Yingneng Zhou

Online detection of endwinding contamination in industrial motors

This paper discusses a novel online technique to detect moisture and surface tracking of stator end-winding insulation in medium/high voltage AC motors. A novel high sensitivity differential current transformer is used as a sensor for monitoring insulation capacitance and dissipation factor of motors online. A 100 hp, 4160V, 3-phase form-wound induction motor is tested with different contaminants sprayed on its end winding. Partial discharge couplers are also used to monitor partial discharge activity during insulation contamination tests. A comparison of both techniques to detect pre-cursors of motor failure due to end-winding tracking is presented in this paper.

Nano-enabled metal oxide varistors

Zinc oxide based metal oxide varistors (MOV) are widely used electrical surge protection components. The design of modern high power, high-density electronic systems necessitate the need for smaller footprint, higher current density and higher nonlinearity MOVs. Such requirements can no longer be satisfied by commercially available MOVs due to their limited voltage capability, high leakage current and mechanical cracking related reliability issues, most of which are associated with the presence of defects and coarse granularity and lack of uniformity in their microstructures. New formulations and processes have been developed to overcome such limitations. This work has developed nano-enabled MOV compositions that can be sintered at relatively lower temperatures than typical commercial MOVs, but with largely improved I-V characteristics due to refined and uniform sub-micron structures. These nano-enabled MOVs show not only high breakdown strength (1.5 kV/mm) with low leakage current, but also a large nonlinear alpha coefficient > 50 at high fields, a measure of the speed of the transition from the insulating to conducting state and the effectiveness of over-voltage protection. A > 10x increase in breakdown strength compared to commercial MOVs, along with much higher nonlinearity, will enable MOV miniaturization, high voltage surge protection, and open up new areas of application.

Nano-Enabled Metal Oxide Varistors for Surge Protection

Commercial metal oxide varistor (MOV) devices provide a combination of high voltage, peak current, pulse energy absorption, and fast response speed. The non-uniformity and defects, however, may lead to relatively low voltage and energy dissipation, high leakage, low reliability and mechanical cracking. GE global research has been studying NanoMOV technology, and has been developing new formulations and processes. New compositions were invented to enable sintering at much lower temperatures, which exhibits improved I-V characteristics and microstructure uniformity. These compositions not only show high resistance at low fields and breakdown voltage (1-5 kV/mm), but also a large alpha at high fields (50-140). The higher breakdown strength (> 10x) compared to commercially available MOVs will enable MOV miniaturization, high voltage surge protection, and open up new areas of usage.