Simulation and Measurement of Lightning-Impulse Voltage Distributions Over Transformer Windings

Silicon-carbide semiconductor technology offers the possibility to synthesize power devices with unprecedented blocking voltage capabilities while achieving outstanding switching and conduction performances. Accordingly, this new semiconductor technology is especially interesting for Solid-State Transformer concepts and is utilized in this paper for designing a 25 kW/50 kHz prototype based on 10 kV SiC devices, featuring a 400 V DC output. The focus is on the DC-DC converter stage while special attention is placed on the large step-down medium frequency transformer, whereby the impact of the rather high operating frequency and high number of turns with respect to the transformer's resonance frequency is analyzed This leads to useful scaling laws for the resonance frequency of transformers in dependence of the operating frequency and construction parameters. Finally, a transformer prototype and efficiency and power density values for the DC-DC stage are presented. I. INTRODUCTIONSolid-State Transformer (SST) technology enables the incorporation of several novel features to the electric power network, easing, for example, the implementation of the envisioned future Smart Grid [1, 2]. Among the main challenges in the construction of SSTs, the strategies to connect to the Medium-Voltage (MV) level can be highlighted [3,4]. This problem has been mainly tackled by synthesizing multi-cellular SST concepts based on modules rated for a fractional portion of the total MV side voltage and performing a series connection of these modules at the input side [2,5].The development of Silicon-Carbide (SiC) semiconductors opens the possibility to fabricate power semiconductor devices with high blocking voltage capabilities while achieving superior switching and conduction performances. These higher voltage semiconductors enable the construction of single-cell SSTs avoiding the series connection of several modules resulting in simple and reliable converter structures known from lower voltage converters.On the other hand, in several applications, the migration from traditional AC power distribution to DC supply systems is considered for future installations. Examples are telecommunications [6], information processing facilities [7], and microgrids [8], among others. Previous research has shown that DC bus voltages around 400 V exhibit a favorable trade-off with respect to costs and efficiency of the installation [7]. For this reason, the SST concept designed in this paper is aimed to supply a 400 V DC bus.One possible implementation of SST technology in DC-supplied facilities is shown in Fig. 1. Here, the MV grid is directly interfaced by respective single-phase SSTs connected in star configuration. These SSTs supply the 400 V loads while providing the required isolation. In addition, battery banks for uninterrupted power supply and/or clean renewable energy sources such as PV arrays can be integrated into the facility. The block diagram of the SST shown in Fig. 1 is shown in Fig. 2 and consists of the input rectifier with its respec...

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“…Equating (17) to the equivalent leakage inductance energy and solving for the leakage inductance Lσ gives…”

Section: ) Constant Number Of Turns N1mentioning

confidence: 99%

“…A commercial FEM solver has been used. • The Partial Element Equivalent Circuit method (PEEC) is used to build a 3D equivalent circuit of the transformer [17,18]. The inductance and capacitance from the 2D FEM simulation are used, completed with direct 3D analytical computation.…”

Section: ) Validation Through Fem Analysismentioning

confidence: 99%

10kV SiC-based isolated DC-DC converter for medium voltage-connected Solid-State Transformers

Rothmund

Ortiz

Guillod

et al. 2015

2015 IEEE Applied Power Electronics Conference and Exposition (APEC)

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“…Transformer winding equivalent circuits are traditionally used to examine the voltage surge distribution in the transformer windings [7][8][9]. Several studies have been carried out to examine the transient voltage surge propagations through simulations and experimental setups [10][11][12][13][14][15][16]. Lumped equivalent circuit model have been widely used to analyze the resonant responses of windings subjected to switching surges [6,[17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

Effect of shield placement for transient voltage mitigation due to switching surges in a 33/11 kV transformer windings

et al. 2020

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This study presents an investigation on the effect of shield placement for mitigation of transient voltage in a 33/11 kV, 30 MVA transformer due to Standard Switching Impulse (SSI) and Oscillating Switching Impulse (OSI) surges. Generally, the winding and insulation in transformers could experience severe voltage stress due to the external impulses i.e. switching events. Hence, it is important to examine the voltage stress and identify the mitigation action i.e. shield placements in order to reduce the adverse effect to the transformer windings. First, the resistances, inductances, and capacitances (RLC) were calculated for disc type transformer in order to develop the winding RLC equivalent circuit. The SSI and OSI transient voltage waveforms were applied to the High Voltage (HV) winding whereby the transient voltages were simulated for each disc. The resulting voltage stresses were mitigated through different configurations of electrostatic shield placements. The resonant oscillations generated due to switching surges were analysed through initial voltage distribution. The analyses on the transient voltages of the transformer winding and standard error of the slope (SEb) reveal that the location of shield placement has a significant effect on the resonant switching voltages. The increment of the shield number in the windings does not guarantee optimize mitigation of the resonant switching transient voltages. It is found that the voltage stress along the windings is linear once a floating shield is placed between the HV and Low Voltage (LV) windings of the disc-type transformer under the SSI and OSI waveforms. These findings could assist the manufacturers with appropriate technical basis for mitigation of the transformer winding against the external transient switching overvoltage surges.

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“…Generally, a transformer's winding responses under impulses are mainly dependent on the design and system configuration. A number of studies have been carried out to examine the transient overvoltage surge propagations through simulations and experimental setups [8][9][10][11][12][13]. Under impulses, resonances in transformers could be initiated due to a frequency of the oscillating components that is similar to its frequency responses [14,15].…”

Section: Introductionmentioning

confidence: 99%

Investigation on the Resonant Oscillations in an 11 kV Distribution Transformer under Standard and Chopped Lightning Impulse Overvoltages with Different Shield Placement Configurations

et al. 2019

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This paper presents an investigation on the resonant oscillations of an 11 kV layer-type winding transformer under standard and chopped lightning impulse overvoltage conditions based on calculated parameters. The resistances, inductances and capacitances were calculated in order to develop the transformer winding equivalent circuit. The impulse overvoltages were applied to the high voltage (HV) winding and the resonant oscillations were simulated for each of the layers based on different electrostatic shield placement configurations. It is found that the placement of grounded shields between layer 13 and layer 14 results in the highest resonant oscillation and non-linear initial voltage distribution. The oscillation and linear stress distributions are at the lowest for shield placement between the HV and low voltage (LV) windings.

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Simulation and Measurement of Lightning-Impulse Voltage Distributions Over Transformer Windings

Cited by 55 publications

References 5 publications

10kV SiC-based isolated DC-DC converter for medium voltage-connected Solid-State Transformers

10kV SiC-based isolated DC-DC converter for medium voltage-connected Solid-State Transformers

Effect of shield placement for transient voltage mitigation due to switching surges in a 33/11 kV transformer windings

Investigation on the Resonant Oscillations in an 11 kV Distribution Transformer under Standard and Chopped Lightning Impulse Overvoltages with Different Shield Placement Configurations

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