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Partial
Discharge in Inverter Driven Medium
Voltage Propulsion Coils
Dr.
Annette von Jouanne, Ph.D., P.E.
- Oregon State University
The
Motor Systems Resource Facility (MSRF) at Oregon State University
(OSU) has been using the DayCor IITM, in collaboration with the
Bonneville Power Administration (BPA), to measure partial discharge
(PD) on medium voltage (4160V) motor coils to help the U.S. Navy
move to the “all-electric” ship. Potential designs for
the all-electric ships will contain medium voltage, 20,000 hp electric
motors, driven by pulse-width modulated (PWM) drive. The Navy needs
to understand the impact of the PWM drives on the electric motors,
with regards to PD.
The test
The
4160V coils are tested in stacked linear induction motor (LIM) laminations
to provide the required mechanical support and representative magnetic
circuit, while allowing convenient handling and testing (Fig. 27).
A pulse generator isused to represent the electric drive, with the
advantage of controllable voltage magnitude, pulse rise-time and
switching frequency to determine the effect of these parameters
on PD.
The test setup includes a stainless steel, double wall oven enclosure
(Fig. 26) to determine the influence of temperature on PD generation.
Significant PD is observed where the coil enters the slots of the
motorette (Fig. 28).
Preliminary
results
A
difference in PD inception levels and pattern was detected between
two tested coil systems.
- The
voltage level has a dominant influence on PD generation, and a compromising
effect of the coil insulations is observed at voltage levels above
PD inception.
- The
voltage rise-time and pulse-width has a combined influence on PD
inception levels.
- The
switching frequency has little affect on PD voltage inception levels,
however higher switching frequencies generate larger amounts of
external PD. --up>
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