Understanding Live Front Three Phase Pad-Mounted Transformer

The primary purpose of a transformer is to “transform” electrical voltage to a usable rating. However, things can get confusing when you have to determine or specify what actual transformer is needed. And, this article by Daelim will be tackling one specific form of transformer, the Live Front-Three Phase Pad Mounted Transformer.

Live Front-Three Phase Pad Mounted Transformer is a loaded term. And to figure it out, we have to break down the terms that comprise it. Generally, it is a utility distribution transformer that is ground-mounted in a lockable metal cabinet on a concrete pad. Also, all live contact points are contained within a grounded metal enclosure. 

DAELIM provides a full range of live front three-phase pad-mounted distribution transformers. These transformers are intended for use in commercial, residential, and industrial settings. If you’re not familiar with this transformer, then it’s important to learn what they do and how they work so you can decide if they might be right for you! Let’s get started! 

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

Dry-type Transformer

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

Three Phase Pad-Mounted Transformer: The Ultimate FAQ Guide

What Does a Live Front Transformer Mean?

Different parts comprise a transformer. Among these are components called bushings. They are attached to the innermost core of an electric machine, and their purpose is to provide a bearing surface for the rotating parts. These bushings can be either live front or dead front types. 

Live Front Bushings vs. Dead Front Bushings

Live front bushing is a traditional type of bushing made of porcelain or epoxy. It refers to terminations that expose the cable and terminal. It has electricity running through it, and touching a live front bushing may result in electrocution.

At the top of the live front bushing is a spade where the actual termination with a crimp lug occurs. The bushings below the spade are made up of little ridges known as waffles that prevent a phenomenon known as creep.

Calculation Method of the Number of Turns of Power Transformer Core

Creep is the movement of an arch across the surface area while accompanied by a small amount of water, dust, or oil. Waffles, with greater surface area, offer the required clearance to prevent creep. Also, there is a stud that links the bushing to the core and the coil inside.

On the other hand, a dead front bushing performs the same function as a live front bushing, but it is fully insulated. The cable and current-carrying elements are encased inside molded rubber components. Because there are no current-carrying parts exposed to the operator, safety is improved.

The advantage of a dead-front transformer is that you can open the cabinet with very little chance of arch-flash. Furthermore, a bushing well, a load break insert, and a load break elbow are its common components.

What is a Three-Phase Transformer?

There are two popular configurations of transformer systems: single and three-phase transformers. Both have their respective advantages and disadvantages to consider. Also, they differ significantly in that the single-phase utilizes one conductor and one neutral wire to complete a circuit. In contrast, the three-phase supply requires three conductors and one neutral wire.

Transformer three-phase dual power supply automatic switching

The primary purpose of using either type is to change the voltage while keeping the current at a constant value. To better understand the difference between the two, you must learn the features and how these transformers work.

Single Phase Transformers

Single phase pad mounted transformer
Single phase pad mounted transformer

single-phase transformer uses two coils, one main and one secondary, to perform voltage translation. It comprises two highly inductive coils wound on an iron or steel core to generate the necessary voltage using these two windings. The winding linked to the alternating current (AC) supply is the first winding, while the other is the secondary winding.

It features four terminals, two on the input and two on the output, with no delta or star connections. In most situations, a single-phase transformer does not require a cooling system. A system’s single-phase power adjusts the supply voltage of an alternating current (AC) power simultaneously. Because it is what most houses use, single-phase electricity is more commonly referred to as “residential voltage.”

How Single Phase Systems Work?

A single-phase power distribution system employs phase and neutral wires. The phase wire carries the current load, whereas the neutral wire serves as a return channel for the current. It generates only a low voltage which commonly begins at 230V. Its frequency is also close to 50Hz.

Single-phase motors require extra circuits to work since a single-phase supply connecting to an AC motor doesn’t generate a rotating magnetic field. Also, the power output of a single-phase supply is not constant, meaning its voltage supply rises and falls.

Furthermore, power lines are an input source in a single-phase power system because they convert high voltage to low voltage, similar to a step-down transformer. Thus, it is best suited for household applications.


Utility pole transformers

Single-phase transformers are used in applications where a low voltage circuit needs to be powered from a higher voltage network. Single Phase Transformers take this one step further and allow more individual systems, each operating at their voltage, to be distributed across a common line.  It greatly increases efficiency and reduces costs associated with the distribution of electricity to numerous systems.

In addition, here are the other benefits of using a single-phase transformer:

  • Single-phase (SP) systems are less complicated to design. It features a lightweight and small device, and the current via the line is reduced when the voltage transmission is high.
  • They have a lower design cost and higher efficiency, effectively delivering an AC power supply of around 1000 watts.
  • SP systems are used in a wide range of industrial, commercial, and residential applications.
  • The current is low, which assures that the unit operates at peak efficiency with enhanced transmission efficiency.


Single-phase transformers are used to increase the voltage of alternating current motors, and they have some advantages. However, they have their disadvantages too, which includes:

  • Because a single-phase supply is insufficient for an initial start-up, small single-phase motors require extra circuitry.
  • Heavy electronic loads are required for industrial motors. As a result, it cannot operate on a single-phase power source. 
  • If one or more transformers operate in parallel, it increases the possibility of a failure occurring.
  • When it comes to high-power industrial machinery and systems, they are less productive.


What is the Difference Between 1 Phase 2 Phase and 3 Phase Power?

Three-Phase Transformers

A three-phase transformer is made by winding three single-phase transformers on one core. It contains six coils, three each for the primary and the secondary sides, separated from the opposite by an angular difference of 120 degrees.

It also features star and delta connectors and twelve terminals with various connections to them. Depending on the power rating of the transformer, three-phase transformers need a powerful cooling system.

Three-phase transformer winding
Three-phase transformer winding

These transformers can transport the appropriate amount of voltage across great distances with only a small conductor, assisting in the smooth operation of industrial equipment. Three-phase transformers are well-known for their effectiveness in meeting the demands of heavy-duty applications, making them ideal for heavy industrial applications.

Three-phase transformers are utilized in various phases of a power transmission system to step up or step down high voltages. It transforms input power to the necessary voltage level while maintaining proper phasing and polarity.

How do Three-Phase Systems work?

Three-phase power works differently in that electricity is created by rotating three coils within the generator through a magnetic field. The three primary coils are linked to give the appropriate polarity and are arranged in a pattern known as Delta.

The three secondary windings are likewise linked at the plant, but they will be arranged as Delta or Wye depending on the voltage needs. The windings are 120 degrees apart and produce electricity as they revolve through the magnetic field. The produced electricity is then distributed across three distinct lines, which is called three-phase power.

Three-phase dual power supply automatic switching power supply circuit
Three-phase dual power supply automatic switching power supply circuit


Three-phase transformers are particularly useful for large motors and other equipment; thus, for industrial uses, three-phase transformers are far more efficient. Aside from that, there are other advantageous features of transformers that operate from a three-phase source:

  •  While three-phase systems are becoming more powerful and quick, they are also affordable. Lower prices paired with high performance may make them more cost-effective in the long run.
  • In three-phase transformers, less copper is required for power delivery.
  • Workers who use three-phase systems are at low risk.
  • It has higher conductor efficiency.
  • This system is designed to work with a wide range of power demands.
  • Three-phase transformers can be used in place of single-phase transformers.


3 phase pad mounted transformer core
3 phase pad mounted transformer core

Three-Phase Transformers are used in most electrical power systems due to their reasonability and efficiency compared with single-phase transformers. However, this type of transformer still has its disadvantages. 

  • A malfunction of one phase causes the entire machine to shut down because all three units share a common core in a three-phase transformer. 
  • If one unit fails, the core of that unit will quickly saturate due to the lack of an opposing magnetic field. As a result, there is a larger escape of magnetic flux from the core to the metal enclosures. It will raise the temperature of the metallic pieces, and in certain circumstances, this heat is enough to start a fire.
  • The cost of repairing a three-phase transformer is higher.
  • The capacity of the transformer is lowered when they are self-cooled.
  • A three-phase transformer cannot be used temporarily in an open delta connection, but three single-phase transformers may (in case of fault at a single unit).

What Does Pad Mounting Mean in Transformers?

three phase pad mounted transformer
three phase pad mounted transformer

A pad-mounted transformer is a ground-based electric power distribution transformer housed in a lockable steel cabinet. It is installed on a pad (often concrete or polymer concrete).  All electrified connection points are safely covered in a grounded metal casing, allowing it to be put in locations where a fenced enclosure is impossible. 

Pad-mount transformers are used at service drops on underground power distribution lines to reduce the primary voltage to the lower secondary voltage provided to utility consumers. A single transformer may service a huge structure or several dwellings. Also, it comes in single-phase and three-phase configurations.

Pad-Mounted Transformer Benefits

Pad-mounted transformers are transformers with superior technical features. They offer many benefits such as:

  • It has reduced land requirements and construction costs. Because a pad-mounted transformer has a smaller footprint than a substation, land-related expenses of securing rights-of-way and permissions are minimized.
  • Pad-mounted transformers have improved aesthetics since they have clear, unobstructed exteriors.
  • Pad-mounted transformers also have improved safety for operating employees due to underground cable access and fully enclosed connections.
  • The device is additionally protected from environmental dangers due to its enclosed construction.
  • Pad-mounted transformers may also be put in unsecured locations since they are self-contained, saving the expense and space of a fence or enclosure. 
  • Access for maintenance is also simplified.
  • Pad-mount transformers include self-protecting fuses with a bayonet mount fuse in a high voltage compartment. It also has a backup high energy current-limiting fuse in series to guard against secondary faults and transformer overload.

Pad-Mounted Transformer Considerations

Oil-type transformer detail

Pad-mounted transformers may not appear dangerous, yet they may transport the same amount of voltage as overhead power lines. The most obvious disadvantage is that the transformer’s pads are sometimes thin and insufficient to provide adequate mechanical support.

Also, pad-mount transformers are oil-filled devices that should be installed outside only. Though this equipment is usually carefully stored in green metal boxes, preventive measures must still be taken. Like,  children should not be allowed to play on or around pad-mounted transformers. Also, replace the lock of the box when it is tampered with or broken.

What is a Live Front-Three Phase Pad Mounted Transformer?

Now that we have defined different terms included in this loaded term, we understand what this transformer is. Live Front-Three Phase Pad Mounted Transformer is designed to distribute three-phase power in industrial and commercial applications. The transformers are packaged in a weatherproof, pad-mounted, light-weight enclosure for easy installation.

Three-phase pad-mounted transformers are commonly used to service three-phase commercial and industrial loads from underground distribution networks.

How Does a Live Front -Three Phase Pad Mounted Transformer Work?

A live front three-phase-pad mounted transformer generates electricity by rotating three coils through a magnetic field. The three main coils are organized in a Delta pattern, while the secondary windings will be arranged as Delta or Wye, depending on the voltage requirements.

This type of transformer increases or decreases power supplied to a building system, such as the main level lighting and electrical load center. Also, its cable at terminals is exposed in the bushing. This transformer is supported on a concrete pad that is cast at the site. 

live front transformers
live front transformers

The main advantages of this type are that they provide a small footprint, require very little space, and can be placed close to loading equipment and power system utilities. They also offer high reliability and the ability to withstand flooding, earthquakes, hurricanes, and other natural disasters.

Standard Ratings of Live Front -Three Phase Pad Mounted Transformer

The transformer load’s electrical size is measured in kVA. This rating specifies the corresponding power output supplied by the loads connected to the transformer on the secondary side of the equipment during a particular period.

For live front – three phase pad transformers, it is available in standard ratings or 45, 75, 112.5, 150, 225, 300, 500, 750, 1000, 1500, 2000, and 2500 kVA. 

60 HZ Pad mounted transforemer
60 HZ Pad mounted transforemer

What are the Applications of Live Front -Three Phase Pad Mounted Transformer?

Live Front-Three Phase Pad Mounted Transformers are installed and used in various ways as part of a residential, commercial and industrial building’s electrical system. Among these application kinds are:

  • Live front three-phase pad-mounted transformers are typically used in high power factor industries and used for monitoring purposes due to their efficiency.
  • They are also used for residential applications since they are available in a wide range of standard ratings and safer than other transformers. 
  • Overall, a live front three-phase pad-mounted transformer is suitable for your every need. It becomes very important to manage the power distribution to ensure reliable electrical service and uninterrupted supply. In addition, it is also necessary for utilities to meet consumer expectations regarding voltage quality, reliability, and safety.

What Is Inside A Pad-Mounted Transformer?

A pad-mounted transformer consists of core and coils housed in a steel oil-filled tank, with transformer terminals accessible through an adjacent lockable wire cabinet. There are high and low voltage wire compartments inside the wiring cabinet, and the underground high and low voltage wires enter the terminal chambers immediately

Carriage bolt-nut assemblies fasten the tank’s top. Also, the wiring cabinet has two end side walls with doors that open sideways to reveal the high and low-voltage wire compartments.

pad mounted transformer production plant
pad mounted transformer production plant

These transformers also feature their protective fusing. They consist of a low-energy Bay-O-Net fuse situated in the high voltage compartment and a backup high energy current limiting fuse connected in series. Both fuses are submerged in oil. The Bay-O-Net fuse is a replaceable field device that protects against secondary faults and transformer overload.

Are Pad-Mounted Transformers Dangerous?

Pad-mounted transformers commonly do not pose risks. However, it still converts high-voltage energy to the lower voltage required for underground cables for power houses’ lights and appliances. They function similarly to the transformers found on electricity poles linked to overhead power lines. Thus, you must be extremely careful around them.

A box that has been pushed sideways by machinery, or has been tampered with and lacks a lock, can pose a severe hazard to anyone, especially youngsters, who frequently use them as a platform. Children should not be near these boxes since they are potentially hazardous and should not be played with.

DAELIM PAD mounted transformer in Canada.
DAELIM PAD mounted transformer in Canada.

Keeping bushes, buildings, or structures away from the pad-mounted transformer is critical. Also, make sure that plant roots do not develop to interfere with wires and underground cables. Lastly, always double-check that the box is securely locked because poorly secured pad-mounted transformers can be a major threat.

Is Live Front Transformer Dangerous?

Yes, because the term “live” refers to the fact that the transformer’s bushing terminal cable is truly exposed. When you come in contact with these transformers, especially to the bushing, you might get electrocuted. Remember that this kind of bushing is not insulated. 

Is It Cheaper To Run Three-Phase Systems?

Yes, it is cheaper to run three-phase systems. First, because it isn’t carrying much current, you can minimize the size of your neutral conductor. In fact, three-phase systems can have three times the power of single-phase systems while utilizing half the amount of copper as a conductor. Given the cost of these materials, this would represent significant savings in the long term.

Three-phase systems provide more control over how much power is supplied to your equipment, which may allow you to utilize less equipment in some instances. It reduces your equipment and power use, which lowers your electricity cost.

DAELIM PAD mounted transformer in Honduras
DAELIM PAD mounted transformer in Honduras

Though three-phase system transformers may have a higher initial cost, you will save in the long term. More efficient power means greater production and, eventually, more money.

How Long Does A Pad-mounted Transformer Last?

Though many factors determine the life expectancy of a transformer, it is expected to have a service life ranging from 30 to 50 years.

How Close Can A Transformer Be To A Building?

Pad Mounted Transformer Service (2)

A transformer situated near a building, in general, requires 4ft clearance from the vertical surfaces of the structure, assuming no windows from grade to 18ft. The sides of the transformer must be 3 feet free of all objects, and the transformer must be 10 feet horizontally from any doors, windows, or fire hydrants.

Transformers must typically be positioned adjacent to buildings such that the front doors face away from the building and there are no balconies or overhangs above. Line trucks must be able to access the transformer for future repair or replacement. 


Live front three-phase pad-mounted transformers give you three-phase electricity without having to fork out thousands on installing a sub-station at extra cost. It is designed for high efficiency and safety when converting electric power from one voltage level to another. 

DAELIM’s live front phase-pad mounted transformers are an ideal solution for any distribution system, all of which are built with enhanced safety and reliability margins. In line with the current industry requirements, all DAELIM transformers are designed and manufactured following IEEE standards. Contact us today for the availability of kVA sizes, features, and designs that best meet your needs!

Custom Pad Mounted Transformer

When you need to find more than just existing transformers, Daelim’s Transformer Service Center can help you design and produce distribution transformers that meet your unique needs.

We have our own factory and a professional team of engineers, which can design and modify application requirements that meet all your conditions.

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