EEE Interview Tips

Define the voltage regulation of the transformer. Why it is important?

noreply@blogger.com (Mrinal Kanti Roy) — Fri, 6 Nov 2020 22:52:00 +0600

Voltage Regulation:

The voltage regulation is defined as the change in the magnitude of receiving and sending voltage of the transformer. 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.

The voltage regulation is represented as:

Importance of Voltage Regulation:

The voltage regulation value provides the efficiency of the transformer & it is best to prefer a transformer with low voltage regulation.

Some Mnemonic phrases for remembering Color Codes of Resistor in Electronics.

noreply@blogger.com (Mrinal Kanti Roy) — Sat, 1 Apr 2017 00:14:00 +0600

Identifying Resistors:

The electronic color code is used to indicate the values or ratings of electronic components, usually for resistors, but also for capacitors, inductors, diodes and others. A separate code, the 25-pair color code, is used to identify wires in some telecommunications cables.

Most axial resistors use a pattern of colored stripes to indicate resistance. SMT ones follow a numerical pattern. Cases are usually brown, blue, or green, though other colors are occasionally found like dark red or dark gray.

Resistor Color Codeing:

Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Gray, White (Gold Silver).

Mnemonic phrases for remembering color codes of resistor:

There are many mnemonic phrases used to remember the order of the colors. They are, but are not limited to, and variations of:

Bad Boys Ravish Our Young Girls But Violet Gives Willingly.
Bad Beer Rots Our Young Guts, But Vodka Goes Well. Get Some Now!
B.B. ROY of Great Britain had a Very Good Wife.
Buffalo Bill Roamed Over Yellow Grass Because Vistas Grand Were God's Sanctuary.
Bully Brown Ran Over a Yodeling Goat, Because Violet's Granny Was Gone Snorkeling.
Buy Better Resistance Or Your Grid Bias May Go Wrong.
Bill Brown Realized Only Yesterday Good Boys Value Good Work.
Better Be Ready Or Your Great Big Plan Goes Wrong.
Better Be Ready Or Your Great Big Venture Goes West.
Black Bananas Really Offend Your Girlfriend But Violets Get Welcomed.
Black Birds Run Over Your Biting Visible Gray Worms.
Big Boys Race Our Young Girls But Violet Generally Wins.
Black Boys Rape Our Young Girls Behind Victory Garden Walls.
Black Boys Rape Our Young Girls But Virgins Go Without.

Explanation:

To remember the color bands on resistors in order of increasing magnitude.

Numerically the value (0-9) of a resistor via the color-coded bands: Black (0), Brown (1), Red (2), Orange (3), Yellow (4), Green (5), Blue (6), Violet (purple, 7), Gray (8), and White (9).
Also, note that the red through violet are the colors of the rainbow (in order). Although the ROY G. BIV mnemonic for rainbow colors includes indigo between blue and violet.

Figure 1: A diagram of a resistor, with four color bands A, B, C, D from left to right.

Figure 2: A diagram of a 2.7 Mega Ω color coded resistor.

To distinguish left from right there is a gap between the C and D bands.

Band A is the first significant figure of component value (left side)
Band B is the second significant figure (some precision resistors have a third significant figure, and thus five bands).
Band C is the decimal multiplier
Band D if present, indicates tolerance of value in percent (no band means 20%)

For example, a resistor with bands of yellow, violet, red, and gold has first digit 4, second digit 7 (violet), followed by 2 (red) zeros: 4,700 ohms. Gold signifies that the tolerance is ±5%, so the real resistance could lie anywhere between 4,465 and 4,935 ohms.

Figure 3: 4.7 Kilo Ω resistor with ±5% tolerance.

All coded components have at least two value bands and a multiplier; other bands are optional.

What is a Resistor? What are the Types of Resistors? What are the Applications of Resistor?

noreply@blogger.com (Mrinal Kanti Roy) — Fri, 31 Mar 2017 23:17:00 +0600

What is a Resistor?

A resistor is a passive two-terminal electrical or electronic component that resists an electric current by producing a voltage drop between its terminals in accordance with Ohm's law. The electrical resistance is equal to the voltage drop across the resistor divided by the current through the resistor.

Figure 1: A typical axial-lead resistor.

Figure 2: Two common schematic symbols of resistor.

In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses. High-power resistors that can dissipate many watts of electrical power as heat may be used as part of motor controls, in power distribution systems, or as test loads for generators. Fixed resistors have resistances that only change slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or as sensing devices for heat, light, humidity, force, or chemical activity.

Theory of Operation:

Ohm's law: The behavior of an ideal resistor is dictated by the relationship specified by Ohm's law:

V = I/R

Ohm's law states that the voltage (V) across a resistor is proportional to the current (I), where the constant of proportionality is the resistance (R). For example, if a 300 ohm resistor is attached across the terminals of a 12 volt battery, then a current of 12 / 300 = 0.04 amperes flows through that resistor.

Practical resistors also have some inductance and capacitance which affect the relation between voltage and current in alternating current circuits.

The ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm. An ohm is equivalent to a volt per ampere. Since resistors are specified and manufactured over a very large range of values, the derived units of milliohm (1 mΩ = 10^-3 Ω), kilohm (1 kΩ = 10³ Ω), and megohm (1 MΩ = 10⁶ Ω) are also in common usage.

Figure 3: A few types of resistors.

Types of Resistors:

1. Linear resistors.

i. Fixed resistors

a) Led arrangement

b) Carbon composition

c) Carbon Pile

d) Carbon film

e) Printed carbon resistor

f) Thick and thin film

g) Metal film

h) Metal oxide film

i) Wire wound

j) Foil resistor

k) Ammeter shunt

l) Grid resistor

m) Special verities

ii. Variable resistor

a) Adjustable resistor

b) Potentiometers

c) Resistance and decade boxes

d) Special devices.

2. Non-linear resistors.

Applications of Resistors:

In general, a resistor is used to create a known voltage-to-current ratio in an electric circuit. If the current in a circuit is known, then a resistor can be used to create a known potential difference proportional to that current. Conversely, if the potential difference between two points in a circuit is known, a resistor can be used to create a known current proportional to that difference.
Current-limiting. By placing a resistor in series with another component, such as a light-emitting diode, the current through that component is reduced to a known safe value.
A series resistor can be used for speed regulation of DC motors, such as used on locomotives and train sets.
An attenuator is a network of two or more resistors (a voltage divider) used to reduce the voltage of a signal.
A line terminator is a resistor at the end of a transmission line or daisy chain bus (such as in SCSI), designed to match impedance and hence minimize reflections of the signal.
All resistors dissipate heat. This is the principle behind electric heaters.

EEE Interview Tips Awarded Top 60 Electronics Websites & Blogs For Electrical & Electronic Engineers.

noreply@blogger.com (Mrinal Kanti Roy) — Fri, 31 Mar 2017 18:29:00 +0600

Recently, a website named Feedspot.com was published a survey regarding 'The best Electronics Blog on the Planet', which ranks 60 blogs from thousands of top Electronics blogs in their index using search and social metrics. According to the survey, EEE Interview Tips blog comes in at the 51^thspot out of 60 blogs.

The blogs are ranked based on following criteria:

Google reputation and Google search ranking
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Feedspot’s editorial team and expert review.

Thank you all visitors for visiting my blog. Keep visiting EEE Interview Tips.

Describe a Starter-Motor Circuit.

noreply@blogger.com (Mrinal Kanti Roy) — Fri, 31 Mar 2017 13:02:00 +0600

Figure 1: Typical Starter-Motor Circuit.

A Starter-Motor Circuit:

Figure 1 shows a very simple diagram of an engine starter-motor circuit. If one day you turn on the ignition switch, push the start button, and nothing happens, this is the circuit diagram you will need. A complete engine wiring diagram would probably contain the same information, but it would also contain all of the meters, idiot lights, and alternator wiring, adding considerable visual confusion.

For the starter-motor circuit all you need to see are the:

Battery switch
Fuse between battery switch common terminal and engine panel
On/Off switch
Momentary start switch
Wire from starting switch to solenoid
Heavy positive cable from battery-select common terminal to solenoid
Heavy negative cable from battery negative terminal to engine negative terminal.

If the engine won’t turn over, the problem probably lies somewhere in this diagram.

Source: Boatowner's Illustrated Electrical Handbook

Wiring Symbols

noreply@blogger.com (Mrinal Kanti Roy) — Fri, 31 Mar 2017 12:47:00 +0600

The Discovery of Electricity Timeline.

noreply@blogger.com (Mrinal Kanti Roy) — Fri, 31 Mar 2017 12:26:00 +0600

The Discovery of Electricity:

Schematic diagram of a copper–zinc voltaic pile.

v	Democritus (460?–370? BC) proposes an “atomic theory” wherein all matter is made up of indivisible particles, or atoms.
v	Charles de Coulomb (1736–1806) discovers that the force of attraction between electric charges is proportional to the product of the two charges and inversely proportional to the distance between them.
v	Luigi Galvani (1737–1798) discovers that two unlike metals immersed in blood cause the muscles of a frog’s legs to twitch.
v	Alessandro Volta (1745–1827) discovers that a current ﬂows between two connected unlike metals in a salt solution and, thus, invents the battery.
v	John Dalton (1766–1844) proposes the ﬁrst table of atomic weights of elements.
v	André Ampere (1775–1836) develops the theory of magnetic lines of force and quantiﬁes electric current for the ﬁrst time.
v	Hans Christian Ørsted (1777–1851) discovers a connection between electric current and magnetism and a way to measure electric current by the deﬂection of a magnet.
v	Georg Ohm (1787–1854) discovers the relationship (Ohm’s Law) between voltage, current, and resistance in a circuit.
v	Michael Faraday (1791–1867) analyzes the chemical reactions in batteries and deﬁnes the terms “electrode,” “anode,” “cathode,” and “electrolyte.”
v	James Clerk Maxwell (1831–1879) develops the mathematical equations relating electricity and magnetism.
v	Joseph Thomson (1856–1940) proves that electricity consists of electrons.

What is the difference between Electric Motor and Electric Generator?

noreply@blogger.com (Mrinal Kanti Roy) — Fri, 17 Mar 2017 13:28:00 +0600

Difference between Electric Motor and Electric Generator:

A generator converts mechanical energy to electrical energy, while motor converts mechanical energy to electrical energy.
In a generator, a shaft attached to the rotor is driven by a mechanical force and electric current is produced in the armature windings, while the shaft of a motor is driven by the magnetic forces developed between the armature and field; current has to be supplied to the armature winding.
Motors (generally a moving charge in a magnetic field) obey Fleming`s left-hand rule, while the generator obeys Fleming’s right-hand rule.

What are the Advantages of Integrated Circuits (ICs)?

noreply@blogger.com (Mrinal Kanti Roy) — Tue, 14 Mar 2017 22:37:00 +0600

Advantages of Integrated Circuits:

The major advantages of integrated circuits over those made by interconnecting discrete components are as follows:

Extremely small size – Thousands times smaller than discrete circuits. It is because of fabrication of various circuit elements in a single chip of semiconductor material.
Very small weight owing to miniaturised circuit.
Very low cost because of simultaneous production of hundreds of similar circuits on a small semiconductor wafer. Owing to mass production of an IC costs as much as an individual transistor.
More reliable because of elimination of soldered joints and need for fewer interconnections.
Lower power consumption because of their smaller size.
Easy replacement as it is more economical to replace them than to repair them.
Increased operating speed because of absence of parasitic capacitance effect.
Close matching of components and temperature coefficients because of bulk production in batches.
Improved functional performance as more complex circuits can be fabricated for achieving better characteristics.
Greater ability of operating at extreme temperatures.
Suitable for small signal operation because of no chance of stray electrical pickup as various components of an INC are located very close to each other on a silicon wafer.
No component project above the chip surface in an INC as all the components are formed within the chip.

What are the limitations of integrated circuits?

noreply@blogger.com (Mrinal Kanti Roy) — Tue, 14 Mar 2017 22:31:00 +0600

The integrated circuits have few limitations also, as listed below:

In an IC the various components are part of a small semi-conductor and the individual component or components cannot be removed, replaced, therefore, if any component in an IC fails, the whole IC has replaced by the new one.
Limited power rating as it is not possible to manufacture high power greater than 10 Watt) ICs.
Need of connecting inductors and transformers exterior to the conductor chip as it is not possible to fabricate inductors and transform on the semi-conductor chip surface.
Operations at low voltage as ICs function at fairly low voltage.
Quite delicate in handling as these cannot withstand rough handling or excessive heat.
Need of connecting capacitor exterior to the semi-conductor chip as it is neither convenient nor economical to fabricate capacitances exceeding 30pF. Therefore, for higher values of capacitance, discrete components, exterior to IC chip are connected.
High grade P-N-P assembly is not possible.
Low temperature coefficient is difficult to be achieved.
Difficult to fabricate an IC with low noise.
Large value of saturation resistance of transistors.
Voltage dependence of resistors and capacitors.
The diffusion processes and other related procedures used in the fabrication process are not good enough to permit a precise control of the parameter values for the circuit elements. However, control of the ratios is at a sufficiently acceptable level.

What is Schmitt trigger? How it works? Where is it used?

noreply@blogger.com (Mrinal Kanti Roy) — Tue, 14 Mar 2017 22:19:00 +0600

Schmitt trigger:

Schmitt trigger is an electronic circuit with positive feedback which holds the output level till the input signal to the comparator is higher than the threshold. It converts a sinusoidal or any analog signal to digital signal. It exhibits hysteresis by which the output transition from high to low and low to high will occur at different thresholds.

Invention:

The Schmitt trigger was invented by American scientist Otto H. Schmitt in 1934. By that time, Otto Schmitt was a student. In the year 1937, he published his invention in his doctoral. The name he gave was "thermionic trigger".

Schmitt Trigger Types:

The two different Schmitt trigger types are:

Non-inverting type, in which the input and output are both high / both low at the same time (no phase shift).
Inverting type, in which there is 180° phase shift between input and output.

Symbols:

There are basically two symbols for the Schmitt Trigger. The symbol is a triangle with an input and an output, just like the one used for the non-inverting buffers. Inside there is the hysteresis symbol. Depending on the type of Schmitt Trigger, inverting or non-inverting (standard), the hysteresis curve sign differs.

Figure 1: Logic Symbols of Schimitt Trigger.

Operations of Schimitt Trigger:

The Schmitt Trigger is a type of comparator with two different threshold voltage levels. Whenever the input voltage goes over the High Threshold Level, the output of the comparator is switched HIGH (if is a standard ST) or LOW (if is an inverting ST). The output will remain in this state, as long as the input voltage is above the second threshold level, the Low Threshold Level. When the input voltage goes below this level, the output of the Schmitt Trigger will switch.

The HIGH and LOW output voltages are actually the POSITIVE and NEGATIVE power supply voltages of the comparator. The comparator needs to have positive and negative power supply (like + and -) to operate as a Schmitt Trigger normally. The following drawing shows how a Schmitt Trigger would react to an AC voltage input:

Figure 2: Basic operation of a Schimitt Trigger.

The orange line is the AC input. The horizontal RED line indicates the High Threshold Level, while the BLUE horizontal line indicates the Low Threshold Level. The green line is the output of the Schmitt Trigger. When the input voltage level goes above the High Threshold Level, then the output of the ST goes High. When the input voltage level goes below the Low Threshold Level, then the output of the ST goes Low. This is the basic operation of a Schmitt Trigger.

Figure 3: The most simple Schmitt Trigger circuit is implemented with a comparator with a positive feedback.

Applications of Schimitt Trigger:

Squaring circuit (where a noisy signal requires squaring up).
Sine-to-Square comparator
Amplitude comparator
Level detector
Oscillator i.e. bistable multivibrator, relaxation oscillator etc.

Why should Dry-Type Transformers never be overloaded?

noreply@blogger.com (Mrinal Kanti Roy) — Sat, 11 Mar 2017 15:59:00 +0600

Overloading of a transformer results in excessive temperature. This excessive temperature causes overheating which will result in rapid deterioration of the insulation and cause complete failure of the transformer coils.

Can transformers be used in parallel?

noreply@blogger.com (Mrinal Kanti Roy) — Sat, 11 Mar 2017 15:52:00 +0600

Figure: Transformers in Parallel

Single phase transformers can be used in parallel only when their impedances and voltages are equal. If unequal voltages are used, a circulating current exists in the closed network between the two transformers, which will cause excess heating and result in a shorter life of the transformer. In addition, impedance values of each transformer must be within 7.5% of each other. For example: Transformer A has an impedance of 4%, transformer B which is to be parallel to A must have an impedance between the limits of 3.7% and 4.3%. When paralleling three phase transformers, the same precautions must be observed as listed above, plus the angular displacement and phasing between the two transformers must be identical.

Can Single Phase Transformers be used for Three Phase applications?

noreply@blogger.com (Mrinal Kanti Roy) — Sat, 11 Mar 2017 15:44:00 +0600

Yes. Three phase transformers are sometimes not readily available, whereas single phase transformers can generally be found in stock. Three single phase transformers can be used in delta connected primary and wye or delta connected secondary. They should never be connected wye primary to wye secondary, since this will result in unstable secondary voltage. The equivalent three phase capacity when properly connected of three single phase transformers is three times the nameplate rating of each single phase transformer.

For example: Three 10 kVA single phase transformers will accommodate a 30 kVA three phase load.

State Possible Troubles in a DC Motor with Reasons.

noreply@blogger.com (Mrinal Kanti Roy) — Sat, 11 Mar 2017 15:18:00 +0600

Several troubles may arise in a d.c. motor and a few of them are discussed below:

i) Failure to start: This may be due to-

Ground fault
Open or short-circuit fault
Wrong connections
Too low supply voltage
Frozen bearing ore
Excessive load.

ii) Sparking at brushes: This may be due to-

Troubles in brushes
Troubles in commutator
Troubles in armature or
Excessive load.

Brush troubles may arise due to insufficient contact surface, too short abrush, too little spring tension or wrong brush setting.
Commutator troubles may be due to dirt on the commutator, high mica, rough surface or eccentricity.
Armature troubles may be due to an open armature coil. An open armature coil will cause sparking each time the open coil passes the brush. The location of this open coil is noticeable by a burnt line between segments connecting the coil.

iii). Vibrations and pounding noises: These may be due to-

Worn bearings
Loose parts
Rotating parts hitting stationary parts
Armature unbalanced
Misalignment of machine
Loose coupling, etc.

iv) Overheating: The overheating of the motor may be due to-

Overloads
Sparking at the brushes
Short-circuited armature or field coils
Too frequent starts or reversals
Poor ventilation
Incorrect voltage.

What is an Autotransformer? Explain Autotransformer Operation. What are the Limitations, Advantages, Disadvantages and Applications of Autotransformer?

noreply@blogger.com (Mrinal Kanti Roy) — Sat, 11 Mar 2017 14:18:00 +0600

Autotransformer:

An autotransformer (sometimes called autostep down transformer) is an electrical transformer with only one winding. In an autotransformer, portions of the same winding act as both the primary and secondary sides of the transformer. The winding has at least three taps where electrical connections are made.

On load condition, a part of the load current is obtained directly from the supply and the remaining part is obtained by transformer action. An Auto transformer works as a voltage regulator.

Figure-1: Single-phase tapped autotransformer with an output voltage range of 40%–115% of input.

Operation:

An autotransformer has a single winding with two end terminals, and one or more terminals at intermediate tap points, or it is a transformer in which the primary and secondary coils have part of, or all of their turns in common. The primary voltage is applied across two of the terminals, and the secondary voltage taken from two terminals, almost always having one terminal in common with the primary voltage. The primary and secondary circuits therefore have a number of windings turns in common. Since the volts-per-turn is the same in both windings, each develops a voltage in proportion to its number of turns. In an autotransformer part of the current flows directly from the input to the output, and only part is transferred inductively, allowing a smaller, lighter, cheaper core to be used as well as requiring only a single winding. However the voltage and current ratio of autotransformers can be formulated the same as other two-winding transformers:

One end of the winding is usually connected in common to both the voltage source and the electrical load. The other end of the source and load are connected to taps along the winding. Different taps on the winding correspond to different voltages, measured from the common end. In a step-down transformer the source is usually connected across the entire winding while the load is connected by a tap across only a portion of the winding. In a step-up transformer, conversely, the load is attached across the full winding while the source is connected to a tap across a portion of the winding.

As in a two-winding transformer, the ratio of secondary to primary voltages is equal to the ratio of the number of turns of the winding they connect to. For example, connecting the load between the middle and bottom of the autotransformer will reduce the voltage by 50%. Depending on the application, that portion of the winding used solely in the higher-voltage (lower current) portion may be wound with wire of a smaller gauge, though the entire winding is directly connected.

If one of the center-taps is used for the ground, then the autotransformer can be used as a balun to convert a balanced line (connected to the two end taps) to an unbalanced line (the side with the ground).

Limitations:

An autotransformer does not provide electrical isolation between its windings as an ordinary transformer does; if the neutral side of the input is not at ground voltage, the neutral side of the output will not be either. A failure of the isolation of the windings of an autotransformer can result in full input voltage applied to the output. Also, a break in the part of the winding that is used as both primary and secondary will result in the transformer acting as an inductor in series with the load (which under light load conditions may result in near full input voltage being applied to the output). These are important safety considerations when deciding to use an autotransformer in a given application.

Because it requires both fewer windings and a smaller core, an autotransformer for power applications is typically lighter and less costly than a two-winding transformer, up to a voltage ratio of about 3:1; beyond that range, a two-winding transformer is usually more economical.

In three phase power transmission applications, autotransformers have the limitations of not suppressing harmonic currents and as acting as another source of ground fault currents. A large three-phase autotransformer may have a "buried" delta winding, not connected to the outside of the tank, to absorb some harmonic currents.

In practice, losses mean that both standard transformers and autotransformers are not perfectly reversible; one designed for stepping down a voltage will deliver slightly less voltage than required if it is used to step up. The difference is usually slight enough to allow reversal where the actual voltage level is not critical.

Like multiple-winding transformers, autotransformers use time-varying magnetic fields to transfer power. They require alternating currents to operate properly and will not function on direct current.

Advantages:

An autotransformer requires less Cu than a two-winding transformer of similar rating.
An autotransformer operates at a higher efficiency than a two-winding transformer of similar rating.
An autotransformer has better voltage regulation than a two-winding transformer of the same rating.
An autotransformer has smaller size than a two-winding transformer of the same rating.
An autotransformer requires smaller exciting current than a two-winding transformer of the same rating.

It may be noted that these advantages of the autotransformer decrease as the ratio of transformation increases. Therefore, an autotransformer has marked advantages only for relatively low values of transformation ratio (i.e. values approaching 1).

Disadvantages:

There is a direct connection between the primary and secondary. Therefore, the output is no longer d.c. isolated from the input.
An autotransformer is not safe for stepping down a high voltage to a low voltage. As an illustration, Figure-2 shows 11000/230 V step-down autotransformer. If an open circuit develops in the common portion 2-3 of the winding, then full-primary voltage (i.e., 11000 V in this case) will appear across the load. In such a case, any one coming in contact with the secondary is subjected to high voltage. This could be dangerous to both the persons and equipment. For this reason, autotransformers are prohibited for general use.
The short-circuit current is much larger than for the two-winding transformer of the same rating. It can be seen from Figure-2 that a short-circuited secondary causes part of the primary also to be short circuited. This reduces the effective resistance and reactance.

Figure-2: 11000/230 V step-down autotransformer.

Applications of Autotransformers:

(i) Power transmission and distribution

Autotransformers are frequently used in power applications to interconnect systems operating at different voltage classes, for example 132 kV to 66 kV for transmission. Another application in industry is to adapt machinery built (for example) for 480 V supplies to operate on a 600 V supply. They are also often used for providing conversions between the two common domestic mains voltage bands in the world (100 V—130 V and 200 V—250 V). The links between the UK 400 kV and 275 kV 'Super Grid' networks are normally three phase autotransformers with taps at the common neutral end.

On long rural power distribution lines, special autotransformers with automatic tap-changing equipment are inserted as voltage regulators, so that customers at the far end of the line receive the same average voltage as those closer to the source. The variable ratio of the autotransformer compensates for the voltage drop along the line.

A special form of autotransformer called a zig zag is used to provide grounding on three-phase systems that otherwise have no connection to ground. A zig-zag transformer provides a path for current that is common to all three phases (so-called zero sequence current).

(ii) Audio system

In audio applications, tapped autotransformers are used to adapt speakers to constant-voltage audio distribution systems, and for impedance matching such as between a low-impedance microphone and a high-impedance amplifier input.

(iii) Railways

In UK railway applications, it is common to power the trains at 25 kV AC. To increase the distance between electricity supply Grid feeder points they can be arranged to supply a 25-0-25 kV supply with the third wire (opposite phase) out of reach of the train's overhead collector pantograph. The 0 V point of the supply is connected to the rail while one 25 kV point is connected to the overhead contact wire. At frequent (about 10 km) intervals, an autotransformer links the contact wire to rail and to the second (antiphase) supply conductor. This system increases usable transmission distance, reduces induced interference into external equipment and reduces cost. A variant is occasionally seen where the supply conductor is at a different voltage to the contact wire with the autotransformer ratio modified to suit.

(iv) Autotransformers are used for reducing the voltage supplied to a.c. motors during the starting period.

(v) Autotransformers are used as a voltage regulator.

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State the main effects of electric current? What are the applications of it?

noreply@blogger.com (Mrinal Kanti Roy) — Thu, 9 Mar 2017 18:58:00 +0600

The three main effects of an electric current are:

Magnetic effect
Chemical effect and
Heating effect.

Some practical applications of the effects of an electric current include:

Magnetic effect:

When electric current flows through a wire, it behaves like a magnet. This is called magnetic effect of electric current.

Figure 1: Electric bell - examples of magnetic effect.

Applications of magnetic effect:

Bells
Relays
Motors
Generators
Transformers
Telephones
Car-ignition and
Lifting magnets.

Chemical effect:

The passage of an electric current through a conducting liquid causes chemical reactions. The resulting effects are called chemical effects of electric current.

Figure 2: Battery - Example of chemecal effect.

Applications of chemical effect:

Primary and secondary cells and
Electroplating.

Heating effect:

When electric current flows through a wire, the wire gets heated. This is called the heating effect of electric current.

Figure 3: Irons - example of heating effects.

Applications of heating effect:

Cookers
Water heaters
Electric ﬁres
Irons
Furnaces
Kettles and
Soldering irons

What will happen when power factor is leading in the distribution of power?

noreply@blogger.com (Mrinal Kanti Roy) — Wed, 22 Feb 2017 00:57:00 +0600

If there is a high power factor, i.e if the power factor is close to one:

Losses in the form of heat will be reduced;
The cable becomes less bulky and easier to carry, and very cheap to afford, &
It also reduces over heating of transformers.

What are the functions of Protective Relays?

noreply@blogger.com (Mrinal Kanti Roy) — Wed, 22 Feb 2017 00:36:00 +0600


Figure: Protective Relaying System

Functions of Protective Relays:

To detect the faults. For Example: Short circuits.
To detect abnormal operating conditions. For example: Overloads, unbalances, low voltage or frequency.
To Initiate the operation of the circuit breaker to isolate the defective element from the rest of the system, thereby protecting the system from damages consequent to the fault.
To Control and supervision. For example: Automatic reclosing, bus transfer, synch-check.

List of Acronyms on Digital Electronics

noreply@blogger.com (Mrinal Kanti Roy) — Tue, 21 Feb 2017 13:11:00 +0600

ACRONYMS ON DIGITAL ELECTRONICS:

ACDS —advanced combat direction system.

ACRO (or CRO) —auxiliary cathode readout.

ALT key —alternate key.

A/N —alphanumeric.

APA —all points addressable.

AM —amplitude modulation.

ASCII —American Standard Code for Information Interchange.

ASTAB —automated status board.

ASW —antisubmarine warfare.

BC —broadcast.

BDU —basic display unit.

BER —bit error rate.

BITE —built-in test equipment.

BPS —bits per second.

C2P —Command and Control Processor.

CAG —central automated status board generator.

CCAEP —computer-controlled action entry panel.

CDB —central data buffer.

C-DITEG —common digital television graphics generator.

CDS —combat direction system.

CED —console electronic drawer.

CEG —central equipment group.

CGA —color graphics adapter.

CIGARS —console internally generated and refreshed symbols.

CIU —computer interface unit.

CONICS —circles and ellipses.

CP —clock pulse.

CPS —cycles per second.

CRO —TV monitor.

CRT —cathode-ray tube.

CTRL —control.

dB —decibels.

DCC —display control console.

DCI —direct computer interface.

DDEU —digital data entry unit.

DDI — (1) digital data indicator; (2) digital display indicator.

DITEG —digital television graphics generator.

DIV —diversity.

DLRP —Data Link Reference Point.

DMU —display multiplexer unit.

DRAC —digital radar azimuth converter.

DSC —digital scan converter.

DTS —data terminal set.

EDAC —error detection and correction.

EF word —external function word.

EGA —enhanced graphics adapter.

EMI/RFI —electromagnetic interference/radio frequency interference.

EPROM —erasable, programmable read-only memory.

ESC key —escape key.

FM —frequency modulation.

GUI —graphic user interface.

HF —high frequency.

HVPS —high voltage power supply.

HZ —hertz.

I/O —input/output.

IFF/SIF —identification, friend or foe/selective identification feature.

JTIDS —Joint Tactical Information Distribution System.

J-SERIES MESSAGE —The fixed format messages containing tactical data and commands that are used to exchange information over the JTIDS system.

JU —JTDS Unit.

LCD —liquid crystal display.

LCLV —liquid crystal light valve.

LED indicator —light-emitting diode indicator.

LINK-4A —The tactical digital data link for controller-to-controlled aircraft communications.

INK-11—The tactical digital data link for communications among a multiple number of units.

LINK-16 —The tactical digital data link for communications among a multiple number of units. This link is a secure, jam resistant, nodeless, high-capacitlinky that uses the JTIDS terminal.

LSB —Lower Side Band.

LSD —large screen display.

VPS —low voltage power supply.

MDA —Monochrome Display Adapter.

M-SERIES MESSAGES —Link-11 messages.

NCS —Net Control Station.

NCT —Net Cycle Time.

NICP —Network Interface Control Program.

N-SERIES MESSAGES —The “normalized” messages exchanged between the C2P computer and the ADCS computer.

NTDS —naval tactical data system.

ODR —output data request.

OJT —on-the-job training.

OSC —operations summary console.

PA/SG —pulse amplifier/symbol generator.

PC —personal computer.

PEFT —peripheral equipment functional test.

PIO —peripheral I/O

PIXEL —picture element.

PMS —planned maintenance system.

POFA —programmed operations functional appraisal.

PPI —plan position indicator.

PPLI —precise participant location and identification.

PPU —projection plotting unit.

PROM —programmable read-only memory.

PU —participating unit.

RAC —radar azimuth converter.

RAM —random access memory.

RC —Roll Call.

RDDS —radar data distribution switchboard.

RELNAV —relative navigation.

RF —radio frequency.

RGB —red, blue, green.

ROM —read-only memory.

ROM BIOS —ready-only memory basic input output system.

R-SERIES MESSAGES —Link-4A messages from the controlled aircraft that are sent in response to a control message

SAC —sonar azimuth converter.

SCG —sensor converter group.

SDDS —sensor data distribution switchboard.

SG —symbol generator.

SRAC —synchro radar azimuth converter.

SVGA —super videographics array.

TDM —tactical DITEG module.

TDS —tactical data system.

TFT —thin film transistor.

TMG —test message generator.

TN —track number.

TQ —track quality.

TSLO —third salvo lock out.

TTL —transistor-transistor logic.

TVC —television converter group.

TVSC —television scan converter.

UHF —ultra-high frequency.

USB —upper side band.

V/C word —velocity/category word.

VDT —video display terminal.

VFK panel —variable function key panel.

VGA —video graphics array.

V-SERIES MESSAGES —Link-4A control messages sent from the controlling station to the controlled aircraft.

VSS —video signals simulator.

XGA —extended graphics array.

What are the Characteristics, Power Ranges and Applications of different types of AC & DC Motors?

noreply@blogger.com (Mrinal Kanti Roy) — Mon, 20 Feb 2017 01:25:00 +0600

Characteristics, Power Range and Applications of some AC & DC Motors:

Motor Types	Characteristics	Power Range	Applications
DC Motors
DC shunt motor	Constant flux constant speed motor creates moderate torque at start.	Up to 200 hp	Machine tools like lathes, milling machines, grinding machines, centrifugal and reciprocating pumps, blowers, and fans.
DC series motor	Creates dangerously high torques at low speeds and should be always connected to the load; speed can be varied.	Up to 200 hp	Preferred for traction-type loads; employed in electric locomotives, conveyors, cranes, elevators, trolleys.
Permanent magnet DC motor	Higher efficiency, smaller size and simpler architecture; magnets can become demagnetized due to excessive use and overheating; produces lower torque.	Up to 10 hp	Power windows in automobiles, computer peripherals.
Separately excited motors	Can be controlled either by varying the voltage applied to the field winding or by varying the voltage applied to the armature; can produce high torques.	Up to 100 hp	Traction applications, to control the speed and torque of the motor by changing both armature voltage and stator current.
AC Motors
Three-phase induction motor (Squirrel cage rotor)	Moderate starting torque. Simple robust and maintenance free construction. Speed control by addition of rotor resistance is not possible.	1–5000 hp	Lathe machines, water pumps, grinders, printing machines, large refrigeration and air-conditioning units, small compressors.
Three-phase induction motor (Slip ring rotor)	Very high starting torque. Speed control by rotor resistance possible. High cost. Complicated construction which requires maintenance due to use of slip rings and brush.	1–5000 hp	Cranes, hoists, elevators, large compressors, industrial fans and blowers.
Three-phase synchronous motor	Constant speed irrespective of load, need of a starting device, need for two different excitation sources, variable frequency drives required for speed control.	Up to 50,000 hp	Motor generator sets, timing devices, centrifugal pumps, textile mills, cement mills, rolling mills.
Special Types of Motors
Single-phase induction motor	Simple and rugged construction.	Up to 5 hp	Fans, water pumps, and refrigerators.
Stepper motor	Smooth rotation, linear relation between electrical input and step rotation.	Sub-fractional horsepower rating	Used for precise position control in printers, floppy disk drives, robotics, process control, machine tools.
Brushless DC motor	No maintenance required, long life, high reliability and efficiency, low inertia and friction, low starting torque and high costs, ability to run at speeds as high as 50,000 rpm.	Up to 300 hp	Video recorders, computer peripherals, biomedical instruments, commercial ovens, film processing equipment, printing technology, and material handling equipment.
Universal motor	High-power-to-weight ratio, can produce high starting torque, can operate at very high speeds, suits wide variety of applications demanding different torques, shorter lifespan.	Used exclusively in fractional horsepower range	Small appliances like mixers, blenders, drills, saws, vacuum cleaners, sewing machines.

Read more: Discuss Different types of Motors & their Uses.

What is the most defining drawback of DC motors in general?

noreply@blogger.com (Mrinal Kanti Roy) — Mon, 20 Feb 2017 00:46:00 +0600

The biggest drawback in any DC motor is the use of the commutator and brush arrangement and the relative motion between them. As a result of this arrangement, they:

Require additional maintenance.
Have a shorter life span.
Possess a higher chance of sparking at the commutator and brush assembly.

Write a short note on AC-to-DC Converter.

noreply@blogger.com (Mrinal Kanti Roy) — Mon, 20 Feb 2017 00:40:00 +0600

Figure (a): AC–DC converter.

AC-to-DC Converter:

Transformers are commonly used in the process of converting AC to low-voltage direct current (DC) used by electronic devices such as computers. The standard voltage available in North America is 120 V AC, 60 Hz. Computers, however, operate on 5 and 12 V DC. In Figure (a), the transformer steps the AC down to a lower AC voltage. Thebridge rectifier, consisting of four diodes, converts this AC into a pulsating DC. This DCis smoothed out by capacitors. In some systems, a voltage regulator is used to remove all remaining fluctuations in the voltage, resulting in a steady DC voltage.

What are the Linear Variable Differential Transformers (LVDT)? Describe some applications of LVDT.

noreply@blogger.com (Mrinal Kanti Roy) — Mon, 20 Feb 2017 00:27:00 +0600

Linear Variable Differential Transformers (LVDT):

The linear variable differential transformer (LVDT) is a displacement sensor, which consists of a transformer with a single primary coil and two identical secondary coils connected in a seriesopposing manner. An LVDT is operated based on the mutual inductance concept.

Some applications of LVDT include the following:

Weighing systems: LVDTs can be used to measure spring deformation in weighing systems. The measured displacement can be used to calculate the applied force based on the characteristics of the spring.
Displacement sensing: An LVDT may be mounted externally in parallel with the cylinder, thus making the core assembly free to move with the piston rod, and allowing measurement of the displacement of a piston.
Bill detector in ATMs: Using an LVDT, ATMs can detect the number of bills inserted. When bills pass, a motion signal is transferred to the LVDT core element and then a changing output signal is generated. As the bills pass between the rollers, the voltages vary according to the thickness of the bills.

What are the Accelerometers? Describe some applications of Accelerometers.

noreply@blogger.com (Mrinal Kanti Roy) — Mon, 20 Feb 2017 00:20:00 +0600

Accelerometers:

Accelerometers (acceleration sensors) are used to measure acceleration, vibration, and mechanical shock. Acceleration is the time rate of change of velocity with respect to a reference system. Acceleration is a vector quantity, and is closely related to velocity and displacement.

Some applications of accelerometers include the following:

Sport watches: When runners wear sport watches, their acceleration and speed can be determined by watches that contain accelerometers.
Digital cameras: Some digital cameras contain accelerometers to determine the orientation of the photo being taken.
Rockets: Accelerometers are used in rocket design to maintain the rocket’s stability.
Vehicles: Accelerometers are used widely in vehicles to measure motion of the vehicle. A typical application is that accelerometers can help decide whether air bags should be deployed.