S. Grubic

Georgia Institute of Technology, Atlanta, GA, United States

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Publications (12)22.84 Total impact

  • Source
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    ABSTRACT: 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 the reliability and to reduce unscheduled downtime. One of the main reasons for the failure of the machine is the breakdown of the stator turn 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 the simulation and experimental results, to validate the concepts.
    IEEE Transactions on Industry Applications 11/2011; · 1.67 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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. One of the main reasons for the 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 shows how to conduct a surge test online. The required hardware and the test procedures are described. A new test setup that emulates the arcing due to a weak turn insulation is used to validate the technique proposed.
    IEEE Transactions on Industry Applications 01/2011; 49(3). · 1.67 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The surge test is a well-known offline method to determine the integrity of the turn-to-turn insulation of coils as they are found in transformers or induction machines. There are different methods used to evaluate the waveform obtained during the surge test. These methods include the examination of the zero crossings of the waveform, i.e., its ringing frequency, the differential error area ratio (EAR) also known as the pulse-to-pulse EAR (P-P EAR) or a corona evaluation. A semi-analytical derivation of the P-P EAR under healthy and faulty conditions as well as a definition of the frequency and EAR sensitivity is given in this paper to gain more insight into the evaluation of the ringing frequency and the P-P EAR. The derivations shown in this paper are supported by simulations and experimental results.
    Electric Machines & Drives Conference (IEMDC), 2011 IEEE International; 01/2011
  • [Show abstract] [Hide abstract]
    ABSTRACT: The surge test is a well-known offline method to determine the integrity of the turn-to-turn insulation of coils as they are found in transformers or induction machines. There has been a lot of research about various topics related to surge testing like the risk to the health of the turn insulation, the influence of the voltage rise time or the applicability to an operating machine. One important aspect to any diagnostic method is the emulation of the fault condition to prove the feasibility of the diagnostic method. This work suggests a low cost and easily reproducible method to emulate the breakdown of the turn insulation during a surge test, which can be used to experimentally validate the surge test and gain a better insight on the test.
    Electric Machines & Drives Conference (IEMDC), 2011 IEEE International; 01/2011
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Energy Conversion Congress and Exposition (ECCE), 2010 IEEE; 10/2010
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    ABSTRACT: 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.
    IEEE Transactions on Industrial Electronics 05/2010; · 6.50 Impact Factor
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    ABSTRACT: 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.
    IEEE Transactions on Industrial Electronics 02/2010; · 6.50 Impact Factor
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    ABSTRACT: This paper proposes an adaptive noise-cancellation (ANC) method for detecting incipient bearing faults, i.e., generalized roughness, with a special focus on dynamic motor operations, including variable-load and variable-frequency conditions. The correlated frequency components in the motor stator current are treated as ldquonoiserdquo to the bearing fault detection and estimated using an adaptive Wiener filter. These estimated noise components are then subtracted from the original motor current and the remaining noise-cancelled current is normalized as the bearing fault index. The Wiener filter parameters are updated for each algorithm iteration, making the calculation of the wideband noise in the motor current (i.e. the bearing fault signatures), and thus adapt to changes of load and frequency, i.e. are independent of load and frequency variations. The feasibility of the proposed method has been primarily validated from experimental results of multiple bearings for different operating conditions. The operating conditions tested in this paper include constant load/frequency, variable load and variable frequency.
    Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE; 10/2009
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE; 10/2009
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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 stator's phase-to-ground and phase-to-phase insulation conditions are included in the tables as well.
    IEEE Transactions on Industrial Electronics 01/2009; · 6.50 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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. In this paper a new evaluation algorithm based on phase current derivation to extract the flux position information is presented. This method is working without additional transient excitation of the machine and requires only the fundamental wave excitation using standard PWM or a slightly modified PWM. Only the current response in the active states of the PWM is exploited, to avoid parasitic influences during the zero switching state. Measurement results are presented to validate the applicability of the presented approach.
    Electrical Machines, 2008. ICEM 2008. 18th International Conference on; 10/2008
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Condition Monitoring and Diagnosis, 2008. CMD 2008. International Conference on; 05/2008

Publication Stats

117 Citations
22.84 Total Impact Points

Institutions

  • 2008–2011
    • Georgia Institute of Technology
      • School of Electrical & Computer Engineering
      Atlanta, GA, United States