Transformer Glossaries (A–Z)

A

• Alternating Current (AC): A current that periodically reverses direction, unlike direct current (DC) which flows in one direction.

• Alternator: A rotating machine that generates alternating current (AC).

• Ambient Temperature: The surrounding environmental temperature.

• Ammeter: A device for measuring electric current in amperes.

• Autotransformer: A transformer with one winding acting as both primary and secondary.

• Air-Core Inductor: An inductor using air (or vacuum) as its magnetic core.

• Ampacity: The maximum amount of electric current a conductor or device can carry before sustaining immediate or progressive deterioration.

• Arc Suppression Coil: A device used to suppress electrical arcs.

B

• Bushing: An insulating component allowing a conductor to pass through a grounded enclosure.

• Buck-Boost Transformer: Used for small voltage adjustments in lighting and control systems.

• Breakdown Voltage: The voltage at which insulation fails and becomes conductive.

• BIL (Basic Insulation Level): The maximum voltage that electrical equipment can withstand without breakdown.

• Banking: Connecting two or more transformers to function as a single unit.

• Buchholz Relay: A gas-actuated relay used for the protection of oil-immersed transformers.

C

• Circuit Diagram: Schematic representing electrical connections using standard symbols.

• Conduction: The transfer of energy (electric or heat) through a conductor.

• Contactor: A large relay used to control power circuits.

• Cooling: The process of dissipating heat from a transformer.

• Copper Losses (I²R): Heat losses due to current flowing through winding resistance.

• Coupling: Transfer of energy between circuits, often via magnetic fields.

• Core Saturation: A condition where an increase in current does not result in an increase in magnetic flux.

• Capacitance: The ability of a system to store an electric charge.

D

• Direct Current (DC): Electric current flowing in a single direction.

• Dielectric: Insulating material between conductors in a capacitor or transformer.

• Distribution Transformer: Steps down voltage for residential or commercial use.

• Delta Connection: A method of connecting three transformer windings in a triangle-like configuration.

• Detuning: Adjusting a circuit to prevent resonance at a particular frequency.

• Duty Cycle: The ratio of operating time to total time in a repeating cycle.

E

• Efficiency: Ratio of output power to input power, expressed as a percentage.

• Electrical Insulation: Material preventing unwanted current flow.

• Electromagnetic Induction: Generating voltage through magnetic field change.

• Exciting Current: The current required to energize the transformer’s core.

• Electrostatic Shield: A grounded conductor placed between windings to reduce capacitive coupling.

• Eddy Currents: Circulating currents induced within conductors by a changing magnetic field.

F

• Flux (Magnetic): Magnetic field lines generated in a transformer core.

• Frequency: Number of AC cycles per second, measured in hertz (Hz).

• Fuse: A safety device that melts under excessive current to break the circuit.

• Faraday’s Law: The principle that a change in magnetic field can induce an electromotive force (EMF).

• Ferrite Core: A type of magnetic core made of ferrite, used in high-frequency transformers.

• Flux Leakage: Magnetic flux that does not follow the intended path in a magnetic circuit.

G

• Grounding (Earthing): Connecting components to the earth for safety.

• Grading Ring: Metal ring used on bushings to manage electric fields.

• Gauss: A unit of magnetic flux density.

• Gap Loss: Losses due to air gaps in the magnetic path.

• Gassing: The release of gas within transformer oil due to decomposition.

• Ground Fault: An unintentional connection between an electric circuit and the ground.

H

• Harmonics: Voltage/current distortions at multiples of the base frequency.

• HV (High Voltage): Voltage levels typically above 1 kV.

• Heat Run Test: A test measuring transformer temperature rise under load.

• Hysteresis Loss: Energy loss due to the lag between magnetic field strength and magnetization.

• Hot Spot Temperature: The highest temperature within the transformer winding.

• Hermetically Sealed Transformer: A transformer sealed to prevent moisture ingress.

I

• Impedance: Resistance to AC, including both resistance and reactance.

• Inrush Current: Surge of current when a transformer is first energized.

• Insulation Resistance: Resistance offered by insulating material to current flow.

• Instrument Transformer: Used to measure voltage or current without directly connecting to high-voltage lines.

• Isolating Transformer: Provides electrical isolation between its primary and secondary windings.

• Inductance: The property of a conductor by which a change in current induces an electromotive force.

J

• Joule Effect: Heat produced by electric current in a conductor.

• Jumper Cable: A temporary cable used for electrical connections.

• Junction Temperature: The temperature at the point where different materials meet in a device.

• Jacket: The outer protective covering of a cable or transformer.

• Jitter: Small, rapid variations in a waveform resulting from fluctuations in the signal.

• Junction Box: An enclosure housing electrical connections.

K

• kVA (Kilovolt-Amperes): Unit of apparent power in a transformer.

• K-Factor: Indicates a transformer’s ability to handle non-linear loads.

• Knee Point Voltage: The voltage at which a transformer’s core begins to saturate.

• Kilowatt (kW): Unit of real power.

• Knee Point: The point on the magnetization curve where the core begins to saturate.

• KVA Rating: The maximum apparent power a transformer can handle.

L

• Load Loss: Power loss when supplying load due to resistance in windings.

• Lightning Arrester: Protects transformer from lightning-induced surges.

• Leakage Reactance: Reactance due to leakage flux not linking both primary and secondary windings.

• Line Voltage: Voltage measured between two lines in a three-phase system.

• Load Tap Changer: A device that adjusts transformer voltage under load conditions.

• Laminations: Thin sheets of electrical steel used to construct the transformer core.

M

• Magnetizing Current: Current needed to energize the magnetic core.

• Mineral Oil: Oil used in transformers for insulation and cooling.

• MVA (Megavolt-Amperes): Unit of apparent power for large transformers.

• Mutual Inductance: The ability of one inductor to induce voltage in another nearby inductor.

• Magnetic Flux Density: The amount of magnetic flux in a given area.

• Moisture Content: The amount of water present in transformer insulation or oil.

N

• No-Load Loss: Power consumed by a transformer energized without load.

• Neutral Point: Common return path for electrical current in three-phase systems.

• Nameplate Rating: The manufacturer’s specified operating limits for a transformer.

• Noise Level: The sound emitted by a transformer during operation.

• Nominal Voltage: The standard operating voltage of a system.

• NEMA Rating: Standards set by the National Electrical Manufacturers Association for equipment.

O

• Oil-Immersed Transformer: A transformer where windings and core are immersed in insulating oil for cooling and insulation.

• Overload Capacity: The ability of a transformer to operate above its rated capacity for short durations.

• Open Circuit Test: A test to determine core losses and magnetizing current.

• OLTC (On-Load Tap Changer): A device allowing voltage regulation without de-energizing the transformer.

• Overvoltage: A voltage higher than the rated maximum for equipment.

• Overtemperature Alarm: A warning triggered when the transformer exceeds a safe operating temperature.

P

• Primary Winding: The input winding connected to the power source.

• Power Factor: The ratio of real power to apparent power in a circuit.

• Partial Discharge: Localized dielectric breakdown of insulation under high voltage.

• Power Transformer: Used in transmission networks to transfer electrical energy at high voltages.

• Protection Relay: A device that trips a circuit breaker in the event of a fault.

• Phase Shift: A change in phase angle between input and output voltages in transformers.

Q

• Quality Factor (Q): A measure of the efficiency of inductors and capacitors in an AC circuit.

• Quenching: The suppression or extinguishing of electrical arcs.

• Quiescent Current: The current drawn by a transformer or circuit when not delivering load.

• Quick Disconnect: Connectors allowing fast disconnection of power circuits.

• Quasi-Resonant Converter: A type of power converter using resonance to reduce switching losses.

R

• Reactance: Opposition to AC caused by inductance and capacitance.

• Regulation (Voltage): The change in secondary voltage from no-load to full-load.

• Rated Capacity: Maximum power output a transformer can deliver under standard conditions.

• Radiator: Component used to dissipate heat from transformer oil.

• Resistance: Opposition to current flow, causing voltage drop and power loss.

• Relay Protection: System used to detect transformer faults and activate protective devices.

S

• Secondary Winding: The winding from which power is delivered to the load.

• Step-Up Transformer: Increases voltage from primary to secondary winding.

• Step-Down Transformer: Decreases voltage from primary to secondary winding.

• Stray Loss: Losses due to leakage flux in transformer structure or tank.

• Surge Arrester: Device protecting against overvoltages or lightning surges.

• Silicon Steel: Magnetic material used in transformer cores to reduce losses.

T

• Tap Changer: Device to adjust transformer output voltage by altering winding turns.

• Temperature Rise: Increase in temperature during transformer operation above ambient level.

• Three-Phase Transformer: Transformer for 3-phase power systems with three sets of windings.

• Thermal Overload: Condition when temperature exceeds safe limits due to overloading.

• Turns Ratio: Ratio of primary to secondary winding turns.

• Toroidal Transformer: Donut-shaped transformer with reduced magnetic flux leakage.

U

• UL Certification: Certification indicating compliance with Underwriters Laboratories safety standards.

• Undervoltage: Operating below rated voltage, which may cause inefficiency or instability.

• Uniform Field: An evenly distributed magnetic or electric field.

• Utility Transformer: Transformer used by power utilities to distribute electrical energy.

• Unbalanced Load: When the loads on the three phases of a transformer are not equal.

• U-Shape Core: A transformer core shape designed for specific space or performance requirements.

V

• Vector Group: Symbolic representation showing winding configuration and phase displacement.

• Voltage Regulation: The ability to maintain constant output voltage despite varying load.

• Vacuum Drying: Process to remove moisture from transformer insulation in manufacturing.

• Volt-Ampere (VA): Unit of apparent power used in transformer ratings.

• VPI (Vacuum Pressure Impregnation): Method to improve insulation of dry-type transformers.

• Voltage Tap: Connection point on a winding to select voltage output.

W

• Winding: Conductive coil in a transformer where EMF is induced.

• Watt Loss: Total power lost as heat due to resistance and core losses.

• Wye (Star) Connection: Three-phase connection where each winding joins at a common neutral point.

• Wattmeter: Instrument used to measure real power in a circuit.

• Winding Resistance: Resistance of the transformer windings affecting voltage drop and losses.

• Weatherproof Transformer: Designed for outdoor use and protected from environmental elements.

X

• X/R Ratio: Ratio of reactance to resistance, used in fault analysis.

• X-Ray Transformer: High-voltage transformer used in medical X-ray machines.

• X-Phase Shift: Adjustable phase shift to control power flow in networks.

• X-Connected Winding: A unique configuration in high-voltage transmission.

• X-Class Insulation: Temperature rating class for insulation materials.

• Xenon Flash Supply: Transformer used in xenon light systems.

Y

• Y-Connection: Another term for Wye connection.

• Yoke: The top and bottom horizontal part of a transformer core.

• Yttrium-Based Insulators: High-performance insulators used in advanced transformer designs.

• Yield Strength: The maximum stress a material can withstand without permanent deformation.

• Y-Δ Transformation: Mathematical conversion between wye and delta configurations.

• Yaw Control Transformer: Used in wind turbines to control nacelle rotation.

Z

• Zero Sequence Current: A current component in unbalanced systems affecting neutral and ground.

• Zigzag Transformer: Provides grounding and reduces harmonics in three-phase systems.

• Zinc-Oxide Arrester: Surge arrester using zinc oxide as its nonlinear resistor material.

• Zonal Heating: Uneven heating in different transformer regions.

• Z-Core Design: A core configuration for compact and efficient transformer layouts.

• Zener Protection: Overvoltage protection using Zener diodes in control transformers.