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Ambient Temperature: The normal surrounding temperature of the environment in which a transformer will operate. Duty Cycle: The amount of time a transformer will actually be supplying the Full Rated Power to the load, expressed in percentage. For example, a transformer operating at a 10% duty cycle only supplies its Full Rated Power 10% of the time, and is usually idle the remaining 90%. Duty Cycle can substantially affect the physical size of a transformer. Electrostatic Shielding: Placed between windings (usually the primary and secondaries) to provide maximum isolation. Additional Electrostatic Shields can be placed between secondary windings if required. Normally connected to the transformer’s core (ground). Encapsulation, Impregnation: A process whereby a transformer, in whole or in part, is completely sealed with epoxy or similar material, usually as a precaution against moisture and corrosion. Exciting Current: The current drawn by a transformer at nominal input voltage in it’s unloaded (open-circuit) condition. Forced Air: One method of cooling a transformer in which air from the outside environment will be forcibly blown into the transformer’s surrounding environment. Another method involves forcibly extracting heated air from the transformer’s surrounding environment. Frequency: Number of cycles per second of a sinewave. Inrush Current: A brief momentary current surge through the transformer experienced at the instant the transformer is energized (switched on) - see Transformer Inrush Current. Natural Convection: One method of cooling a transformer in which the normal convection of ambient air surrounding the transformer will provide its only cooling. Enclosure: An enclosure surrounding a transformer, usually constructed of metal, that provides some measure of protection against weather. Different ratings determine the degree of protection. Suitable for outdoor use or where indoor location may constitute a shock hazard if connections are left exposed. Open Frame: A method of transformer construction in which no special precautions are taken against weather or corrosion. Suitable for indoor use in which the transformer will sit within a larger enclosure with other components. Primary Winding: The coil winding connected to the input power available. Rated Power: The total output power available from all secondary windings, expressed in Voltamperes (VA) or Kilovoltamperes (kVA). Arrived at for single-phase transformers by multiplying full-load voltage and full-load current for each secondary winding and adding the products. A similar process is used to calculate the Rated Power for three-phase transformers. Regulation: The difference between a secondary winding’s output voltage when operating under unloaded (open-circuit) and fully loaded (full-load) conditions, expressed as a percentage no-load to full-load. Secondary Winding(s): The coil winding(s) supplying the load(s). Taps or Voltage Taps: Additional connections to a winding allowing different voltages to be obtained from the same winding. Often used on the primary winding to allow the transformer to be used in different countries having different line voltages available. Temperature Rise: The additional maximum heat, above Ambient Temperature, that the transformer itself will generate in the normal course of operation. Test Potential: A voltage applied to a winding to insure adequate insulation performance. Normally applied between a winding and all other windings, and between a winding and ground. Also known as the Dielectric Withstanding Voltage and the Hipot Voltage (or simply as the Hipot). Copyright 2000 |