Transformer Shield

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Transformer Shield

Call TEMCo today for delivering leading industry products that will supply your electrical needs and help sustain your business functions, such as ordering a transformer shield in a transformer for a new building or power expansion.  Call us today at 510-490-2187. 

Transformer Shield Introduction

Transformer shields are often called Faraday shields or static shields.  A more in-depth discussion of what a shield is will be found on the Triple Shielded Transformer page.  This Transformer Shield page will be dedicated to describing the shield, itself, details about its use, and some alternative shield designs or configurations. 

Transformer Shield Construction

Most transformer shields are made of either a copper or aluminum layer and are of a thickness that is usually referred to as foil.  Some applications can use an additional single-winding layer between primary and secondary windings to act as the shield.  For instance, wrapping a very small coil with a foil shield can be harder than simply inserting a wire layer.  In this case, one end of such a winding would be run to a ground.  But the bulk of transformers use a foil of some kind.  This metallic foil must be carefully placed between the primary and secondary windings of the transformer. 

The transformer shield cannot overlap itself in any way that it completes a circuit of its own.  A transformer shield does not have the wiring to complete a full circuit.  This is deliberate and is intended to prevent unwanted capacitive coupling.  Capacitive coupling is a term that refers to a condition in which a current in one conductor or circuit is passed into an adjacent circuit or conductive materials.  This would cause a condition known as a Shorted Turn and simply means that it has become one single winding around the core.  When any one of the windings or the shield does this it receives the bulk of the induced current and can overheat, causing fires and burnouts.  Generally, the shield has to remain slightly incomplete so that a gap keeps this from occurring. 

Sometimes, also, the edges of the shield are folded under to suppress what is called the Corona Effect.  When a conductor approaches its limit of capacitance a leakage of energy can occur at any point there are inconsistencies in the surface or edges of the conductor.  The energy will tend to ionize the surrounding air and bleed off the energy.  This, in itself, can create additional charges and "noise" that were what the transformer shield was to suppress.  Unshielded transformers will often exhibit coronas, so will tend to be electronically "noisy". 

Transformer Shield Function

The primary functions of a transformer shield are to limit:

•  the effects of build-up of charges that will leak directly across from primary to secondary windings
• surges from the power source or from conditions that result in surges on the primary side of the transformer
• and ambient conditions leading to the transformer being affected by those environmental situations.

  Unwanted inductances of any conductor in use can add or subtract form power characteristics.  Induction is calculated on a one-for-one basis where transfer from primary to secondary is ideally proportional.  However, because many factors exist that modify this relationship, one has to allow for those influences. 

Picture a man pulling a donkey.  He starts to pull on the reigns but the donkey balks.  The man jerks harder and the donkey moves, but now at an unexpected rate which causes him to have to compensate.  The compensation is overdone and there is a waste of energies all along this process.  Such things happen within a transformer as it operates.  These things are governed by the many factors of quality of conductors, shape of core, composition of core, quality of electrical power in the power source, quality of transformer insulation, ambient conditions having to do with presence of other electrical equipment and their operation, frequencies involved, magnitudes of voltages, presence of moisture and other atmospheric conditions, resistance characteristics of the winding conductor, and many others.  Though the actual measurable amounts of unwanted charges can even be relatively quite small, their effects can be very undesirable when under certain applications. 

Actual oscilloscopic tests can graphically show how interference and undesirable added electrical characteristics coming from the power service is deleted by using adequate shielding practices.

Alternatives in Transformer Shield Use

Transformer shields, as indicated on the Triple Shielded Transformer page, can be ganged up for increased protection.  Often, the shield closest to the primary windings are grounded to the primary ground and the shield closest to the secondary winding is grounded to the secondary ground.  A third ground can be made from the third shield to the safety (chassis) ground.  This is an added strategy towards isolating the unwanted characteristics from being passed from primary to secondary.  Additionally, lead-in wiring from service to transformer can be shielded by a foil or braided wire covering to inhibit local transfer of unwanted characteristics from the presence of other equipment operating in the area.  Finally, the entire transformer can be enclosed in a Faraday cage (grounded metal enclosure) to block affects that the transformer might pick up from high frequency or high voltage equipment activity nearby.  Such transformer shields are called "box shields".

Most standard transformers can have shielding added to good advantage if needed.  Custom ordered transformers are also available on request.  All Acme general purpose isolation transformers 250 VA and larger are shielded at no added cost as a standard feature.

Highest Quality Transformer Shields

Call TEMCo with your specific needs. TEMCo’s technical sales department has many years of applications experience providing design and engineering assistance for all types of transformer shield installations.

Call Our Transformer Shield Specialists Today!

 *Custom Shielded Transformer Voltage Combinations Available*

Contact our team at TEMCo Transformer at 510-490-2187 to get your quote, place your order and arrange for shipping.

TEMCo Transformer Manufacturer Distribution: The Custom Shielded Transformer Manufacturer Supplier of Choice for Electricians and Manufacturers.

TEMCo Transformer Manufacturer Distribution: High Quality, Efficient, Fast Turnaround of Custom Transformers with a Transformer Shield Manufactured to your Specs!