What is electrostatic interference in Transformers

Common Sources of Transformer Electrostatic Interference

Your transformer can face electrostatic interference from three different sources. 

• A high voltage power line moving into or out of the transformer or even passing near to a transformer can develop electrostatic interference due to huge amounts of current moving through it.
• Different types of electronics and electrical devices like inverters or rectifiers can also induce electrostatic interference in transformer winding or in its other electrical parts.
• The environmental static charge developed in clouds due to natural and man made factors, can also play a role in transformer electrostatic interference. 

What is a transformer electrostatic shield?

The transformer electrostatic shield is a physical shield placed between the transformer primary winding and secondary winding. It's a conductive layer of non magnetic metal that works to reduce the electrostatic coupling thus blocking electrostatic interference.

In its simplest form, it is a thin sheet of non magnetic metal placed between the transformer primary and secondary winding that does not allow the coupling of electrostatic charge from primary to secondary winding. This prevents electrostatic interference that might happen between transformer windings or other conductive parts. 

This electrostatic interference can disrupt working of different electronics and electrical connection of transformers and can compromise transformer performance. In transformers with multiple coils, a single conductor is used to bond all the electrostatic shields to make a one unified transformer electrostatic shield.

How does a transformer electrostatic shield work?

As we explained, electrostatic interference occurs due to capacitive coupling. The capacitive coupling itself is the transfer of electrical energy from one electrical circuit to a nearby electrical circuit. The transformer electrostatic shield works on the Faraday Cage principle to block the transfer of its capacitive coupling from primary to secondary winding of the transformer.

It does so by absorbing that capacitive coupling or can say electrostatic interference and transferring it to ground by effectively grounding itself. The electrostatic interference developed due to capacitive coupling is redirected into the ground rather than from one electrical circuit to another electrical circuit. 

So a transformer electrostatic shield is a simple sheet of metal that works as a grounded barrier that intercept, absorb, and redirect all the electrostatic interference and unwanted signals into the ground before they reach and affect the transformer output signal.

Why Transformer Electrostatic Shielding is Important?

There are three main reasons why electrostatic shielding of transformers is important

Prevent Transmission of Noise

The transmission of electricity from any electrical device can produce electrical noise. If this noise has significant intensity, it can interfere with either input or output signal coming into or out of the transformer. The transformer electrostatic shield works to block all electrical noises generated as a result of electrostatic charge. It acts as a barrier to block noise generated by primary winding from passing to secondary winding and potentially disturbing the output signal.

More about:Analysis of electric transformer noise problem

Enhance Transformer Performance

Transformer electrostatic shielding is crucial for consistent performance. Electrostatic shielding blocks all electrical noises, and other electrical interferences which keep the output signal clear and consistent. Transformer electrostatic shielding also reduces unwanted capacitive coupling, ensuring efficient energy transfer.

Improve Equipment Lifespan

Transformer electrostatic shields not only work to block unwanted noises and interferences for your transformer to keep its output signal clear. It also works to protect the sensitive electronics of the transformer from unwanted voltage spikes and external interferences. This improves the equipment lifespan by protecting it from any accidental failure.

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Types of Electrostatic Shields

There can be three different types of transformer electrostatic shielding depending on the transformer type, size, power rating, and the output required.

Copper Foil Shielding

Copper foil electrostatic shield is the most effective and high performance electrostatic shield you can use in any transformer. Simply made from copper foil, the copper electrostatic shield relly on its high electrical conductivity to block and redirect all the electrostatic interference, electrical noises, and unwanted signal away from transformer electronics and into the ground. The copper foil shielding is used in all types and sizes of precision and dedicated transformers.

Aluminum Shielding

Made from a very thin sheet of aluminum, the aluminum electrostatic shield is the most widely used and cost effective solution to block and redirect all types of electrostatic interferences and ground all the electrical noises and unwanted signals. They are used in almost all types, size, power capacity transformers where keeping manufacturing cost low is crucial.

Conductive Paints and Coatings

Transformers are not only those big electrical devices that you see installed on poles or on ground. These also came in small enough size to be a part of a machine and in sensitive machines, even a smallest of electrostatic interferences can be problematic. So in those applications, a conductive paint or coating is used for electrostatic shielding due to space constraint.

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Design Consideration for Transformer Electrostatic Shielding

Transformer electrostatic shielding is so crucial especially in applications where transformer performance and output signal quality is very important. Your ability to do a proper design calculator and implementing the concept properly will have a significant impact on transformer performance and efficiency especially in sensitive applications.

The following factors must be considered when designing an effective electrostatic shield.

Placement and Grounding

To do an effective transformer electrostatic shielding job, you need to do a proper placement and grounding job for shielding metal sheets. Other than this you should also consider the minimizing of loop and need of multiple shieldinging if required. 

Location

The non magnetic thing sheet of metal should be positioned between the transformer primary and secondary winding and no area of winding should be exposed to each other. Sheet should cover the entire length, width and height of the winding for a perfect electrostatic shielding.

Grounding

The electrostatic shield should be properly grounded to either transformer ground or the chassis ground. Any issue with the grounding work will result in the failure of the entire shielding job. 

Minimizing Loop

The grounding path you made for the grounding work of the electrostatic shield should be kept as short as possible. This is very important as current always takes the shortest and lower resistant path, so keeping the grounding distance as short and straight as possible.

Multiple Shields

You might need to install multiple electrostatic shields depending on the application of the transformer. One case is where you need ultra low noise performance and extremely high quality output signal. A transformer with multiple primary and secondary windings needs at least one shield per winding. All shields are then connected and grounded with one single connection. 

Material Selection

Material you choose for your transformer electrostatic shield is very important. Material conductivity and performance in absorbing and redirecting electrostatic interference will define the performance. You can choose from the following.

• Choose copper if you are looking for high performance and excellent shielding effect from your transformer electrostatic shield. If your transformer is for high performance application and cost is not an issue, then copper is best for your transformer shield. It has conductivity rating of 100% IACS  (International Annealed Copper Standard)
• If your transformer is for general purpose and has no precision or dedicated application, then aluminum sheet is best for your transformer electrostatic shielding. It has a conductivity rating of about 61% IACS. This is lower than copper but acceptable in many applications. It is good at blocking electrostatic interference and costs much lower than copper.

Thickness of the Shield

The thickness of the transformer electrostatic shield will define the intensity of the electrostatic interference it can block. The thickness of the shield depends on the transformer type, size, and power rating. 

A thicker shield will provide a better electrostatic shielding with improved noise diversion but it also increases the physical size and weight of the transformer. A thick electrostatic shield can also lead to eddy current losses if it is not properly installed. 

To avoid eddy current losses and have a shield that blocks all the electrostatic interference, a sheet thickness must be selected that maintains a balance between electrostatic shielding and transformer efficiency. Typically a shield thickness ranges from 0.1 mm to 1 mm, depending on application requirements.

Additional Consideration

There are some additional considerations for you to know as they can come handy when designing the transformer electrostatic shielding. Some additional considerations are as follows.

• When installing the electrostatic shield, the shield has to be spaced adequately from winding. This space is important to prevent any unintended arcing between winding and shield.
• The material selection should be done after considering the transformer specification specially the transformer temperature. Shield should be able to resist the maximum operating temperature of the transformer without any degradation or compromise of performance.
• The shield design, shape, and sheet thickness should be in consideration of other design aspects of the transformer. The shield should be compatible with transformer winding and assembly processes to avoid unnecessary complexity and cost increases.

Reading more about Transformer Design

Application of Transformer Electrostatic Shielding
 

The transformer electrostatic shielding is not limited to industrial transformers for transformers you see hanging on poles. It is also done on any voltage regulating electrical device that can be called a transformer. Some of the most common applications of transformer electrostatic shielding are as follows.

Medical Equipment

Big medical equipment like X rays machines, CT scan machines, and MRI machines rely totally on consistent supply of electricity to operate efficiently. These machines have huge electrical power consumption due to their working mechanism which is managed by a builtin transformer. As these machines are involved in sensitive work and any change in electricity coming into the machine can affect their working. So to ensure accuracy in devices like MRI scanners and ECG machines, electrostatic shielding is heavily used in builtin transformers and other related electronics.

Aerospace and Defense

Aerospace and defense are two fields that heavily rely on electronics, electrical, and telecom equipment like sensors, transmitter and radars. All these machines basically do all their work consuming electricity. Any change in incoming electrical signal can affect their working and can prove catastrophic. So all these machines have electrostatic shielding to protect their sensitive electronics.

Conclusion

Transformer electrostatic shielding is an essential technique for minimizing electrical noise and unwanted signals in transformers. This is absolutely necessary to ensure stable electrical performance of transformers. Whether the transformer is for industrial applications or precision electronics, proper shielding enhances transformer efficiency and protects connected equipment.

Read more: How to choose the best distribution transformer?

Follow Up

Proper transformer electrical shielding is very crucial for having steady performance and high efficiency. We at Daelim design, manufacture, and supply transformers with high quality  electrostatic shielding by following and satisfying all international standards. We deliver transformers of all types, sizes, and power ratings with proper electrostatic shielding in the USA, Europe, Australia and other countries around the globe. 

If you have any question about transformer electrostatic shielding or about transformer design, manufacturing and supply. Contact Us and our team will talk you through the process.