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Shielded Isolation Transformers

As most of us are aware, the transformer principle was propounded by Michael Faraday in 1831. A transformer, simply stated, is a device used to transfer electrical energy from one circuit to another. A transformer, as its very name suggests, transforms electricity from high voltage to low voltage.

The purpose of an isolation transformer usually has symmetrical windings meant to decouple two circuits. In other words, an isolation transformer helps an AC signal or power to be taken from any one device and fed into another without electrically connecting the two circuits. Isolation transformers can also be used to block transmission of DC signals from one circuit to the other. Isolation transformers with electrostatic shields are used for power supplies for sensitive equipment such as computer equipments, electronic devices and laboratory instruments.

In a 3 phase transformer, there is a three-legged iron core with each leg having a respective primary and secondary winding. A 3 phase isolation transformer has isolated primary and secondary windings to allow the power input to be isolated from the power output. There are three types of 2 phase isolation transformers: Standard 3 phase isolation transformers and 3 phase shielded isolation transformers. The shielded 3 phase isolation transformer is preferred over a standard 3 phase isolation transformer because of the protection it provides.

Shielded isolation transformers are not true power-conditioning devices because they care not capable of adjusting their output voltage to compensate for sags or surges on the input line. To accomplish this, you would need to add surge suppressors to the system. Instead, isolation transformers reject noises and they provide good electrical noise isolation.

Shielded isolation transformers have all the features of a standard isolation transformer but they come with a full copper or aluminum shielding between the primary and secondary windings. The Faraday Shield of the shielded isolation transformer is connected to earth ground to filter voltage spikes and common mode noise.

Shielded Isolation Transformers isolates electrical power from the normal supply source to reduce effects of power surges. They are available with electrostatic shields between the primary and secondary to reduce line interference. Primary surge suppression and secondary filters can be added for additional reduction of transient and across-the-line surges. For several sensitive and critical equipments, these shielded AC Isolation Transformers are preferred over standard isolation transformers because they offer better protection.

Isolation transformers can be designed with a 1:1 ratio, for isolation only, or to provide voltage transformation. While unshielded transformers use capacitance coupling between the primary and secondary windings, a shielded isolation transformer uses primary-to-shield capacitance.

While unshielded transformers use capacitance coupling between the primary and secondary windings, a shielded isolation transformer uses primary-to-shield capacitance. It also uses the shield-to-secondary capacitance resulting from the small electrostatic field around the shield. The primary-to-shield capacitance conducts most of the transient energy to ground so the effective capacitance between primary and secondary windings of a shielded isolation transformer is much less than that of an unshielded transformer.

Since the early beginnings of computer power isolation, manufacturers have supplied shielded transformers for reducing common mode noise and transients. Some uses of shielded transformers, however, require additional protection from across-the-line, or transverse mode power disturbances.