The Complete Guide to Ground Mounted Transformer

Pad transformers have not been around for as long as the other types of distribution transformers. Its demand is much less as well, but this does not mean that Ground Mounted Transformers are not worth considering.

Cooper Pad-Mounted Transformers have their own functions, mechanisms, and performance level. In fact, they are primarily used for advanced purposes that other distribution transformers cannot perform.

This is why in this article, DAELIM, an electrical company that has been specializing in transformers for more than 20 years is providing you with all the essential information you need to know about pad transformers.

This is for you to have a better understanding of what this electrical device is capable of, along with professional help from DAELIM’s team.

Ground Mounted Transformer: The Ultimate FAQ Guide

What Are Pad-Mount Transformers?

To begin with, what exactly are Pad-Mount Transformers or Pad Transformers? For starters, this electrical device has several names, but the most common term or name for this electrical device is Pad Transformer.

The Complete Pad-mounted Liquid Filled Compartmental Transformer Guide

Basically, it is an electrical device, specifically; an electrical power distribution transformer that is mounted on the ground. Normally, these electrical devices are locked inside a steel cabinet on a flat concrete pad.

Regardless, Pad Transformers can also be installed in locations that do not have room for a fenced enclosure, but they must go through several restrictions first to see if it is safe to use. All energized connection points are stored in a metal housing that is grounded.

Daelim's pad mounted transformer installed in Venezuela
Daelim's pad mounted transformer installed in Venezuela

Ground Mounted Transformers are also commonly used with electric power distribution lines that are from service drops. This is to decrease the voltage level to the secondary voltage that is being supplied to consumers. This is the reason why some buildings are powered by their own transformer, commonly seen on industrial buildings, businesses, large buildings, etc.

In terms of the power rating of Cooper Pad-Mounted Transformers, this usually ranges from 15 kVA to 5000 kVA (Kilovolt amperes). Moreover, this type of transformer has built-in fuses and switches with them for security purposes. 

When it comes to the primary cables, they can be associated with elbow connections. This can be operated by energizing a hot stick that allows flexibility for easy repair and maintenance in the case that the transformer needs it.

Design

Pad transformers are versatile when it comes to electrical and mechanical configurations because they are available in variants. But in a usual setting, Pad Transformers work at medium voltages from distribution systems of up to about 35 kV.

This low-voltage winding is suitable for customer requirements. This could either be a single-phase or three-phase, depending on the consumer.

It is also worth noting that Ground Mounted Transformers are usually oil-filled, which means that this does not meet the fire code of most buildings. This is why Pad Transformers are only best for outdoor locations.

Cooper Pad-Mounted Transformers also have a core along with their coils, and these components are usually enclosed in steel oil-filled tanks with terminals for the transformer to be accessible. They are normally adjacent lockable wiring cabinets.

Seven Technical parameters of Pad-mounted Transformers

When it comes to its wiring cabinet, you can expect to find high voltage and low voltage wiring compartments in it. The high and low voltage cables that are beneath the ground, enter the terminal compartments directly.

Another security part of the tank is its cover at the top of the tank. The cover will be secured with carriage bolt assemblies for maximum security. The wiring cabinet also has sidewalls on both ends with doors that open sideways, the purpose of this is to expose the high and low voltage wiring compartments, which then again, is best for outdoors.

Transformer three-phase dual power supply automatic switching

As mentioned, this type of transformer has fuses that are self-protecting that consist of a bayonet mount fused that are settled in a high voltage compartment that is joined with a high energy current limiting fuse as a backup in case of secondary faults and transformer overload.

This is why bayonet fuses are used in Ground Mounted Transformers to prevent secondary faults and overloads from transformers. In addition to that, bayonet fuses are also field-replaceable devices.

Bay-O-Net Fuses for pad-mounted transformer

The backup current-limiting fuse only activates, triggers, or functions when there is a transformer failure. This makes the current-limiting fuse not replaceable, unlike bayonet fuses. Cooper Pad-Mounted Transformers are also designed to serve conventional low voltage fusing requirements.

For switching and isolation to be possible, polymeric cables and load break elbows are utilized. This is for the switching and isolation to proceed in the HV chamber or also known as the dead front. It is also worth noting that all terminations are completely screened and watertight.

Both single-phase and three-phase Pad Transformers are commonly used in underground industrial power distribution systems. This is where a standard is to be met, specifically, safety, reliability, and an aesthetic or appealing transformer design.

Transformer three-phase dual power supply automatic switching

This is where the enclosed construction comes in handy because this allows the installation of the Pad Transformer in public locations without protective fencing. In residential locations, you would normally see Ground Mounted Transformers that are located in easements that supply electricity to numerous households.

Most Pad Transformers are put in a concrete pad or polypad base. You would normally see this underneath them. Some are already mounted, while others build the concrete or polypad base first for connection and switching.

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

Appropriate Location

Pad Mounted Transformer Maintained

If installed by your own, or your own team, DAELIM recommends the post to be located at least 8 to 10 feet away from the pad. This is to not obstruct or block the opening of the access doors that are on the front of the transformer.

The post should also be 8 inches in diameter concrete-filled pipe (steel), that is set in the concrete of a depth of up to about 30 inches or more. This should also be spaced no more than 5 feet apart.

Pad Transformer Longevity

Normally, the majority of transformers have an expected life expectancy of 30 years, and some transformers can even reach up to 50 years. This goes the same for ground mounted transformers because the design and build of pad transformers are specifically made to be sustainable and durable.

But other factors should be considered as well when it comes to its longevity such as maintenance and repairs.

Single-phase Pad Transformer Components

Single Phase Pad-Mounted transformer

For single-phase pad transformers, these electrical devices consist of several parts with unique functions and mechanisms. The number of parts the single-phase pad transformer has is what makes it versatile as well.

These parts were carefully measured by expert manufacturers to perfectly make ground mounted transformers as versatile as possible despite their size and compatibility. These parts can also be found in three-phase transformers.

Door

To begin with, single-phase pad transformers have doors with them, and not just ordinary doors, but rather doors that are made of solid material that is able to withstand high voltage levels as well. This design is specifically engineered to keep the ground mounted transformer safe from outside elements such as people, animals, calamities, etc.

The doors could either open sideways or up and down, depending on the manufacturer, but you can also make a request of your own if you prefer a specific material or way on how to open doors.

Single Phase Pad Mounted Distribution Transformer (2)

Name Plate

The name plate is where you will find the detailed specifications of the single-phase pad transformer such as:

  • Brand or the name of the company/manufacturer
  • Transformer Serial Number
  • Date of Manufacturing
  • Supply Ability
  • Kilovolt Ampere Rating or Megavolt Ampere Rating
  • Frequency
  • Voltage Ratings
  • Tap voltages Specifications
  • Type of Connection Diagram
  • Cooling Medium
  • Rated temperature in °C 
  • Polarity 
  • Phasor or vector diagram 
  • Impedance of Percentage
  • Weight of the Transformer
  • Type of Cooling Medium
  • Material of each winding.
  • Oil Volume Details
  • Instruction for Installation and Operation (Can be Assisted by DAELIM)

Automatic Pressure Relief Device

Pressure relief valves are responsible for protecting against excessive pressure. The excessive pressure can come from various sources such as distribution systems, transmission mains, and pump stations as well.

Opening the inlet pressure will exceed the preset value, and it discharges high-pressure water for the purpose of wasting pump suction or a zone that is of low pressure.

Furthermore, this prevents the transformer from encountering other electrical complications such as overpressure, shortages, overloading, etc. 

Daelim's pad mounted transformer installed in Canada
Daelim's pad mounted transformer installed in Canada

Strips for Tamper Resistance

The strips on the single-phase Cooper Pad-Mounted Transformer are made out of non-corrosive material for the durability and sustainability of the electrical device.

Grounding Provisions

Based on its name alone, the ground mounted transformer features a grounding system or earthing system. This is a well-known technique that stabilizes the transformer into a pad of concrete (material can also vary).

What are the main neutral grounding methods of power systems?

This helps the transformer avoid tipping or falling as well in case there is an earthquake, typhoon, or even a tsunami. This form of attachment relies on the physics of earthing science, wherein proper tightness of the transformer should be followed. 

Dual Voltage Switch

In general, a dual voltage switch is a switch that is used to select the primary windings of a transformer. Moreover, its operation allows a single-pole switch to control the loads that are operating at two distinct voltages.

This function or part alone contributes greatly to the versatility of pad transformers.

Single Phase Pad Mounted Distribution Transformer (5)

Parking Stand

A parking stand of a transformer is basically a metal or steel bracket that is primarily used to support a specific parking bushing that is designed to “park” or settle a voltage that is at medium voltages.

The cable will be terminated with a 200 Amp rated elbow.

Low-voltage Bushing

Most ground mounted transformers have a low-voltage bushing with them, the purpose of the low-voltage bushing is to be used on a surface pad. These are also known as ABB low voltage bushings, and they are specifically designed to be suitable for the pad, and surface-mounted distribution transformers like pad transformers.

These bushings terminate the internal low voltages from transformers that lead to the tank wall for a threaded connection for cable circuits in low external voltages.

High-voltage Bushing

When it comes to the high-voltage switchyards the main function of this is to provide a better or insulated entrance for a more energized conductor for high-voltage electrical devices, apparatus tanks, or electrical chambers.

Bushings play a vital role to serve as a support for other energized parts of the apparatus as well. This is why transformers are normally designed to have low and high-voltage bushings. But this could also depend on the model of the single-phase pad transformer you are getting.

Fig 21B

Bayonet Fuse

Bayonet fuse holders are primarily used to give the transformer an extra amount of protection. This also includes the switchgear along with the distribution systems.

This device is also designed for oil-filled three-phase pad transformers, submersible transformers, and switchgear.

Grounding Strap

The grounding strap is a material that is made for additional stabilization. This strap helps the ground-mounted transformer to be in place at all times. For stronger stabilization, the manufacturers will provide you with the best and suitable grounding strap for the pad transformer of your choice, because not all grounding straps are the same.

Removable Sill

The removable sill of Cooper Pad-Mounted Transformer is another excellent support component that makes installation easy. However, not all ground mounted transformers have this, but this component can be commonly found in single-phase transformers.

Floating Lock Pocket

A floating lock pocket is a safety component to keep the single-phase pad transformer in place. This increases the level of security for your pad transformer. However, just like the removable sill, this component is almost exclusive to single-phase Cooper Pad-Mounted Transformers.

So, you will have to assess this with the manufacturer you are dealing with if you want a floating lock pocket or not.

Floating Lock Pocket
Floating Lock Pocket

Distribution Transformers and Pad Mount Transformers

These two types of transformers are closely related to one another. This is because pad transformers are usually capable of doing what distribution transformers can do. However, there is a limit to this since ground-mounted transformers are compact.

This means that there are some compensations done on pad mount transformers, such as fewer ratings, less versatility, etc.

DAELIM Pad-Mounted Transformers

As mentioned, DAELIM is an electrical company that has been specializing in various types of electrical devices and transformers for over 20 years. DAELIM has received numerous awards and certificates for its excellent manufacturing skills.

From small single-phase transformers to big power transformers, DAELIM has a page full of expertise with the best service. Including a two-year warranty along with an excellent after-sales installation service team that is available abroad as well.

Below are DAELIM best-selling Ground Mounted Transformers:

Daelim's certification
Daelim's certification

Packaging and Delivery for All of the Electrical Devices

  • Wooden Case ( Can be changed depending on client’s preference)
  • The packaging will be in accordance with international standards.
  • Shipping will be via Land or Water Transportation
  • Shipping is available worldwide with an extensive logistic network for the best transportation 
  • Fast Delivery
Pad mounted transformer manufactuer - Daelim
Pad mounted transformer manufactuer - Daelim

2500kVA Loop-feed Pad-mounted Transformer

The 2500 kVA Loop-feed Pad-mounted Transformer is great for low to medium voltage use, but it can withstand high voltages as well. This has been tested and designed in accordance with international industry standards for worldwide usage. Specifically, CSA, DOE, IEEE, and ANSI C.57.

Supply Ability: 

2500kVA 34.5KV 60Hz

Liquid-Filled Loop Feed Pad Mounted Transformer

Another best-selling Pad Transformer from DAELIM is the Liquid-Filled Loop Feed Pad Mounted Transformer that is designed to be versatile. This Ground Mounted Transformer can be used in underground distribution systems.

Their compartments ensure maximum security with their sealed high and low-voltage safety compartments for optimal operations with reduction of risks and electrical complications. This makes this Pad Transformer suitable for public use.

This also includes the cabinet itself along with the doors and locks. Pad Transformers normally have two configurations, radial, and loop feed, this depends on the type of circuit the transformer has installed. The transformer uses either aluminum or copper windings for maximum efficiency and footprint.

In this transformer, the DAELIM Liquid-Filled Loop Feed Pad-Mounted Transformer follows a loop feed design.

DAELIM provides high-quality Pad Transformers with no drifting or neutral points to avoid electrical complications. This Pad Transformer also promotes low loss and cost-effectiveness with a beautiful exterior design.

Supply Ability:

2500kVA 34.5KV 60Hz 

Liquid-Filled Radial Feed Pad Mounted Transformer

For consumers that prefer a radial feed mechanism compared to loop feeds, this DAELIM Liquid-Filled Radial Feed Pad Mounted Transformer is the best option. Contrary to the loop feed pad transformer, the radial feed pad-mounted transformer goes in accordance with international standards as well.

This Ground Mounted Transformer is capable of supplying electricity in sets per month with its three-phase technology.

Supply Ability: 

200 Set/Sets per Month Three-phase pad-mounted transformer 75-2500kva

Radial feed Pad-mounted transformer
Radial feed Pad-mounted transformer

Low loss 1500kVA 13.8KV 60Hz Loop-feed Pad-mounted Transformer

Lastly, the DAELIM Single Phase Pad Mounted Distribution Transformer is one of DAELIM’s top-selling products due to its improved design and performance when it comes to kilovolt ampere rating, weight, safety, sustainability, longevity, and compact dimensions.

As mentioned, Pad Transformers are recommended to be placed outdoors, but for Single-phase Pad-Mounted Distribution Transformers, they can be placed indoors and outdoors, and even on the streets.

This is why most consumers that purchased this electrical device used it in residential areas, airports, factories, schools, stations, and many more! 

It has a low profile that follows a compartment design that supplies electricity from its mounting pad. If placed outdoors, DAELIM will handle the additional protective enclosure that follows the international standards for safe operation and protection.

Supply Ability: 

200 Set/Sets per Month Single-phase pad-mounted transformer

Single-Phase Pad-Mounted Distribution Transformer
Single-Phase Pad-Mounted Distribution Transformer

DAELIM Distribution Transformers

Now since pad transformers or ground mounted transformers are closely related to distribution transformers and power transformers, you check some of DAELIM’s best-selling distribution and power transformers below for a better comparison between these three different types of transformers.

110KV Class Three Phase Three Winding NLTC Power Transformer

110 kV power transformers are specifically designed to utilize advanced technologies at home and abroad to regulate the transformer’s coils, body, leads, fuel tank, and as well as its core. This also includes other components as well.

This feature also includes low partial discharge, lightweight, low loss, and high reliability. These components bring out excellent performance that has gained the approval of thousands of users worldwide.

This electrical device also promotes durability, sustainability, and longevity. Moreover, this protects the environment even though they are more suitable for substations and power plants.

Supply Ability: 

100 Set/Sets per Year

Packaging & Delivery

Standard international package, proper for any special customer air or sea requirements, one set one case

110KV NLTC Power Transformer
110KV NLTC Power Transformer

220KV Class Three Phase Two Winding NLTC Power Transformer

When it comes to the DAELIM 220 kilovolt ampere Three Phase Two Winding NLTC Power Transformer, high-rated transformers like this are known for encountering electrical losses. But with this electrical device, features low-loss protection.

This is independently developed by a new generation of transformers that on based on China and advanced international technologies including low discharge, strong protection, and high reliability.

The same goes for DAELIM 11 kV Power Transformers and other DAELIM transformers. Rest assured, the manufacturers are using high technology utilities for the best customer experience.

Supply Ability

50 Set/Sets per Year High Middle Low Voltage big transformer 10mva 110kv or 121kv

Packaging & Delivery

Packaging Details: International Standard Wooden Case. One unit, one case for big transformer 10mva 110kv or 121kv

220KV Class Three Phase Two Winding NLTC Power Transformer
220KV Class Three Phase Two Winding NLTC Power Transformer

Frequently Asked Questions about Pad-Mounted Transformers

Below are commonly asked questions asked from interested consumers, businesses, and companies that are considering using Pad Transformers. This section can greatly help you with your purchase decision as you are presented with more information from questions that interested consumers like you might be wondering about.

What Are Ground Mounted Transformers For?

Typically, Ground Mounted Transformers are used to step down or decrease high voltages to low voltage for distribution since high voltages or transmission voltages are not suitable for distribution levels.

The energy distribution mainly goes to metropolitan areas and industrial establishments.

What Are Pad Transformers in General?

Basically, the short answer to what pad transformers really are is that they are transformers that are mounted on a pad that is either made of poly crepe or concrete for stabilization. This type of transformer is commonly used in underground services, but they can be used on the surface and even indoors, but under strict conditions and regulations.

Ground mounted transformers are also another term for the pad transformer. This type of transformer comes in two variants, single-phase and three-phase configurations.

Are Pad Transformers Dangerous?

Normally, people that have little to almost knowledge about electrical devices, would usually stay as far as possible from the boxes of Pad Transformers. So, this generates the question if it is really that dangerous.

These boxes may contain electrical components to step up or step down electricity but the short answer here is that Ground Mounted Transformers are not dangerous, unless bumped into or exposed to fire.

There is simply no scientific evidence that supports the rumor that these electrical devices are dangerous when you pass by or stand near them.

Are Pad Transformers Safe?

Contrary to the question: Are Pad Transformers Dangerous, Pad Transformers aren’t entirely as safe as they seem to be. In fact, when it comes to maintenance, you would need a hot stick for safe repair and maintenance.

But naturally, they are considered safe after installment. DAELIM’s Pad Transformers are in accordance with the standards, which means that after installation, the Ground Mounted Transformer is ready to operate safely.

How Close can Pad Transformers be to Buildings?

Transformers including the Cooper Pad-Mounted Transformer requires to be at least accessible to line trucks, in which the size, shape, and weight are similar to a large truck. This is for the installation, repair, and maintenance to be easy to access.

But overall, transformers are quite near to buildings since it only requires a 4 to 5 feet clearance from the nearest building. As long as there are no possible outside elements that can disturb the operation of the transformer – it is considered a safe distance.

Can Ground Mounted Transformers Be Moved?

This is one of the common questions from consumers. The answer to this question is – Yes, but you must ask for the professional help from the transformer’s manufacturer or your resident’s electrical company.

Relocating Pad Transformers will also make the connections with it to be relocated, which is why relocating it can be a long and hassle process if done alone. So, before purchasing one, make sure that the area you will choose is permanent.

Can Ground Mounted Transformers Explode?

The short answer here is Yes – and it can even catch fire. But this is only a rare scenario that happens due to various reasons. According to international statistics, the most common way a transformer exploding is due to a lightning strike.

A lightning strike can easily cause the transformer to malfunction, overload, and burn the insides. This also damages the wires or lines that are connected with it because of too much electricity flowing in the transformer, which results in fire or most likely an explosion.

Grounding requirements for lightning protection in Pad-mounted substations

Advantages and Disadvantages of Pad-Mounted Transformers

In this section, you will learn the main advantages and drawbacks of ground mounted transformers. This section aims to help you get a better understanding of this electrical device as well, and also to help you with your purchase decision.

Advantages

Below are the main advantages of ground mounted transformers.

Compact

As you probably know, pad transformers are much more compact compared to large distribution transformers. If you are looking for a more convenient distribution transformer that is still capable of regulating voltages despite its size, then pad transformers are a great choice.

Easy to Maintain

Since it is well protected and durable with or without protection, you can expect to have little to almost no maintenance with this device. But proper and regular monitoring should be done in order to keep the ground mounted transformer in pristine condition.

Daelim's pad mounted transformer installed in Honduras
Daelim's pad mounted transformer installed in Honduras

Less Versatile

This type of transformer is also known to be less versatile compared to distribution substations or distribution transformers. This is because of the size that compensates a lot of features from the original distribution transformer.

Regardless, these electrical devices are still great for what they are made to do.

Can Easily Catch Fire

This device can easily catch fire since it is filled with mineral oil or transformer oil. This is why this electrical device is not suitable for indoor uses, and it does not pass the fire code of most buildings and establishments that are usually filled with people.

If you plan on purchasing a ground-mounted transformer, then only use it outdoors for safety purposes. A metal fence or protective fence will be surrounding the device to prevent outside elements from disturbing its operation.

Pad mounted transformer in Canada
Pad mounted transformer in Canada

Final Thoughts on Pad-Mounted Transformers

Pad Transformers are excellent electrical devices that are easy to access and maintain with the right equipment. Depending on what type of or model you are purchasing, Ground Mounted Transformers can be used indoors and outdoors.

Rest assured, they are great electrical devices that are highly efficient in what they are designed to do. Moreover, they are sustainable with superior longevity for long-term use. As long as you do your part in maintaining the electrical device, you can expect to use for a very long time.

If you have any questions or concerns, do not hesitate to contact DAELIM’s team of professionals for immediate accommodation.

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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