Magnetism

MAGNETISM

-natural phenomenon in which some material (ferromagnetic) can be attracted by a magnet but not other material (non-magnetic)

MAGNET

- a substance that attract pieces of iron and its compound, steel, nickel, cobalt

MAGNETIC FORCE

- a field force, like electricity and earth's gravitational force, which acts without physical contact is measured in Newton's

Natural and Artificial

types of magnet

MAGNETIC FIELD

- a region in which a magnetic materials is acted upon by s magnetic force

- made up of magnetic lines of force

MAGNETIC LINES OF FORCE

-represents the lines that seems to emanate from North Pole terminates to South Pole of the magnets

POLES

- the areas where the effect of magnetic field is concentrated

- They possess a positive direction

- They repel one another

- They always form a complete loop

- Like poles repel one another

- They to become as short as possible

- They arrange to set up their maximum number

CHARACTERISTICS OF MAGNETIC LINES OF FORCE

MAGNETIC FIELD AROUND A CURRENT CARRYING CONDUCTOR

- is produced around an electric conductor whenever current flows through it

ELECTROMAGNET

- a coil of wire around a core material that can be easily magnetized

MAGNETIC FLUX 𝛟

- the total number of magnetic lines of force in a magnetic field

MAGNETOMOTIVE FORCE Fm (mmf)

- establishes the magnetic flux in a magnetic circuit - the counterpart of EMF in an electric

1x10^18 Maxwells

1 Weber is equivalent to

RELUCTANCE (Rm)

- the limiter of magnetic circuit to the establishment of magnetic flux

PERMEANCE (Pm)

- a measure of the ability of a magnetic circuit to permit the setting up of flux

- counterpart of CONDUCTANCE in an electric circuit

PERMEABILITY (µ)

- a figure indicating the ability of a material to permit the setting up of flux

RELATIVE PERMEABILITY (µr)

- ratio of absolute permeability of a material to permeability of vacuum

TRUE

A relative permeability greater than one simply means that is easier to establish flux lines in that material than it is to establish them in a vacuum.

FLUX DENSITY (B)

- the flux per cross-sectional area

MAGNETIC FIELD INTENSITY (H)

- magneto motive force per unit length

- sometimes called: (a.) magnetic field strength, (b) magnetizing force, (c) mmf gradient

HYSTERESIS (Hys)

- a characteristics of magnetic materials whereby a change in a magnetization LAGS the application of magnetizing force

HYSTERESIS LOOP

- Resultant curve with lack of retrace ability if alternating mmf is applied to a magnetic material

COERCIVE FORCE (Hc)

- The negative field intensity required force residual magnetism to zero

RETENTIVITY

- residual magnetism

- the ability of a material, once magnetized, to maintain a magnetized state without the presence of magnetizing force

EDDY CURRENTS (Ieddy)

- circulating current produced by transformer action in the iron cores of electrical apparatus

Current

Magnetic flux is analogous to?

Electromotive force

Magneto motive force is analogous to?

Resistance

Reluctance is the same as?

Conductance

Equivalent of Permeance in Electric Circuit?

Flux Density

Equivalent of Current Density in Magnetic Circuit?

Reflectivity - 1/μ

In magnetic circuit, resistivity is like the?

Conductivity

In electric circuit, permeability is analogous to?

Maxwell

What is the unit of flux density in cgs?

Gilbert

What is the cgs unit of Magneto motive force?

Amp-turn/Wb

SI Unit of Reluctance?

Tesla

SI unit of Flux Density?

Amp-turn/meter

SI unit of Coercive Force?

Measurement

Act of determining certain values compared with known standards

Testing

a process of knowing the condition

- Absolute Instruments

- Secondary Instruments

2 Broad Classifications of Electrical Instruments

Absolute Instruments

- indicate the quantity to be measured in terms of the constant of the instruments (Dimensions, turns, etc.)

- used within laboratories as standardizing instruments

- Example: tangent galvanometer

Secondary Instruments

- are the most generally used in everyday work

- In which the value of electrical quantity to be measured can be determined by from the deflection of the instrument

-Indicating Instruments

-Integrating Instruments

-Recording Instruments

Secondary Instruments Classifications

Indicating Instruments

- indicate the instantaneous value of the electrical quantity being measured at the time at which it is being measured.

- given by pointers moving over calibrated scales

- examples: ammeters, voltmeters, ohmmeters, wattmeter's

Integrating Instruments

- measure the total quantity of electricity delivered in a particular time - examples: Kilo-Watt Hour (kWHr) meter and Ampere-hour (Ah) meter.

Recording Instruments

- give a continuous record of the variations of an electrical quantity over a selected period of time.

- their pointer is an in fed pen which leaves a trace on a paper put over a moving drum

AC, DC, AC/DC

3 Kinds of Current

Moving-Coil Meter Movement

-sometimes referred as D Arson Val Movement

-also known as Weston Movement

Moving Iron Movement

-more economical movement for use primarily in alternating - current (AC) circuits

-it consists of a stationary solenoid with two soft-iron vanes within the coil

Electrodynamometer Movement

-where the two poles of the permanent magnet in moving-coil meter were replaced by electromagnet, consisting of two stationary coils.

- since it contains no iron, it is used as the basic movement for either DC or AC instruments.

Galvanometer

- a sensitive instrument used for measuring small amount of current

Ammeter

- an instrument connected in series with the load to measure current common units: micro amp, milliamp, amp

- types: DC & AC

Shunt Resistance

- it extends the range of analog ammeter

- it's very LOW resistance is connected in PARALLEL with the moving coil

Voltmeter

- an instrument connected in parallel with the load, or voltage, source, to measure voltage

- common units: mV, V, and kV

MULTIPLIER

- it extends the range of analog voltmeter

- it's very HIGH internal resistance is connected in SERIES with the moving coil

Ohmmeter

- an instrument that (1) measures resistance and (2) check continuity of electric circuit, coils, heaters, relay contact, switches, fuses, etc.

Multi-tester (VOM)

- an instrument that can measure: current, voltage, & resistance

- types: analog & digital

- scales: usually volts, amperes, and ohms

Selector Switch

used for changing the mode of measurements

Wattmeter

- an instrument that measures true power and have a current, voltage and power rating

CURRENT COIL

- a stationary coil connected in series that responds to curren

POTENTIAL COIL

- a moving coil connected in parallel that responds to voltage

Kilo-Watt-Hour Meter

- an instrument that records the electrical energy consumption of electrical utilization equipment used by residential, commercial, and industrial customers

Insulation Tester

- used to measure insulation resistance in Mega-Ohms by applying high voltage across the insulation and the frame, or wiring

Wheatstone Bridge

- a resistance bridge that can measure resistance with great precision

- where the meter used in the bridge is a zero-center-scale of a galvanometer

- the bridge is balanced when no current flows through the meter.

MURRAY LOOP TEST

- replaces the galvanometer with a slide wire bridge to locate grounds in cables and wires.

VARLEY LOOP TEST

- best adapted to fault location in high-resistance loops, such as long communication lines.

Current Transformers

- a transformer that reduce high line or phase current to a value capable of being measured by a low range ammeter (usually 5 Amp range)

- protect personnel from taking measurements from high voltage wire

Potential Transformers

- a transformer used primarily for isolating voltmeter (usually with 150 Volt range) for measuring high line or phase voltage.

Clamp-On Ammeter

- used to avoid the problem of breaking the circuit under test for reading current

- consists of current transformer and an ammeter combined in one instrument

Power- Factor Meter

- installed in the lines of industrial establishment to monitor the pf of its equipment

Tachometer

- an instrument for measuring the shaft rational speed, in RPM, of an electrical dynamo

Phase Sequence Meter and Open Phase Indicator

- is used to determine if the proper phase sequence is indicated

- assures that the load can be transferred to emergency electrical system in case there is a main power failure without any problem on reverse phase sequence

Synchroscope

- use for generator synchronization at power plants

- it assured that the voltages of the alternator to be paralleled with the other alternator is the same.

Thermocouple

- a device that converts heat energy directly into electric energy by Seed beck effect

SEED-BECK EFFECT

- the development of voltage due to the difference in temperature between two junctions of dissimilar metals in the same circuit

Wire Length Meter

- useful for contractors and electricians to determine inventories of wire

- useful in determining whether there is enough wire left on the reel for a particular installation.

Circuit Tracer

- Also known as continuity tester, consists of a driver (power source), a couple of test leads, and a device that makes noise, such as buzzer or bell

- can be used for continuity test, short circuit test, and ground fault test with all the test made with the power OFF

Tester

- A compact tester that may be used for testing circuits rated 110,220,277, and 460 V

Proximity Voltage Tester

- used to check live insulated circuits, fuses, heating elements, power tools, and high-voltage circuits without actually touching them

Ground Resistance Tester

- is used to read the ground resistance of the ground electrode

at least 1900 mm

distance from one electrode to another electrode if it's not 25 ohms or less

Motor Rotation Indicator

- It indicate which way that a motor will turn before the motor is energized

Wire Sorter

- used by the electrician to identify conductors

Tone Test Set

- uses Wire sorter to determine short and grounds with its tester, sort and identify conductors within a group when used with the inductive amplifier

Infrared Thermography

- An infrared heat scanning equipment, is an ideal inspection technique for scanning electrical equipment for defective components

- It consists of an infrared camera, with optics transparent only to infrared radiation, and a TV type display monitor.

Thermos Gram

heat pictures that is composed of gray scale with continuous contrast ranging from black to white