| Accurate Ratio Transformer
| A small transformer which transforms at an accurate ratio to allow an attached instrument to gauge the current or voltage without actually running full power through the instrument. |
| Ammeter
| An instrument used to measure current. |
| Autotransformer
| A special type of power transformer, consisting of a single, continuous winding that is tapped on one side to provide either a step-up or step-down function. |
| Basic Impulse Level
| A measure of the ability of a transformer’s insulation system to withstand very high-voltage, short-time surges Burden Term applied to the tiny load that an instrument’s delicate moving elements places on an accurate-ratio transformer. |
| Coefficient of Coupling
| The amount of coupling that takes place between the two windings in a transformer. This amount should ideally be 100%, but this is not achievable in the real world. |
| Coils
| See “Winding.” |
| Copper Loss
| The energy wasted as heat in the copper (or aluminum) windings, as copper/aluminum is not a perfect conductor of electricity. |
| Core
| A component of a transformer. The iron or steel core provides a controlled path for the magnetic flux generated in the transformer by the current flowing through the windings. |
| Core and Coils
| A non-enclosed, dry type transformer, mounted on a base as one unit. |
| Core Type
| A type of core where the windings surround the laminated iron core. |
| Current Transformer
| A type of instrument transformer used to measure current. |
| Deflection
| Literally, the amount of movement the indicator of an instrument makes when sensing. Also called the reading of the instrument. |
| Distribution Transformer
| A transformer used to supply relatively small amounts of power to residences. It is used at the end of the electrical utility’s delivery system. Often mounted on a pole. |
| Delta
| A three-phase transformer connection where the phases are connected in a manner which resembles the Greek letter Delta. |
| Dry Type Transformer
| A transformer designed to operate in air. The design does not require the assistance of a liquid to dissipate excess heat. Natural or fan-assisted circulation through ventilation openings is all that is required to meet temperature classification requirements. |
| Eddy Current
| Induced voltage in the core as a result of transformer operation. The currents move through the core in circular paths. |
| Eddy-Current Loss
| The energy wasted by eddy currents creating heat in the core, as this does not aid in the induction process. |
| Efficiency
| A rating of the percentage of input power transmitted through the transformer. This number will never be 100% in the real world due to copper losses, eddy-current losses and other inefficiencies. |
| Encapsulated Transformer
| A specialty dry type transformer, sealed in an enclosure. It is capable of moving excessive heat away from the core and coils without ventilation openings. |
| Full Capacity Above Normal Tap
| A special voltage tap used to account for voltage fluctuations on the input side. Allows for fine-tuning of the output voltage when the input voltage is higher than expected. |
| Full Capacity Below Normal Tap
| A special voltage tap used to account for voltage fluctuations on the input side. Allows for fine-tuning of the output voltage when the input voltage is lower than expected. |
| Input
| The voltage source coming into the transformer through the primary winding. |
| Instrument Transformer
| A small transformer which transforms at an accurate ratio to allow an attached instrument to gauge the current or voltage without actually running full power through the instrument. |
| Insulation System Temperature Classification
| A statement of the maximum temperature permitted in the hottest spot in the winding, at a specified ambient temperature, usually 40°C. Exceeding this figure will likely result in an insulation failure. |
| Isolation Transformer
| A transformer with a 1:1 turns ratio. It does not step voltage up or down. It serves as a safety device, isolating the grounded conductor of a power line from a chassis or any portion of a circuit load. |
| Liquid-Filled Transformer
| A type of transformer cooled by mounting in a sealed tank filled with liquid. The liquid is normally oil, but silicone and other liquids may also be used. |
| Magnetic Coupling
| The method by which one circuit is linked to another circuit by a common magnetic field. |
| Magnetic Flux
| Lines of magnetic force surrounding a magnet or electromagnet. |
| NEMA
| Abbreviation for National Electrical Manufacturers Association. An organization of manufacturers of electrical products. |
| Output
| The transformed voltage exiting the transformer through the secondary winding, and going out to the load. |
| Potential Transformer
| A type of instrument transformer used to measure voltage. |
| Power Transformer
| A transformer used primarily to couple electrical energy from a power supply line to a circuit system. |
| Primary Side
| The side of the transformer where the power to be changed comes from. |
| Primary Winding
| Turns of wire on the core, used to connect the input to the core. |
| Rectifier Transformer
| A type of power transformer used with solid state circuits. |
| Secondary Side
| The side of the transformer where the power is sent to the equipment it needs to power. Depending upon the requirement of the load, the voltage was either increased or decreased from the primary voltage. |
| Secondary Winding
| Turns of wire on the core, used to connect the output to the core. |
| Shell Type
| A type of core where the core surrounds the windings. |
| Step-Up Transformer
| A transformer in which the output voltage is higher than the input voltage. The secondary winding has more turns of wire than the primary winding. |
| Step-Down Transformer
| A transformer in which the output voltage is lower than the input voltage. The secondary winding has fewer turns of wire than the primary winding. |
| Three-Phase Transformer
| A transformer used to transform power provided by a three-phase power system. |
| Transformer
| A device that transfers electrical energy from one electric circuit to another, without changing the frequency, by the principles of electromagnetic induction. The energy transfer usually takes place with a change of voltage. |
| Transformer Bank
| An arrangement of three single-phase transformers, configured to transform three-phase power. |
| Turns
| The number of times the wire of a winding actually goes around the core. |
| Turns Ratio
| A comparison of the number of turns in the primary versus the number of turns in the secondary. Directly related to the voltage ratio. |
| Voltage Ratio
| A comparison of the voltage entering the primary versus the voltage exiting the secondary. Directly related to the turns ratio. |
| Voltage Tap
| An additional connection to a winding, which permits use of only a specific part of the winding. This allows the same winding to handle multiple voltage levels. |
| Voltmeter
| An instrument used to measure voltage. |
| Wattmeter
| An instrument used to measure wattage. |
| Winding
| Turns of wire around the core of the transformer. Connects the core to either the input, in the case of the primary winding, or the output, in the case of the secondary winding. |
| Wye
| A three-phase transformer connection where the phases are connected in a manner which resembles the letter “Y.” Often called a “star connection.” |
