Transformers

Earth

Biggest magnet

Lodestone

Natural Magnets

Permanent magnet

magnets that do not require power or any force to maintain their fields

Law of magnetism

states that energy is required to create a magnetic field, but no energy is required to maintain a magnetic field.

iron, nickel and cobalt

three substances that form natural magnets

electron spin patterns

each electron spins on on its axis as it orbits around the nucleus.

Magnetic Domains or Magnetic Molecules

The additive effect forms regions in the molecular structure of the metal.

Ferromagnetic

metals that are easily magnetized

Paramagnetic

metals that can be magnetized

Diamagnetic

either metals or nonmetals that cannot be magnetized

Flux

magnetic lines of force

Basic law of magnetism

unlike pole attracts and like poles repel

Electromagnetics

A basic law of physics that states whenever an electric current flows through a conductor, magnetic field is formed around the conductor.

Electromagnets

depend on electric current flow to produce a magnetic field

Permeability

a measure of a materials willingness to become magnetized

Reluctance

resistance to magnetism

Saturation

occurs when all the molecules of the magnetic material lined up.

Residual Magnetism

The amount of magnetism left in a material after the magnetizing force has stopped.

Coercive Force/ Retentivity

measure of a materials ability to retain magnetism.

Flux Density

measured in lines per square inch

Magnetomotive Force

total force producing a magnetic field

Maxwell

In CGS system, defined as the amount of magnetism induced through one square centimeter by a perpendicular magnetic field of 1 gauss.

Gauss

represents a magnetic force of one maxwell per square centimeter, or is equal to ten thousanth of a tesla.

Tesla

In the MKS system, the _______ is the unit of magnetic field intensity.

Left hand rule

The polarity of the electromagnet can be determined using the______.

demagnitized

When an object is to be _______, its molecules must be disarranged as they are in a nonmagnetized material.

Magnetic Induction

states that whenever a conductor cuts through magnetic lines of flux, a voltage is induced in a conductor.

polarity of the magnetic field

The polarity of the induced voltage is determined by the __________________ in relation to the direction of movement.

1. the number of turns of wire, length of a conductor.
2. the strength of the magnetic field
3. the speed of the cutting action

Three factors that determine the amount of voltage that will be induced in a conductor.

One Weber(Wb)

In magnetic measurement, 100,000,000 lines of flux is equal to

Lenz’s Law

States that an induced voltage or current opposes the motion that causes it.

Oppose

Inductor always ______ a change of current

Proportional

The induced voltage is __________ to the rate of change of current.

exponential curve

Describes the rate of certain occurrences.

Inductance

Measured in units called Henry(H) and is represented by letter L.

Air-core

A coil wound on a non-magnetic core material such as wood or plastic is referred to as

Iron-core

If a core is wound on a core made of magnetic material such as silicon steel or soft iron is referred to as

eddy current loss, hysteresis loss

Iron-core inductors cannot be used for high frequency applications, however, because of______ __and ______ in the core material.

R-L Time Constant

The time necessary for current in an inductor to reach its full Ohm’s law value.

Voltage Spike

occurs when the current through an inductor stops.

Metal Oxide Varistor (MOV)

A device that can be used for spike suppression in either direct or alternating current.

exponential

Current rises in an inductor at an __________ rate.

Resistor and Diode

Two devices used to help prevent large spike voltage

Inductance(L)

one of the primary types of loads in an alternating circuit.

180

The induced voltage is ____ degrees out of phase with the applied voltage and is always in opposition for a change of current.

Reactance

The current-limiting property of the inductor is called __________, and is symbolized by letter X.

Inductive Reactance

This reactance is caused by inductance, so it is called_______

2(pi)fL

formula for XL

IL = I1+I2+I3

Inductors connected in series formula

lags, 90 degrees

In a pure inductive circuit the current _____ the voltage by ________

reactive

An electrical measurement called VARs is used to measure ___________ power in a pure inductive circuit.

Volt-Amp-Reactive

VARs

Quality(Q)

Inductors that have a higher ratio of inductive reactance to resistance are considered to be inductors of higher ________

Impedance (Z)

The current-limiting effect of the inductor which is a combination of the inductive reactance and resistance.

no

Pure inductive circuits consume ______ true power or watts.

neutral conductor

If the center is tapped then it becomes

Control Transformers

Used to reduce the line voltage to the value needed to operate control circuits

Distribution Transformers

This transformer is used to supply power to most homes and business.

Potential Transformers

an isolation transformer with a high voltage rating on the primary winding, and that is intended for use in metering circuits.

Reactors(Choke)

are often connected in series with the primary winding of a large KVA transformer to prevent inrush current from becoming excessive when the circuit is turned off.

Magnetic Domains

Contain tiny magnetic structures in their molecular material known as_______.

1. Amount of applied voltage
2. Resistance of the wire in the primary winding
3. Flux change of the magnetic field in the core

The amount of inrush current in the primary of the transformer is limited by three factors:

connecting one lead of the primary to one lead of the secondary and testing for an increase or decrease in voltage.

The polarity of the transformer winding can be determined by

Transformer Impedance

determined by the physical construction of the transformer.

American National Standard Institute

set standardization rules concerning the way in which the terminals of transformers are to be marked.

turns ratio

Voltage, current and impedance in a transformer are proportional to

frequency

Transformer can change values of voltage, current and impedance but cannot change the

the power line

The primary winding is connected to

the load

The secondary winding is connected to

isolation

An _______ transformer has its primary and secondary windings electrically and mechanically separated from each other

Polarity Dots

are often added to schematic diagrams to indicate transformers polarity

a percentage

Transformer impedance is expressed as

H, X

The high voltage leads of a transformer are marked with an _____ and low voltage are marked with an _.

autotransformer

The _____ has only one winding, which is used as both primary and secondary.

95% to 98%

Autotransformers have efficiencies that range from about __ to __.

sliding tap

Autotransformer can be made to provide a variable-output voltage by connecting a _____ to the windings.