Patents by Inventor Zoran Gajic

Zoran Gajic has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Publication number: 20200103453
    Abstract: An arrangement for injection-based ground fault protection handling including a number of stator windings of an electric machine that are connected to a neutral point, a first transformer including at least one primary winding connected to at least one measurement point of the stator windings and at least one secondary winding for measuring an electrical quantity of the machine at the measurement point. There is also a second transformer having a primary winding connected between the neutral point and a ground potential and a secondary winding for connection to a signal generation and detection unit in order to inject a signal into the neutral point and receive a response. The impedance of the second transformer is in the range of the impedance of the machine.
    Type: Application
    Filed: July 31, 2019
    Publication date: April 2, 2020
    Inventors: Stefan Roxenborg, Zoran Gajic, Tord Bengtsson, Mikael Sehlstedt
  • Patent number: 10254155
    Abstract: A monitoring device and a method for detecting mechanical torsional oscillations in a rotor shaft of a turbine-generator system. Specifically, the monitoring device and a method for detecting mechanical torsional oscillations in a turbine-generator system having a plurality of, such as two, three, four, five, six or more, turbines that are interconnected by means of a common turbine shaft.
    Type: Grant
    Filed: September 5, 2014
    Date of Patent: April 9, 2019
    Assignee: ABB Schweiz AG
    Inventors: Tord Bengtsson, Zoran Gajic, Stefan Roxenborg
  • Publication number: 20170276539
    Abstract: A monitoring device and a method for detecting mechanical torsional oscillations in a rotor shaft of a turbine-generator system. Specifically, the monitoring device and a method for detecting mechanical torsional oscillations in a turbine-generator system having a plurality of, such as two, three, four, five, six or more, turbines that are interconnected by means of a common turbine shaft.
    Type: Application
    Filed: September 5, 2014
    Publication date: September 28, 2017
    Inventors: Tord BENGTSSON, Zoran GAJIC, Stefan ROXENBORG
  • Patent number: 8972209
    Abstract: A method for detecting an internal failure in a capacitor bank connected in one phase or more phases respectively to a power system. The capacitor bank includes a plurality of capacitor units. Each of the capacitor units includes a plurality of capacitor elements connected in parallel and/or series. The capacitor units are further divided into two strings and a current transformer is arranged in the midpoints of the two strings so that the capacitor units are further divided into four quadrants and the internal failure(s) may occur in one or more capacitor elements or units and involves one or more capacitor quadrants. The method includes initiating an alarm and/or a trip signal when the determined total number of internal elements failures exceeds a first or a second threshold value.
    Type: Grant
    Filed: August 16, 2013
    Date of Patent: March 3, 2015
    Assignee: ABB Research Ltd.
    Inventors: Zoran Gajic, Jianping Wang, Mustafa Ibrahim
  • Patent number: 8912801
    Abstract: A method for detecting an internal failure in a capacitor bank connected to a power system, wherein the capacitor bank includes a plurality of capacitor units that are divided into two Y sections. Each phase in each of the Y sections defines a leg and each leg includes series and/or parallel-connected capacitor units. The internal failure may occur in one or more capacitor elements or units or involve one or more legs. The method includes measuring the phase current in one of the phases, calculating the root mean square value, denoted by RMS, of the measured phase currents, measuring the unbalanced current between the two sections, calculating the RMS value of the measured unbalanced currents, and detecting the phase angle between the measured phase current and the measured unbalanced current.
    Type: Grant
    Filed: August 14, 2013
    Date of Patent: December 16, 2014
    Assignee: ABB Research Ltd.
    Inventors: Zoran Gajic, Mustafa Ibrahim, Jianping Wang
  • Patent number: 8847603
    Abstract: An arrangement to detect a ground fault in an AC electric circuit including an electric machine having a neutral point connecting to a neutral point and a terminal side, and a unit transformer connected to the terminal side of the machine, wherein the arrangement includes a signal injection unit, a voltage transformer having a primary winding connected to the terminal side of the electric machine and a secondary winding that is open delta-connected, an instrument transformer having a primary winding connected to the neutral point of the electric machine and a secondary winding, and a ground fault detecting unit. The signal injection unit is configured to inject a signal to the secondary winding of the voltage transformer. The instrument transformer is configured to measure the resultant injected signal at its secondary winding The ground fault detecting unit is configured to detect a ground fault based on the measured signal.
    Type: Grant
    Filed: January 22, 2013
    Date of Patent: September 30, 2014
    Assignee: ABB Technology AG
    Inventor: Zoran Gajic
  • Patent number: 8823307
    Abstract: A system, method and computer program product for monitoring including detecting internal faults especially inter-turn faults of a synchronous generator and thus protecting the synchronous generator. The synchronous generator includes a winding for each phase of a power network, a terminal for each phase arranged on a terminal side of the synchronous generator, and connected to the respective winding, the terminals on the terminal side are connected to an electrical power network, and the synchronous generator is arranged to input power to the electrical power network by means of the terminals.
    Type: Grant
    Filed: January 3, 2014
    Date of Patent: September 2, 2014
    Assignee: ABB Research Ltd.
    Inventors: Zoran Gajic, Mustafa Ibrahim, Antonis Marinopoulos, Pedro Rodriguez, Jianping Wang, Liwei Wang
  • Patent number: 8792216
    Abstract: A method for protecting against a failure within a multi-phase capacitor bank including a plurality of capacitor units each including a plurality of capacitor elements connected to each other, wherein capacitor units are connected to each other and the failure may involve two neighboring capacitor units. The method includes steps of measuring the current of each individual phase of the capacitor bank, calculating the magnitude of an unbalanced current based on the measured currents, measuring the voltage of each individual phase of the capacitor bank, calculating the magnitude of an unbalanced voltage based on the measured voltages, determining an operating point based on the calculated magnitudes of the unbalanced current and the unbalanced voltage, examining where the defined operating point is located in a specified operating region, and initializing a trip signal based on the location of the defined operating point in the specified operating region.
    Type: Grant
    Filed: January 16, 2013
    Date of Patent: July 29, 2014
    Assignee: ABB Technology AG
    Inventor: Zoran Gajic
  • Patent number: 8791730
    Abstract: A synchronization method for current differential protection comprises: selecting a point on the transmission line protected by the current differential protection; measuring the current and the voltage of each of the terminals of said transmission line; calculating the compensating voltage at the selected point respectively according to the measured current and the voltage of the each terminal; detecting and calculating the synchronization error by comparing all the compensating voltages.
    Type: Grant
    Filed: November 9, 2010
    Date of Patent: July 29, 2014
    Assignee: ABB Research Ltd.
    Inventors: Youyi Li, Bin Su, Ying Yang, Torbjorn Einarsson, Zoran Gajic
  • Publication number: 20140117912
    Abstract: A system, method and computer program product for monitoring including detecting internal faults especially inter-turn faults of a synchronous generator and thus protecting the synchronous generator. The synchronous generator includes a winding for each phase of a power network, a terminal for each phase arranged on a terminal side of the synchronous generator, and connected to the respective winding, the terminals on the terminal side are connected to an electrical power network, and the synchronous generator is arranged to input power to the electrical power network by means of the terminals.
    Type: Application
    Filed: January 3, 2014
    Publication date: May 1, 2014
    Inventors: Zoran Gajic, Mustafa Ibrahim, Antonis Marinopoulos, Pedro Rodriguez, Jianping Wang, Liwei Wang
  • Publication number: 20130338946
    Abstract: A method for detecting an internal failure in a capacitor bank connected in one phase or more phases respectively to a power system. The capacitor bank includes a plurality of capacitor units. Each of the capacitor units includes a plurality of capacitor elements connected in parallel and/or series. The capacitor units are further divided into two strings and a current transformer is arranged in the midpoints of the two strings so that the capacitor units are further divided into four quadrants and the internal failure(s) may occur in one or more capacitor elements or units and involves one or more capacitor quadrants. The method includes initiating an alarm and/or a trip signal when the determined total number of internal elements failures exceeds a first or a second threshold value.
    Type: Application
    Filed: August 16, 2013
    Publication date: December 19, 2013
    Inventors: Zoran Gajic, Jianping Wang, Mustafa Ibrahim
  • Publication number: 20130328569
    Abstract: A method for detecting an internal failure in a capacitor bank connected to a power system, wherein the capacitor bank includes a plurality of capacitor units that are divided into two Y sections. Each phase in each of the Y sections define a leg and each leg includes series and/or parallel-connected capacitor units. The internal failure may occur in one or more capacitor elements or units or involve one or more legs. The method includes measuring the phase current in one of the phases, calculating the root mean square value, denoted by RMS, of the measured phase currents, measuring the unbalance current between the two sections, calculating the RMS value of the measured unbalance currents, and detecting the phase angle between the measured phase current and the measured unbalance current.
    Type: Application
    Filed: August 14, 2013
    Publication date: December 12, 2013
    Inventors: Zoran Gajic, Mustafa Ibrahim, Jianping Wang
  • Publication number: 20130193979
    Abstract: An arrangement to detect a ground fault in an AC electric circuit including an electric machine having a neutral point connecting to a neutral point and a terminal side, and a unit transformer connected to the terminal side of the machine, wherein the arrangement includes a signal injection unit, a voltage transformer having a primary winding connected to the terminal side of the electric machine and a secondary winding that is open delta-connected, an instrument transformer having a primary winding connected to the neutral point of the electric machine and a secondary winding, and a ground fault detecting unit. The signal injection unit is configured to inject a signal to the secondary winding of the voltage transformer. The instrument transformer is configured to measure the resultant injected signal at its secondary winding The ground fault detecting unit is configured to detect a ground fault based on the measured signal.
    Type: Application
    Filed: January 22, 2013
    Publication date: August 1, 2013
    Inventor: Zoran Gajic
  • Publication number: 20130181755
    Abstract: A synchronization method for current differential protection comprises: selecting a point on the transmission line protected by the current differential protection; measuring the current and the voltage of each of the terminals of said transmission line; calculating the compensating voltage at the selected point respectively according to the measured current and the voltage of the each terminal; detecting and calculating the synchronization error by comparing all the compensating voltages.
    Type: Application
    Filed: November 9, 2010
    Publication date: July 18, 2013
    Applicant: ABB RESEARCH LTD.
    Inventors: Youyi Li, Bin Su, Ying Yang, Torbjorn Einarsson, Zoran Gajic
  • Publication number: 20130128393
    Abstract: A method for protecting against a failure within a multi-phase capacitor bank including a plurality of capacitor units each including a plurality of capacitor elements connected to each other, wherein capacitor units are connected to each other and the failure may involve two neighboring capacitor units. The method includes steps of measuring the current of each individual phase of the capacitor bank, calculating the magnitude of an unbalanced current based on the measured currents, measuring the voltage of each individual phase of the capacitor bank, calculating the magnitude of an unbalanced voltage based on the measured voltages, determining an operating point based on the calculated magnitudes of the unbalanced current and the unbalanced voltage, examining where the defined operating point is located in a specified operating region, and initializing a trip signal based on the location of the defined operating point in the specified operating region.
    Type: Application
    Filed: January 16, 2013
    Publication date: May 23, 2013
    Inventor: Zoran Gajic
  • Patent number: 8340930
    Abstract: An arrangement for protecting equipment of an AC electrical power system comprises first means configured to measure the frequency of the current and voltage at at least one location in the electrical power system along an interconnection between two theoretical electric machines of an equivalent two machine system. Fourth means are configured to use the values of the frequency of the current and voltage measured to determine whether a power swing has occurred and if an occurrence of a power swing has been determined determine whether the measuring location is located on a motor side or a generator side of a potential pole slip electrical centre along said interconnection, the electrical centre being defined as the location where the voltage becomes zero during a pole slip, and send this information further to third means for use in a control for protecting equipment of the electrical power system.
    Type: Grant
    Filed: December 15, 2011
    Date of Patent: December 25, 2012
    Assignee: ABB Technology AG
    Inventor: Zoran Gajic
  • Publication number: 20120081817
    Abstract: An arrangement for protecting equipment of an AC electrical power system comprises first means configured to measure the frequency of the current and voltage at at least one location in the electrical power system along an interconnection between two theoretical electric machines of an equivalent two machine system. Fourth means are configured to use the values of the frequency of the current and voltage measured to determine whether a power swing has occurred and if an occurrence of a power swing has been determined determine whether the measuring location is located on a motor side or a generator side of a potential pole slip electrical centre along said interconnection, the electrical centre being defined as the location where the voltage becomes zero during a pole slip, and send this information further to third means for use in a control for protecting equipment of the electrical power system.
    Type: Application
    Filed: December 15, 2011
    Publication date: April 5, 2012
    Inventor: Zoran Gajic
  • Patent number: 8102634
    Abstract: A differential protection method in a power network for determining type of fault occurring within the power network. The power network includes a protected object having two or more ends, and a current differential protection device and a current transformer are arranged at each end. The method includes the steps obtaining, at a first end of the protected object, measured values from a second end of the protected object; comparing, at the first end, changes in measured values taken at the first end with changes in the measured values obtained from the second end; and determining, upon the step of comparing changes in measured values showing differing results, type of fault occurring within the power network.
    Type: Grant
    Filed: April 20, 2010
    Date of Patent: January 24, 2012
    Assignee: ABB Technology AG
    Inventors: Zoran Gajic, Bertil Lundqvist
  • Patent number: 7873496
    Abstract: A method and a device for fault detection in an n-winding, three-phase power transformer. For each of the windings (Wi) the three phase currents (IL1—Wi; IL2—Wi; IL3—Wi) are measured. For each of the windings (Wi) deciding if a zero sequence current (I0—Wi) reduction is to be performed depending on at least one user setting (kWi) and if so, deducting the zero sequence current (I0—Wi) from each of the three phase currents (IL1—Wi; IL2—Wi; IL3—Wi). For each of the windings (Wi) generating normalized currents by performing a magnitude compensation and a phase angle shift compensation on the results of the previous step. For each of the three phases (Lx) comparing the normalized current of a single winding with the normalized currents of all other windings. For each phase (Lx) generating a fault signal, if a difference between the single winding (W1) and all other windings (W2, . . . , Wn) exceeds a predefined level.
    Type: Grant
    Filed: August 24, 2006
    Date of Patent: January 18, 2011
    Assignee: ABB Technology Ltd.
    Inventor: Zoran Gajic
  • Patent number: 7812615
    Abstract: A method for fault detection in a power transformer/autotransformer and/or interconnected power lines, which are within the zone protected by the differential protection, and particularly suitable for detecting turn-to-turn faults in power transformer/autotransformer windings. All individual instantaneous phase currents of the protected object are measured, individual phase currents as fundamental frequency phasors are calculated, the contributions of the individual protected object sides negative sequence currents to the total negative sequence differential current are calculated by compensating for the phase shift of an eventual power transformer within the protected zone, the relative positions of the compensated individual sides negative sequence currents in the complex plane are compared, in order to determine whether the source of the negative sequence currents, i.e.
    Type: Grant
    Filed: December 22, 2004
    Date of Patent: October 12, 2010
    Assignee: ABB AB
    Inventors: Zoran Gajic, Ivo Brncic