Analyzing Distribution Transformer Degradation with Increased Power Electronic Loads Bhaskar Mitra Ankit Singhal Soumya Kundu and James P. Ogle

2025-04-30 0 0 3.45MB 5 页 10玖币

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Analyzing Distribution Transformer Degradation

with Increased Power Electronic Loads

Bhaskar Mitra, Ankit Singhal, Soumya Kundu and James P. Ogle

Electricity Infrastructure and Buildings Division

Paciﬁc Northwest National Laboratory

Richland, WA 99354, USA

Email: {bhaskar.mitra, ankit.singhal, soumya.kundu, james.ogle}@pnnl.gov

Abstract—The inﬂux of non-linear power electronic loads into

the distribution network has the potential to disrupt the existing

distribution transformer operations. They were not designed

to mediate the excessive heating losses generated from the

harmonics. To have a good understanding of current standing

challenges, a knowledge of the generation and load mix as well

as the current harmonic estimations are essential for designing

transformers and evaluating their performance. In this paper,

we investigate a mixture of essential power electronic loads for

a household designed in PSCAD/EMTdc and their potential

impacts on transformer eddy current losses and derating using

harmonic analysis. The various scenarios have been studied with

increasing PV penetrations. The peak load conditions are chosen

for each scenario to perform a transformer derating analysis.

Our ﬁndings reveal that in the presence of high power electronic

loads (especially third harmonics), along with increasing PV

generation may worsen transformer degradation. However, with

a low amount of power electronic loads, additional PV generation

helps to reduce the harmonic content in the current and improve

transformer performance.

Index Terms—eddy current, harmonics, power transformer,

PV, THD

I. INTRODUCTION

Power electronic loads have found a wider application in

power system networks especially after their advancement in

the late 1900s. Many loads require essential power electronic

converters for stage conversion. Some common examples of

power electronic loads include uninterrupted power supply

(UPS) devices, personal computers, laptops, electric vehicle

chargers, etc. These non-linear loads contribute to non-linear

sinusoidal currents. The non-sinusoidal currents, when passing

through network impedance, create a non-sinusoidal voltage

drop [1]. The non-sinusoidal voltage and current components

are integer multiples of the fundamental component called

“harmonics”. The deterioration of the supply voltage creates

stress on the electrical equipment and can potentially damage

it, resulting in increased operating costs and downtime [2].

Increased voltage and current harmonics are found to have

a direct relationship to premature aging and degradation of

transformers. Initial transformer designs were made consid-

ering conventional load models, i.e., Constant Impedance

(Z), Constant Current (I), and Constant Power (P) or “ZIP”

This work was supported by the Sensors and Data Analytics Program of

the U.S. Department of Energy Ofﬁce of Electricity, under Contract No. DE-

AC05-76RL01830.

models, that would operate at fundamental 60Hz or 50Hz

frequency [3, 4]. Under the increased penetration of non-linear

loads, the design of power transformers needs to be reassessed

to ensure proper and safe operation. Increased non-linear loads

increase the transformer losses due to overheating of the core,

creating a larger derating factor [5, 6].

The problem of harmonics is more evident with customers

on the low-voltage end. The common household equipment

includes but not limited to desktops, laptops, LED lamps,

variable speed drives, solar panels, etc. To compound the

challenges, as more and more electric vehicles come to the

market, they rely majorly on at-home charging that produces

a large fraction of non-linear voltage and current. Certain

power electronic devices like VFD’s contribute more 3rd

harmonics, if they are not properly compensated it would lead

to additional losses and loss-of-life for the transformer. The

addition of harmonics has an effect on transformer protection

as well. Addition of the 5th harmonic needs to be compensated

below a certain threshold before the protection relays can be

engaged. The distorted harmonic waveforms results in loss of

essential information for protection, this might result in the

protection devices operating slower [7].

Currently, there is a gap in high-ﬁdelity load models that can

capture the typical characteristics of non-linear models, i.e.,

the cross-coupling effect of voltages and current. A harmonic-

rich current/voltage dataset is essential to understand the effect

on transformer losses, heating, etc. “ZIP” based harmonic load

models suffer from a lack of enhanced harmonic spectrum that

can be observed through the operation of various non-linear

devices [8]. Real-world ﬁeld data is not publicly available to

perform such analysis. Methods relying on laboratory setups

to develop such datasets fail to capture the effect on other

nonlinear load currents.

Therefore, in this paper, (i) we perform an analysis of

residential transformer heating and losses encountered due to

the presence of non-linear power electronic residential loads

using PSCAD/EMTdc. Detailed power electronic models are

developed to create harmonic rich datasets to entail their effect

on transformer operation; (ii) Different loading scenarios on

the transformer are assessed with increasing PV penetration

to understand its effect on THD(%), eddy current losses, and

the subsequent impact on transformer derating.

The rest of the paper has been organized in the following

arXiv:2210.14824v1 [eess.SY] 26 Oct 2022

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AnalyzingDistributionTransformerDegradationwithIncreasedPowerElectronicLoadsBhaskarMitra,AnkitSinghal,SoumyaKunduandJamesP.OgleElectricityInfrastructureandBuildingsDivisionPacicNorthwestNationalLaboratoryRichland,WA99354,USAEmail:fbhaskar.mitra,ankit.singhal,soumya.kundu,james.ogleg@pnnl.govAbstrac...

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Analyzing Distribution Transformer Degradation with Increased Power Electronic Loads Bhaskar Mitra Ankit Singhal Soumya Kundu and James P. Ogle

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