Magnetic reluctance is defined as the opposition offered by a magnetic circuit to the production of magnetic flux. Magnetic reluctance is the property of the material that opposes the creation of magnetic flux in a magnetic circuit.

Magnetic reluctance also known as reluctance, magnetic resistance, or a magnetic insulator.

In an electrical circuit, the resistance opposes the flow of current in the circuit and it dissipates the electric energy. The magnetic the magnetic reluctance is similar to the resistance of an electrical circuit as it withstands the production of magnetic fluctuations in the magnetic circuit but does not provide a cause for the dispersion of energy instead it retains the magnetic field.

Reluctance is directly related to the length of the magnetic field and measures against the location of the cross section of the magnetic path.

It is a scalar quantity and denoted by S. Note that a scalar quantity is one which is fully described by a magnitude (or numerical value) only. No direction is required to define the scalar quantity.

Reluctance of Magnetic Bar

Mathematically it can be expressed as

where, l = length of the magnetic path in meters

= permeability of free space (vacuum) = Henry/meter

= relative permeability of a magnetic material

= Cross sectional area in square meters ()

In AC as well as DC magnetic fields, the reluctance is the ratio of the magnetomotive force (m.m.f) to the magnetic flux in a magnetic circuit. In a pulsating AC or DC field, the reluctance is also pulsating.

Thus it can be expressed as

Reluctance in a Series Magnetic Circuit

Like in a series electrical circuit, the total resistance is equal to the sum of the individual resistances,

Where,

Similarly, in a series of magnetic circuits, the total reluctance equals the sum of the individual reluctances encountered around the closed flux path.

Where,

Reluctance Units

The unit of reluctance is ampere-turns per Weber (AT/Wb) or 1/Henry or H^-1.

Reluctance Formula

(1) 

Where, (In an electrical circuit )

Therefore,

Where,  = permeability of the magnetic material

(2) 

Comparing Equation (1) and (2), we get

Rearranging terms, we get

(3) 

But and

put this into equation (3) we get,

Applications of Reluctance

• In the transformer, reluctance used to reduce the effect of magnetic saturation. Fixed wind gaps in the transformer increase circuit suspicion and thus retain additional magnetic strength before filling the space.
• Reluctance motor used for many speed applications such as the clock timer, signature devices, recording tools, etc., which is works on the principle of variable reluctance.
• One of the main characteristics of the magnetically hard materials is that it has a strong magnetic reluctance which is used to create permanent magnets. Example: Tungsten steel, cobalt steel, chromium steel, alnico, etc….
• The speaker magnet is covered with a soft magnetic material such as soft iron to minimize the effect of the stray magnetic field.
• Multimedia loudspeakers are magnetically shielded in order to reduce magnetic interference caused to TV (televisions) and CRTs (Cathode Ray Tube).

Source: electrical4u.com

Permeance is a measure of the ease with which a magnetic flow is applied using an object or a magnetic circuit. Permeance is the reciprocal of reluctance.

Permeance is directly proportional to the magnetic flux and is denoted by the letter P.

From the above equation we can say that the quantity of magnetic flux for a number of ampere-turns is depended on permeance.

In terms of magnetic permeability, permeance is given by

In an electrical circuit, conductance is the level at which an object transmits electricity; similarly, permeance is the degree to which a magnetic flux conducts a magnetic field. Therefore, the permeance is greater in large cross-sections and smaller in smaller cross-sections. This concept of working in a magnetic circuit is similar to operating in electricity c

Permeance vs Reluctance

Permeance	Reluctance
Permeance is a measure of the ease with which magnetic flux can be set up in the magnetic circuit.	Reluctance opposes the production of magnetic flux in a magnetic circuit.
It is denoted by P.	It is denoted by S.
Its unit is Wb/AT or Henry.	Its unit is AT/Wb or 1/Henry or H-1.
It is analogous to conductance in an electric circuit.	It is analogous to resistance in an electric circuit.

Permeance Coefficient

Permeance coefficient is defined as the ratio of magnetic flux density to magnetic field strength at the operating slope of the B-H curve.

It is used to express the “operating point” or “operating slope” of the magnet on the load line or B-H curve. Thus the permeance coefficient is very useful in designing magnetic circuits. It is denoted by PC.

Where,

• = Magnetic flux density at the operating point of B-H curve
•  = Magnetic field strength at the operating point of B-H curve

In the above graph, the straight line OP passing between the origin and the B_d and H_d points on the B-H curve (also called as demagnetization curve) is called the permeance line and the slope of the permeance line is the permeance coefficient PC.

For the only single magnet, that is when there is no other permanent magnet (hard magnetic material) or soft magnetic material placed nearby, we can calculate the permeance coefficient PC from the shape and the dimensions of the magnet. Therefore, we can say that the permeance coefficient is a figure of merit for a magnet.

An instrument can measure the electric current called an ammeter. To measure current ammeter must connect in series with the circuit whose current is to be measured.

The measurement of current through the resistor by using an ammeter is shown in the below figure.

The electric current can also be measured using a galvanometer. The galvanometer gives both the direction and the magnitude of the electric current.

The current can be measured by detecting the magnetic field associated with the current without breaking the circuit. There are various instruments used to measure the current without breaking the circuit.

• Hall effect current sensor transducers
• Current transformer (CT) (Only measure AC)
• Clamp-on meter
• Shunt resistors
• Magneto resistive field sensors

The particles that carry the electric charge through the conductors are either moving or free electrons. The direction of the electric field within the circuit, by definition, the rule that good test charges are pushed. Thus, these negative charge particles, i.e., electrons, flow opposite the electric field.

According to electron theory, when a voltage or potential difference is applied to the entire conductor, the charged particles flow into a circuit, which creates electrical energy.

These chargeable particles flow from high power to low power, that is, from the positive terminal to the negative battery terminal through an external circuit.

However, in a metal conductor, positively charged particles are stored in a fixed location, and poorly charged particles, i.e., electrons, are free to move. In semiconductors, the flow of charged particles can be positive or negative.

The flow of good charging carriers and negative charging carriers on the other hand has the same effect on the electrical circuit. As the current flows due to good or bad costs, or both, a meeting is needed to get an independent current guide to the types of network companies.

The direction of conventional current is considered the direction in which positive charge carriers flow, i.e., from higher potential to lower potential. Therefore, Negative charge carriers, i.e., electrons flow in the opposite direction of conventional current flow, i.e., from lower potential to higher potential. Hence, the conventional current and electron flow go in opposite directions which is shown in the image below.

• Conventional Current: The flow of positive charge carriers from a positive terminal to a negative terminal of the battery is known as conventional current.
• Electron Flow: The flow of electrons is termed electron current. The flow of negative charge carriers – i.e., electrons – from a negative terminal to a positive terminal of the battery is known as electron flow. Electron flow is the opposite of conventional current flow.

AC Current

The flow of electric charge in a periodically reverse direction is known as alternating current (AC). AC is also referred to as “AC Current”. Although this is technically saying the same thing twice “AC Current”.

An alternating current changes its a direction at a periodic interval of time. The alternating current starts from zero, rises to maximum, decreases to zero, then reverses and reaches a maximum in the opposite direction, then again returns to the original value and repeats this cycle infinitely.

The type of alternating current waveform may be sinusoidal, triangular, square, or sawtooth, etc. In most electrical circuits, the typical waveform of alternating current is a sine wave. A typical sine waveform that you might see as an alternating current is shown in the image below.

An alternator can generate an alternating current. The alternator is a special type of electrical generator designed to generate alternating current.

AC electric power is widely used in industrial and residential applications.

DC Current

The flow of electric charge in only one direction is known as direct current (DC). DC is also referred to as “DC Current”. Although this is technically saying the same thing twice “Direct Current ”.

As DC flows only in one direction; hence it is also referred to as unidirectional current. A waveform of a direct current is shown in the image below.

DC can be generated by batteries, fuel cell, thermocouples, solar cells, commutator type electrical generators, etc. An alternating current can be converted to direct current by using a rectifier.

DC electric power is generally used in low-voltage applications. Most electronic circuits need a DC power supply for its operations

An electric current is defined as a stream of charged particles such as electrons or ions that run through an electric conductor or space. Flow charge rate using a conducting medium with respect to time. Electricity is expressed mathematically (eg in formulas) using the symbol “I” or “i”. The current unit says ampere or amp. This was revealed by A.

In other words, a stream of charged particles flowing into an electrical conductor or space is known as an electric current. Charging moving particles are called charging carriers which may be electrons, holes, ions, etc.

The current flow depends on the conductive medium, below are conductive material examples

• In a conductor, the current flow is due to electrons.
• In semiconductors, the current flow is due to electrons or holes.
• In the electrolyte, the current flow is due to ions as well
• In plasma-ionized gas, energy flows are caused by ions and electrons.

When a potential voltage difference is used between two points in a conductive medium, the electrical energy begins to flow from high power to low power. The higher the voltage or the potential difference, the more current flows between the two points.

If two points in a cycle have the same force, then the current cannot flow. The magnitude of the current depends on the voltage or potential difference between the two points. Therefore, we can say that the current is the result of voltage.

Electric power can generate electric fields, which are used in inductors, transformers, generators, motors. In an electric conductor, the current causes an opposing heat or joule heat that creates light in an incandescent lamp.

SI unit of current

The SI unit for current is ampere or amp. This is represented by A. Ampere, or amp is the base SI unit of electric current. The unit ampere is named in honor of the great physicist Andrew Marie Ampere.

In the SI system, 1 ampere is the flow of electric charge between two points at the rate of one coulomb per second. Thus,

Hence current is also measured in coulomb per second or C/S.

Electric Current Formula

The basic formulas for current are:

1. The relationship between Current, Voltage and Resistance (Ohm’s Law)
2. The relationship between Current, Power and Voltage
3. The relationship between Current, Power and Resistance

Current Formula 1 (Ohm’s Law)

According’s to ohm’s law,

Thus,

Current Formula 2 (Power and Voltage)

The Power transferred is the product of supply voltage and electric current.

Thus, we get current equals the power divided by voltage. Mathematically,

Where stands for amperes or amps (the units for electric current).

Current Formula 3 (Power and Resistance, Ohmic Loss, Resistive Heating)

We know that,

Now put in the above equation we get,

Thus, the current is the square root of the ratio of power and resistance. Mathematically,

Dimensions of Current

Dimensions of current in terms of mass (M), length (L), time (T), and ampere (A) is given by .

Current (I) is a representation of the coulomb per second. Thus,

Electrical switches can adapt to misunderstandings in the application / application to ensure no leakage current and make them available in multiple circuits, actuators, and housing styles. Disadvantages include their number, limited communication life cycle, large size and slow response.

Solid Switch

Solid switches electric appliances that do not have aging moving parts. They are able to switch quickly without any spark between contacts or problems with communication rust. Their disadvantages include high construction costs at current very high rates.

When selecting a level switch, the user needs to determine if the power circuit needs a switch that is usually open or closed.

Normally Open (NO)

The switches do not currently allow for free access. They need to “create” a contact in order to activate it.

Normally Closed (NC)

The switches currently allow free access and require a “break” contact (open) to be activated.

Stick / Throw

Most switches have one or two poles and one or two throws, but some manufacturers will produce custom-level switches for specialized apps. The number of poles indicates the number of different circuits that can be switched on at the same time.

The cast number describes the number of circuits each pole can control. This is indicated by a circuit configuration (NO / NC). Pause is a circuit breaker caused by contacts that are separated by a switch that introduces each circuit that opens or interrupts the circuit.

Electrical Changing System and Types

Single Pole, One Throw (SPST)

Single pole, single throw switches (SPST) make or break a single conductor connection in a single branch circuit. They usually have two terminals and are called single-pole switches

Single pole, Double Throw (SPDT)

A single pole, dual switches (SPDT) makes or breaks a single conductor connection with one of two conductors. They usually have three terminals and are usually used in pairs. SPDT switches are sometimes called three-way switches.

Double Pole, Single Throw (DPST)

Double pole, single throw switches (DPST) make or break the connection of two circuit conductors in a single branch circuit. They usually have six terminals and are available in both temporary and maintenance communication versions.

Double Pole, Double Throw (DPDT)

Double pole switches, double throw (DPDT) make or break the connection of two conductors in two different circuits. They usually have six terminals and are available in both temporary and maintenance communication versions.

Electrical switch contacts are either normally-open or normally-closed, depending upon the open or closed status of the contacts under “normal” conditions.

But what exactly defines “normal” for a switch? The answer is not complicated, but it is often misunderstood because of the ambiguous nature of the common word.

The “normal” state of the switch is the state of electrical contacts in the state of non-physical regeneration. One way to think of a “normal” situation is to think of a change in relaxation.

With the change of the temporary contact button, this may be the status of the switch contact if it is not pressed. Electric switches are always designed with scheme drawings in their “normal” conditions, regardless of the type of operation.

The “normal” state of the switch (closed) is actually an abnormal state of the internal process (low flow), for the simple reason that the switch should be stimulated and not rested while the process is running. as it should.

Below listing of “normal” definitions for various process switch types:

• Limit switch: target not contacting the switch
• Proximity switch: target far away
• Pressure switch: low pressure (or even a vacuum)
• Level switch: low level (empty)
• Temperature switch: low temperature (cold)
• Flow switch: low flow rate (fluid stopped)

Symbols of electrical switches

Capacitance can be mathematically expressed by

Also, it is defined as the ratio of charge stored by capacitor to voltage V across the same capacitor.

Note: When the voltage across the capacitor or the capacitor voltage reaches or equal to source voltage means capacitor does not charge. No charge flows.

In circuits capacitor acts a water tank and it stores energy. It releases and more interruption of supply. A capacitor is like a storage tank it can used for smooth out interruption to the supply.

One side of the capacitor is connected to the positive side of the circuit and other side is connected with negative side of the capacitor. The stripe in symbol indicates which side is negative. If we connect capacitor to battery the voltage will push the electron from negative terminal over the capacitor.

The electron will build up in the one plate of capacitor and other plate will turn and release some electrons. Electrons can pass through capacitor through capacitor because of insulating material eventually the capacitor is the same voltage as the battery. Then no more electrons will flow.

There is a build up an electrons on one side this means we have stored energy. This can be released to do work because more electrons in one side to compare to other electron are negatively charged. This means we have one side negative and other side positive.

So there is difference in potential or voltage difference between the two. The voltages we are compare difference between two points. If we measure 1.5 V batteries then we read the difference between the 1.5V each end. But if we measure same end there voltage is zero there is no difference.

The unit of capacitance is Farad (F). To Honor Sir Michal Faraday (the inventor of most popular electrical law of electromagnetic induction), the unit of capacitor is named in Farad. Actually, one Farad is very large unit which means the size of the capacitor comes very bigger and most capacitors are rated in micro Farad (uF= 1 x 10^-6) or micro farad (pF) or Pico Farad (pF) 1 pF = 1 x 10-12F

If Q=1 coulomb and V=1 volt, then capacitance is 1F. That’s we can say that 1 Farad is equal to 1 Coulombs/1volt.

One Farad

One Farad is defined as the capacitance of a capacitor between the plates of which there appears a potential difference of I volt when it is charged by 1 coulomb of electricity.

Calculate capacitance value for two parallel plates capacitor

Let us consider a parallel plate capacitor in which the upper and lower plates are separated by some distance of d meters. There is a potential difference of V volts between the two plates, therefore work required in transferring coulomb of charge from one plate to another is V Joules; since the work is the product of force and distance d the force experienced by the charge is the electric field strength E is given by ..

The electric flux density D is given by

The relation between electric flux density and electric field in terminals is given by

The parallel plate capacitor

Here the relative permeability of the material vary according to the type of dielectric material is used to construct a capacitor.

Capacitor stores electric charge. It is looks like battery it stores energy in a different way. It is stores much energy in battery. It releases charge very faster. Capacitor is very useful that’s why it is used in all circuit boards.

It is one of the fundamental passive components. It is separately or jointly used with other circuit components such as inductor or resistor or others. But in AC Power circuit it is used in power factor correction. It is a two terminal device which stores energy in an electric field. It is consisting of two parallel plates.

They are made of conducting materials such as copper or silver or iron (mostly silver) and they are separated by a layer of dielectric material. The dielectric material is filled in between the capacitor’s terminal. Here, The dielectric material is an efficient insulator, so that it prevents electron flow across the terminal.

Working Principle of Capacitor

Positive Q+ as Plate A and Negative Q- as Plate B,

Consider two parallel plates A and B, and A is connected with positive terminal of the voltage source and B is connected with a negative terminal of the same source. The electron flows from negative terminal and accumulates on the plate B developing negative charge, due to this the equal number of positive charges accumulate in plate A.

Here the electric field is established in the dielectric between the plates. The direction of electric field always drives electrons from the positively charged plate to positive terminal of the source. The amount of negative charge stored on plate B is equal to the amount of positive charge on the plate A. Due to this, the two plates A and B carry equal and opposite charges, since, there is a voltage across these two plates.

Let us consider voltage across the capacitor is Vc, and it is opposite that of applied voltage V. As the charge on the plate increases, the voltage across the plates also increases simultaneously. AT the same time, if the voltage across the parallel plates reaches to the source voltage V, then, there is not flow of electrons from the source.

Symbol of the capacitor

We can measure the capacitance of the capacitor in the unit of farads. This is mentioned as ‘F’ in capacitor. his is a very large unit.

In circuit boards typically use micro-farads. It is used like letter ‘μ’ other value is voltage which we can measure in volts ‘V’. In the capacitor the voltage is the maximum value which capacitor can handle. The capacitor is rated at certain voltage it exceeds the capacitor will explode.

Microfarad capacitors mainly used in electrical power system and power factor correction circuit

The small capacitor in the range of below one microfarad Capacitors is mainly used in electronics circuit. There are many types of capacitors are in the market.