Electromagnetics Flashcards
Polarity
Magnetic Field
Magnetic Flux (Φ)
Commutator
A commutator is a rotary electrical switch in certain types of electric motors and electrical generators that periodically reverses the current direction between the rotor and the external circuit. It consists of a cylinder composed of multiple metal contact segments on the rotating armature of the machine.
Solenoid
An electromagnetically-activated switch.
1 Right Hand Rule
Grabbing an inductor with your right hand, with your thumb pointing the direction of the (conventional) current, your fingers are pointing in the direction of the magnetic field.
This same rule applies in reverse for solenoids. With your fingers following the current coil, your thumb indicates the direction of magnetic flux.
Reduction Factor
Reduction Factor of the Strength is found by dividing the value of elastic strength by the yield strength
Reed Switch
The reed switch is an electrical switch operated by an applied magnetic field. It was invented at Bell Telephone Laboratories in 1936 by Walter B. Ellwood. In its simplest and most common form, it consists of a pair of ferromagnetic flexible metal contacts in a hermetically sealed glass envelope.
Magnetomotive Force
Ampere-turns: current multiplied by number of turns in coil
Magnetic Diversion
Ampere
The Ampere is defined as the current that would cause 2 x 10-7 newtons of force between two conductors one metre apart
Equation for calculating Force
2 x 10^-7 x I1 x I2 / s
Permeability (μ) and Reluctance
How easily a magnetic field can permeate an object. Relative permeability can be calculated by B/H.
Lodestone
Naturally occuring magnets
Alnico
A common magnetic alloy - Aluminium, Nickel, Cobalt
Fringing
…
Hysteresis
…
Leakage
…
The three most important magnetic materials:
Iron, Nickel and Cobalt
Residual Magnetism
…
Newton (unit)
One newton is the force needed to accelerate one kilogram of mass at the rate of one metre per second squared in the direction of the applied force. F = BIL.
Lamination
…
Sintering
…
The Lanthanide elements are considered:
Rare Earth Materials - not because they are rare, but because of the difficulty in isolating them from surrounding material
Magnetic Shields are often made from:
‘Mu-Metal’; a nickel-iron alloy (with several compositions)
Magnetomotive Force Ohm’s Law
MMF = IN (Ampere-Turns) = Flux (Webers) times Reluctance (We
Ampere-Turns
…
Magnetic Flux Density (B)
Measured in ‘Teslas’ = Webers per square metre.
Magnetising Force (H)
The unit is Ampere-turns per Metre. Or MMF divided by Length
MMF
Magnetomotive Force
Residual Flux (Br)
…
Coercive Force (Hc)
Coercivity, also called the magnetic coercivity, coercive field or coercive force, is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without becoming demagnetized. Coercive Force is used to overcome Residual Magnetism.
BH Curve
…
Saturation
…
Henry (unit)
The henry (symbol: H) is the SI derived unit of electrical inductance.
Weber (unit)
The weber is the unit of magnetic flux. If a wire cutting through a magnetic field produces one volt of EMF, this means there is 1Wb of flux per second.
Tesla (unit)
The tesla (symbol: T) is a derived unit of the magnetic flux density. One tesla is equal to one Weber per square metre.
μ0
(4π×10^−7) Permeability in a vacuum
Ampere-turns (unit)
A.t is the unit of MMF
Formula for Reluctance from Permeability and object dimensions
r = l/μA
Permeability (Unit)
Henries per Metre. Calculated from B (Flux Density) divided by H (Magnetising Force)
Absolute Permeability (μ) is calculated by:
μo (Vacuum Permeability) times μr (Relative Permeability)
Lenz’s Law
Lenz’s law, named after the physicist Emil Lenz who formulated it in 1834, states that the direction of the electric current which is induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes the initial changing magnetic field.
Faraday’s Law
Faraday’s law of induction is a basic law of electromagnetism predicting how a magnetic field will interact with an electric circuit to produce an electromotive force —a phenomenon known as electromagnetic induction.
Inductive Proximity Switch
…
Fleming’s Hand Rules
Fleming’s left-hand rule is used for electric motors, while Fleming’s right-hand rule is used for electric generators.
Formula for calculating Force (Newtons) in two conductors where current is flowing in the same direction.
F = BIL
Curie Temperature
In physics and materials science, the Curie temperature, or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can be replaced by induced magnetism.
Reluctance (unit)
At/W (Ampere-turns per Weber)
Formula for calculating Force (Newtons) in two conductors where current is flowing in a different direction.
F = 2×10^(-7) × I1 × I2 ÷ s (s = distance separating conductors)
Force (Newtons) between two conductors carrying 1 Amp placed 1 Metre apart:
2×10^(-7)
Vacuum Permeability Constant:
4×π×10^(-7)
Former SI Definiton of Ampere (until 2019):
The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between these conductors a force equal to 2×10^(−7) newtons per metre of length.
Self-Inductance
Self inductance is defined as the induction of a voltage in a current-carrying wire when the current in the wire itself is changing. In the case of self-inductance, the magnetic field created by a changing current in the circuit itself induces a voltage in the same circuit. Therefore, the voltage is self-induced.
Bifilar
A bifilar coil is an electromagnetic coil that contains two closely spaced, parallel windings. In engineering, the word bifilar describes wire which is made of two filaments or strands. It is commonly used to denote special types of winding wire for transformers.
Copper Loss
Copper loss is the term often given to heat produced by electrical currents in the conductors of transformer windings, or other electrical devices. Copper losses are an undesirable transfer of energy, as are core losses, which result from induced currents in adjacent components.
Snubber Circuit
Snubbers are energy-absorbing circuits used to suppress the voltage spikes caused by the circuit’s inductance when a switch, electrical or mechanical, opens. The most common snubber circuit is a capacitor and resistor connected in series across the switch (transistor).
Two types of Analogue Measurement Devices
Moving Iron and Moving Core
Two types of Moving Iron Instruments
Attraction Type and Repulsion Type
D’Arsonval Movement (also known as PMMC)
The D’Arsonval movement is a current sensing mechanism which is used in DC Ammeter, ohm meter and Voltmeter. Priniciple of D’Arsonval Movement. When an electric current is passed through a coil placed in a magnetic field, it experiences a force. This force causes a torque in the coil that is fixed to a spindle.
FSD
In analog systems, full scale may be defined by the maximum voltage available, or the maximum deflection (full scale deflection or FSD) or indication of an analog instrument such as a moving coil meter or galvanometer . Now FSD Current is the value of current needed to get a full scale deflection in the instrument.
Hall Effect
The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor, transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. It was discovered by Edwin Hall in 1879.
Self-Inductance
Self inductance is defined as the induction of a voltage in a current-carrying wire when the current in the wire itself is changing. In the case of self-inductance, the magnetic field created by a changing current in the circuit itself induces a voltage in the same circuit. Therefore, the voltage is self-induced.
Magnetostriction
Magnetostriction is a property of magnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of materials’ magnetization due to the applied magnetic field changes the magnetostrictive strain until reaching its saturation value, λ
Hall Effect Sensor
A Hall effect sensor is a device that is used to measure the magnitude of a magnetic field. Its output voltage is directly proportional to the magnetic field strength through it. Hall effect sensors are used for proximity sensing, positioning, speed detection, and current sensing applications.
Dynamo
The Dynamo consists of 3 major components: the stator, the armature, and the commutator. Brushes are part of the commutator, the brushes must conduct electricity as the keep contact with the rotating armature.
Voltage Regulator
A voltage regulator is a system designed to automatically maintain a constant voltage level. A voltage regulator may use a simple feed-forward design or may include negative feedback. It may use an electromechanical mechanism, or electronic components.
Rectifier
A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation is performed by the inverter. The process is known as rectification, since it “straightens” the direction of current.
B = Φ/A E = B L V sin θ
Magnetic Flux Density (measured in Teslas) is equal to Magnetic Flux divided by area.
Separately-Excited Generator
A separately excited dc motor is a motor whose field circuit is supplied from a separate constant-voltage power supply, while a shunt dc motor is a motor whose field circuit gets its power directly across the armature terminals of the motor.
(Self-Excited) Shunt Generator
A shunt DC motor connects the armature and field windings in parallel or shunt with a common D.C. power source. This type of motor has good speed regulation even as the load varies, but does not have the starting torque of a series DC motor.[4] It is typically used for industrial, adjustable speed applications, such as machine tools, winding/unwinding machines and tensioners.
Open Circuit Characteristic Curve
Open circuit characteristic is also known as magnetic characteristic or no-load saturation characteristic. … curve is obtained by operating the generator at no load and keeping a constant speed. Field current is gradually increased and the corresponding terminal voltage is recorded.
Transducer
A transducer is an electronic device that converts energy from one form to another. Common examples include microphones, loudspeakers, thermometers, position and pressure sensors, and antenna.
Instrumentation
Instrumentation is a collective term for measuring instruments that are used for indicating, measuring and recording physical quantities. The term has its origins in the art and science of scientific instrument-making.
(Self-Excited) Series Generator
A series motor is a direct current motor that has two windings that are in series, with the same current flowing through each. … The series motor provides high starting torque and is able to move very large shaft loads when it is first energized.
Voltage Regulation
Voltage regulation is a measure of change in the voltage magnitude between the sending and receiving end of a component. It is commonly used in power engineering to describe the percentage voltage difference between no load and full load voltages distribution lines, transmission lines, and transformers.
(Self-Excited) Compound Generator
In a Compound Wound Generator, there are two sets of the field winding on each pole. One of them is connected in series having few turns of thick wire, and the other is connected in parallel having many turns of fine wire with the armature windings.
Lap Winding
Lap Winding is one type of winding with two layers, and it is used in electric machines. Every coil in the machine is allied in series with the one nearby coil to it. The applications of lap winding mainly include low voltage as well as high current machines.
Wave Winding
Wave winding is one type of armature winding. In this winding, we connect the end of one coil to the starting of another coil of the same polarity as that of the first coil.
Generator converts:
Mechanical energy to Electrical
Motor converts:
Electrical energy to Mechanical
Schmitt Trigger
In electronics, a Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the noninverting input of a comparator or differential amplifier. It is an active circuit which converts an analog input signal to a digital output signal.
Five types of magnetic material:
Diamagnetism, Paramagnetism, Ferromagnetism, Ferrimagnetism, Antiferromagnetism
Types of Motor Losses:
Copper, Core, Brush, Mechanical, Stray
Eddy Current
Eddy currents are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday’s law of induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field.
Efficiency (η)
Pout / Pin * 100%
Transient and Steady State
The steady state is the state that is established after a certain time in your system. The transient state is basically between the beginning of the event and the steady state. To come back to real life: When you open the shower, the water is suddenly released and the temperature is in a transient state.
Equivalent Circuits
In electrical engineering and science, an equivalent circuit refers to a theoretical circuit that retains all of the electrical characteristics of a given circuit.
Piezoelectric Effect
Piezoelectric Effect is the ability of certain materials to generate an electric charge in response to applied mechanical stress. The word Piezoelectric is derived from the Greek piezein, which means to squeeze or press, and piezo, which is Greek for “push”.
PCB Motor
A Printed Circuit Board or a Disc Armature motor consists of a rotor disc made of non-magnetic and non-conducting material. The disc armature is placed between two sets of permanent magnets mounted on the ferromagnetic plates. … Brushes are placed around the inner periphery.
Armature Reaction
The armature reaction simply shows the effect of armature field on the main field. In other words, the armature reaction represents the impact of the armature flux on the main field flux. The armature field is produced by the armature conductors when current flows through them.
Interpoles
An auxiliary set of field poles carrying armature current to reduce the field flux caused by armature reaction in a d-c motor. Interpoles – Are coils that are placed between the field coils that generate a field that is used to prevent excessive sparking of the brushes.
For the terminal voltage in a compound generator:
Subtract the voltage drop across the armature from the generated voltage
Parallel Paths in Lap and Wave Windings
In Lap Winding, number of parallel paths is equal to number of poles. In Wave Winding, number of parallel paths equals 2.
Methods for reducing Armature Reaction:
Brush Shift (not effective for varying loads, Interpoles, Compensating Windings.
Servomotor
A servomotor is a rotary actuator or linear actuator that allows for precise control of angular or linear position, velocity and acceleration. It consists of a suitable motor coupled to a sensor for position feedback.
