The Ultimate Guide to Dead Front Transformers
The dead front transformer is a type of pad-mounted transformer commonly used in North and South American markets.
Daelim Transformer is a professional manufacturer specializing in ANSI/IEEE and CSA Std pad-mounted transformers. Their professional technical team is capable of designing both dead front and live front transformers that fully adhere to ANSI/IEEE, DOE, CSA, and other international standards. Daelim Transformer holds various transformer test reports from SGS, CESI, IEEEC 57, IEC60076, CSA C227.3, CSA C227.4， and CSA C227.5, as well as UL and cUL certificates. Their quality and expertise have earned recognition from numerous professional customers in the United States and Canada, including long-term collaborations with top 500 companies in North America.
What is a dead front transformer?
A dead front transformer is a pad-mounted transformer that features fully enclosed electrical connections and components, ensuring that there are no exposed live parts or terminals on the front panel. This design enhances safety by preventing accidental contact with energized elements. Dead front transformers are commonly used in outdoor applications for secure electrical power distribution.
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"Post-death transformer" is the radial feed that seals the high voltage bushing and current-carrying parts of the transformer with rubber material. It is usually composed of a bushing well, a break load insert,s, and a break load elbow, so it is completely insulated. Safety improvements that do not expose load current elements.
There are two kinds of the transformer before dead front transformer, one is loop feed, and the other is radial feed. The three-phase loop feed transformer is composed of 6 high voltage bushings, and the three-phase RF is 3 high voltage bushings. The single-phase dead-front transformer has two high voltage bushings. You can choose according to your actual needs.
The transformer uses the backup fuse and the Bay-O-Net fuse in series to provide protection, the backup fuse is installed in the box inside, only in the pad-mounted transformer internal phase fault action used to protect the high voltage line, and the Bay-O-Net fuse in the secondary side short circuit or overload when the fuse.
The high voltage cable is connected to the bushing with good insulation performance, the bushing is connected to the elbow-type cable plug, and the live part is sealed. The elbow-type cable plug is a fully shielded insulation plug, which can be inserted and removed with full load, equivalent to the load switch, Its dead front structure is shown below, but if it is closed to the breaking point, both the elbow-type plug and the bushing should be replaced.
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Are dead front transformers fully insulated?
My experience is that pad mounted transformers and their definitions are easy to understand. If you open the second side, you'll see an exposed busbar, which is a charged front end. If you see an insulated elbow joint, that's a blind spot.
In general, "live front" means "power on," "easily," "death," and "trying to kill the" pry "from the" master."
The live front transformer has the power supply on it and the primary cable is exposed, whereas the dead front transformer without power supply has an insulated elbow.
Read more: What is a Live Front 25kv Pad-Mounted and Substation Transformer Specification?
What are the types of dead-front transformers?
There are two types of dead-front transformers. Single-phase and three-phase transformer
Three-phase dead front transformer
This pad-mounted transformer is commonly used in underground power systems with a three-phase power supply. According to CSA Std, the maximum width of the transformer should not exceed 1730mm. When opening the high voltage door, you will find six(also can be 3) high voltage bushing wells along with load break bushing inserts or surge arresters. The high voltage bushings in this structure are separate, fully insulated, and provide reliable safety.
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Single phase dead front transformer
This type of pad-mounted transformer is primarily used in underground single-phase power systems. It features two high-pressure cased wells and two load break bushing inserts. Single-phase dead-front transformers are typically installed in parks, hotels, and single-family houses to provide lighting and power supply for electrical equipment.
Learn more: Single Phase Pad Mounted Transformer
What is the difference between single-phase and three-phase dead front transformers?
The main difference between single-phase and three-phase dead front transformers lies in their structure and functionality. In a three-phase transformer, both the high and low voltage sides require three coils connected in specific ways known as connection groups. This enables the transformer to provide the necessary power to users. On the other hand, a single-phase transformer only requires one coil on each side, connected respectively to the power supply and the load.
In terms of physical features, a three-phase dead front transformer typically has three or six high-voltage bushings on the high-voltage side, while a single-phase dead front transformer has only two high-voltage bushings. The cover of a three-phase transformer is commonly opened on the side, whereas the cover of a single-phase transformer is opened from the top.
The conventional capacity of three-phase dead front transformers can reach up to 5000kVA, whereas single-phase transformers have a conventional capacity of up to 250kVA. Both types can operate at voltage levels up to 34.5kV.
In terms of construction, the iron core of a three-phase transformer is typically a flat "day" type, providing three magnetic circuits for the three-phase electricity. Conversely, the iron core of a single-phase transformer is a "mouth" type, featuring only one magnetic circuit.
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What are the loop feed transformer and the radial type feed transformer difference?
Pad mounted transformer can be divided into the radial type and loop feed type according to their purpose. radial type mainly distributes electric energy to low voltage power users. The loop feed type is also used for ring network function and power distribution, Loop feed type generally has more than two incoming lines.
Loop feed and radial type pad mounted transformer difference is mainly reflected in the high voltage inlet and outlet, loop feed type transformer in addition to the high voltage outlet of the transformer itself, there is another high voltage outlet, the formation of loop feed type power supply; Radial feed pad-mounted transformer has only the high voltage outlet for its transformer.
Loop feed type pad-mounted transformer allows users to obtain power from two directions. The power supply network is usually connected to a ring to provide stability to the power supply. This power supply mode is referred to as ring power supply. Box substation with loop feed power supply is called ring box transformer, which is located at the middle-end of the bus trunk system.
Radial type pad-mounted transformer only appears for their own transformer high voltage, placed at the end of the busbar trunk system, relative to the loop feed pad-mounted transformer, the use of one inlet and outlet cabinet, and loop feed pad mounted transformer at least two outlet cabinet.
Loop feed type pad mounted high voltage using loop feed cabinet, the so-called ring network cabinet is each distribution branch set a switch cabinet, the switch cabinet bus is also a part of the loop feed trunk. The ring trunk is composed of the busbar connected by each outlet cabinet.
The number of loop feed transformer high voltage cabinets is more than that of radial feed pad mounted transformer, and the shell size of pad mounted transformer is larger, so the cost of loop feed transformer is much higher than that of radial feed transformer substation.
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What is the application of dead front transformer?
The dead front transformer is a type of distribution transformer commonly utilized in power distribution systems throughout North America. It finds extensive application in various settings, including residential areas, shopping malls, industries, schools, secured mining facilities, skid pad-mounted substations, and more.
One of its key features is the presence of high-voltage and low-voltage enclosed compartments, ensuring safe operation and preventing public accidents. The pad-mounted design makes it suitable for outdoor installations, with a medium-pressure termination and a lockable door. To counter the effects of ferromagnetic materials, the transformer employs a primary transformer as the power source.
The transformer comes in two main construction types: radial and ring networks. The radial configuration involves connecting the transformer to the primary power supply and cannot be used as a primary power grid structure. The ring network arrangement, on the other hand, allows the transformer to be connected to the primary power supply and provides electricity to other loads within the system.
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What is a live-front transformer?
A live front transformer is a pad-mounted transformer with accessible live components on the front panel. It allows direct access to the energized parts for maintenance and testing purposes. Caution must be exercised when working with a live front transformer due to the presence of exposed live elements.
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Live Front VS Dead Front transformer
Dead front and live front transformers both fall under the category of pad-mounted transformers. They share similarities but differ in some aspects.
Dead front transformers have separable insulated high voltage connectors, providing a casing well with detachable studs for connection to the power distribution system. High voltage bushings comply with IEEE 386 Std and are equipped with protective caps. They can have three or six high voltage bushings, depending on the configuration.
On the other hand, live front transformers feature one-piece high voltage connectors, usually porcelain bottle type or spiral style, with spade terminal blocks on top. They typically have three high voltage bushings.
In terms of safety, dead front transformers have fully insulated high voltage parts, ensuring a higher level of safety. In contrast, the high voltage parts of live front transformers are exposed, with current passing through the spiral porcelain bottle, making them comparatively less safe.
Overall, the key distinction lies in the design of the high voltage bushing section. Due to safety considerations, a majority of users (approximately 80%) prefer dead front transformers in the market.
What are the CSA standard specifications of the pad mounted transformer?
CSA standards for transformers are a requirement to enter the Canadian market. CSA standard for three-phase 60 Hz pad-mounted transformer. The capacity is below 3000kV•A, the insulation level is below 18kV. Transformers are suitable for outdoor mounting on mats without the need for additional protective enclosures.
Read my article on How To Purchase 3000kVA Transformer In USA & Canada?
The CSA standard has made clear instructions on the Electrical characteristics, Mechanical characteristics, Bushings, terminals, and grounding, Tests, Quality of work and finish, Markings, Optional items, Packaging, etc. of transformers.
1. Physical sizes of transformers
| Rated kVA capacity | Type of feed | Transformer maximum BIL, kV | Width, mm |
| 75, 150 | Radial | 95 | 1280 |
| 75, 150, 225, 300 | Loop | 95 | 1480 |
| 75, 150, 225, 300, 500 | Radial | 125 | 1480 |
| 75, 150, 225, 300, 500 | Loop | 125 | 1480 |
| 750, 1000, 1500, 2000, 2500, 3000 | Radial | 125 | 1730 |
| 750, 1000, 1500, 2000, 2500, 3000 | Loop | 125 | 1730 |
2. High-voltage electrical characteristics of transformers and assembled load-break terminals
| Transformer | Assembled high-voltage load-break terminals, 200 A | ||
| Insulation class, kV Preferred rated voltage, V BIL, kV | Recommended voltage rating, kV (rms) BIL, kV | ||
| 5 | 4 160GrdY/2 400 | 60 | 8.3/14.4* 95 |
| 5 | 4 160 | 60 | 8.3/14.4* 95 |
| 8.7 | 8 320GrdY/4 800 | 75 | 8.3/14.4* 95 |
| 8.7 | 8 320 | 75 | 8.3/14.4* 95 |
| 15 | 12 470GrdY/7 200 | 95 | 8.3/14.4 95 |
| 15 | 12 470 95 | 95 | 8.3/14.4 95 |
| 15 | 13 860GrdY/8 000 | 95 | 8.3/14.4 95 |
| 15 | 13 860 | 95 | 8.3/14.4 95 |
| 18 | 24 940GrdY/14 400 | 125 | 15.2/26.3 125 |
| 18 | 27 600GrdY/15 935 | 125 | 16.2/28.0 125 |
3. Preferred low-voltage and required BIL rating
| Insulation class, kV | Rated voltage, V | BIL, kV |
| 1.2 | 208Y/120* | 30 |
| 1.2 | 480Y/277 | 30 |
| 1.2 | 600Y/347 | 30 |
4. Minimum transformer impedance
| Transformer size, kV•A | Minimum transformer impedance, % |
| 0–150 | 1.8 |
| 225 –300 | 2.0 |
| 500 | 3.0 |
| 750–1000 | 4.0 |
| >1000 | 5.0 |
Read more: Knowing More about A Pad Transformer
Dead front transformer custom and for sale
Daelim is a top pad mounted transformer supplier in China. A professional technical team can design various standard dead-front transformers. The highest voltage level of conventional transformers is 34.5kV, and the power rating is up to 10MVA. Daelim's dead-front transformers can be customized according to your needs and technical parameters. The highest voltage level can reach 44kV, and the capacity can reach 10MVA. If you have transformer requirements or technical problems, you can contact the Daelim team to give you the most complete solution and a detailed price list.
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