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 Glossary of Terms
Glossary of Terms (N-Z)

Houston Transformer Company, Ltd.
Glossary of Terms (A-M)


Alternating Current (AC): An electrical current flow of continuously changing polarity, which rises to a maximum voltage in one direction, decreases to zero and then sinks to the maximum voltage in the other direction before changing polarity once again. This pattern is referred to as a sinusoidal wave and the number of cycles per second is equal to the frequency, which is measured in "Hertz".

Ambient Temperature: The normal surrounding temperature of the environment in which a transformer will operate.

Auto Transformer: A transformer used to step voltage up or down. The primary and secondary windings share common turns and thus provide no electrical isolation.

ANSI: ANSI was formed in 1918. American National Standards Institute is a recognized body which approves standards for transformers. ANSI 89.1 is mostly used for dry type transformers.

Air cooled Transformer: A transformer which uses air as the cooling medium. This may be a forced air with the use of fans.

Ambient Noise level: The level of acoustic noise existing at a given location like room or compartment etc. Ambient noise level is measured based on sound level meter or in decibels (db).

Arc voltage: The amount of voltage present between electrodes of different potential or between an electrode and ground. The magnitude is determined by the distance between electrodes and the dielectric constant of the medium surrounding them.


BIL Basic Insulation level: It is an insulation system that can withstand very high voltage surges.

Breakdown voltage: The voltage at which an electrical breakdown occurs. It is also known as breakdown potential, sparking potential or sparking voltage.


Core: The ferrous center part of a transformer or inductor used to increase the strength of the magnetic field. It carries the flux and forms the magnetic coupling between primary and secondary

Core Saturation: Condition that occurs when an inductor or transformer core has reached maximum magnetic strength.

Current Transformer (CT): A transformer used in instrumentation to assist in measuring current. It utilizes the strength of the magnetic field around the conductor to form an induced current that can then be applied across a resistance to form a proportional voltage.

Compensated Transformer: A transformer with a turn’s ratio which provides a higher than rated voltage at no load, and, rated voltage at rated load.

Core Loss: Core loss is also known as iron loss. Core loss is a form of energy loss that occurs in electrical transformers and other inductors. Core losses do not include the losses due to resistance in the conductors of the windings, which is often termed copper loss. It does not vary with load and hence also called constant losses. It mainly consists of eddy current and hysteresis losses.


Double conversion: A UPS design in which the primary power path consists of a rectifier and inverter.

Dropout voltage: The voltage at which a device fails to operate properly or safely. Computer systems will reboot, reset, or lose data.

Delta: Delta is a three phase connection where the ends of each phase winding connection in series to form a closed loop with each phase 120 electrical degrees from the other.

Delta-Delta: The connection between a delta source and a delta load.

Delta-Wye: The connection between a delta source and a wye load.

Duty Cycle: The percentage of time a transformer will be supplying the Full Rated Power to the load. Percentage of time a unit is expected to perform at Full Rated power versus time spent in idle can significantly affect the physical size of a transformer.


Electrostatic Shield: A grounded conductor sheet which provides a ground shield between primary and secondary windings to decrease or eliminate line to line or line to ground noise. It is also known as Faraday Shield.

Effective Voltage or current: The amount of power being delivered to a DC circuit load can be calculated easily by dividing the load resistance into the applied DC voltage squared.

Eddy Currents: It is induced into a metal when magnetic lines of force move across it.

Efficiency: Ratio of its power output to its total power input

Excitation Current: Current required magnetizing a core..

Electrostatic Shielding: Placed between windings (usually the primary and secondary) to provide maximum isolation. Additional Electrostatic Shields can be placed between secondary windings as required. Shielding is normally connected to the transformer's ground.

Encapsulation: A process in which a transformer or one of its components is completely sealed with epoxy or a similar material. This process is normally performed when a unit might encounter harsh environmental conditions such as moisture, salt spray, full-water submersion or corrosive elements.

Exciting Current: The current drawn by a transformer at nominal input voltage in its unloaded (open-circuit) condition.


FCAN Taps: Full Capacity above nominal. This is used to specify that a transformer will deliver rated KVA when connected to a voltage source which is higher than rated voltage.

FCBN (Full Capacity below Nominal) Taps: It is the same as FCAN except that the taps are below rated voltage.

Filter Press: A device for filtering and absorbing moisture from oil.

Frequency: It means the number of times an AC voltage will change from positive to negative and vice versa within a precise time, usually expressed in cycles per second and identified as Hz as in 60 Hz.

Faraday’s Law: A law that states an electro motive force is induced in any system in which a magnetic field is changing with time and is directly proportional to the rate of change of flux.

Filtered: Removing the ripple effect caused by a rectifier. Can also refer to reduced non-sinusoidal or unwanted harmonic frequencies in a power sources.

Faraday Shield: A grounded metallic barrier that can be used for improved isolation between the windings of a transformer. In this application, the shield basically reduces the leakage capacitance between the primary and secondary.

Ferroresonance: Resonance resulting when the iron core of an inductive component of an LC circuit is saturated, increasing the inductive reactance with respect to the capacitance reactance.

Ferroresonant Transformer: A voltage-regulating transformer that depends on core saturation and output capacitance.

Filter: A selective network of resistor, inductors, or capacitors which offers comparatively little opposition to certain frequencies or direct current, while blocking or attenuating other frequencies.

Flux: The lines of forces of a magnetic field.

Forced Air: A method of temperature regulation that involves air from an external environment being forcibly exchanged with a transformer's enclosed environment.


Generator: A device that converts mechanical energy into electrical energy by magnetic induction.

Ground: A conducting path, whether intended or unintended, between an electric circuit or equipment and the earth or some other conductor.

Grounded: Connected to the earth or some other conductor.

Ground Fault: Any undesirable current flow from a current carrying conductor to ground.

Ground Fault Interrupter (GFI): A device whose function is to interrupt the electric circuit to the load when a fault current to ground exceeds a predetermined value that is less than that required to operate the over-current protective device of the supply circuit.


Horsepower (HP): One horsepower is 33,000 lb.-ft /minute or 746 watts

H type core: It is one type of transformer core that surrounds the windings on four sides. This helps lessen flux leakage.

Hydroelectric: Electricity produced by turbines that are turned by water flow.

Hertz (Hz): Cycles per second


Isolating Transformer: Transformer in which input windings are connected to the line and are completely isolated from those connected to the load.

Insulation: Material with high electrical resistance.

Insulator: Device used for supporting or separating electrical conductors

Instrument Transformer: A transformer designed to transform the conditions of current or voltage and phase position in the primary with a specified accuracy of the secondary circuit.

Impedance: Forces, including resistance and capacitive or inductive reactance, which resist current flow in AC circuits.

Inductance: The ability of a coil to store energy and oppose changes in current flowing through it. A function of the cross sectional area, number of turns of coil, length of coil and core material.

Inductor: A coiled conductor that opposes change in current.

Inrush Current: A brief and momentary surge of current through the transformer, due to residual flux, experienced at the instant the transformer is energized.

Inverter: A device used to change DC into AC power.


Jack Pads: Structural member at bottom of transformer which provides lifting points which are used to lift the device onto rollers for repositioning.


Kilowatt (KW): 1,000 Watts

KWH: Kilowatt hour, one kilowatt for one hour – a unit of energy.

KVA: Kilovolt-ampere, or thousand volt-ampere. When multiplied by the power factor, will give kilowatts, or KW.

K-Factor: this is a rating used to denote a rated transformer which is specifically designed to handle non-linear loads. Numerical values indicate both the magnitude and frequency of any component of a current waveform which have been considered in the transformer design.


Linear Load: A load in which the relationship between current and voltage is directly proportional. For example: water heater, resistance heating etc.

Line voltage: Voltage of a power line

Lamination: The sheets of steel making up the core of the transformer.


Magnetic Shielding: Conductive material placed around a transformer's coils to attenuate stray magnetic fields.

Multiple Winding: A winding which consists of two or more sections that can be paralleled to specific mode of operation.


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