Solar Transformer - Your ultimate guide

Solar energy is the most abundant energy source on earth, and contemporary solar energy can be used to produce other renewable energy sources. We can convert solar energy into electricity. At present, there are two main conversion forms in the world, one is solar photovoltaic power stations, and the other is solar thermal power stations. Whether it is photovoltaic power generation or solar thermal power generation, solar transformers are used.

2500kva solar transformersolar power transformer

2000 kva solar transformer2500 kva solar power transformer

Daelim is a professional and famous transformer supplier. Its design and production of pad mounted transformers, substation transformers and dry transformers can provide solar power solutions for your project. With its professional competence and strict quality control system, Daelim can supply high-quality transformers all over the world. The designed and produced transformers fully comply with IEEE/IEC, DOE, AS/NZS60076, CSA, and other international standards, and the transformers have UL/cUL, CSA, IEEE, CESI, SGS, and other certificates and reports


This page contains all of the information you need to know about Solar Transformers.

Continue reading for more details.

Table of contents

1. What precisely is a solar transformer?

2. What are the core features of solar transformers?

3. Specification and Model Selection of Solar Transformer

4. Introduction of special transformers used in photovoltaic power plants

5. Selection principle of photovoltaic power generation transformer

6. Daelim solar transformer Selection Parameters

7. Daelim Solar Transformer Design

8. What are the types of solar transformers?

9. What is the difference between solar photovoltaic and solar thermal power generation?

10. What are the requirements for transformers used in solar power generation?

11. What exactly is the function of a solar transformer?

12. Do you need a transformer for solar panels?

13. In solar power facilities, which transformer is used?

14. What is a three-phase transformer?

15. How do you size a solar transformer?

16. What kind of voltage or current waveform will the PV Inverter provide to the transformer?

17. Conclusion


What precisely is a solar transformer?

The solar transformer is also called a photovoltaic transformer, referred to as a PV transformer. Transformers play a significant role in the production and distribution of solar energy. Transformers are used in photovoltaic projects, mainly to increase the voltage output by the inverter. Help the photovoltaic system to better connect with the grid system. Non-renewable energy sources have produced two types of transformers: step-up transformers and step-down transformers. Most use step-up transformers


Solar transformers are classified as distribution, station, auxiliary station, pad mounting, and grounding. All solar transformers have unique requirements that affect the machine's cost.


What are the core features of solar transformers?

The transformers designed and produced by Daelim mainly have the following characteristics:

1. FR3 dielectric fluid provides fire safety, equipment reliability, and a projected lifespan well beyond that of a traditional mineral-oil transformer making it a key component in the balance of system (BOS) distributed energy resources (DER) solutions

2. Custom-optimized transformer designs for specific loading profiles, impedance requirements, and single or multiple inverter connections

3. Increased overload capability above nameplate without loss of insulation life

4. Fully complements solar/energy balance of system (BOS) solutions including DC and AC combiners, disconnects, fuses, breakers and AC recombiners, pad-mounted switchgear, pole-mounted reclosers, air switches, capacitors, and a full offering of services  


In the photovoltaic grid-connected power generation system, the step-up transformer is one of the key pieces of equipment. How optimize the selection, reducing the loss of the transformer itself, and improving the efficiency of the transformer is one of the factors to improve the efficiency of the photovoltaic power generation system. Next, we will make a reasonable selection of step-up transformers in photovoltaic grid-connected power generation systems by comparing and analyzing different types of transformers.

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Specification and Model Selection of Solar Transformer

Transformer capacity selection750 kva solar transformer

According to active power/power factor = apparent power, this formula is used to calculate the required transformer capacity. The power specified by the power supply bureaus in different regions is not the same, but basically, the power factor of construction electricity and small industry is 0.85. The power factor of large industrial electricity is 0.9. Therefore, assuming a 550kW construction equipment, the transformer size that should be selected = 550kW/0.85=647kVA, so a 630kVA transformer should be selected. The sum of the load power cannot exceed 80% of the selected transformer power.

Learn more: 750 kVA Transformer Introduction

Transformer voltage selection

The primary voltage of the transformer is selected according to the voltage value generated in the photovoltaic power generation system, and the voltage of the secondary coil is selected according to the integrated grid voltage. It is best to choose a low-voltage three-phase four-wire power supply. For example, if the output voltage of the solar inverter is 600V, then the primary side voltage of the transformer is 600V. The integrated power grid is 13.8kV, then the secondary side voltage is 13.8kV.


Selection of transformer phases

Solar photovoltaic power generation projects usually use three-phase transformers.


Selection of transformer connection group

The step-up transformers used in solar photovoltaic power generation projects are mainly composed of: Dy1, Dy5, and Dy11.

Photovoltaic transformers are usually Dy-connected. At present, the solar transformers in most countries in the world use Dy connection, mainly because the use of Dy connection has advantages compared with the use of Yy connection:

D connection has a great effect on suppressing the bad influence of higher harmonics

In the D-connected transformer winding, its third harmonic circulating current can generate the third harmonic magnetomotive force in the transformer, which can be balanced and offset with the harmonic magnetomotive force of the low-voltage winding;

The harmonic electromotive force of the high-voltage winding circulates in the D-connected loop, and the harmonic current can form a circulating current in the D-connected primary winding so that it does not enter the public high-voltage power grid.

The zero-sequence impedance of Dy-connected transformers is much smaller than that of Yy-connected transformers, which is beneficial to the removal of low-voltage single-phase-to-ground short-circuit faults.

The Dy connection makes the transformer's ability to withstand unbalanced loads far greater than the Yy connection.

Dy connection transformer is more protective and safer than Yy. When one high-voltage phase of the transformer fails, when the first-phase fuse on the high-voltage side is blown, the other two-phase loads of the transformer can still operate normally, but the transformer connected to Yy cannot.

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Transformer load loss, no-load loss, and impedance voltage

Considering the particularity of photovoltaic power generation, that is, power generation during the day, no matter whether the power generation device outputs power or not, as long as the transformer is connected to the system, the transformer will always produce no-load loss. The load loss of the transformer is required to be as low as possible. If the transformer runs at night, the no-load loss is also required to be low;

Transformer working environment

The working place of the transformer is clean, and the dust-free capacity is not very large. Usually, the dry-type transformer can be selected if the capacity is less than 800kVA. Otherwise, the oil-immersed transformer should be selected. The oil-immersed transformer will naturally decide for you whether it is natural cooling or air cooling according to the size of the capacity.


The main features of dry-type transformers are small size, lightweight, fire-proof and explosion-proof, and maintenance-free, but once the dry-type transformer fails, it will be scrapped directly and need to be repurchased.


Characteristics of oil-immersed transformers

The main feature of oil-immersed transformers is that the cooling effect is good, which can meet the needs of large capacity. The selection of vegetable oil for transformer oil is also environmentally friendly, pollution-free, and has a longer service life. The disadvantage is that frequent inspections and regular maintenance are required to avoid the danger of failure or even transformer explosion due to oil leakage, oil shortage, insulation aging, etc.

Read more: How much do you know about oil-immersed distribution transformers?

Introduction of special transformers used in photovoltaic power plants

Split transformer

The difference between a split transformer and an ordinary transformer is that in its low-voltage winding, one or more windings are split into several branches with equal rated capacity. There is no electrical connection between these branches, but only weak magnetic connection. , and there is a large impedance between the branches. The most widely used is the double-winding double-split transformer, which has one high-voltage winding and two split low-voltage windings, and the rated voltage and rated capacity of the split windings are the same. When a split transformer is used to supply power to two busbars, when a short circuit occurs on one busbar, in addition to effectively limiting the short-circuit current, the voltage on the other busbar can be kept at a certain level without affecting the user's operation.


A photovoltaic step-up transformer is the splitting of the low-voltage side into two windings of the same capacity, connecting the windings of the group and voltage level, and connecting two photovoltaic cells respectively. The main purpose is to limit the short-circuit current and reduce the number of transformers.


Isolation transformer

Its main feature is safety: it completely insulates the electrical appliances on the primary side and the secondary side and also isolates the circuit. The high-frequency loss of its iron core is large, thereby suppressing the introduction of high-frequency clutter into the control loop. However, it can only be used in small-scale power supply areas and places with short lines. Because the current to the ground is very small, it can protect personal safety, but it is not enough to cause personal injury. Another very important role is to protect personal safety!


Selection principle of photovoltaic power generation transformer

1 Self-cooling, low-loss power transformers should be preferred.

2 The capacity of the step-up transformer can be selected according to the maximum output power of the photovoltaic square array unit module.

3 High-voltage/low-voltage prefabricated box-type substations or open-type equipment composed of transformers and high and low-voltage electrical components can be selected. For photovoltaic power stations located on the coast or with heavy wind and sand, when the outdoor layout is used, the coastal protection level should reach IP65, and the protection level of photovoltaic power stations with heavy wind and sand should reach IP54.

4 The on-site step-up transformer can be a double-winding transformer or a split transformer.

5 The on-site step-up transformer should be a non-excitation voltage-regulating transformer.

6 Prevent electrostatic shielding layer between high and low voltage to prevent high and low voltage mutual inductance.


Daelim solar transformer Selection Parameters

1. Rated output kVA:
• Based on inverter output ratings, load diagram, harmonic content, weather patterns, and unusual service conditions
500 kva solar transformer

2. Nominal Voltage:
• Designed for Inverter Transformer to be compatible with Pulse voltage shape of inverters
3. Winding connection diagram and vector group:
• Inverter operation is not affected by vector groups like Dy1, Dy5 or Dy11
• No Neutral required on the Primary LV side
• Isolated neutral point on Secondary HV side transformer
4. Electrostatic Shield (ES):
• Recommended installation of ES between primary and secondary windings to minimize the potential transfer of high-frequency voltage disturbances (harmonics, pulses, surges) from primary to secondary
• Windings typically connected to inverter circuits are ungrounded
DAELIM fully complies with C57.159 – 2016 IEEE Guide for application in DPV Power Generation Systems.

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Daelim Solar Transformer Design

1. Pad mount transformer

Phases: Three
Frequency: 50 Hz, 60Hz
Standard: IEEE, CSA
Tank Type: Padmount
Base rating: 750 kVA through 10,000 KVA
High Voltage (HV): 2.5 kV through 35 kV
Low Voltage (LV): 208Y/120 to 25,000 V
Windings: Copper, Aluminum
Solar pads are available in various configurations to accommodate typical inverter connections and performances


2. Substation transformer

Phases: Three
Frequency: 50 Hz, 60Hz
Standard: IEEE, CSA
Base rating: 750 kVA through 10,000 KVA
High Voltage (HV): 2.5 kV through 35 kV
Low Voltage (LV): 208Y/120 to 25,000 V
Windings: Copper, Aluminum
Solar pads are available in various configurations to accommodate typical inverter connections and performances


3. Solar energy transformer solution

The transformers provided by Daelim can match any size inverter in solar photovoltaic power generation.

Click here for specific solar transformer solutions.

3000 kva solar power transformer1500 kva solar transformer

What are the types of solar transformer?

There are different types of solar transformers including three-phase pad mounted, oil immersed, substation, and dry transformer. All solar transformers have special needs that affect cost. Dry uses air as the cooling medium, while liquid uses oil.

Learn more: How Much You Know For The Different Types Of Transformers?


Three phase pad mounted transformer

A 3-phase pad-mounted transformer is a kind of oil transformer, and it is also a very common solar transformer in recent years. Especially in the US and Canada markets in North America. The pad-mounted transformer is widely loved by the market due to its compact structure, tamper-proof design, and easy maintenance.


Daelim's pad mount transformer has SGS, CESI, CSA and other test reports, UL/cUL, CSA, IEEE, and other certificates, transformers less than 2500kVA can also be designed to meet the US DOE efficiency value standard. Daelim's pad mount transformers are exported to North America in large quantities, and there are after-sales service teams in markets such as the United States and Canada.

Read more about pad mount transformer: 3 Phase Pad Mounted Transformer-Daelim Belefic


Daelim's pad mount transformer can be designed with dual voltage and meet K factor rating. Pad mount transformer conventional capacity has 300 kVA, 500 kVA, 750 kVA, 1000 kVA, 1500 kVA, 2000 kVA, 2500kVA, 3000kVA, 3750 kVA, and 5000kVA, Daelim's 3-phase pad mount transformer A capacity of 10MVA can be achieved.


Daelim's pad mount transformer optional accessories: Oil level gauge, Liquide temperature gauge, Pressure vacuum gauge, Primary termination: externally clamped bushing wells with load break inserts/Integral load break or non-load break bushings, Secondary termination: externally clamped bushings with NEMA 4-hole, 6-hole, 8-hole, 10-hole or 12-hole spades, overvoltage protection, etc. For the above accessories, you can choose Qualitrol, ABB, and other internationally famous brands.


Substation transformer

A substation transformer is also a commonly used transformer in solar power plants. It is characterized by low loss, and the radiator and air terminal chamber can be disassembled for easy transportation and movement.


Daelim's substation transformer with high voltage up to 34.5kV, and rating up to 20 MVA. Design and production conform to CSA/ASUL/DOE and other standards, with a UL certificate. There are four structural layouts of American Standard. The high and low voltage bushings are sides out on both sides, the high and low voltage bushings are on top sides, and one side is out and the other side is on top. Substation transformers are usually colored gray and green.

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Oil-immersed transformers

This type of transformer, often known as oil-filled transformers, is an electric voltage that uses ways to cool the oil in order to lower transformer temperatures.


Unlike dry transformers, the body of an oil-immersed transformer is fitted inside a welded steel tank that has been filled with oil insulation. When an oil-immersed transformer operates, its iron core heats the coil, which is subsequently transported into the insulation fluid and then onto the medium to cool. The voltage of Daelim's oil-immersed transformer can reach 220kV, and the maximum capacity can reach 240MVA.

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Dry-Type Transformers

This type of transformer has no moving parts. They are inert devices that utilize thermal insulation technologies that are environmentally friendly.


The word "dry" refers to the fact that the transformer is kept cool through natural ventilation rather than using silicone, oil, or liquids to cool the coils and electrical core.


Dry-type transformers are not required to be housed in fireproof vaults or catch basins. This type of transformer is safe and may be used in a variety of locations, they can be placed close to the equipment and indoors, making the entire process more efficient.

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Dry-type liquid-cooled transformers

For enhanced performance, some systems combine dry-type units with tanks. These transformers are appropriate for both indoor and outdoor installations. They are dry-type liquid-cooled transformers, often referred to as dry-and-liquid transformers or hybrids.


What is the difference between solar photovoltaic and solar thermal power generation?

The main difference between solar photovoltaic power generation and solar thermal power generation is:

1. Solar thermal power generation has large investment, large construction site, long construction period, and high construction cost;

2. Solar thermal power generation is more controllable than photovoltaic power generation, and the power is stable and adjustable;

3. The transformer capacity for solar thermal power generation is larger and the running time is longer

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What are the requirements for transformers used in solar power generation?

1. Requires lower loss;

2. Strong voltage overload capability;

3. There are both DC waves, and a shielding layer should be placed between the high and low to prevent high and low voltage mutual inductance


What exactly is the function of a solar transformer?

The function of a solar transformer is very simple, it converts direct current (DC) electricity generated by a solar panel to alternating current (AC) electricity used by the power grid.


Do you need a transformer for solar panels?

Yes, absolutely! Transformers are essential components in both the production and delivery of solar energy. Transformers have previously been used to step-up or step-down electricity from renewable sources.


In solar power facilities, which transformer is used?

Three-phase transformers are the most common type of transformer used in power plants. Three-phase systems are more efficient and can handle larger voltages. They can also power three-phase motors, power tools, and major companies. Furthermore, its system structure allows for longer power distribution distances. Transformers are commonly used in solar power generation, the voltage is 6.3-38.5kV, and the capacity is 630kVA-3150kVA.


What is a three-phase transformer?

A three-phase transformer is an electromagnetic device that is used to transfer energy or send electrical signals between circuits using Faraday's electromagnetic induction phenomenon. Three-phase transformers play a crucial part in the transmission of power. They are primarily used in industrial applications to create the power to transmit, distribute and store electricity. Dry type transformer, small substation transformer, pad mounted transformer, and power transformer all have three phases.  Three-phase transformers are installed in locations that use an enormous amount of electricity, such as hospital buildings, apartment buildings power stations, and solar power plants.

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How do you size solar transformers?

There are two primary aspects to be considered when designing transformers powered by inverters that are which are powered by PV arrays.


What kind of voltage or current waveform will the PV Inverter provide to the transformer?

Considerations for the environment, typically ambient temperature.


Modern PV inverters usually produce the sinusoidal voltage and the current waveform is similar to the ideal sine wave. So grid-tie transformers generally do not need to be large in the event that solar power inverters operate them. General-purpose transformers are typically specifically designed. Non-linear loads could cause the voltage and current to cause Total Harmonic Distortion (THD) which could impact the transformer's performance and cause an increase in heating. A K=4 transformer can manage the distortion typical of non-linear loads when that's an issue. Changes in load speed should not have any effect on the effectiveness of dry-type transformers.


The environmental conditions, like ambient temperature, must also be taken into consideration. Grid-tie transformers typically don't experience a maximum load or, if they do, it will last less than an hour, based on typical load curves for solar facilities. Dry-type transformers with 220 to C insulation and 150 degrees C temperatures are built to handle their highest load for as long as the temperature of the surrounding area is not more than 40 degrees C and averages around 30 degrees C to during any 24-hour time period. In areas that have high temperatures in the air in the winter, lower temperatures for dry-type transformers must be taken into consideration. 130 o C Temperature rise raises the maximum ambient temperature to sixty 60C while the median of 50 o C in a 24-hour span. A 115 or C temperature rise is capable of handling more extreme ambient temperatures if required. It is usually more economical to choose transformers with lower temperature rises rather than manually increase the power for the particular transformer.

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1000 kva solar power transformer
Daelim is a transformer manufacturer that provides a broad range of pad-mounted transformers, substation transformers, oil-immersed transformers, and dry transformers for solar energy applications. Pad-mount and oil-immersed transformers are rated based on their solar power capacity as well as array voltage, and meet the requirements of all standards and regulations in force as well as energy efficiency.


1. Experience in supplying multiple projects in the  American Countries such as U.S. and Canada 
2. Qualified with UL, cUL, CSA certificate, SGS test report, etc.   
3. Complete after-sales service and installation teams in Canada, USA, etc. 
4. Strong design ability for high efficiency, special ambient, low sound level,50 Hz and 60 Hz ,k-factor rating, etc 
5. 6-7 weeks of production time


Daelim believes that it is essential to produce high-quality products at reasonable prices. Within each component, they never compromise on performance or environmental responsibility. Because of this dedication, they are your one-stop shop for all things electrical. If you have any questions about your project, you can contact the Daelim team, and their professional team will provide quick feedback.

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