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3 Phase Isolation Transformers

3 Phase Electrical Power Isolation Transformer

A 3 phase transformer, there is a three-legged iron core as shown below. Each leg has a respective primary and secondary winding.  Thus a 3 phase isolation transformers is a 3 phase transformer which has isolated primary and secondary windings to allow the power input to be isolated from the power output.

There a number of power transformer manufacturers of quality 3 phase isolation transformers today.  The primary 3 phase isolation transformers manufacturers are: GE Industrial, TEMCo Isolation Transformer, Marcus Transformer, Hammond Transformers, and Acme Transformers with capacity ranges 0.05 KVA through 5000 KVA. The isolation transformer manufacturer TEMCo also acts as a one stop wholesale outlet for the other transformer brands.

Standard 3 Phase Isolation Transformers

3 phase isolation transformers have 3 primary and 3 secondary windings that are physically separated from each other. Sometimes these isolation transformers are referred to as "insulated". This is because the windings are insulated from each other.

In a 3 phase isolation transformer the output windings will be isolated, or floating from earth ground unless bonded at the time of installation.

3 Phase Shielded Isolation Transformers

Shielded 3 phase isolation transformers have all the feature of the standard 3 phase isolation transformers plus they also incorporate a full metallic shield (usually copper or aluminum) between the 3 phase primary and 3 phase secondary windings. This electrostatic shield ("Faraday Shield") is connected to earth ground and performs two functions:

One, it attenuates (filters) voltage transients (voltage spikes). These shielded 3 phase isolation transformers have an attenuation ratio of 100 to 1.

Two, It also filters common mode noise. Attenuation of approximately 30 decibels.

Shielded 3 Phase Isolation Transformers Are Preferred

The shielded 3 phase isolation transformer is preferred over a standard 3 phase isolation transformer because it provides protection for sensitive and other sensitive and critical equipment.

When more than one shielded 3 phase isolation transformer is installed between the source and the load, this is referred to as "cascading" and vastly improves power quality.

As of this publishing all of the Acme and TEMCo general purpose isolation transformers 250 VA and larger are shielded at no added cost as a standard feature. Shielded TEMCo and Acme isolation transformers have an "s" as the last digit of the part number.

Most power is distributed in the form of three-phase AC. Therefore, before proceeding any further you should understand what is meant by 3 phase power. Basically, the power company generators produce electricity by rotating (3) coils or windings through a magnetic field within the generator . These coils or windings are spaced 120 degrees apart. As they rotate through the magnetic field they generate power which is then sent out on three (3) lines as in three-phase power. 3 phase transformers must have (3) coils or windings connected in the proper sequence in order to match the incoming power and therefore transform the power company voltage to the level of voltage we need and maintain the proper phasing or polarity.

3 Phase Power Is More Efficient Than Single Phase

Three phase electricity powers large industrial loads more efficiently than single-phase electricity. When single-phase electricity is needed, It is available between any two phases of a three-phase system, or in some systems , between one of the phases and ground. By the use of three conductors a 3 phase system can provide 173% more power than the two conductors of a single-phase system. Three-phase power allows heavy duty industrial equipment to operate more smoothly and efficiently. 3 phase power can be transmitted over long distances with smaller conductor size.

(Also read about 3 phase isolation transformers here.)

In a three-phase transformer, there is a three-legged iron core as shown below. Each leg has a respective primary and secondary winding.

The three primary windings (P1, P2, P3) will be connected at the factory to provide the proper sequence (or correct polarity) required and will be in a configuration known as Delta. The three secondary windings (S1, S2, S3) will also be connected at the factory to provide the proper sequence (or correct polarity) required. However, the secondary windings, depending on our voltage requirements, will be in either ?Delta? or a ?Wye? configuration.  

3 Phase Transformers Overview

3 phase transformers are used throughout industry to change values of 3 phase voltage and current. Since 3 phase power is the most common way in which power is produced, transmitted, an used, an understanding of how 3 phase transformer connections are made is essential. In this section it will discuss different types of 3 phase transformers connections, and present examples of how values of voltage and current for these connections are computed.

3 phase Transformer Construction:

A 3 phase transformer is constructed by winding three single phase transformers on a single core. These transformers are put into an enclosure which is then filled with dielectric oil. The dielectric oil performs several functions. Since it is a dielectric, a nonconductor of electricity, it provides electrical insulation between the windings and the case. It is also used to help provide cooling and to prevent the formation of moisture, which can deteriorate the winding insulation.

Three-Phase Transformer Connections:

There are only 4 possible transformer combinations:

Delta to Delta - use: industrial applications

Delta to Wye - use : most common; commercial and industrial

Wye to Delta - use : high voltage transmissions

Wye to Wye - use : rare, don't use causes harmonics and balancing problems.

3 phase transformers are connected in delta or wye configurations. A wye-delta transformer has its primary winding connected in a wye and its secondary winding connected in a delta (see figure 1-1). A delta-wye transformer has its primary winding connected in delta and its secondary winding connected in a wye (see figure 1-2).

Delta Connections:

A delta system is a good short-distance distribution system. It is used for neighborhood and small commercial loads close to the supplying substation. Only one voltage is available between any two wires in a delta system. The delta system can be illustrated by a simple triangle. A wire from each point of the triangle would represent a three-phase, three-wire delta system. The voltage would be the same between any two wires (see figure 1-3).

Wye Connections:

In a wye system the voltage between any two wires will always give the same amount of voltage on a 3 phase system. However, the voltage between any one of the phase conductors (X1, X2, X3) and the neutral (X0) will be less than the power conductors. For example, if the voltage between the power conductors of any two phases of a three wire system is 208v, then the voltage from any phase conductor to ground will be 120v. This is due to the square root of 3 phase power. In a wye system, the voltage between any two power conductors will always be 1.732 (which is the square root of 3) times the voltage between the neutral and any one of the power phase conductors. The phase-to-ground voltage can be found by dividing the phase-to-phase voltage by 1.732 (see figure 1-4).

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