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  Glossary Basic order Information Glossary

AC (Alternating Current)
Current which passes from the generator in one direction and then the other, alternately.

AC Ripple
The alternating current superimposed on the dc bias after rectification in a power supply.

Ambient Temperature
The temperature of the air or oil surrounding and in contact with the capacitor. To determine the maximum capacitor temperature, add this value to the internal working heat rise that the capacitor will develop.

Anode
The electrode through which a direct current enters the liquid, gas, or other discrete part of an electrical circuit; the positively charged pole of an electrochemical cell.

Arc
Intense luminous discharge formed by the passage of electric current across a space between electrodes.

Arcover Voltage
The minimum voltage required to create an arc between electrodes separated by an insulation under specified conditions. To increase the Arcover Voltage, clean the area between the terminals and improve the insulation medium between the terminals (by immersing the capacitor in oil).

Ballast
Device for starting and regulating fluorescent and high intensity discharge lamps.

Blocking 
A situation where Direct Current (DC) is kept from a circuit element due to the high series impedance of a capacitor.

Breakdown (Puncture)
A disruptive discharge through insulation. If plain dielectric films are used, this is usually catastrophic. If metallized films are used, self-healing should maintain the capacitor's integrity.

Breakdown Voltage
The voltage at which the insulation between two conductors will break down. This voltage should be at least 50% ~ 100% greater than the capacitor's rated voltage.

Burn-In-Test
Test designed to simulate conditions a product would encounter in actual operation. To shorten the duration of the test, it is conducted at maximum temperature and greater than rated voltage.

Bypass (De-Coupling)
The use of a capacitor to prevent the AC portion of a signal from a circuit element via a low impedance path in parallel with the circuit element.

Canadian Standards Association (CSA)
Group that generates product performance and/or safety standards for many Canadian industries.

Capacitance (Capacity)
That property of a system of conductors and dielectrics which permits the storage of electricity when potential difference exists between the conductors.  Its value is expressed as the ratio of a quantity of electricity to a potential difference.  A capacitance value is always positive.

Capacitive Reactance (Xc)
The opposition to the flow of alternating or pulsating current by a capacitor measured in ohms. The non-heating impedance component of the capacitor when AC flows:  Xc = 1/(6.28fC)  

Capacitor
An electrical/electronic part that stores electrical charges.  In its simplest form it consists of two conducting surfaces separated by a dielectric.

Cathode
The electrode through which an electric current leaves a liquid, gas, or other discrete part of an electric current; the negatively charged pole of an electrochemical cell.

Charge
The amount of electricity present upon the capacitor's plates. Also, the act of forcing of electrons onto the capacitor's plates. See Coulomb.

Conductance
The reciprocal of resistance.  It is the ratio of current passing through a material to the potential difference at its ends.

Conductivity
Reciprocal of volume resistivity.  Conductance of a unit cube of any material.

Conductor
An electrical path which offers comparatively little resistance.  A wire or combination of wires not insulated from one another, suitable for carrying a single electric current.

Corona
A luminous discharge due to ionization of the gas surrounding a conductor around which exists a voltage gradient exceeding a certain critical value.  A type of discharge--sometimes visible--in the dielectric of an insulation system caused by an electric field and characterized by the rapid development of an ionized channel which does not completely bridge the electrode.  May be continuous or intermittent.  Not a materials property, but related to the system, including electrodes.

Corona Resistance
The time that insulation will withstand a specified level field-intensified ionization that does not result in the immediate complete breakdown of the insulation.

Crest Factor (Lamp Current Crest Factor)
Ratio of peak lamp current to RMS or average lamp operating current.

Coulomb
Unit quantity of electricity; i.e., the quantity transferred by 1 ampere in one second.

Coupling
The use of a capacitor to connect two circuits. In using the capacitor, only the AC voltage (component) is passed.

Creepage
Electrical leakage on a solid dielectric surface

Critical Voltage (of gas)
The voltage at which a gas ionizes and corona occurs, preliminary to dielectric breakdown of the gas.

Dielectric
The insulating material between the plates of the capacitor. The material is chosen for its ability to permit electrostatic attraction and repulsion to take place across it. The material will have the property that energy required to establish an electric field is recoverable in whole or in part, as electric energy. In other words, a good dielectric material is a poor conductor of electricity while being an effective supporter of electrostatic fields.

Dielectric Absorption
That property of an imperfect dielectric whereby there is an accumulation of electric charges within the body of the material when it is placed in an electric field.

Dielectric Constant
That property of a dielectric which determines the electrostatic energy stored per unit volume for unit potential gradient. 

Dielectric Loss
The time rate at which electric energy is transformed into heat in a dielectric when it is subjected to a changing electric field.

Dielectric Loss Angle
The difference between ninety degress (90) and the dielectric phase angle.

Dielectric Phase Angle
The angular difference in phase between the sinusoidal alternating potential difference applied to a dielectric and the component of the resulting alternating current having the same period as the potential difference.

Dielectric Power Factor
The cosine of the dielectric phase angle (or sine of the dielectric loss angle).

Dielectric Strength
The voltage which an insulating material can withstand before breakdown (puncture) occurs, usually expressed as a voltage gradient (such as volts per mil). The voltage figure used is the average RMS voltage gradient between two electrodes at the time of failure.

Dielectric Test
Tests which consist of the application of a voltage higher than the rated voltage for a specified time for the purpose of determining the adequacy against breakdown of insulating materials and spacings under normal conditions.

Discharge Lamp
A light producing device that depends on an electric arc, rather than a filament, to create illumination.

Displacement Current
A current which exists in addition to ordinary conduction current in ACcircuits.  It is proportional to the rate of change of the electric field.

Disruptive Discharge 
The sudden and large increase in current through an insulation medium due to the complete failure of the medium under the electrostatic stress.

Dissipation Factor
The tangent of the loss angle of the insulating material. A measure of the power factor (or losses) of a capacitor, given as D.F. = 6.28 fRC X 100%, where R is the equivalent series resistance (ESR) of the capacitor, f is the frequency (Hz.), and C is capacitance (Farads). Dissipation Factor varies with frequency and temperature.

dV/dT
Change in Voltage divided by Change in Time, usually expressed in Volts per uSec.

Electrode
A conductor, not necessarily metal, through which a current enters or leaves a capacitor.

Electromagnetic and Electronic Ballasts
An Electromagnetic Ballast (Magnetic Ballast) is one that uses a Core & Coil assembly to transform electrical current to start and operate fluorescent and high intensity discharge (HID) lamps. An Electronic (High Frequency) Ballast is one that, with the help of electronic components, transforms current at high frequency to operate discharge lamps.  Electronic ballasts typically operate at frequencies at or above 20,000 Hz.

Electrolytic Capacitor
A polarized capacitor exhibiting a very high capacitance/volume ratio that consists of two electrodes immersed in an electrolyte, with a chemical film that acts as a dielectric on one or both electrodes. Electrolytic capacitors are made by winding either plain or etched foils on which an oxide has been formed on the surface of one (either anode or cathode) film. The etching of the foil increases the surface area and a considerable increase in capacitance can thus be obtained.

EMI (Electromagnetic Interference)
Electrical interference (noise) generated by electrical and electronic devices.

ESR (Equivalent Series Resistance)
A resistive element of the capacitor model found in both the AC and DC domains. Contributing factors: electrodes, leads, dielectric. This value can change with frequency, time, etc. A measure of the total lossiness of a capacitor which includes the leads, electrodes, dielectric losses, leakage (IR) and most important, the end spray connecting the leads to the metallized film. The lower the ESR the higher the current carrying ability the capacitor will have.

Farad
Unit of capacitance.  The capacitance of a capacitor which, when charged with one coulomb, gives a difference of a potential of one volt.

Flame Resistance
Ability of the material to extinguish a flame once the source of heat is removed.

Flammability
Measure of the material's ability to support combustion.

Flashover
A disruptive discharge around or over the surface of a solid or liquid insulator.

Frequency
The number of complete cycles or vibrations per unit of time. Rate of alternation in an AC current.  Expressed in cycles per second or hertz (Hz).

Grounded
Parts which are connected so that when the installation is complete, it is substantially of the same potential as the earth.

Harmonic
An integral multiple of the fundamental frequency (60 Hz) that becomes a component of the current.

Harmonic Distortion
Distortion of an AC waveform caused by multiples of the fundamental frequency (harmonics).  Odd triplet harmonics (thirds, ninths, etc.) may result in large currents on the neutral line in a four-wire Wye three-phase system.

Heat Sink
Any device that absorbs and draws heat off a hot object, radiating it into the surrounding atmosphere.

Hertz
(Hz) A term replacing cycles-per-second as an indication of frequency.

Hygroscopic
Tending to absorb moisture.

Hysteresis
An effect in which the magnitude of a resulting quantity is different during increases in the magnitude of the cause than during decreases due to internal friction in a substance and accompanied by the production of heat within the substance.  Electric hysteresis occurs when a dielectric material is subjected to a varying electric field as in a capacitor in an alternating current circuit.

Impedance
The total opposition that a circuit offers to the flow of alternating current or any other varying current at a particular frequency. It is a combination of resistance R and reactance X, measured in ohms.

Impregnate
To fill the voids and interstices of a material with a compound.

Impulse
A surge of unidirectional polarity.

Insulation
Material having a high resistance to the flow of electric current, which prevents leakage of current from a conductor.

Insulation Resistance
The ratio of the applied Voltage to the total current between two electrodes in contact with a specific insulator. A measure of the resistance to a DC current flow through the capacitor under steady state conditions. Values for film and ceramic capacitors are usually expressed in megohm-microfarads for a given design and dielectric. The actual resistance of the capacitor is obtained by dividing the megohm-microfarads by the capacitance.

Insulator
A material of such low electrical conductivity that the flow of current through it can usually be neglected.

Internal Fuse
A device that disconnects capacitor operation from power distribution system in the event of excessive current.

Lon, lonization
An electrified portion of matter of sub-atomic, atomic, or molecular dimensions such as is formed when a molecule of gas loses an electron (when the gas is stressed electrically beyond the critical voltage) or when a neutral atom or group of atoms in a fluid loses or gains one or more electrons. Ionization is the dissociation of an atom or molecule into positive or negative ions or electrons.  Restrictively, the state of an insulator whereby it facilitates the passage of current due to the presence of charged particles usually induced artificially.

Joule (watt second)
Joule = 0.5 X Capacitance (Farads) X Voltage^2. The Joule is a measure of the amount of energy delivered by one WATT of power in one second or 1 million watts of power in one microsecond. The Joule rating of a surge protection device is the amount of energy that it can absorb before it becomes damaged.

Moisture Resistance
The ability of a material to resist absorbing moisture from the air or when immersed in water

Overvoltage
A voltage above the normal operating voltage of a device or circuit. In a dielectric withstand test, capacitors are overvoltage-tested (Hi-potted) at 1.5X or 2X its rated voltage to assure quality and workmanship.

Parallel Lamp Operation
Refers to ballasts that employ multiple-output current paths from a single ballast to allow lamps to operate independently of one another, allowing other lamps operated by ballast to remain lit should companion lamp(s) fail.

Partial Discharge
A partial discharge is an electric discharge that only partially bridges the insulation betwen conductors when the voltage stress exceeds a critical value.  Partial discharges may, or may not, occur adjacent to a conductor. Partial discharge is often referred to as corona but the term corona is preferably reserved for localized discharges in cases around a conductor, bare or insulated, remote from any other solid insulation.

PCB (Polychlorinated Biphenyls)
Chemical pollutant formerly used in oil-filled capacitors which have been outlawed since the 1970's and are no longer used in the capacitor and transformer industries.

Permittivity
Preferred term for dielectric constant.

Polarity
An electrical condition determining the direction in which current tends to flow. The quality of having two opposite charges.

Polycarbonate Resins
Polymers derived from the direct reaction between aromatic and aliphatic dihydroxy compounds with phosgene or by the ester exchange reaction with appropriate phosgene derived precursors.

Polyester
A resin formed by the reaction between a dibasic acid and a dihydroxy alcohol.

Polyethylene
A thermoplastic material composed of polymers of ethylene.

Polymer
A compound formed by polymerization which results in the chemical union of monomers or the continued reaction between lower molecular weight polymers.

Polymerize
To unite chemically two or more monomers or polymers of the same kind to form a molecule with higher molecular weight.

Polypropylene
A plastic made by the polymerization of high-purity propylene gas in the presence of an organometallic catalyst at relative low pressures and temperatures.

Polystyrene
A thermoplastic produced by the polymerization of styrene (vinyl benzene).

Potential Voltage
The work per unit charge required to bring any charge to the point at which the potential exists.

Potting
Similar to encapsulating, except that steps are taken to insure complete penetration of all voids in the object before the resin polymerizes.

Potting
Material used to completely surround and cover the capacitor winding.  Potting compounds protect components, dampen sound, and dissipate heat.

Power
The time rate at which work is done; equal to W/t where W is amount of work done in time t. Power will be obtained in watts if W is expressed in joules and t in seconds.

Power Factor
Measurement of the relationship between the AC source voltage and current. Formula: Power Factor equals Watts input divided by the product of Line Volts multiplied by Line Amps.

Pressure
Force measured per unit area.  Absolute pressure is measured with respect to zero pressure.  Gauge pressure is measured with respect to atmospheric pressure.

Radio Frequency Interference (RFI)
Form of electromagnetic interference that can be radiated through the air.

Relative Humidity
Ratio of the quantity of water vapor present in the air to the quantity which would saturate it at any given temperature.

Resistance
Property of a conductor that determines the current produced by a given difference of potential.  The ohm is the practical unit of resistance.

Resistivity
The ability of a material to resist passage of electrical current either through its bulk or on a surface.  The unit of volume resistivity is the ohm-cm, of surface resistivity, the ohm.

Roentgen
The amount-of radiation that will produce one electrostatic unit of ions per cubic centimeter volume.

Schering Bridge
An alternating current form of Wheatstone bridge, used for comparing capacitances or for measuring the phase angle of a capacitor by comparison with a standard capacitor.

Semiconductor
A material whose resistivity is between that of insulators and conductors.  The resistivity is often changed by light, heat, an electric field, or magnetic field.  Current flow is often achieved by transfer of positive holes as well as by movements of electrons.  Examples include germanium, lead sulfide, lead telluride, selenium, silicon, and silicon carbide.  Used in diodes, photocells, thermistors, transistors, etc.

Series Lamp Operation
Refers to ballasts that employ a single current path passing through all lamps operated by the ballast If one lamp should fail, companion lamps operated by the same ballast will also extinguish.

Silicone
Polymeric materials in which the recurring chemical group contains silicon and oxygen atoms as links in the main chain.

Sine Wave
A mathematical function used to represent voltage and current.

Sparkover
A disruptive discharge between electrodes of a measuring gap, such as a sphere gap or oil testing gap.

Specific Gravity
The density (mass per unit volume) of any material divided by that of water at a standard temperature.

Surface Leakage
The passing of current over the boundary surfaces of an insulator as distinguished from passage through its volume.

Surge
A transient variation in the current and/or potential at a point in the circuit.

Temperature Coefficient
The change in capacitance with temperature expressed linearly as parts per million per degree centigrade (PPM/C), or as a percent change over a specified temperature range. Most film capacitors are not linear and TC is expressed in percent.

Thermal Conductivity
Ability of a material to conduct heat.

Thermal Expansion (Coefficient of Transients)
The fractional change in length (sometimes volume) of a material for a unit change in temperature.

Transients
High voltage surges through an electrical system caused by lightning strikes to nearby transformers, overhead lines, or the ground.  May also be caused by switching of motors and compressors, as well as by short circuits or utility system switching.

UL (Underwriters' Laboratories, Inc)
Laboratory that sets safety standards for building materials, electrical appliances, and other products.

Viscosity
A measure of the resistance of a fluid to flow (usually through a specific orifice).

Volt
Unit of Electromotive Force.  It is the difference of potential required to make a current of one ampere flow through a resistance of one ohm.

Voltage
Electromotive Force, potential, potential difference, or voltage drop, to designate electric pressure that exists between two points and is capable of producing a flow of current when a closed circuit is connected between the two points.

Voltage Sag
Drop in voltage levels of electrical distribution system which interferes with the operation of electrical and electronic equipment. Commonly called brownout. Results when demand for electricity exceeds capacity of the distribution system.  

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