Isolation Transformer - Applications

Applications

In electronics testing and servicing an isolation transformer is a 1:1 (under load) power transformer used for safety. Without it, exposed live metal in a device under test is at a hazardous voltage relative to grounded objects such as a heating radiator or oscilloscope ground lead (a particular hazard with some old vacuum-tube equipment with live chassis). With the transformer, as there is no conductive connection between transformer secondary and earth, there is no danger in touching a live part of the circuit while another part of the body is earthed.

Electrical isolation is considered to be particularly important on medical equipment, and special standards apply. Often the system must additionally be designed so that fault conditions do not interrupt power, but generate a warning.

Isolation transformers are also used for the power supply of devices not at ground potential. An example is the Austin transformer for the power supply of air-traffic obstacle warning lamps on radio antenna masts. Without the isolation transformer, the lighting circuits on the mast would conduct radio-frequency energy to ground through the power supply.

Metal boats are subject to corrosion if they use earthed power from shore when moored, due to galvanic currents that flow through the water between shore earth and the hull. This can be avoided by using an isolation transformer with the primary and case connected to shore earth, and the secondary "floating". A metal safety screen between primary and secondary is connected to shore earth; in the event of a fault current in the primary (due, e.g., to insulation breakdown) it will cause the fault current to return and trip a shore-based circuit breaker rather than making the hull live.