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Choose DOE Energy Efficient Single Phase Pad Mounted Transformer

single phase pad mounted transformer (1)

The US Department of Energy (DOE) defines the efficiency levels for distribution transformers including single phase pad mounted transformer sine January 1, 2016.

The efficiency increased from “TP1”to DOE 2016. This new efficiency level are indicated in 10 CFR Part 431 (, check below efficiency for single phase pad mounted transformers.

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

Single Phase Pad Mounted Transformer

residential transformer (2)


DOE 2016

















Daelim single phase pad mounted transformer is designed as per

Power Calculation and Selection of Building Residential Transformer

The calculation of residential transformer capacity selection is based on the conventional calculation method; it is the total designed capacity of residential users in the community, which is the sum of the capacity of – households – households, and because the residential electricity is single-phase, we need to convert this number into three Phase four-wire electricity, then, the relationship between phase current and line current is the problem of root number 3, that is, the sum of this single-phase power divided by 1.732, is converted into three-phase four-wire power.

700 households, each household consumes 4KW of electricity, the sum of one household is 2800/1.732 = 1616KW, this number is the maximum power of all electrical appliances in the community at the same time, then, in actual use, this situation will not happen. If yes, then there is a called simultaneous power consumption rate, generally 70-80%, which is determined according to the user structure characteristics of the cell. However, according to the economic operation value of the transformer is 75%, then we can offset these two values, and calculate the capacity of the transformer according to this power. Then, the capacity of this transformer is the total total power of 2800/1.732=1616KW. According to In the case of residential electricity, the power factor is now 0.85-0.9, and the apparent power Sp= P+0.85 = 1616/0.85 =1901KVA.

How to calculate, first divide the total 2800 power into three lines of power, which is single-phase power, 2800/3=933KW, then convert this single-phase power into three-phase power, 933×1.732 ≈ 808KW, and then Divided by the power factor of 0.85 = 1901KVA.

According to the standard capacity of this data set of transformers, it is recommended to select one transformer with a total capacity of 1900KVA. If future development is considered, two 1000KVA transformers can also be selected, or one 2000KVA transformer can be directly selected.

We know that the power KVA of the transformer represents the apparent power, and there is no need to calculate the power factor when calculating the three-phase AC current. Therefore, Sp= l3xUxl. When selecting, the data should be larger than the actual data, so as to ensure the safe operation of the equipment. 

Daelim single phase pad mounted transformer is designed as per NEMA,IEEE/ANSI C57.12.38 and  IEEE/ANSI C57.12.00, all transformers meets with DOE energy efficiency.

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Where is single-phase pad mounted transformer is used?

residential transformer (4)

Pad mounted transformers have some characteristics of military products. 

According to relevant information, in the 1970s and early 1980s, the U.S. military ordered batches of small-sized and easy-to-install simple integrated power supplies from relevant electrical manufacturers in order to adapt to desert and field needs. The station, for military purposes, is of course relatively simple in design, and there are no metering devices and capacitive reactive power compensation devices in the compartment.

The single phase pad mounted transformer is small in size and compact in structure, only one-third of the European box transformer of the same capacity. This design has also been introduced in China. Novel and beautiful appearance, simple structure, small footprint. In some cities, because the land is getting less and less, especially the land in the main urban area is more expensive, so pad mounted transformer, which is easy to install and cheaper than similar European cabinets, is more and more favored by customers. Similar products can be seen everywhere in factories, shopping malls, hotels, agricultural and sideline markets in the main urban area.

Daelim single phase pad mounted transformer offers an economical design with a low profile that blends visually with surrounding shrubs, low hedges and home air conditioners, making it ideal for residential applications. It is a very compact pad-mounted transformer.

Daelim ANSI standard single-phase pad mounted transformer adopts a clamshell design, which is convenient for the connection of cables and electrical components. The cabinet also has a multifunctional design to meet the configuration of protection devices and switches.

The general configuration for Daelim Single Phase Pad Mounted Transformer
A typical single phase pad mounted transformer design is shown in the figure. It is self-cooled, 250kva and smaller, high voltage equals or below 34.5GrdY/19.92kV, low voltage equals or below 480/240V. 

single phase pad mounted transformer (2)

Single Phase Pad Mounted Transformer has below standard specification:


Loop feed/radial feed

2 separable HV bushings

2 ground pads

1 parking stand

3 low voltage terminal, vertical spades

1 nameplate

Mineral oil

Hinged door

1 Lock

Ground strap (connected to X2)

UL listed

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Tap changer with different


single phase pad mounted transformer (3)

More spades

2 position or 4 position load break switch

Oil level indicator

Oil temperature indicator

Bayonet fuses with fuse holder

Current limiting fuses

Pressure relief valve

Drain&fill plug


Single phase pad mounted transformer impedance

Generally for capacity below 25kva, the there is no minimum impedance requirement, for capacity 50kva and above, the minimum impedance is 1.5%.

Keep on reading 110 kv Oil Filled Power Transformer – DAELIM BELEFIC

What is single phase transformer?

A single-phase transformer is a transformer in which both the primary and secondary windings are single-phase windings.

Unipolar switching power supply means that the output is unipolar, that is, only positive and negative output. Compared with bipolar switching power supply, bipolar switching power supply has three outputs, which are divided into positive power supply, negative power supply and ground wire. .

The single-phase transformer is simple in structure, small in size and low in loss, mainly due to small iron loss, and is suitable for application and promotion in low-voltage distribution networks with small load density. Some data show that single-phase transformers are widely used in developed countries, such as the United States and Japan, and single-phase power supply has become the main way of power supply for residents. Under this kind of publicity, some people think that single-phase power supply has “loss reduction” Magic, believes that single-phase transformers are more energy efficient than three-phase transformers, and that single-phase power supply system is superior to three-phase power supply system. In fact, the single-phase transformer and the single-phase power supply system are only supplementary forms of the current three-phase power supply system. Due to the constraints of its own characteristics, it can only be used in some specific fields.

You may interested in Oil Type transformer – DAELIM BELEFIC

What is the delivery time for Daelim single phase pad mounted transformer?

It depends on the quantity. Our production time is 12 weeks after confirmation of the drawing for one container goods.

What is the difference of loop feed single phase pad mounted transformer and radial feed single phase pad mounted transformer?

The radial feed is only the incoming line but not the outgoing line, and the transformer is at the end of the line.

The loop feed single phase pad mounted transformer has both incoming and outgoing lines, and several transformers form a ring. There can be multiple points on the ring connected to the grid. The advantage of the loop feed is that a certain device or line in the line fails, and the other end can bypass the fault point to supply power to other devices. Once the line in front of the radial feed fails, the equipment will not be able to obtain energy from the grid until the fault is restored.

What is load break bushing for single phase pad mounted transformer?

Load break bushings are widely used in the connection of single phase pad mounted transformer and other electrical equipment. 

Load break bushing are fully insulated, fully sealed and fully shielded. The terminal cable head and elbow cable plug have a rated current of 200A and are suitable for a cable cross-section of 35-120mm square. The end of its conductive rod is connected with an arc extinguishing function, so it can be operated in a live state, but cannot cut off short-circuit current. Elbow connectors can be installed on the outgoing side of 200A series bushings, 200A busbars and 200A load changers. Its test points can be installed with live indicator or fault indicator

What is the advantages of vegetable transformer oil?

Mineral oil transformers have been widely used for over 100 years for their higher efficiency, better load capacity, smaller size and longer life. However, the transportation of mineral oil, oil spill pollution, carbon emissions, fire risk and other issues not only require special treatment, but also need to fully consider their impact on the environment and fire safety.

In the 1990s, American manufacturers developed a natural ester, a non-flammable insulating cooling oil.

This oil is derived from plants, and its ignition point exceeds 300 ℃, which is much higher than that of similar products such as hydrocarbon oil and silicone oil. At the same time, with the same level of fire safety record, it has become an epoch-making new product that can be used in buildings or surrounding areas. 

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In addition to its excellent fire safety properties, this new vegetable insulating oil is also EPA compliant for its “excellent biodegradation properties.” Compared with traditional insulating oils, natural esters greatly ensure fire safety and environmental compatibility, and vegetable insulating oils extend the service life of transformers. Since oil-immersed transformers have many advantages over VPI and epoxy cast dry type transformers, considering economy, safety and environmental protection, VPI and epoxy cast dry type transformers are no longer the first choice for installation in sensitive areas. At the same time, insurers such as FM Global are beginning to realize that the fire-resistant properties of natural esters can reduce fire safety requirements and offer lower premiums.


Test Items

Vegetable Oil

Test Methods

ASTM D6871

Electric Parameter

Breakdown voltage (kV/2.5mm)


IEC 156


Dissipation factor (%)










Volume resistivity (Q«cm @25°C)


DL/T 421

Physical and Chemical Properties

Relative density (gem1 @15°C)


ASTM D1298




ASTM D1500


Total acid number (mgKOH/g)







GB/T 265





GB/T 265


Thermal Properties

Flash point(open cup)/*C



GB/T 3536


Fire point/°C



GB/T 3536


Pour point/°C



GB/T 3535


Single phase pad mounted transformer cost

For different specification, transformer cost will be different. Contact Daelim sales for the inquiry.

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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.