes of 50kHz and 100kHz operating frequency have been designed to verify the leakage and parasitic capacitance model based design and the losses of the transformers.