Peristaltic pumps work by pushing a fluid through a tube. The liquid is moved in a tube due to the formation of constrictions. The impeller of the pump consists of two wheels which press against the tube and move the constrictions and the liquid.
The diaphragm is operated by an external mechanism which moves the diaphragm up and down. When the diaphragm is pulled up, low pressure is created and the liquid is drawn inside the pump. When diaphragm is pushed down, the fluid inside is pressurized and released through the outlet valve.
Plunger Pumps and Piston pumps work on the same principle. They both draw a fixed volume of liquid through the inlet and pressurize the liquid and then release the liquid.
A plunger pump is a positive displacement pump. In a plunger pump, the plunger moves up and down a cylinder.
In Pump design, shear sensitivity is an important factor. Shear sensitivity refers to the response of a liquid when the shear forces inside a pump increase. Shear forces increase as the pump speed increases. |
| Impeller of a screw pump (positive displacement) |
Velocity head is the difference in velocity of the liquid at the suction nozzle and the discharge nozzle. This difference in velocity is caused by difference in the size of the nozzles.
The centrifugal pump is not self-priming. The pump needs to be primed before it can function. Priming involves filling the pump casing with water and removing the air inside.
A Diffuser pump is on in which stationary vanes called diffusers are fitted radially facing the discharge from the impeller. These vanes which gradually increase in space as the water moves outwards serve to convert the velocity of the water exiting the impeller into pressure.The Hydraulic Efficiency of a pump is the ratio of the useful hydrodynamic energy in the fluid to the energy supplied to the rotor of the pump.
The volute refers to the part of the casing which expands along its curvature around the pump. The primary function of the volute is to convert the kinetic velocity of the water developed by the impeller into pressure. 
Water Extraction Pumps are pumps which are specially designed to extract water from sources such as underground wells, lakes and tanks.
A circulation pump is a pump which is used to circulate a liquid within a closed circuit. They differ from other pumps in that they do not have to pump the fluid through a head.Pumps are manufactured in standard sizes by manufacturers. The actual requirement for an individual application may be different from the standard size.
Wet Rotor Pumps are pumps in which the medium, that is, the liquid being pumped is used to cool the rotor. The rotor is designed such that the water being pumped surrounds the rotor and provides a cooling effect.
The losses in the pump can be categorized into three categories
Wire to Water Efficiency refers to the the overall efficiency of the pumping system. The pumping system has a prime mover, usually a motor and the pump. The Wire to Water efficiency is calculated as the energy supplied through the wire to the final quantity of water pumped by the system.
A boiler, as the name suggests, boils the water before turning it into steam at subcritical pressure - the pressure at which bubbles can form. Steam generators, on the other hand, convert water into steam into steam without boiling at a super-critical pressure.According to the standards of the ASME (American Society of Mechanical Engineers), Boilers can be classified on the basis of pressure into the following types.
Low Pressure Boilers
Boilers with operating steam pressure not exceeding 1.021 atmosphere and a temperature of 394 K.
Power Boilers
Power Boilers are those boilers whose pressure rating and temperature are above those of Low pressure boilers.
Miniature Boilers
These are boilers with very small capacity with a pressure less than 6.8 atmospheres and a gross volume less than 0.1415 cubic metres.
Steam Traps are devices which are used to release condensate which may form in steam lines. Steam traps allow only the condensate and prevent the useful steam from escaping.
Condensate should be removed from steam lines. Condensates can cause hammering in the pipelines and corrosion.
In addition to Steam, Steam traps also release air and other gases.
There are many different types of steam traps. The most simple can be a nipple in a pipeline. Since condensate (water) is heavier than steam, it will collect at the lowest point. The trap opens once sufficient amount of condensate has collected.
Water present in a steam system moves at a very high velocity driven by the steam pressure. In some cases, the acceleration is even greater than that of steam. When this water at high speed hits a fitting such as valve or a bend, violent impact resulting in noise or a pressure shock which travels through the system is produced. This is called water hammeringConductivity in metals is due to the presence of free electrons in the atomic lattice. When the metal is heated, the atoms in the lattice vibrate. This results in reduced movement of the electrons as they hit against the vibrating atoms.
This results in an increase in resistance of the metals.
Most Metals have positive temperature coefficient of resistance. There are , however, exceptions such as carbon and semiconductor metals such as Silicon and Germanium. Some Alloys have zero temperature coefficient of temperature which means that the resistance does not change with increase of temperature. Manganin is an example.
The Q factor of an inductor is a very important parameter. The Q factor tell us how close the inductor to an ideal inductor.
An ideal inductor is an inductor which has no losses. That is, its series resistance is zero. It is not possible to construct an ideal inductor as all inductors are made of wires which have resistances.
Q factor is the ratio of the inductive reactance to the series resistance of the inductor at a given frequency.
Q= XL/ R
The Q factor is an crucial parameter when designing resonant circuits as it will affect the damping. Higher the Q factor, higher is the efficiency of the inductor.
| Optical Fibre | Metallic Wire |
| Not a lightning hazard as it is non conducting | Can attract and transmit lightning |
| Lighter in weight | Heavier in weight |
| Not affected by Interference | Affected by interference |
| High data bandwidth | Lower data bandwidth |
| Lower data loss | Data loss is more |
| Faster data transmission | Relatively slower data transmission |
| Unauthorised tapping of data is difficult | Easier to tap data without authorization. |
| Difficult to terminate | Easier to terminate |
| High initial cost | Lower initial cost |
| Less affected by chemicals and pollution | More prone to effects of pollution |
| No risk of sparking. Hence, can be used in petroleum and chemical industries. | Risk of sparking and fire. Hence, cannot be used in hazardous environments. |
Terminating resistors are used in communication cables to prevent reflection of the transmitted signal. The reflected signal can cause interference which may affect data transmission. Hence, to prevent this resistances are connected in parallel.
The value of the impedance will match the wave impedance of the line. Thus a communication line with an impedance of 120 ohms will have a 120 ohm resistor connected across it. Short cables can function without terminating resistors.
A Band pass filter combines the characteristics of the High Pass and Low Pass Filters.
The Band pass Filter, as the name suggests, allows only signals of a particular band or range of frequencies to pass through. All other signals are blocked or shorted. 
Band pass Filters can be made by connecting a high pass filter in series to a low pass filter or vice versa.
A Band pass filter can be made by connecting an inductor in parallel to filter the low frequency components which lie below the desired frequency. Another inductor in series will then block the high frequency components which lie above the desired frequency.
Likewise, the Band pass filter can also be made using capacitors as in the second figure. Here, the first capacitor filters the high frequency components and the second capacitor in series blocks the low frequency components.
A High Pass Filter is a filter which permits high frequency signals to pass through and blocks only low frequency signals. The high pass filter has a relatively simple construction. The filter can be constructed by either providing a low impedance path to high frequency signals from the input to the output or by providing a low impedance path to low frequency
If a capacitor is connected in series between the input and the output, it will provide low impedance to high frequency signals and high impedance to low frequency signals. High frequency signals alone will be able to pass the capacitor.
Alternatively, if an inductor is connected in parallel to the input, it will offer low impedance to low frequency signals which will get shorted across the input. High frequency signals will alone reach the output.
A Low pass filter is a filter which permits only low frequency signals to pass through. High frequency signals are blocked or shorted across the input. The low pass filter offers low impedance to low frequencies and high impedance to high frequencies.
There are two ways of constructing a Low Pass Filter.
The first method is to connect an inductor in series to the output. The reactance of the inductor is so chosen that it offers high reactance to high frequency signals. Thus, high frequency voltages are blocked. At low frequency, the reactance is low and thus low frequency signals are allowed to pass.
Another method is to connect a capacitor in parallel to the input. The capacitor provides low reactance to high frequency signals which are shorted across the input. The low frequency signals see a high reactance in the capacitor and they alone reach the output. The series resistance serves to limit the current.
Air Termination Rods are used to provide lightning protection to parts of a building which protrude from the superstructure. Air termination rods can fixed to terraces, beams, etc. Air termination rods consist of a rod or any pointed surface which is connected to the lightning protection system of the building.
Air Termination Rods are also used for equipment which are kept in exposed flat surfaces such as solar panels and pipelines.
Air Termination Rods may need to be supported against winds by means of suitable support structures.
Bonded Connections are used to connect a conductor to another body such as a pipe, gate, door or a railing. All metallic objects in a building or a facility need to be connected to the earth. This is necessary to prevent accidental voltage getting induced in them due to contact
Bonded Connectors are usually galvanized to prevent corrosion. They have flat surfaces which increase the contact area with the object to be bonded. They are made of a material similar to the conductor material such as copper or aluminium.
Voltage limiting devices are used in Electric Traction systems, to prevent dangerous voltages from appearing the insulated tracks and the earthed components of the installation.
Overvoltages can occur due to lightning or due to short circuits. Voltage limiting devices typically use a MOV (metal oxide varistor) and and air gap mechanism to conduct the high voltage impulse to the ground.
If case of minor overvoltages, the MOV operates and diverts the surge. It then returns to its normal non-conducting state. In case of severe overvoltages, a permanent short circuit occurs between the protective electrodes and the device has to be replaced.
Recurrent Surge Oscillation is done on the windings of large generators such as turbo alternators. The Recurrent Surge Oscillation Test (RSO) helps identify shorts in the winding.
Shorts in the winding occur as the insulation between turns deteriorates and fails. Shorts can cause localised heating and arcing which can further damage the alternators. Shorts can also become earth faults in course of time. Multi-turn shorts can also result in a drop in the voltage.
The Recurrent surge oscillation tests is done by sending voltages of low voltage and high frequency through the winding and checking the waveform at the other terminal. If the waveform has suffered any distortion, it may indicate an abnormality. The waveform can give information such as the location of the fault and its severity.
Some short circuits may not be obvious when the rotor is at rest. The conductors will come in contact with each other only during the running condition, due to the centrifugal force. To identify such faults, the rotor is made to rotate and the test is conducted.
The Half Wave Rectifier functions using a single diode. It rectifies only half of the sine wave. 
During the positive half cycle, the diode D1 is in forward bias and current flows to the load. In the negative half cycle, when the voltage is applied in the opposite direction, the diode is in reverse bias and no current flows.
The Half wave rectifier is a simple device which requires only one diode to be put in series with the load.
The half wave rectifier has a low power output.
Besides, the ripple content of the rectified DC supply is very high. This can damage the loads.
It has very few applications and is only used in emergencies as a temporary measure.
This Full Wave rectifier has only two diodes. Each diode conducts during one half cycle. In the first half cycle, diode D1 is forward bias and the current flows into the load and returns through the centre tap of the transformer.
During the negative half cycle, diode D2 is in conduction. The current flows through the load in the same direction and returns through the centre tap. Thus the current is in the same direction through the load.
This means of rectifier has generally been replaced by the bridge rectifier as the centre tap is not always available.
Controlled Rectifiers are rectifiers which have thyristors in place of a diode. A thyristor is a three terminal device which can be switched on by applying a suitable gate voltage. 
In a Controlled Rectifier, generally two of the diodes are replaced with a thyristor. The thyristor enables the enables switching on the output of the rectifier at the desired time. This allows the output voltage and current to be controlled.
A rectifier with two thyristors is called a half controlled rectifier while a rectifier where all the diodes have been replaced with thyristors is called a fully controlled rectifier.
Controlled Rectifiers are also known as converters.
A Bridge Rectifier is a very popular and widely used circuit. The Rectifier converts an AC supply into a DC supply. The circuit requires only four diodes.
The four diodes operate two at a time. That is, during the positive half cycle, diodes D1 and D4 are in forward bias and conduct. Diodes D2 and D3 are in reverse bias. 
In the negative half cycle of the AC supply, diodes D2 and D3 are in conduction while D1 and D4 are in reverse bias.
Thus the current from the rectifier flows in only one direction.
Bridge rectifiers are used in Alternators for excitation of the field. They are also used in welding machines for DC welding and in battery Chargers
Bridge Rectifiers are also used in measurement circuits to measure the amplitude of an alternating signal.
Controlled rectifiers contain thyristors instead of diodes. This enables control of the output supply.
The Class B Chopper is typically used in applications which require transfer of power from the load to the source. An example would be regenerative braking in trains, where the power from the driving motor is sent to the power mains. This is also known as inverting operation. 
In the Class B chopper, the output voltage is positive while the output current is negative.
In a class B chopper, a diode, in reverse bias, blocks power from the source to the load. The chopper is connected parallel to the load and the source. The load voltage is the back-emf of the winding of a DC motor. When the chopper is in the ON condition, the current due to the back-emf flows through the inductance and the resistance through the chopper. The diode does not conduct as the voltage across the chopper is zero as the chopper is 'ON'. No Current flows into the source.
When the chopper is switched OFF, the voltage across the chopper increases and this biases the diode in the forward direction. The diode conducts and the power reaches the source. The source may be a battery or any other power source.
There are wide range of choppers which are used for different applications. These circuits differ in the voltage level, method of functioning and the output waveform.
Choppers can be classified into the following types
Step Up or Step Down Choppers
Step up Choppers, as the name suggests, step up the voltage. These choppers are used when the voltage has to increased to a higher level.
AC and DC Choppers
Choppers can be classified into AC and DC choppers depending on the supply
Circuit Operation
On the basis of Circuit Operation, Choppers can be classified into
On the Basis of Commutation
Depending on the Direction of Current
Class A
Class B
Class C
Class D and
Class E
In recent times, Choppers are usually classified based on their application such as switched mode power supplies, Class D Electronic Amplfiers, etc.
A Chopper is an electronic circuit which controls or reduces a dc supply. Their function can be compared to an ac transformer. In an AC transformer, voltage is controlled by changing the turns ratio of the transformer. In a chopper, voltage is varied by connecting and disconnecting the load from the source many times in a second.
The chopper is essentially a switching circuit which switches off and on many times. The output of a chopper is a square wave form while the input is a unidirectional dc waveform.
Choppers can be used in motor speed controls. They are increasingly being used in electric automobile technology.
Choppers are used widely in Electronics in circuits in solar power conversion, speed control of motors in the industry. They are used to reduce DC voltage to different levels in machines and other electronic equipments
Choppers have high efficiency and can be designed to have very fine control.
Electrical conduction in materials occurs due to the free electrons which drift about the atomic lattice. In an atom, the electrons in the outer most orbit are called the valence electrons. If the electrons have sufficient energy , they can break free of the atom and flow through the lattice when a voltage is applied.
If the energy levels are graphically represented, we will get a band diagram.
In the Band Diagram, there is the box representing the Conduction band and the box representing the valence band.
Valence Band
The Valence band is the range of energy levels of the electrons in the outermost orbit of the atom.
Conduction Band
The conduction band is the range of energy levels all electrons which are involved in conduction.
In conductors, the valence and the conduction bands overlap. In Insulators, the valence and conduction bands are far apart.
In semiconductors, the distance between the valance and the conduction bands are small. When external energy in the form of heat or light is applied to the semiconductors, the electrons get excited and jump from the valence to the conduction band.
The difference between the valence and the conduction band is called the energy gap.
Germanium is used in specific applications such as communication, spectroscopy, etc. They have largely been replaced with silicon. Germanium diodes are more expensive compared to silicon.
Germanium diodes have a lower forward bias voltage compared to silicon 0.15 volts. This enables the use of the Germanium diode at low voltages where silicon cannot be used.
Germanium is also used in photoelectronics application. Germanium diodes have a smaller band gap 0.66 eV. This means that the electrons can be excited even by near-infrared radiation.
Germanium is used in solar cells to capture the energy in near-infrared regions of the light spectrum. Germanium based sensors are used spectroscopy to detect light radiation at low frequencies.
Silicon diodes are diodes in which the P and N materials are made of silicon. Silicon Diode have a a forward bias voltage of 0.7 volts. That is, the diode conducts when the voltage across the it in the forward bias is 0.7 volts or greater.
They are the most widely used diodes in the industry. Other diodes such as Germanium diodes are used at voltages below 0.7 volts.
The diode can withstand a voltage of 50V or more in the reverse direction. This is known as the peak inverse Voltage.
Silicon is the most popular and widely used of the semiconductors. There are many factors which have made silicon the material of choice in the world of electronics.
Some of the advantages are
When a P type material and a N type material are brought in contact with each other, some of the holes in the P material migrate to the N region and combine with electrons. Similarly, some of the electrons of N material migrate to the P region and combine with holes.
Thus, at the point of contact of the P and N materials, a layer is formed which has no majority charge carriers such as holes or electrons. This region is called the depletion region as the region has been depleted of its charge carriers.
The depletion region behaves almost like an insulator. When a voltage exceeding the barrier potential is applied across the PN junction, current starts to flow.
Barrier Potential in a PN junction refers to the potential required to overcome the barrier at the PN junction.
When a P material and N material are brought in contact in a junction, some of the electrons of the N material near the junction cross over to the P material. These electrons combine with the holes in the P material. Similarly, the some of the holes of the P material near the Junction cross over to the N material and combine with the electrons.
The region in the contact area is thus depleted of holes and electrons. This region is called the Depletion Layer. The majority charge carriers are absent in this region. This region almost becomes like an insulator. Thus, there is no conduction after the depletion layer is formed.
For current to flow through this layer, a specific voltage has to be exceeded. This is known as the barrier potential. When an external voltage greater than the barrier potential is applied, the PN junction conducts.
P type Materials
The P type material is obtained when a semiconductor is doped with a trivalent impurity such as Aluminium or Boron. P type material is a material which has holes as its majority carriers. Electrons are the minority Charge Carriers in P type materials. When a trivalent impurity is added to the crystal lattice of a semiconductor, there is a vacancy for every impurity atom added. This vacancy is called a hole.
N type Materials
N type materials are made when a semiconductor is doped with a pentavalent impurity. A pentavalent impurity is one whose atom has five electrons in its outermost orbit (valence electrons). Examples of pentavalent impurities are Phosphorous, Antimony, Bismuth. In an N type Material, electrons are the majority charge carriers while holes are the minority charge carriers.
When a semiconductor is doped with a pentavalent impurity for every impurity atom added, there is a free electron. These electrons are responsible for conduction.
When the PN junction is formed, there is movement of the charge carriers across the junction. The electrons move from the N material across the junction into the P material. The holes from the P material cross into the N junction.
This movement of charge carriers results in a current across the junction.
This current is known as diffusion current. This current occurs in the absence of potential.
Cable Sleeves are used to enclose a single wire or a group of wires. Cable sleeves are used to arrange a set of wires going through a panel or to an equipment like a motor. Cable sleeves are made of different materials from braided metals to rubber and even kevlar.
Sleeves serve to protect the wires and their insulation from sharp edges. They can protect wires from UV radiation, moisture, oil and temperature. 
In automobiles, special heat resistant sleeves are used to protect the wires from hot surfaces.
Teflon sleeves have great cut resistance. Nylon sleeves have great abrasion resistance.
Sleeves are available in two broad categories depending on the method of installation.
The first is the slit sleeve which is cut and the wires are inserted into the sleeve. The second is the wrap-around, side entry type of sleeve.
Heat Shrinkable Sleeves
Some sleeves are heat shrinkable. Heat shrinkable sleeves are made of a polymer which contracts when heat is applied. A stream of hot air from a blower is passed on the sleeve. This results in the sleeves shrinking and wrapping the wires.
Electrical Safety Mats are important safety equipment. Safety mats protect personnel from electric shock by providing an insulated surface to work on. If the worker comes in contact with a live conductor by mistake, he will not get an electric shock as his feet are insulated from the ground by the safety mat.
Safety mats come in different colours. They are usually made of rubber. The surface of the mats is ribbed to provide an anti-slip surface to workers.
Safety mats are also designed to resist aging and ozone.
Safety mats should also be age and fire resistant.
Safety mats come in different voltage ratings. They should also be resistant to acids and oils.
The following is the list of mats and their working voltages
| Class of Mats | Working Voltage | Colour |
| 0 | 1000 | Red |
| 1 | 7500 | White |
| 2 | 17000 | Yellow |
| 3 | 26500 | Green |
| 4 | 36000 | Orange |
The most common class of safety mats is the type 0 which is rated for a working voltage of 1000 V.
A synchronous phase modifier is a synchronous motor which is not connected to any load. The motor can be made to behave like an inductor or a capacitor by decreasing or increasing the excitation.
Synchronous Phase modifiers are used to regulate the voltage in transmission lines.
| Series Capacitors | Shunt Capacitors |
| Used to reduce the line reactance | Has no impact on the line reactance |
| Voltage rise only occurs across terminals. | Can be used to raise the line voltage |
| No effect on system stability | Improves system stability |
| Does not affect the power factor | Used to improve power factor |
The ratio of capacitive reactance to the inductive reactance in a transmission line is called the percentage compensation of the Transmission Line. The inductive reactance is mainly caused by the nature of the load. The capacitive reactance is caused by the line capacitances and by series capacitors, if any.
Submarine Power Cables are used to carry power underwater. They are used to connect small islands with the mainland. Sometimes, the route through the water is shorter than through land. Submarine Cables are used for both AC as well as DC transmission.
AC is used up to 80 km while DC is used for long distance transmission. Submarine cables are mostly gas filled cables. The cable laying is done by special ships. XLPE cables fpr submarine transmission are also available.
AC cables can be laid as three separate cables or as a single 3 phase cable.
Offshore wind farms are connected to the mainland by submarine cables.
Damage to these cables by shipping is a matter of concern. The routes which contain submarine cables are specially marked in nautical maps.
Gas filled cables are used in many applications. In these cables, the insulation is filled with gas, usually nitrogen. The inert gas fills up the voids which may form in the insulation. There are low pressure and high pressure variants in this type of cable.
The gas is filled in the insulation and is enclosed by means of a sheath. Since Nitrogen is easily available, any losses can be easily replaced during installation.
However, the gas has a low dielectric strength. It cannot be used at very high voltages. Gas filled cables can be used up to 275 kV.
Oil Filled cables have almost replaced Gas filled cables in recent times. However, there are situations where oil filled cables cannot be used such as undersea applications and in hilly terrain.
High Voltage Dielectrics are used for insulation of cables at high voltages. These dielectrics are subjected to very high stresses and temperatures. They also have very demanding reliability requirements.
Some of the common properties of High Voltage Dielectrics are
Impregnated Cables are cables which have insulation which is impregnated with an insulating material. For instance Paper insulation can be impregnated with oil or synthetic fluid with good dielectric properties. The impregnated insulation is enclosed in a lead sheath to prevent the ingress of water.
Some cables have insulation which requires the insulating compound to be maintained at a particular pressure. This may require the installation of pumps at periodic locations.
Oil impregnated cables have special channels for the flow of oil. The oil which is pressurized fills up any void which may develop in the insulation.
Modern Impregnated Cables do not require pumps or any pressurizing devices.
Oil impregnated cables can have their own cooling systems if used at voltages above 525 kV
Dust in electrical Equipment can affect the operation of the equipment. Dust can result in tracking which causes current to flow over the insulation eventually leading to failure. Dust on the surfaces of conductive parts such as breaker poles or relay contacts can affect the conductivity and cause heating and voltage drops
Dust when combined with oil or water in the atmosphere can form acids which can corrode and weaken the insulation.
A layer of dust on the surface of an equipment can affect the heat transfer and prevent adequate cooling.
Hence, equipment which are to be installed in dust prone environments should be adequately dust proof. Panels should have filters which prevent the entry of dust.