Controlled switching of transformers - effects of closing time scatter and residual flux uncertainty

Ebner, Andreas; Bosch, M.; Cortesi, Rebecca L.

doi:10.1109/upec.2008.4651646

Cited by 19 publications

(11 citation statements)

References 7 publications

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“…The sampling rate of 162 samples per cycle has been chosen for all cases. [23], Frequency response method [18], voltage accumulator method [19], and voltage integration method [24] have been used to portray the level of demagnetization status of transformer core. These methods discussed only nil-demagnetization case and other possible states of natural de-magnetization are not addressed.…”

Section: Nil De-magnetizationmentioning

confidence: 99%

Evaluation of Natural de-Magnetization of Power Transformer Due to Capacitor Interaction with Area Under the Curve Method

et.al.¹

2019

IJCDS

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Transformer energization at random point presents inrush phenomena and is unfavorable for equipment due to high magnitude asymmetric current flow. These asymmetric currents are largely affected by level and polarity of residual flux presents in transformer core post its de-energization. Controlled switching technology is widely used to limit inrush current. Moreover, ignorance of residual flux would yield only moderate level of inrush current. Also, inaccurate estimation of de-magnetization status leads to improper estimation of energization instants during independent pole switching and the resulting inrush currents could not be reduced below desired level. Therefore it is quite important to know the exact level of residual flux post every de-energization operation of power transformer. Presence of capacitor bank, filter banks and connected XLPE cables offer natural de-magnetization of power transformers. The de-magnetization is categorized in no, partial and full de-magnetization. This paper presents novel approach for detection of natural de-magnetization of Power Transformer using load side measurements. Numerical integration has been used for the evaluation. Suggested method has been verified from field data collected from power transformers of different design and connection configuration across globe used for various grid voltage levels. Lastly, the effect of variation in sampling rate and level of residual fluxes is analyzed and the suggested method is found to be equally effective for said variations. The categorization of natural de-magnetization play important role in deciding energization instant for next switching of transformer

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Section: Nil De-magnetizationmentioning

confidence: 99%

Evaluation of Natural de-Magnetization of Power Transformer Due to Capacitor Interaction with Area Under the Curve Method

et.al.¹

2019

IJCDS

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“…This is defined by the conditions imposed on the transformer at the moment that precedes its interruption. The correct estimation of the residual flux is extremely important for the success of the controlled switching strategy [7], as it defines the point on the voltage waveform at which the switches are to be closed next.…”

Section: Residual Flux Determinationmentioning

confidence: 99%

A controlled switching methodology for transformer inrush current elimination: Theory and experimental validation

Reis

Oliveira

Apolonio

et al. 2011

11th International Conference on Electrical Power Quality and Utilisation

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Transformers are generally energized by closing the circuit breakers at random times. Consequently, this operation generates high transient inrush currents as a result of the asymmetrical magnetic flux produced in the windings. In light of these facts, this paper presents a strategy to control the switching phenomena which occurs during power transformer inrush. The general idea consists of calculating the pre-existing magnetic fluxes left on the core limbs as a function of operating voltage previously applied to the transformer, just prior to the moment in which de-energization has happened. By using these data and the equations to predict the most suitable closing moments, it is shown the proposal effectiveness at accomplishing the main target here pointed out. Experimental investigations are carried out in order to demonstrate the application method and its validation. The results show the feasibility of building hardware and software structures to drastically reduce the transformer inrush currents.

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“…For each simulation and for each phase, the controller module finally evaluates the maximum inrush current value (inrush current peak) and the voltage across the circuit-breaker immediately before it is closed (amplitude of the voltage wave front) and stores these values in a matrix. A more detailed description of the controller interface can be found in [14], chapters IV.A, IV.C and IV.D where similar algorithms were used for systematic inrush current studies in the laboratory. Prague, 8-11 June 2009 Paper 0194 CIRED2009 Session 1…”

Section: Controller Interface Between Matlab and Emtp-atpmentioning

confidence: 99%

Reduction of voltage stress and inrush current of power transformers using controlled switching

Ebner

2009

IET Conference Publications

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Random energisation of power transformers often causes significant inrush currents and steep switching voltage wave fronts that are responsible for several adverse effects like huge current forces in the transformer windings, dielectric stress of the transformer winding insulation and temporary overvoltages. Controlled switching taking into account the residual flux is able to eliminate these inrush currents, but significant voltage wave fronts emerge from the switching action in almost all cases. Thus, a new algorithm is presented that extends the existing one so that a combined reduction of all stresses can be achieved. Systematic energisation studies were carried out in EMTP-ATP to calculate the optimal closing times of a three-legged 400 kVA transformer. Thereby, an inrush current peak of 1 pu will be tolerated so that the voltage wave front amplitude can be reduced. Depending on the strategy for controlled switching, the maximum voltage wave front amplitude of all phases can be limited to 0.75 pu ("Delayed Closing", reduction of 11.7 %) respectively to 0.7 pu for "Rapid Closing" (reduction of 22 %).

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Controlled switching of transformers - effects of closing time scatter and residual flux uncertainty

Cited by 19 publications

References 7 publications

Evaluation of Natural de-Magnetization of Power Transformer Due to Capacitor Interaction with Area Under the Curve Method

Evaluation of Natural de-Magnetization of Power Transformer Due to Capacitor Interaction with Area Under the Curve Method

A controlled switching methodology for transformer inrush current elimination: Theory and experimental validation

Reduction of voltage stress and inrush current of power transformers using controlled switching

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