Power Transformer

A power transformer is a passive electromagnetic device that transfers energy from one circuit to another circuit by means of inductive coupling. Power transformers differ from other transformer types in that they are designed to comply with regulatory requirements for mains power interfacing, working at mains voltages and relatively high currents. The most important specification of a power transformer is its primary to secondary transformer galvanic isolation, which is usually specified in kV. This is a fundamental safety aspect in protecting humans from potentially lethal earth fault conditions.
Power transformers typically have a single primary (mains side) winding and one or more secondary windings. The secondary winding may be tapped at different points to generate multiple voltage outputs. A power transformer operates according to Faradays Law of Induction. A transformer’s secondary voltage is equal to the negative rate of change of the magnetic flux enclosing the circuit. The magnetic flux enclosing the secondary circuit is caused by the AC flowing in the primary winding. This AC generates a changing flux that couples through a common core into the secondary winding. Voltage ratio is equivalent to the winding turn ratio. Transformers are extremely efficient when operating within their design specifications.
Core type is an important consideration. Typical power transformer supplies include: laminated core, semi-toroidal and toroidal. Laminations can be important as they help prevent eddy currents flowing in the core that cause loss of efficiency. Maximum output current is specified at the point where the core is saturated or the windings current rating is exceeded. There are many mounting options including: chassis mount, DIN rail, wall mount and PCB mount. Terminations can be solder lugs, wire leads and terminal blocks. Galvanic isolation is typically rated between 1.5kV and 5kV.
Power transformers are found in any application that requires mains power. They are also used as 1:1 isolating transformers for equipment safety. 120-240V transformers are also available for conversion between mains standards.
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