Glossary

Appendix I

GLOSSARY AIR-CORE TRANSFORMER—A transformer co mposed of two or more coils, which are wound around a non-metallic core. ALTERNATING CURRENT— An electrical current which constantly changes amplitude and changes polarity at regular intervals. APPARENT POWER— That power apparently available for use in an ac circuit containing a reactive element. It is the product of effective voltage times effective current expressed in voltamperes. It must be multiplied by the power factor to obtain true power available. AVERAGE VALUE OF AC—The av erage of all the instantaneous values of one-half cycle of alternating current.

CAPACITANCE—The p roperty of an electrical circuit that opposes changes in voltage. CAPACITOR—An ele ctrical device capable of storing electrical energy in an electrostatic field. CAPACITIVE REACTANCE—The opp osition offered to the flow of an alternating current by capacitance, expressed in ohms. The symbol for capacitive reactance is Xc. CHARGE CYCLE—The period of time that a capacitor in an electrical circuit is storing a charge. COIL—An inductive devi ce created by looping turns of wire around a core. COPPER LOSS (I2R LOSS)—The power lost due to the resistan ce of the conductors. In transformers the power lost due to heating because of current flow (I) through the resistance (R) of the windings.

CORE—An y material that affords a path for magnetic flux lines in a coil. COUNTER EMF—Counter electro motive force; an electromotive force (voltage) induced in a coil that opposes the applied voltage. COUPLING, COEFFICIENT OF—An expression of the extent to which two inductors are coupled by magnetic lines of force. This is expressed as a decimal or percentage of maximum possible coupling and represented by the letter K. CYCLE—One com plete positive and one complete negative alternation of a current or voltage. DIELECTRIC—An insulator; a ter m applied to the insulating material between the plates of a capacitor.

DIELECTRIC CONSTANT—The rati o of the capacitance of a capacitor with a dielectric between the electrodes to the capacitance of a capacitor with air between the electrodes. DIELECTRIC HYSTERESIS LOSS—Power loss of a capacitor due to t he changes in orientation of electron orbits in the dielectric caused by rapid reversal in polarity of line voltage. The higher the frequency, the greater the loss. AI-1 DIELECTRIC LEAKAGE—Pow er loss of a capacitor due to the leakage of current through the dielectric. Also relates to leakage resistance, the higher the leakage resistance, the lower the dielectric leakage.

DISPLACEMENT CURRENT—The current which appears to flow throu gh a capacitor. EDDY CURRENT—Induced circulating currents in a conducting material that are caused by a varying magnetic field. EDDY CURRENT LOSS—Losses caused by random current flowing in the core of a transformer. Power is lost in the form of heat. EFFECTIVE VALUE—Sam e as root-mean-square. ELECTROMAGNETIC INDUCTION—The production of a voltage in a coil due to the change in the number of magnetic lines of force (flux linkage) passing through the coil. ELECTROMAGNETISM—The generation of a magnetic fiel d around a current carrying conductor.

ELECTROMOTIVE FORCE (emf)—The force (voltage) that produces an electric current in a circuit ELECTROSTATIC FIELD—The field of infl uence between two charged bodies. EXCITING CURRENT—The current that flows in the primary winding of a transformer, which produces a magnetic flux field. Also called magnetizing current. FARAD—T he basic unit of capacitance. A capacitor has a capacitance of 1 farad when a voltage change of 1 volt per second across it produces a current of 1 ampere. FLUX—Electrostatic or magnetic lines of force.

FREQUENCY (f)—The number of complete cycles per second existing in any form of wave motion; such as the number of cycles per second of an alternating current. HENRY (H)—The electro magnetic unit of inductance or mutual inductance. The inductance of a circuit is 1 henry when a current variation of 1 ampere per second induces 1 volt. It is the basic unit of inductance. In radio, smaller units are used such as the millihenry (mH), which is one-thousandth of a henry (H), and the microhenry (µH) which is one-millionth of a henry.

HERTZ (Hz)—The basic unit of frequency equal to one cycle per second. HYSTERESIS—The tim e lag of the magnetic flux in a magnetic material behind the magnetizing force producing it, caused by the molecular friction of the molecules trying to align themselves with the magnetic force applied to the material. HYSTERESIS LOSS—The power loss in an iro n-core transformer or other alternating-current device as a result of magnetic hysteresis. IMPEDANCE—The total oppositi on offered to the flow of an alternating current. It may consist of any combination of resistance, inductive reactance, and capacitive reactance. The symbol for impedance is Z.

IN PHASE—Applied to the condition that exists when two waves of the same frequency pass through their maximum and minimum values of like polarity at the same instant. AI-2 INDUCTANCE—The property of a circuit which tends to oppose a change in the existing current flow. The symbol for inductance is L. INDUCTIVE COUPLING—Coupling of two coils by means of magnetic lines of force. In transformers, coupling applied through magnetic lines of force between the primary and secondary windings. INDUCTIVE REACTANCE—The o pposition to the flow of an alternating current caused by the inductance of a circuit, expressed in ohms. Identified by the letter X L.

INSTANTANEOUS VALUE—The magnitude at any particular instant when a value is continually varying with respect to time. LAG—The am ount one wave is behind another in time; expressed in electrical degrees. LAMINATED CORE—A core built up from thin sheets of metal insulated from each other and used in transformers. LEAD—The opp osite of lag. Also a wire or connection. LEAKAGE FLUX—Magnetic flux line s produced by the primary winding which do not link the turns of the secondary winding. LEAKAGE RESISTANCE—The electrical resistance which op poses the flow of current through the dielectric of a capacitor. The higher the leakage resistance the slower the capacitor will discharge or leak across the dielectric.

LEFT-HAND-RULE FOR GENERATORS—A rule or procedu re used to determine the direction of electron current flow in the windings of a generator. LENZ'S LAW—The curr ent induced in a circuit due to its motion in a magnetic field or to a change in its magnetic flux in such a direction as to exert a mechanical force opposing the motion or to oppose the change in flux. MAGNETIC FIELD— Region in which the magnetic forces created by a permanent magnet or by a current-carrying conductor or coil can be detected. MAGNETIC LINES OF FORCE—Im aginary lines used for convenience to designate the direction in which magnetic forces are acting as a result of magneto-motive force.

MUTUAL FLUX—The total flux i n the core of a transformer that is common to both the primary and secondary windings. The flux links both windings. MUTUAL INDUCTANCE—A circuit property existing when the relative position of two inductors causes the magnetic lines of force from one to link with the turns of the other. The symbol for mutual inductance is M. NEGATIVE ALTERNATION—The negative half of an ac waveform NO-LOAD CONDITION—The condition that exis ts when an electrical source or secondary of a transformer is operated without an electrical load.

PEAK-TO-PEAK—The measure of absolute m agnitude of an ac waveform, measured from the greatest positive alternation to greatest negative alternation. AI-3 PEAK VALUE—The maximum instantaneous value of a varying current, voltage, or power. It is equal to 1.414 times the effective value of a sine wave. PERIOD TIME—The time required to com plete one cycle of a waveform. PHASE—The angular relationship between two alternating currents or voltages when the voltage or current is plotted as a function of time. When the two are in phase, the angle is zero, and both reach their peak simultaneously. When out of phase, one will lead or lag the other; at the instant when one is at its peak, the other will not be at peak value and (depending on the phase angle) may differ in polarity as well as magnitude.

PHASE ANGLE—The n umber of electrical degrees of lead or lag between the voltage and current waveforms in an ac circuit. PHASE DIFFERENCE—The tim e in electrical degrees by which one wave leads or lags another. POLARIZATION—The magnetic orientation of molecules in a magnetizable material in a magnetic field, whereby tiny internal magnets tend to line up in the field. POSITIVE ALTERNATION—The positive half of an ac waveform. POWER FACTOR—The ratio of the a ctual power of an alternating or pulsating current, as measured by a wattmeter, to the apparent power, as indicated by ammeter and voltmeter readings. The power factor of an inductor, capacitor, or insulator is an expression of their losses POWER LOSS—The elec trical power supplied to a circuit that does no work, usually dissipated as heat.

PRIMARY WINDING—The winding of a transfor mer connected to the electrical source. Q—Figure of merit of effic iency of a circuit or coil. Ratio of inductive reactance to resistance in servos. Relationship between stored energy (capacitance) and rate of dissipation in certain types of electric elements, structures, or materials. RADIO FREQUENCY (RF)—Any frequency of electrical energy capable of propagation into space. RATIO—Th e value obtained by dividing one number by another, indicating their relative proportions. RC CONSTANT—Ti me constant of a resistor-capacitor circuit; equal in seconds to the resistance value in ohms multiplied by the capacitance value in farads.

REACTANCE—The opposition offered to the flow of an alternating current by the inductance, capacitance, or both, in any circuit. RESONANCE—The co ndition existing in a circuit when the values of inductance, capacitance, and the applied frequency are such that the inductive reactance and capacitive reactance cancel each other. RLC CIRCUIT—An electrical circuit which has the pr operties of resistance, inductance, and capacitance. RMS—Abbreviation of R oot Mean Square. ROOT MEAN SQUARE (RMS)—The equivalent h eating value of an alternating current or voltage, as compared to a direct current or voltage. It is 0.707 times the peak value of a sine wave.

SECONDARY—The output coil of a transformer. AI-4 SELF-INDUCTION—Th e production of a counter-electromotive force in a conductor when its own magnetic field collapses or expands with a change in current in the conductor SINE WAVE—The curve traced by the projection on a uniform time scale of the end of a rotating arm, or vector. Also known as a sinusoidal wave. THETA—T he greek letter (θ) used to represent phase angle. TIME CONSTANT—The ti me required to charge a capacitor to 63.2 percent of maximum voltage or discharge to 36.8 percent of its final voltage. The time required for the current in an inductor to increase to 63.2 percent of maximum current or decay to 36.8 percent of its final current.

TRANSFORMER—A device co mposed of two or more coils, linked by magnetic lines of force, used to transfer electrical energy from one circuit to another. TRANSFORMER EFFICIENCY—The ratio of ou tput power to input power, generally expressed as a percentage. TRANSFORMER, STEP-DOWN—A transformer so constructed that the number of turns in the secondary winding is less than the number of turns in the primary winding. This construction will provide less voltage in the secondary circuit than in the primary circuit. TRANSFORMER, STEP-UP—A transformer so constructed that the number of turns in the secondary winding is more than the number of turns in the primary winding. This construction will provide more voltage in the secondary circuit than in the primary circuit.

TRUE POWER—The power dissipated in the resistance of the circuit, or the power actually used in the circuit. TURN—One com plete loop of a conductor about a core. TURNS RATIO—The ratio of num ber of turns in the primary winding to the number of turns in the secondary winding of a transformer. UNIVERSAL TIME CONSTANT CHART—A chart used to find the time constant of a circuit if the impressed voltage and the values of R and C or R and L are known. WAVEFORM—The shape of the wave obtained when instan taneous values of an ac quantity are plotted against time in rectangular coordinates.

WAVELENGTH (λ)—The distance, usually expressed in meters, traveled by a wave during the time interval of one complete cycle. It is equal to the velocity of light divided by the frequency. WORKING VOLTAGE—The maximum voltage that a capacitor may operate at without the risk of damage. VAR—Abbreviation for Volt-Amperes Reactive. VECTOR—A line used to represent both direction and magnitude. AI-5

Appendix Ii

Greek Alphabet

Name Upper Case Lower Case Designates Alpha… … . A a Angles. Beta… … ... B β Angles, flux density. Gamma….. Г γ Conductivity. Delta…….. ∆ ό Variation of a quantity, increment. Epsilon… ... E ε Base of natural logarithms (2.71828). Zeta…… … Z ζ Impedance, coefficients, coordinates. Eta… … … . H η Hysteresis coefficient, efficiency, magnetizing force. Theta…….. Θ θ Phase angle. Iota… … … . I L Kappa… … K K Dielectric constant, coupling coefficient, susceptibility. Lambda….. Λ λ Wavelength. Mu… … … . M µ Permeability, micro, amplification factor.

Nu… … … .. N ν Reluctivity. Xi………... Ξ ξ Omicron…. Ο о Pi………... П π 3.1416 Rho… … … P ρ Resistivity. Sigma……. Σ σ Tau… … … . T т Time constant, time-phase displacement. Upsilon….. Υ υ Phi………. Φ φ Angles, magnetic flux. Chi… … … . X χ Psi……….. Ψ ψ Dielectric flux, phase difference. Omega…... Ω ω Ohms (upper case), angular velocity (2 π f) (lower case). AII-1

Appendix Iii

Square And Square Roots

AIII-1