Safety in Electronics Design

The effect of insulation requirements is significant enough to change the form factor, performance, cost, and of course, reliability of the transformer. Read on to learn more about insulation types and techniques.

Functional, Basic and Reinforced Insulation

In general terms, functional insulation is the easiest insulation to achieve. It allows for magnet wire to be in contact with other magnet wire and has no creepage or clearance requirements. The insulation strength is tested by a simple dielectric (hipot) test.

Both basic and reinforced insulation are common to parts subject to offline voltages (85-265VAC). The primary difference between these two types of insulation and functional insulation is that basic and reinforced require physical separation between windings, solder joints, and cores. These distances are known as creepage and clearance.

There are a several methods to achieve distance requirements; multi-section bobbins, encapsulation, margin tape, and extruded insulated wire are the most common. You can imagine certain drawbacks to the special insulation: increased size, reduced coupling, lower efficiency, decreased manufacturing capacity, and limited pin configuration options.

The distance requirements and lead isolation are set by specific standards. Reinforced insulation is typically twice that of basic insulation. In some cases, special materials can be used to reduce the distance requirements. In other cases, lead-in routing rules can cause significant manual production processes, especially when pin configuration is fixed.

Definitions

Basic Insulation- Insulation applies to hazardous live parts to provide basic protection against electric shock

Double Insulation- Insulation comprising both basic insulation and supplementary insulation.

Functional Insulation- Insulation that is necessary only for the functioning of the equipment

Reinforced Insulation- Single insulation system that provides a degree of protection against electric shock equivalent to double insulation

Creepage Distance- Shortest distance through air along the surface of an insulation material between two conductive parts

Clearance Distance- Shortest distance in air between two conductive parts

Working Voltage- Highest voltage to which the insulation or the component under consideration is, or can be, subjected when the equipment is operating under conditions of normal use.