Snubber Circuits are circuits which are placed across thyristors to protect it from transient high voltages which may occur during switching off.  When the current flowing through a thyristor is interrupted, the voltage across the thyristor can increase rapidly according to Faraday's second law.  This high voltage can cause damage to the thyristor or to other components in the circuit.

The snubber circuit works by preventing the voltage from rising too high across the component to be protected.  The snubber is normally used in circuits with inductance.

The Basic Snubber Circuit is a capacitor and a resistor connected in series.  The Snubber works on the principle that the current across a capacitor cannot fall to zero instantly.  Hence, a small current keeps flowing through the capacitor.  This current is enough to prevent the voltage from rising to high levels.

The Flyback resistor is also another example of the snubber circuit.

Shielding in Instrumentation Cables is vital in order to prevent stray coupling from other circuits nearby. 

When an instrumentation cables is laid beside a power cable, there are chances of  electromagnetic coupling taking place which can induce voltages in the instrumentation cable.  This can distort the signal in the instrumentation cable.  To prevent this, instrumentation cables are provided with a shield, usually made of aluminium.  

This shield magnetically shields the wires inside it.  This eliminates the chances of stray coupling.  The shielding needs to be grounded at one end.  Grounding the shield at two ends will cause grounding loops which can cause interference.

A Backplane is a system of parallel electrical conductors in a PCB which are used to connect the connectors.  Backplanes are advantageous over traditional cable-type connections as they are mechanically stronger.  The cards are mounted on backplanes on slots.  This facilitates easy replacement of the cards.  

Backplanes are widely used in computers and in industrial automation such as PLCs, DECS systems, etc.

Backplanes can be classified into Active and Passive Backplanes

Active backplanes are backplanes which have some computing circuitry in built into them.  Passive backplanes are backplanes with no computing circuits.  

A mid-plane is a backplane which has got slots on both sides.  

A ribbon cable is a cable with multiple insulated wires on a single flat plane.  It is called a ribbon cable as it resembles a ribbon.  Ribbon cables are used in computer peripherals such as printers, hard drives.
Ribbon cables are flexible and hence are suited for application such as dot-matrix printers where the printing head has to move back and forth across the page.  Ribbon cables also take up very little space as they are flat and can be accommodated even in cramped locations.  

By convention, one end of the cable is marked red.  This is to be connected to terminal no. 1 in the connector.  One downside of the ribbon cables is that it does not allow flexing in the sideways.  The cable can only bend up or down.

Non-Polarized plug and socket. 
Polarized Power sockets refer to sockets where the phase and neutral connections are fixed.  That is, the plug can be inserted in any direction.  Polarized connections, on the other hand, are designed that the phase and neutral pins can go into specific holes.  Three pin connectors are in general polarized connectors. An exception is the Italian mains connector with three pins which can be connected either way.

Polarized power sockets are used in applications where interchanging the phase and the neutral conductors can result in shocks as in a toaster.  Since the switch is connected to the phase line, send the phase supply through the neutral would mean that the appliance will have power even when it is switched off.
Observe the difference in pin width

A table lamp needs a polarized socket as interchanging the phase and the neutral lines would result in supply reaching the lamp holder even in the power off condition.

A condenser and a capacitor are essentially the same thing.  They are just two different names.  Capacitors were called condensers earlier.  The term "condenser" is still used in the automotive industry.  A capacitor is a electric component which consists of two conducting plates separated by a dielectric.

Capacitors find wide application in the electric and electronic industry.

Polarized capacitors are capacitors which can be connected only in one polarity.  That is, the positive and negative terminals cannot be changed. Electrolytic capacitors which use capacitors which use rubber, paper or glass are examples of non-polarized capacitors.

Electrolytic capacitors are examples of polarized capacitors.  In these capacitors the polarity is fixed.  The positive and the negative terminals of the capacitor should be connected properly.

Interchanging the positive and negative terminals can cause the capacitor to explode.

Galvanotechnics is the science and technology of Electroplating.  Galvanotechnics deals with the principles and processes of electroplating, electrodeposition and electrorefining.

Insulation displacement connectors are connectors which can be mounted directly over an insulated wire without stripping the insulation.  These connectors come with a sharp blade like arrangement which slices through the insulation and makes contact with the conductor.  

The blade and the conductor are cold welded to form a strong connection.  Insulation displacement connectors are used in telephone and network circuits.  Ribbon cables are generally used with insulation displacement connectors.  Ethernet cables are also mounted to insulation displacement connectors.

Conductive paint is a special type of paint which conducts electricity.  The conduction continues even after the paint has dried.  Conductive paint is a paint which contains micron-sized particles of silver, copper or nickel.  These particles give the paint its conductive property.  

Conductive paint is spray painted on to the surface.  The thickness of the conductive paint can be between 0.125mm to 0.5 mm thick.  

Conductive paint is used in electronic devices to provide shielding from Electromagnetic fields and Radio waves.  

As conductive paint is a suspension with metallic particles, it is necessary to shake the paint container before painting.  If the particles settle down at the bottom of the container and are not uniformly distributed, the conductive properties of the paint will be less.  

This is a question we come across often.  Electroplating involves depositing one metal which is connected to the anode on to another metal which is connected to the cathode.

Non-metals such as glass, plastic can be electroplated after they have been coated with a conductive paint.  The conductive paint provides a surface on which the coating can take place.  Another method of providing a conductive surface is the use of amorphous carbon powder over which the coating can be done.  

More recent techniques involve etching the plastic surface with Chromic acid.  The acid is then neutralized.  The surface of the plastic is activated by with a solution containing tin or palladium. The surface is then coated with a layer of nickel or copper. 

Magnetic Hydraulic Circuit Breakers work on the principle of the magnetic effects of the overcurrents.  However, they differ from standard magnetic circuit breakers as they have a hydraulic time delay mechanism.

The delay is created by forcing the core to move through a cylinder filled with silicone fluid.  When the overcurrent occurs, the magnetic field created pulls the core.  The  core has to pass through a cylinder filled with silicone fluid.  This introduces the time delay.

Thus if the overcurrent is momentary, the core goes back after the current comes back to normal.  If the overcurrent persists, the core travels towards the coil.

When the core reaches the coil, the reluctance of the  magnetic circuit changes.  This creates sufficient flux to attract the armature which causes the protecting device to trip and the contacts to separate.

Once the contacts separate, the current becomes zero.  The magnetic field ceases and the core returns to its original position.

The advantage of the magnetic hydraulic circuit breakers is that they can be reset immediately after tripping unlike thermal overcurrent elements which require a cooling period.

Magnetic Hydraulic Circuit Breakers provide accurate, relatively inexpensive and reliable overcurrent protection.  They are independent of ambient temperature.

Magnetic Hydraulic Circuit Breakers are available both for AC and DC applications.

Electronic Overcurrent Protection is a form of overcurrent protection which is increasingly used in Low voltage Switchgear.  Electronic overcurrent is used as an alternative to the Thermal Magnetic Trip which uses the Thermal and the magnetic effects of overcurrent to effect a trip in the circuit breaker.

The Electronic overcurrent protection works by sensing the current through the circuit using a current transformer.  The output of the current transformer is fed into an electronic circuit.  

The electronic circuit makes decisions relating to overcurrent response.  Electronic overcurrent protection devices have a transistor through which the load current flows.  In an overcurrent scenario, they are able to quickly switch off the transistor and interrupt the fault current.  

This helps in preventing a general undervoltage of the system and very fast response in isolating the fault.

Thermal Magnetic Trip is a method of over current protection which is widely used in LV switch gear such as MCBs and circuit breakers.  The Thermal Magnetic Trip works by sensing the current and tripping the breaker.

The Thermal magnetic element, as the name suggests, has two units viz. the thermal unit and the magnetic unit.  The thermal unit is used to sense the current using the heating effect of current.

The Thermal unit consists of a bimetallic strip which bends due the heat produced by high current passing through it.  The bimetallic strip takes time to bend.  This enables the element to have a time delay feature.  The time delay depends on the magnitude of the over current protection.

The Magnetic Trip element comes into play in case of severe faults.  When the current is extremely high, say 400 %, the current causes the magnetic trip element to attract a trip element which causes the unit to trip.

Thus, the thermal element is used to trigger a delayed response to minor overcurrents while the magnetic element is used to swiftly respond to high overcurrents.

Air Circuit Breakers are Circuit breakers where air is used as the medium of extinguishing the arc.  The air is usually compressed and kept in a cylinder.  When the breaker operates and the contact separation occurs,
the arc is driven into special arc chutes by means of compressed air which is blown through specially designed nozzles.  

Air Circuit Breakers are mostly used in the LV range.  They can interrupt currents of several thousand amperes.  

Air Circuit breakers are provided with an inherent current sensing mechanism like the thermo-magnetic release.

Arc Chute used in Air Circuit Breakers
The Arc chute is a component which is used to weaken and quench the arc.  The Arc Chute contains a number of splitters which split the arc into a number of sections.  This increases the length of the arc and quenches it.  The arc which is formed during the separation of the fixed and the moving contact is driven into the chute by means of the pressurized air.  The arc chute is usually made of composite refractory materials.  

Air Circuit Breakers are available in both Three pole and Four pole versions.

Air Circuit breakers are used widely in the industry for the protection of facilities and transmission lines.  They are also used for protection of electric equipment such as transformers, motors, etc.   Air circuit breakers are also used in mines and on board ships.  

Twisted pair cables, as the name suggests, are cables where a pair of conductors are twisted.  The pair of wires are twisted in order to cancel out the effects of electromagnetic coupling. 

The twist rate or the pitch of the pair refers to the number of twists per metre.  When two twisted pairs are lying together over large distances, there is a possibility of coupling between the two.  Hence, the twist rates of two pairs laid together should be different.

The number of poles is selected such that the frequency of the armature emf is between 25 Hz and 50 Hz.  A higher frequency can result in hysteresis losses in the armature.

The number of poles is an even number like 2, 4, or 6.

Probable number of poles such as 2,4 or 6 are considered and the prospective frequency for each of the number of poles is calculated using the formula

F = N x P/ 120

where  P is the number of poles
           F is the frequency of the armature emf and 
           N is the speed of the motor in rpm

Capacitors Protection Relays are dedicated relays which are designed to provide a range of protection functions for capacitors.

Capacitors are widely used in power systems for VAr regulation and PF control.  They are also used for filtering harmonics.  

Capacitor banks need to be protected against overload by harmonic currents. They also need to be protected against system overvoltages. 

Capacitor Protection Relays consist of a number of different protection elements such as overcurrent, overvoltage, differential protection, etc.    They also have protective interlocks such as preventing an energised capacitor from being connected to the network.

Hot Conductors are conductors in transmission lines which can high currents through normal cross section. They can thus tolerate high current density.  
Hot Conductors are made of special high grade aluminium to which is added many other elements particularly zirconium.  
On further processing, a microstructure is created which gives the alloy a high recrystallization temperature.  This enables the conductor to withstand the high temperatures generated by the high currents.  

A hot conductor can carry about 50% more than a normal conductor of the same cross section.

By giving a black coating of polyurethane to the conductor, the radiation of the heat is increased.  This permits the conductor to carry current up to 70% more than a conventional conductor.

Liquid Cooled Resistors are used in applications where large amount of heat needs to be dissipated through resistors.  Liquid Cooling helps design resistors which are compact.  Liquid Cooling Resistors use water or a glycol-water mixture.  The resistors are cooled directly with water which has been de-ionized or through water-cooled heat sinks.

The Resistors are made of materials such as copper, stainless steel and aluminium.  Cooling mediums used also vary.  Deionized water, salt water, Glycol and other non-conductive liquids can be used for cooling.

Aluminium Clad Wound resistors are used in applications which require dissipation of a large amount of heat in a confined space.  The resistor used is of a wound type.  The resistor assembly is encased in an aluminium
casing with fins for effective heat dissipation.

Aluminium Clad wound resistors can be used as Charging resistors.  They can also be used in dynamic braking applications to absorb the energy of the braking action.  These resistors are also widely used in Cranes, Hoists and CNC Machines.

In power systems, reactive power stability is extremely important.  Reactive power is dependent on the nature of the load, the line capacitances and the line reactances.  Large power lines which are lightly loaded may need reactors to balance the line capacitances.  Hence accurate control of the reactors in line is one of the requirement for the proper maintenance of reactive power.

This Variable Shunt Reactors are used in applications where the range of the reactive power to be adjusted is large but the regulation is not dynamic, that is, the change in the reactive loading is gradual.

Dynamic regulation will require Static VAr compensators with thyristorised controls.

Variable Shunt Reactors are fitted with reactors whose values can be adjusted through tappings.  These tappings are selected using motorised controls.  These adjustments can be made on load.

In Electronics, a mother board is a board which contains all the other boards.  In computers, the mother board may contain the video card, the network adaptor card, the LAN card and so on.  It will also have a slot for the microprocessor.

The boards which are mounted on the mother board are called the daughter boards.  The daughter boards are mounted on the mother boards using slots.

Mother boards which are used in laptops come with integrated video cards.  They also have USB and HDMI ports.

When two metals are brought in close contact, current flows from the one metal to another due to electrochemical action.  For example, when aluminium conductors and copper conductors are jointed, current can flow between the two metals due to the presence of moisture, conductive salts or dirt on the surface.  This causes corrosion known as galvanic corrosion which increases contact resistance.  This can result in localized heating and failure.

This can be prevented by the use of bimetallic strips and washers when an electrical connection is needed to be made with two dissimilar metals.  Bimetallic strips are made by cladding two metals such as copper and aluminium.  The cladding ensures proper contact between the two metals.  The aluminium side of the bimetallic strip is connected to the aluminium conductor while the copper side of the bimetallic strip is connected to the copper conductor.

Bimetallic Strips are used in bus bars where sections made of different metals need to be connected.  They are also used when electric equipment which usually have windings made of copper are to be connected with cables made of aluminium.

Camouflaged Conductors are normal power line conductors which are painted with a specific color to blend in with the surrounding.  

This is particularly essential where environmental clearances are required for a power lines passing through a scenic environment or a forested area.

Normal conductors may have high contrast against the background environment and may cause visual disharmony.

Camouflaged lines are spray painted with a layer of polyurethane on the conductor surface.  The color is usually decided in consultation with the local administration and the environmental agency.  The coating is design to have UV and temperature stability.  The coating can be removed at the clamping location.

Contact grease is a special type of grease used in electrical contacts.  Contact grease serves to protect the contact surfaces from corrosion.  Contact grease are usually silicone based.  Contact greases are used in all types of electrical contacts ranging from electronic contacts to high voltage switchgear. 
Electrical contacts come under chemical attack from chemical fumes in the industries, from battery acid, moisture, etc.  This results in the formation of oxides or sulphates on the surface of the contacts.  This reduces the conductivity and damages the contacts eventually leading to failure.  

Contact greases work by providing a protective film over the contacts.  Contact protection can come in the form of greases or in the form of aerosols which can be sprayed on to the surfaces.  

Electrorefining is a process in which a metal is extracted from its ore through the process of electro-deposition.  In Electrorefining, the impure metal is taken as the anode while the pure metal is the cathode.  For instance, impure copper is taken as the anode while pure copper is the cathode.  The elecrolyte is a solution of sulphuric acid and copper (II) sulphate.

When current is passed, the copper at the anode gets ionized into copper(II) ions which pass through the electrolyte and get deposited at the cathode.  The process of Electrorefining can last many days.   

The impurities in the anode fall off into the  tank.  This material is known as anode slime.  The anode slime contains many other elements which can be extracted through further processing.

A sectionalizer is a current monitoring device which isolates faulty sections of electrical systems.  It is generally used alongside other protective devices such as breakers and reclosers.  The sectionalizer contains a current monitoring device which senses the current.  

The sectionalizer trips by both sensing the current and sensing the absence of voltage when the upstream breaker has tripped.  


When the breaker closes and the supply resumes, the sectionalizer in the faulty line remains open.  The supply is thus resumed to the other healthy feeders.  

The sectionalizer is not a interrupting device. It cannot interupt a circuit.  It can only isolate a de-energised circuit.  Hence, it is is always used in conjunction with the immediate upstream breaker.  Sectionalizers are relatively inexpensive equipment used to isolate and localise a fault.  

Magneto-motive force is considered to be the force derived from a magnetic field.  It is usually considered analogous to the Electromotive force or voltage.  However, the magneto-motive force is not really a force.  It can be better described as the property of certain materials to generate a magnetic field.  

The unit of magneto-motive force is the Ampere-turns in the SI system. In the CGS system, the unit is gilbert.  
One Ampere-turn in the magneto-motive force when one ampere of steady dc current flows through one turn.

The ampere turns can be calculated as the product of the number of turns and the current flowing through it.

F = N x I