In this paper,a new simulating method is presented,using only the normal magnetizing curve (B-H) of the transformer core material,its geometric dimensions,the no-load power loss data and the concept of instantaneous p...In this paper,a new simulating method is presented,using only the normal magnetizing curve (B-H) of the transformer core material,its geometric dimensions,the no-load power loss data and the concept of instantaneous power. At the end of this paper the simulating calculation using EMTP has been also performed for the same transformer. The comparison shows that the two sets of results are very close to each other,and proves the correctness of the new method. The new method presented in this paper is helpful to verify the correctness of the power transformer design,analyze the behavior of the transformer protection under switching and study the new transformer protection principles.展开更多
The primary winding of the transformer will generate large inrush current due to the saturation of iron core when an unloaded transformer is switched-on. The inrush current not only causes mechanical interaction force...The primary winding of the transformer will generate large inrush current due to the saturation of iron core when an unloaded transformer is switched-on. The inrush current not only causes mechanical interaction force due to which the windings are damaged, but also induces the differential protection relays to operate incorrectly. In this paper, the mathematical model of unloaded single phase transformer in switch-on is analyzed; the computation formulas of the inrush current and its interruption angle are presented. The experiment investigation of single phase transformers with different capacities shows that the inrush current measurement result is consistent with theoretical analysis. The inrush current waveform is typically a steeple top waveform with high order harmonics and damping in one direction. In the same condition, large inrush current amplitude will be induced with smaller switching angle, larger residual flux and smaller saturation flux.展开更多
Transformer Differential and overcurrent schemes are traditionally used as main and backup protection respectively. The differential protection relay (SEL487E) has dedicated harmonic restraint function which blocks th...Transformer Differential and overcurrent schemes are traditionally used as main and backup protection respectively. The differential protection relay (SEL487E) has dedicated harmonic restraint function which blocks the relay tripping during the transformer magnetizing inrush conditions. However, the backup overcurrent relay (SEL751A) applied to the transformer protection does not have harmonic restraint element and trip the overcurrent relay during the inrush conditions. Therefore, major contribution of this research work is the developed harmonic blocking scheme for transformer which uses element (87HB) of the transformer differential relay (SEL487E) to send an IEC61850 GOOSE-based harmonic blocking signal to the backup overcurrent relay (SEL751A) to inhibit from tripping during the transformer magnetizing inrush current conditions. The simulation results proved that IEC61850 standard-based protection scheme is faster than the hardwired signals. Therefore, the speed and reliability of the transformer scheme are improved using the IEC61850 standard-based GOOSE applications.展开更多
文摘In this paper,a new simulating method is presented,using only the normal magnetizing curve (B-H) of the transformer core material,its geometric dimensions,the no-load power loss data and the concept of instantaneous power. At the end of this paper the simulating calculation using EMTP has been also performed for the same transformer. The comparison shows that the two sets of results are very close to each other,and proves the correctness of the new method. The new method presented in this paper is helpful to verify the correctness of the power transformer design,analyze the behavior of the transformer protection under switching and study the new transformer protection principles.
文摘The primary winding of the transformer will generate large inrush current due to the saturation of iron core when an unloaded transformer is switched-on. The inrush current not only causes mechanical interaction force due to which the windings are damaged, but also induces the differential protection relays to operate incorrectly. In this paper, the mathematical model of unloaded single phase transformer in switch-on is analyzed; the computation formulas of the inrush current and its interruption angle are presented. The experiment investigation of single phase transformers with different capacities shows that the inrush current measurement result is consistent with theoretical analysis. The inrush current waveform is typically a steeple top waveform with high order harmonics and damping in one direction. In the same condition, large inrush current amplitude will be induced with smaller switching angle, larger residual flux and smaller saturation flux.
基金funded by the National Research Foundation(NRF)THRIP grant TP2011061100004,ESKOM TESP(Capacitor Banks Placement)ESKOM Academy of Learning,ESKOM Power Plants Energy Institute(EPPEI)and CPUT(Prestigious Project)grant for the Centre of Substation Automation and Energy Management Systems(CSAEMS)development and growth.
文摘Transformer Differential and overcurrent schemes are traditionally used as main and backup protection respectively. The differential protection relay (SEL487E) has dedicated harmonic restraint function which blocks the relay tripping during the transformer magnetizing inrush conditions. However, the backup overcurrent relay (SEL751A) applied to the transformer protection does not have harmonic restraint element and trip the overcurrent relay during the inrush conditions. Therefore, major contribution of this research work is the developed harmonic blocking scheme for transformer which uses element (87HB) of the transformer differential relay (SEL487E) to send an IEC61850 GOOSE-based harmonic blocking signal to the backup overcurrent relay (SEL751A) to inhibit from tripping during the transformer magnetizing inrush current conditions. The simulation results proved that IEC61850 standard-based protection scheme is faster than the hardwired signals. Therefore, the speed and reliability of the transformer scheme are improved using the IEC61850 standard-based GOOSE applications.
