Konrad Roman Weeber

On-line capacitance and dissipation factor monitoring of AC stator insulation

A new on-line technique for monitoring the insulation condition of ac motor and generator stator windings is proposed. The approach uses a newly developed High-Sensitivity Current Transformer (HSCT) to precisely and non-invasively measure the differential current (e.g., the insulation current) of each phase winding from the motor junction box. Conventional differential current transformers (CT) used for fault protection can be replaced with the new HSCT to measure the winding insulation current with higher sensitivity and accuracy. The HSCT can serve both motor health monitoring and motor protection functions. Presently, indicators for insulation condition such as capacitance (C), dissipation factor (DF), or insulation power factor (PF) are only obtainable off-line. The new approach can provide a low-cost solution for on-line motor insulation condition assessment. Validation of the new HSCT technology was carried out during an accelerated life testing of a 460 V, 100 HP, 1200 RPM form wound induction motor. The motor discussed in this paper was aged at high temperature (255 °C) as the load cycled between 0 % and 200 % every 5 minutes. Although this highly accelerated life test does not represent how a motor ages in service under real operating conditions precisely, the principal goal was to prove the capability of the new HSCT to accurately detect the insulation current and quantitatively monitor motor insulation gradual aging and health. On-line data from the HSCT correlated well with off-line data from a commercial capacitance and DF bridge. It is hoped that the benefits of the on-line motor health monitoring are fully realized and the method extended to other electrical assets as well.

High Speed Permanent-Magnet Motors for the Oil and Gas Industry

Recent years have seen an increase in high-speed electric compression for Oil & Gas applications where high-speed electric motors drive compressors directly without intermediate gears. To date induction machines have been the predominant workhorse of the industry. The permanent-magnet machine technology provides an alternative that promises a highly reliable and robust system design, especially in applications where motor and compressor are fully integrated and share the same process gas environment. This paper provides an update on the recent progress in developing the permanent magnet technology for Oil & Gas applications in which the process gas may contain corrosive elements.Copyright

Advanced permanent magnet machines for a wide range of industrial applications

This paper provides an overview of four distinct applications of advanced permanent magnet machine technologies. It describes the specific application benefits that are accomplished with permanent magnet solutions for Oil&Gas, aviation, automotive, and wind turbine applications. The technology development for these four first-of-a-kind machines is presented, each of which advancing the state of the art in power density, torque density, or speed.

AC losses in a high temperature superconducting generator

As part of the DOE-SPI funded project a commercial HTS utility-size generator is being developed based on GEs iron core superconducting generator technology. The iron core concept has significant advantages over air core designs. The rotor consists of a cold superconducting field coil and coil supports and a warm iron core, which takes the torque and transmits to the shafts. Heat load due to AC losses in the cold mass of the rotor are a key design constraint. Analyses have been performed both at the component and system levels. AC loss tests have been conducted on an HTS generator. This paper presents and discusses the analytical and test results.

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.

A high-speed HVDC breaker topology with integral voltage-changing capability

GE Global Research center has developed a system topology that has been validated experimentally by constructing hardware prototypes, to combine the HVDC breaker and transformer functions in a single system. This is implemented with a resonant converter at high frequency to minimize physical footprint, and to maximize efficiency.

Active fault-current foldback control in thyrister rectifier for DC shipboard electrical system

Turbine-generator set integrated with the thyristor-based rectifier system provides the dc power for the emerging medium voltage dc (MVDC) shipboard electrical distribution systems. Active foldback via firing-angle control can be implemented in the thyristor rectifier to protect the primary distribution bus, thereby possibly eliminating the bulky dc circuit breakers. This paper presents the detailed modeling and design of the active foldback control by considering multiple impact factors, like dc inductor, control bandwidth, generator frequency, and rectifier topologies. A new foldback control method is proposed to minimize the fault isolation time. The complete design of fault detection, fault current foldback, and post-fault recovery is proposed and simulated for the breakerless MVDC architectures.

Online capacitance and dissipation factor monitoring of AC motor stator insulation

A new on-line technique for monitoring the insulation condition of AC motor stator winding is proposed. The approach uses a newly developed, High-Sensitivity Current Transformer (HSCT) to precisely and non-invasively measure the differential current (e.g., the insulation leakage current) of each phase winding from the motor junction box. Conventional differential current transformers (CT) used for fault protection can be replaced with the new HSCT to measure the winding insulation leakage current with higher sensitivity and accuracy. The HSCT can serve both motor health monitoring and motor protection functions. Presently, indicators for insulation condition such as capacitance (C), dissipation factor (DF), or insulation power factor (PF) are only obtainable off-line. The new approach can provide a low-cost solution for on-line motor insulation condition assessment. Validation of the new HSCT technology is carried out during an accelerated life testing of a 460 V, 100 HP, 1200 RPM form wound induction motor. The motor used in this work was aged at high temperature (255 °C) as the load cycled between 0 % and 200 % every 5 minutes.

Active Fault-Current Foldback Control in Thyristor Rectifier for DC Shipboard Electrical System

Next generation shipboard power system is moving toward medium-voltage dc (MVdc) architecture. Thyristor rectifier integrated turbine-generator system provides the dc power to the MVdc distribution bus. Active foldback via firing-angle control can be implemented in the thyristor rectifier to protect the system from short-circuit fault, thereby potentially eliminating the bulky dc circuit breakers. This paper presents the detailed modeling and analysis of the active foldback control by considering multiple impact factors, like dc inductor, control bandwidth, generator frequency, and rectifier topologies. The maximum fault-current level can be estimated, and several different foldback methods are compared for the purpose of minimizing the fault isolation time. The complete design of fault detection, fault-current foldback, and postfault recovery is proposed and simulated in a breakerless MVdc architecture.

Advancements in high power high frequency transformer design for resonant converter circuits

Medium and high frequency converters are gaining increasing interest for high power applications such as renewable energy and dc grids. Medium and high frequency transformers are an essential component in such converters. Advancing resonant converters to higher power levels challenges the transformer design in multiple aspects including power levels, switching frequency, ac and dc voltages insulation requirements and parasitic parameters. This paper presents design methods and recommendations for transformers that accomplish an industry-leading combination of power levels in the MW-class resonant frequencies up to 20kHz, operating AC voltages up to 5 kV, and dc offset voltages up to 300 kV. Design examples and test results of prototypes are presented along with results from applications where the transformers are integrated within high frequency converters.