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Impact on the Technical Performance of a Utility-Scale PV Plant when Using Different Sizes and Numbers of Transformers

Lindblom, Oliver LU and Elfström, Jens LU (2024) In CODEN:LUTEDX/TEIE EIEM01 20241
Industrial Electrical Engineering and Automation
Abstract
The main focus of this thesis has been to examine and compare how the size and number of internal power transformers affects the technical performance
(robustness, power quality and efficiency) of a utility-scale PV plant. The technical performance was examined in a simulation environment (MATLAB Simulink), where a PV plant with a fixed number of PV arrays and converters, corresponding to a rated power of 40 MW, was connected to the
grid in four different ways, resulting in four simulation models. First off two models, using 4 x 10 MVA transformers respectively 20 x 2 MVA transformers, were built and simulated under different site conditions (grid strength and distance to PCC) and disturbances (varying solar irradiation and grid... (More)
The main focus of this thesis has been to examine and compare how the size and number of internal power transformers affects the technical performance
(robustness, power quality and efficiency) of a utility-scale PV plant. The technical performance was examined in a simulation environment (MATLAB Simulink), where a PV plant with a fixed number of PV arrays and converters, corresponding to a rated power of 40 MW, was connected to the
grid in four different ways, resulting in four simulation models. First off two models, using 4 x 10 MVA transformers respectively 20 x 2 MVA transformers, were built and simulated under different site conditions (grid strength and distance to PCC) and disturbances (varying solar irradiation and grid frequency). The simulations showed no significant performance difference between the two models.

Further, two more models, using 1 x 40 MVA transformer and 40 x 1 MVA transformers, were introduced as the first two showed no difference in performance. These, along with the old models, were then stress tested in order to get further indications if the size and number of transformers affects the performance, and now more specifically the robustness of a PV plant. The stress test was performed by decreasing the grid strength until the control systems no longer could follow their set-points. This corresponds to the system no longer being stable. The stress test showed small differences between the robustness of the four models, but no correlation between the number of transformers and robustness was observed.

As a whole the simulations showed that the size and number of transformers had no significant impact on the technical performance of the PV plant. In
addition to the technical simulations, a brief qualitative economical comparison, between using a few large versus many small transformers was conducted. The comparison was made in three aspects; components and labour, logistics and reliability/redundancy. Regarding the amount of components
and labour needed, using a few large transformers was clearly favorable. The logistical aspect was very case dependent and could favor either many
small or a few large. In terms of reliability and redundancy many small transformers was favorable. (Less)
Popular Abstract (Swedish)
Solcellsparker blir både allt vanligare och allt större. I denna studie undersöks hur storleken och antalet transformatorer i en solcellspark påverkar dennas förmåga att leverera el.

De rådande klimatförändringarna är en av de största utmaningar mänskligheten ställts inför. Fossil elproduktion är en stor bidragande faktor till utsläpp av växthusgaser globalt. Solceller ser ut att spela en avgörande roll i att bryta världens beroende av fossil elproduktion. Solceller har tidigare främst förekommit i liten skala, exempelvis på villatak, medan stora parker, på en area motsvarande upp emot och över 100 fotbollsplaner, blir allt vanligare.

Utöver solcellerna behövs ett gäng andra komponenter för att elen ska kunna skickas ut på elnätet.... (More)
Solcellsparker blir både allt vanligare och allt större. I denna studie undersöks hur storleken och antalet transformatorer i en solcellspark påverkar dennas förmåga att leverera el.

De rådande klimatförändringarna är en av de största utmaningar mänskligheten ställts inför. Fossil elproduktion är en stor bidragande faktor till utsläpp av växthusgaser globalt. Solceller ser ut att spela en avgörande roll i att bryta världens beroende av fossil elproduktion. Solceller har tidigare främst förekommit i liten skala, exempelvis på villatak, medan stora parker, på en area motsvarande upp emot och över 100 fotbollsplaner, blir allt vanligare.

Utöver solcellerna behövs ett gäng andra komponenter för att elen ska kunna skickas ut på elnätet. En viktigt sådan är transformatorn. Den används för att öka spänningen som solcellerna ger ut till den nivån som nätet använder sig av. Detta kan liknas vid att använda en växellåda för att koppla ihop axlar som roterar med olika hastighet.

Transformatorns storlek kan variera från att rymma i liten byggnad och väga något ton till enstor utomhusanläggning som väger tiotals ton.
Detta är beroende av hur många solceller som är kopplade till den. För en solcellspark blir det ett viktigt designval om små grupper av solceller ska
kopplas till många små transformatorer, eller om större grupper ska kopplas till färre stora transformatorer.

I dagsläget finns ingen etablerad standard för detta designval. Efter en kort analys drog vi slutsatsen att det finns för och nackdelar med att använda många små kontra få stora transformatorer. Många små transformatorer gör solcellsparken mindre beroende av enskilda komponenter, det är därmed inte lika kostsamt om något går sönder. Små transformatorer har dessutom betydligt kortare ledtider vilket minskar risken att försena projekt. Å andra sidan innebär få stora transformatorer mindre total kostnad för själva transformatorerna och övrig utrustning, samt billigare arbetskostnader vid
installation och drift.

Solcellsparkens förmåga att leverera el är dock dess viktigaste egenskap och bör stå i centrum vid design. I detta arbete har vi undersökt hur denna förmåga hos en solcellspark påverkas av antal och storlek på transformatorerna som används. Undersökningen har gjorts i ett datorprogram där samma antal solceller kopplades till elnätet via ett fåtal stora respektive många små transformatorer.

Resultaten från undersökningen visar inte att antalet och storleken på transformatorer som används på något sätt skulle påverka solcellsparkens förmåga att leverera el. Detta var inte helt väntat, men på många sätt positivt då det innebär att valet kan göras helt på ekonomiska grunder. (Less)
Please use this url to cite or link to this publication:
author
Lindblom, Oliver LU and Elfström, Jens LU
supervisor
organization
course
EIEM01 20241
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
transformers, photovoltaics, utility-scale PV, power quality, robustness
publication/series
CODEN:LUTEDX/TEIE
report number
5516
language
English
id
9163705
date added to LUP
2025-02-05 17:02:22
date last changed
2025-02-05 17:02:22
@misc{9163705,
  abstract     = {{The main focus of this thesis has been to examine and compare how the size and number of internal power transformers affects the technical performance
(robustness, power quality and efficiency) of a utility-scale PV plant. The technical performance was examined in a simulation environment (MATLAB Simulink), where a PV plant with a fixed number of PV arrays and converters, corresponding to a rated power of 40 MW, was connected to the
grid in four different ways, resulting in four simulation models. First off two models, using 4 x 10 MVA transformers respectively 20 x 2 MVA transformers, were built and simulated under different site conditions (grid strength and distance to PCC) and disturbances (varying solar irradiation and grid frequency). The simulations showed no significant performance difference between the two models.

Further, two more models, using 1 x 40 MVA transformer and 40 x 1 MVA transformers, were introduced as the first two showed no difference in performance. These, along with the old models, were then stress tested in order to get further indications if the size and number of transformers affects the performance, and now more specifically the robustness of a PV plant. The stress test was performed by decreasing the grid strength until the control systems no longer could follow their set-points. This corresponds to the system no longer being stable. The stress test showed small differences between the robustness of the four models, but no correlation between the number of transformers and robustness was observed.

As a whole the simulations showed that the size and number of transformers had no significant impact on the technical performance of the PV plant. In
addition to the technical simulations, a brief qualitative economical comparison, between using a few large versus many small transformers was conducted. The comparison was made in three aspects; components and labour, logistics and reliability/redundancy. Regarding the amount of components
and labour needed, using a few large transformers was clearly favorable. The logistical aspect was very case dependent and could favor either many
small or a few large. In terms of reliability and redundancy many small transformers was favorable.}},
  author       = {{Lindblom, Oliver and Elfström, Jens}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{CODEN:LUTEDX/TEIE}},
  title        = {{Impact on the Technical Performance of a Utility-Scale PV Plant when Using Different Sizes and Numbers of Transformers}},
  year         = {{2024}},
}