Stefan Grubic

A Survey on Testing and Monitoring Methods for Stator Insulation Systems of Low-Voltage Induction Machines Focusing on Turn Insulation Problems

A breakdown of the electrical insulation system causes catastrophic failure of the electrical machine and brings large process downtime losses. To determine the conditions of the stator insulation system of motor drive systems, various testing and monitoring methods have been developed. This paper presents an in-depth literature review of testing and monitoring methods, categorizing them into online and offline methods, each of which is further grouped into specific areas according to their physical nature. The main focus of this paper is on testing and monitoring techniques that diagnose the condition of the turn-to-turn insulation of low-voltage machines, which is a rapidly expanding area for both research and product development efforts. In order to give a compact overview, the results are summarized in two tables. In addition to monitoring methods on turn-to-turn insulation, some of the most common methods to assess the stators phase-to-ground and phase-to-phase insulation conditions are included in the tables as well.

Using PWM-Induced Transient Excitation and Advanced Signal Processing for Zero-Speed Sensorless Control of AC Machines

The sensorless control of induction machines, particularly for operation at low speed, has received significant attention in recent years. To realize a field-oriented control of AC machines that is able to work at zero speed, the most commonly used methods are either sensor-based models or transient-signal-excitation methods. The major disadvantage of present signal-injection methods is that they are intrusive to pulsewidth modulation (PWM). An additional switching sequence has to be embedded in the control that will cause a torque and current ripple. In order to overcome these problems, a new flux-estimation algorithm that uses the phase current derivative to extract the flux-position information is presented. In contrast to previously introduced methods, this new approach operates without additional transient excitation of the machine and requires only fundamental-wave excitation using standard PWM or slightly modified PWM. Furthermore, only the current response in the two active states of PWM is used. This makes it possible to use sensorless control for the whole speed range including overmodulation and removes the distortion and parasitic influence of the zero switching states during the estimation of the flux. Experimental results are presented to validate the applicability of the presented approach.

A High-Performance Electronic Hardware-in-the-Loop Drive–Load Simulation Using a Linear Inverter (LinVerter)

In modern drive systems, inverters are a fundamental component. To improve the performance of this component, ensure their operability, and check their reliability, motor-load testbeds are used during the process of development. Unfortunately, there are several drawbacks and disadvantages inherent to conventional motor-load testbeds. In order to avoid these problems, a new concept for a hardware-in-the-loop-based electronic testbed has been developed. A well-defined second inverter in combination with a mathematical model of the machine-load combination is used to replace the conventional test setup. Different machine-load combinations can be easily simulated with one system by simply changing the mathematical models. This paper shows the system topology, analyzes the components of the testbed, and presents the experimental results that verify the feasibility and capability of the method proposed.

Reduced Rare-Earth Flux-Switching Machines for Traction Applications

There has been growing interest in electrical machines that reduce or eliminate rare-earth material content. Traction applications are among the key applications where reducing cost and, hence, reduction of rare-earth materials are key requirements. This paper will assess the potential of different variants of flux-switching machines (FSMs) that either reduce or eliminate rare-earth materials in the context of traction applications. Two designs use different grades of dysprosium-free permanent magnets (PMs), and the third design is a wound-field variant that does not include PMs at all. A detailed analysis of all three designs in comparison to the required set of specifications will be presented. The key opportunities and challenges will be highlighted. The impact of the high pole-count/frequency of the FSMs will also be evaluated. Experimental results for one of the designs with dysprosium-free PMs will also be presented.

A survey of testing and monitoring methods for stator insulation systems in induction machines

A breakdown of the electrical insulation system causes catastrophic failure of the electrical machine and brings large process downtime losses. To determine the conditions of the stator insulation system of motor drive systems, various testing and monitoring methods have been developed. This paper presents an in-depth literature review of more than 20 existing methods, including the most common methods to assess the phase-to-ground, phase-to-phase, and turn-to-turn insulation conditions. The methods are categorized into as online and offline methods, each of which are further grouped into specific areas according to their physical nature. The paper focuses on turn-to-turn insulation testing and monitoring of low-voltage machines, which is a rapidly expanding area for both research and product development efforts. Finally, a new approach to online monitoring of turn-to-turn insulation faults for low-voltage induction motors is recommended.

A new concept for online surge testing for the detection of winding insulation deterioration

A breakdown of the electrical insulation system causes catastrophic failure of the electrical machine and brings large process downtime losses. Preventive maintenance and online monitoring are some of the methods to improve reliability and reduce unscheduled downtime. One of the main reasons for failure is the breakdown of the stator insulation. The offline surge test is the most commonly used offline test to assess the condition of the turn insulation. There is no online monitoring method that is applicable to low voltage machines and has the same capabilities as the surge test. This paper introduces new concepts to implement an online surge test. The possibilities and limitations of the online surge test are presented as well as simulation and experimental results to validate the concepts.

Robust non-permanent magnet motors for vehicle propulsion

There has been growing interest in electrical machines that reduce or eliminate rare-earth material content. Traction applications are among the key applications where reducing cost and hence reduction or elimination of rare-earth materials is a key requirement. This paper will assess the potential of three non-permanent magnet options in the context of vehicle propulsion applications: 1) a conventional Switched Reluctance Machine (SRM), 2) a DC-biased Reluctance Machine (DCRM) and, 3) a Wound Field Flux Switching Machine (WFFSM). The three machines were designed to achieve the hybrid vehicle traction requirements of 55kW peak and 30kW continuous over a speed range going from 2800rpm to 14000rpm. Their performance will be compared and the key opportunities and challenges will be highlighted. Preliminary experimental results for the DCRM will be presented.

Online Surge Testing Applied to an Induction Machine With Emulated Insulation Breakdown

A breakdown of the electrical insulation system can cause catastrophic failure of the electrical machine and bring large process downtime losses. Preventive maintenance and online monitoring are some of the methods to improve reliability and reduce unscheduled downtime. The offline surge test is the most commonly used offline test to assess the condition of the turn insulation. There is no online monitoring method that is applicable to low-voltage machines and has the same capabilities as the surge test. This paper shows how to conduct a surge test online on 460-V/230-V rated induction machines that are connected in the low-voltage configuration. The required hardware, test procedures, and evaluation of the results are described. Instead of using a bolted short to emulate the insulation breakdown, a new approach is used for the experimental validation. The arcing is emulated either by using an insulation sample that breaks down at a certain test voltage or by using a circuit that emulates the breakdown.

Reduced rare-earth flux switching machines for traction applications

There has been growing interest in electrical machines that reduce or eliminate rare-earth material content. Traction applications are among the key applications where reducing cost and hence reduction of rare-earth materials is a key requirement. This paper will assess the potential of different variants of flux-switching machines that either reduce or eliminate rare-earth materials in the context of traction applications. Two designs use different grades of Dysprosium-free permanent magnets and the third design is a wound-field variant that does not include permanent magnets at all. Detailed analysis of all three designs in comparison to the required set of specifications will be presented. The key opportunities and challenges will be highlighted. The impact of the high pole-count/frequency of the flux-switching machines will also be evaluated. Preliminary experimental results for one of the designs with Dysprosium-free permanent magnets will also be presented.

Investigation on surge testing for winding insulation fault detection in an online environment

A breakdown of the electrical insulation system causes catastrophic failure of the electrical machine and brings large process downtime losses. Preventive maintenance and online monitoring are some of the methods to improve reliability and reduce unscheduled downtime. One of the main reasons for failure is the breakdown of the stator insulation. The offline surge test is the most commonly used offline test to assess the condition of the turn insulation. There is no online monitoring method that is applicable to low voltage machines and has the same capabilities as the surge test. This paper investigates the applicability of the surge test in an online environment and shows possibilities and limitations of the online test. The investigtion is verified by experimental results.