How to Choose a Pad Mounted Transformer and Delta Wye Transformer?

Delta Wye Transformer (3)

This article is for the bid requirement for the pad mounted transformer; and the description of the Delta Wye transformer, 
There are Delta connection and Wye connection for the transformer. Delta connection and Wye connection are different.
As a pad mounted transformer manufacturer and exporter with rich experience in China, we won a lot of projects for pad mounted transformer, mini substation transformer, power transformer etc…
Both directly purchase project and the tender, Daelim and our clients support each other to win them.
The example is a bid for 44kv 1000kva pad mounted transformer in Canada,

Pad-mounted Transformer

We can provide you single phase and three phase pad mounted transformer

Dry-type Transformer

Type:Cast resin; Rated Capacity: Up to 25MVA; Rated Voltage: Up to 36KV;

Pole Transformer

TypeCSP type Frequency: 50/60Hz; Rated Power: 5~167kva

Oil immersed transformer

Frequency: 50/60Hz Rated voltage:10kv, 20kv,30kv Rated Power: 400~2500kva

Table of Content

General for the pad mounted transformer

The part 1 for the bid document requirement is General, there will have standard requirement for the whole pad mounted transformer and the standard for the accessories like the bushings, the test and the efficiency…
Because this transformer connection is Dyn1, so this is a Delta-Wye transformer.

The customer will write the drawing request in the general, they will need us to Submit Shop Drawings and product data in accordance. In the drawings, should Indicate the Dimensioned positions of the mounting devices, the Dimensioned positions of the terminations. The Identified internal and external component layout on assembly drawing, and the Insulating liquid capacity. Besides them, we need to Provide certificates of compliance with the requirements to demonstrated the ability to function after the test before the delivery, we should finish and pass all of the type test as requirement. 

Let’s know learn more about the How to purchase a 10 mva substation transformer

The 44kv 1000kva pas mounted transformer product requirement

First should be the CHARACTERISTICS of the pad mounted transformer, they will show the detailed tech specification requirement, the capacity is 1000kva, the high voltage is 44kv, the low voltage is 480v, the Liquid cooled transformer to be ONAN, 3phase, and the frequency. Include the impedance, the BIL etc… According above information, we can identify this bid is for a 1000kva pad mounted transformer.

As always, the tap should be ±2×2.5%, it is same as the requirement in the CSA standard.

Delta Wye Transformer (4)

The second, there will have detailed requirement for the connection of the high voltage bushings and low voltage bushings, As CSA C227.4 standard for the bushings, if it is dead front, shall meet the dimensional and electrical requirement of IEEE 386. The low voltage shall be the spade type, so they will be named as low voltage terminals. If there have no requirement, the number of the holes have standard requirement in the CSA standard.

Delta Wye Transformer (5)

Third, they will always have the oil type requirement, the widely used for the pad mounted transformer are FR3 oil (or vegetable oil) and the mineral oil. If the insulating oil is FR3 or vegetable oil, the cooling type for the pad mounted transformer should be KNAN, if the insulating oil is mineral oil, the cooling type should be ONAN.

The accessories for the pad mounted transformer

1. liquid level gauge for pad mounted transformer, if it with the alarm contacts and tripped contacts, it should be a protection device, when the liquid is in the lowest level, the liquid level gauge will alarm or trip.

2. liquid temperature gauge for pad mounted transformer, if it with the alarm contacts and tripped contacts, it should be a protection device, when the liquid temperature is in the highest level, the liquid temperature gauge will alarm or trip.

3. Winding temperature gauge for pad mounted transformer, if it with the alarm contacts and tripped contacts, it should be a protection device, when the winding temperature is in the highest level, the liquid temperature gauge will alarm or trip.

4. Pressure relief device for the pad mounted transformer, there are different type for the pressure relief device, like the pressure relief valve should be little ring, and the pressure relief device can be a disc type in the top cover.

5. Others accessories include Rapid pressure rise relay, the pressure-vacuum gauge etc…

The test for the pad mounted transformer

As the CSA C227.4 standard, there have the type test, and the other test. Our solution will include the routine test as standard, 1). Resistance, 2). temperature rise; 3). Impulse strength; 4). radio influence voltage; 5). short-circuit; 6). transformer integrity; 7) audible sound.

1) . the Resistance testis a design test for distribution transformers rated 2500kva and smaller and a routine test for distribution transformer rated greater than 2500kva.

2) Ratio test on the rated voltage connection and on all tap positiions as listed on the nameplate. For multiple winding or dual voltage units, ratio tests shall be performed on all connections.

3) Polarity and phase relation tests on the rated voltage connection.

4) No load losses at 105% rated voltage;

5) Exciting current at 105% rated voltage;

6) Load loss and impedance st rated current, on the rated voltage connection, corrected to 85℃. This test shall be performed on the high-voltage connection that has the highest measured loss value;

7) And other tests

High voltage

30kv, 33kv, 44kv or others

Low voltage

6.3kv, 6.6kv, 4.16kv or others

Rated capacity




Core and winding material

Crgo slicon steel Metal Core, AL or CU Winding

On-load tap changer

Germany MR, ABB, Huaming China…


Provide 24 months guarantee period normally

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INSTALLATION for the pad mounted transformer

Delta Wye Transformer (6)

The installation should in accordance with the manufacturer’s instructions.
If building a cast concrete pad instead of a precast manhole, ensure the concrete pad is fully cured for 28 days before installing the transformer.
Use the spreader on the sling when hoisting the transformer into place.

Set up and fix the transformer in a rigid, vertical and square position.Make sure the internal connections are mechanically tight.Make connections at the high and low voltage terminals. Connect the transformer ground terminal to the system ground.

Fill the transformer with metal hose as needed, and ensure care is taken to prevent contamination of the liquid and components.Set the tap to produce the rated secondary voltage at no load.

Connect one set of contacts on the liquid temperature measurement device to sound an alarm when an unsafe condition is reached, and connect a second set of contacts to the trip transformer circuit breaker.

Power up the transformer and verify that the phase rotation on the secondary side of the transformer is correct. For transformer replacement, check the phase rotation before removing the existing transformer and after installing the new transformer. Phase rotation checks should be performed using the same rotometer.

The application for the pad mounted transformer

The pad mounted transformer are widely used for the cryptocurrency mining, we have rich experience in the pad mounted transformer for cryptocurrency mining projects, the most used for it is 2500kva or 3000kva. Also the substation transformer also widely used for the BTC mining.

With the rise of cryptocurrency mining, the demand for the pad mounted transformer or small substation in the US and Canadian markets has grown rapidly.

Recently we have received a lot of inquiries for Cryptocurrency mining transformers from the United States, Canada and other countries. DAELIM also exported many units for NA market Cryptocurrency mining projects

And the pad mounted transformers can be used for the solar, the These pad-mounted transformers are filled with a more environmentally friendly, biodegradable and sustainable FR3 dielectric fluid for improved fire protection and longer life. These solar and energy storage transformers are rated at 45-12,000 kVA and can also be customized with various site-specific characteristics to optimize safety and system integration.

Daelim Transformer can provide our best price and best lead time also with the best service.

What is the purpose of a Delta Wye transformer

The Delta and Wye are the two different connection types. Delta-Wye transformer (3 phase 4 wire, 3 phase system)
The angular displacement: angular displacement of the transformer shall be 0°and 30°, if the angular displacement is 0°, the connection should be YNyn0, the high voltage connection is Wye and the low voltage connection is Wye; if the angular displacement is 30°, the connection should be Dyn1, then the high voltage connection is Delta, and the low voltage connection should be Wye.
Some times, we say Wye is “Wye” connection, Delta is “Mesh”connection.

Read my article on Know More About Tips of single phase transformer

What's the difference between Delta and Wye transformers?

Delta Wye Transformer (1)

From the connection method, the Wye connection method is that one end of the three coils is shorted to each other.

The other end is connected to the three-phase power supply respectively. The Delta connection method is that the three coils are connected end to end in the shape of a Delta, and the three connection points are respectively connected to the three-phase power supply. In terms of voltage at both ends, the voltage at both ends of each coil of the Wye connection is equal to the phase voltage. In the delta connection, the voltage across each coil is equal to the line voltage. Therefore, for the same three sets of coils, if the connection is Wye, the power is lower than that of the delta connection.
The Wye connection (Y) connection can have a neutral point; the Delta (D) connection cannot have a neutral point.

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What is Delta and Wye connection

Delta Wye Transformer (2)

1. The Wye connection is characterized by fewer coils and a large current, and the corner connection is characterized by many coils and a small current. Due to the high voltage on the high-voltage side of a large transformer, the number of coils connected by angular connection will increase, which increases the coil making time, and the use of Wye connection reduces the number of coils. Although the current increases, the high-voltage current is small and cannot increase much; Corner connection, reduce the current, reduce the cross-sectional area of the wire, and facilitate the processing and production of the coil.
2. The high-voltage side of large transformers are all above 110KV, and the zero-line grounding operation mode is adopted. The Wye connection is used to facilitate the grounding of the zero-line (neutral line); the low-voltage side of large-scale transformers are all 35KV or 10KV. Reliability, use the neutral point ungrounded operation, choose the angle shape, can save materials.
The Delta Wye transformer is widely used by USA and Canada market, it is the regular requirement for the connection, we exported to USA and Canada and other NA market a lot of transformers, include the pad mounted transformer and substation transformers… and most of them are Delta Wye transformers.

Our projects in Canada, to start from hundreds of single-phase transformer, to three phase pad mounted transformers, and then to the substation transformers, we from 37.5 kva single phase into the Canadian market, it has been cooperation in 13.3 mva small substation transformer. Based on the experience of these years in Canada, we have a very rich learning and understanding for the CSA standard and Canada market, In order to better expand our business in Canada, we have applied for CSA certification.

CSA certification: Products such as electronics and electrical appliances sold in the North American market need to obtain safety certifications. CSA is the largest safety certification body in Canada and one of the most famous safety certification bodies in the world.
In order to expend more business in Canada, we applied the CSA certification through this substation, this substation transformer is also a Delta Wye transformer. it spend our fews weeks to prepare, more than two weeks to get certified, then, we got it!
Daelim can meet your requirement and provide our best service for our sales team and provide our best tech support of our engineer team, we are the professional transformer manufacturer in China, we have rich experience in the transformer market, we will support you with our solution, and give you our best price and competitive lead time, to win more projects with our clients and gain win-win.


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About Bin Dong

Hello, I am Bin, General manager of Daelim which is a leading transformer manufacturer. If you have problems when you are looking for the equipment, what you need to do is tell us.