PhD position in FastTrans project - II

SINTEF Energy and NTNU announces a PhD on "High frequency stresses in windings", a study on how connected motor/generator/transformer windings are stressed by fast rise-time transients from high voltage power electronic modules. The PhD will be organized at NTNU's institute for Electric Power Technology.

The challenge
Power electronic converters are central for the effective integration of wind and solar power into the energy system, for electric drives and ship propulsion, and for HVDC systems. Cutting edge wide-bandgap semiconductor power electronic components are rapidly developing toward higher voltage ratings and faster turn on/off times fueled by the development of new materials and the need for reducing energy losses. However, the rapid switching of power converters cause voltage surges with fast rise times that can inflict more severe stress on electrical apparatus than the stress caused by pure sinusoidal voltages. There is a need to investigate and understand how these fast voltage surges affect the electrical insulation in high voltage equipment under the influence of power electronic converters, including how signals propagate into connected motor/generator windings.

Background for PhD task
The pulses generated in the converters become distorted as they propagate along the electrical path due to normal skin and proximity effects in the leads and cables. Since the typical rise time of the emitted voltage fronts are only fractions of a microsecond, they are highly sensitive to any parasitic series inductances or shunt capacitances along the propagation path, e.g. due to connection leads, switching elements and voltage/current measuring devices. When the voltage pulses reach motors or transformers, they become partly reflected and partly transmitted into the motor/transformer windings: voltage doubling may occur. Steep voltage wave fronts cause uneven voltage distributions along the winding that can initiate discharges and damage the initial part of the winding, followed by oscillations in the winding that can potentially be stimulated by repetitive pulses.

The PhD project
This PhD project will study how steep pulses propagate into connected windings of generators, motors and transformers. The PhD will work closely with industry partners to establish test designs and objects of relevance and interest. Topics of interest are:

• Electromagnetic modeling of windings, analytically and numerically (FEM)
• Measurement setup for winding stress investigations
• Validation of modeling by measurement of pulses in windings
• Develop principles for PD detection and stress mitigation

The FastTrans project
The FastTrans project include a wide range of topics: insulation in transformers, generators and motors as well as fast transient pulse propagation. The partners in the project range from manufacturers of power electronic modules (Infinion), high voltage components (ABB), to end user such as broad energy companies (Equinor, Total and Aker BP) and power utilities (Statnett, Statkraft and Elvia).

Contact at NTNU:
Prof Hans Kr. Høidalen