Step-Up Transformers for PV Plants: Load Loss Estimation under Harmonic Conditions

Distributed Solar Photovoltaic (DSP) Plants are one of the fastest growing renewable energy systems in South Africa. The primary components forming an integral part of the point of common coupling (PCC) are, the inverter used to convert dc voltage to ac voltage and stepup transformers which step-up low voltage input to the desired output level. However, DSP plant step-up transformers are considered to be one of the most sensitive equipment on the plant. These transformers are challenged with various electrical problems including abnormal levels of harmonics. The presence of harmonics in these transformers results in higher service losses thereby raising the hotspot (HS) temperature, in which, consequently introduce the stray gassing phenomena of the insulating oils. This calls for understanding of the nature of the problem and possible remediation to ensure enhanced power quality. Present work, an extension of previous work, investigate a reported case of peculiar stray gassing of transformer insulation oils during service. Initially, the harmonic spectrum of the DSP plant is presented and the related service losses at fundamental and under harmonic conditions are computed. Furthermore, the thermal performance of the transformer under these conditions is investigated. Lastly, the Dissolved Gas Analysis (DGA) results of the oil samples are presented. Novelty, findings of this work indicate that the generation of hydrogen arising from stray gassing may stem from severely hydro-treated mineral oil, but is also strenuously affected by transformer thermal aging of polymers, choice of core steel grade, zinc tank walls and vanishes. The production surplus of methane and ethane are also witnessed in the first years of service and reaches substantial concentration levels. Potentially, these occurrences also arises from the thermal aging of polymers. The authors make some recommendations to utility owners to make a distinction of stray gassing from transformer fault by means of routine inspection aside from DGA value basis withal to the increase in gas diffusion rate. Further, the authors make some significant contribution by further recommending procedures that can be employed as remedies during the design phase and manufacturing processes. Lastly, the authors highlight the need to establish standards that will provide support for transformers intended to operate in DSP applications.

Section: Case Scenariomentioning

confidence: 99%

“…Thereafter, a harmonic loss factor is computed based on the supplied harmonic spectrum. The authors have presented a detailed computation of the harmonic loss factor in [17] and [18]. The Harmonic factor is in essence intended to predict the increase in the transformer losses under harmonics condition.…”

Section: Harmonic Ordermentioning

confidence: 99%

Peculiar Stray Gassing Occurrences in Solar Photovoltaic Transformers during Service

Thango¹,

Jordaan²

2021

“…Transformers are commonly designed under the presumption of sinusoidal loading conditions [6][7]. It is widely known that distorted harmonic load currents accentuates the service losses in transformer and ultimately the temperature rise and generation of hotspots in metallic structures, resulting in degradation of insulation materials and untimely failures as shown in Figure 1 (b) [8][9][10].…”

Section: Introductionmentioning

confidence: 99%

A Novel Approach for Evaluating Eddy Current Loss in Wind Turbine Generator Step-Up Transformers

Thango¹,

Jordaan²,

Nnachi³

2021

South Africa is aiming to achieve a generation capacity of about 11.4GW through wind energy systems, which will contribute nearly 15.1% of the country's energy mix by 2030. Wind energy is one of the principal renewable energy determinations by the South African government, owing to affluent heavy winds in vast and remote coastal areas. In the design of newfangled Wind Turbine Generator Step-Up (WTGSU) transformers, all feasible measures are now being made to drive the optimal use of active components with the purpose to raise frugality and to lighten the weight of these transformers. This undertaking is allied with numerous challenges and one of them, which is particularly theoretical, is delineated by the Eddy currents. Many times the transformer manufacturer and also the buyer will be inclined to come to terms with some shortcomings triggered by Eddy currents. Still and all, it is critical to understand where Eddy currents emanate and the amount of losses and wherefore the temperature rise that may be produced in various active part components of WTGSU transformers. This is the most ideal choice to inhibit potential failure of WTGSU transformers arising from excessive heating especially under distorted harmonic load conditions. In the current work, an extension of the author's previous work, new analytical formulae for the Eddy loss computation in WTGSU transformer winding conductors have been explicitly derived, with appropriate contemplation of the fundamental and harmonic load current. These formulae allow the distribution of the skin effect and computation of the winding Eddy losses as a result of individual harmonics in the winding conductors. These results can be utilized to enhance the design of WTGSU transformers and consequently minimize the generation of hotspots in metallic structures.

“…The use of transformers has enabled the renewable energy market to grow steadily, with the transformer market expected to increase annually by approximately 16% between 2019 and 2020 [1]. The increased attention by the government to broaden investments in renewable energy resources to satisfy environmental and sustainable objectives is the main driver of this market growth [2]- [5].…”

Section: Introductionmentioning

confidence: 99%

Application of Polynomial Regression Analysis in Evaluating the Techno-Economic Performance of DSPV Transformers

Thango¹,

Jordaan²,

Nnachi³

2021

To this extent, the delineation of techno-economic evaluations for transformers becomes more intricate through a lens of Distributed Solar Photovoltaic (DSPV) market in South Africa. Essentially, the transformer price and loss evaluation techniques should be tailored for calculating the Total Ownership Cost (TOC) of transformers facilitating decentralized energy systems. In South Africa, the traditional coal power generation and renewables operate concurrently under liberalized energy markets but have distinct operational requirements and therefore have distinct methods for evaluating their generating states, service loss costs and TOC. As a result, their techno-economic evaluations should be different. In this work, new formulae have been developed to contemplate on a comprehensive technique for calculating the transformer prices and losses necessitated to estimate the cost of service losses and TOC for DSPV transformers. These formulae are based on experimental studies undertaken on a fleet of DSPV transformers ranging from 1.25 to 250MVA. In order to substantiate these new formulae, 4 case studies have been presented. The calculated losses and associated cost results against the pragmatic values from the case studies yield an error of estimation of less than 1% and 2% respectively in all cases. Further, these results are used to calculate the cost of losses and TOC using a methodology that has been proposed in previous work exclusively for power producers who are proprietors of DSPV generation systems.