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

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.

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

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.

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

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.  

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The Discovery of Electricity Timeline.

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.

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

The three main effects of an electric current are:

1. Magnetic effect
2. Chemical effect and
3. 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

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What are the advantages of Three Phase Systems?

Three-phase systems offer several advantages:

1. For a given amount of power transmitted through a system, three-phase systems require conductors with a smaller cross section than single-phase systems. This means saving copper (or aluminum) and thus lowers original installation costs. In addition, the weight of cables in a three-phase system is lower, also lowering the installation costs. 
2. Two voltages (phase voltage/line voltage) are available. 
3. When compared to single-phase motors, three-phase motors, as loads, are very robust, relatively cheap, are generally smaller, have self-starting properties, provide a steadier output, and require little maintenance.

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Why are alternating voltages and currents expressed in r.m.s values and not average values?

An alternating current and voltage varies from instant to instant. The average value cannot be used to specify an alternating voltage or current because it is zero over one cycle. The obvious choice would be to define an alternating currents in terms of the average power which it may cause.

Consider an alternating current, i=i_msin

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What is the difference between Grounding and Earthing?

Difference between Grounding and Earthing:

There is no major difference between earthing and Grounding, both means “Connecting an electrical circuit or device to the Earth”. This serves various purposes like to drain away unwanted currents, to provide a reference voltage for circuits needing one, to lead lightning away from delicate equipment.

Even though there is a micro difference between grounding and earthing:

	Grounding	Earthing
Definition	Grounding means connecting the live part (it means the part which carries current under normal condition) to the earth for example neutral of power transformer.	Earthing means connecting the dead part (it means the part which does not carries current under normal condition) to the earth for example electrical equipment’s frames, enclosures, supports etc .
Difference in Terminology	Grounding is the commonly word used for earthing in the North American standards like IEEE, NEC, ANSI.	Earthing is used in European, Commonwealth countries and Britain standards like IS and IEC etc.
Purpose	Grounding refers the current carrying part of the system such as neutral (of the transformer or generator).	The purpose of earthing is to minimize the risk of receiving an electric shock if touching metal parts when a fault is present. Generally green wire is used for this as a nomenclature.
Balancing the Load Vs Safety	Ground is a source for unwanted currents and also as a return path for main current sometimes.	Earthing is done not for return path but only for protection of delicate equipments. It is an alternate low resistance path for current.
	When we take out the neutral for a three phase unbalanced connection and send it to ground, it is called grounding. Grounding is done to balance unbalanced load.	While earthing is used between the equipment and earth pit so as to avoid electrical shock and equipment damage.
Equipment Protection Vs Human Safety	Because of lightening, line surges or unintentional contact with other high voltage lines, dangerously high voltages can develop in the electrical distribution system wires. Grounding provides a safe, alternate path around the electrical system of your house thus minimizing damage from such occurrences. It is just a return path.	Earthing is to ensure safety or Protection of electrical equipment and Human by discharging the electrical energy to the earth. Earthing is a preventive measure.
Example	Grounding of neutral point of a star connected transformer.	Earthing of electrical equipment’s frames, enclosures, supports etc.

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Explain the terms real power, apparent power and reactive power for ac circuits and also the units used.

Explanation of terms real power, apparent power and reactive power for AC circuits:

Diagram: Power triangle relating apparent power to true power and reactive power.

Definition	Real Power	Apparent power	Reactive Power
	It is the product of voltage, current and power factor.	It is the product of voltage and current.	It is the product of voltage, current and sine of angle between the voltage and current.
Unit	Basic unit of real power is watt. i.e. Expressed as W or kW.	Basic unit of apparent power is volt- ampere. Expressed as VA (Volt Ampere) or KVA.	Has no other unit but expressed in VAR (Volt Ampere Reactive) or KVAR.
Formulas	Real power (P) = V I                                  (In DC circuits) P = VI Cosθ                         (in Single phase AC Circuits) P = √3 VL IL Cosθ         or P = 3 VPhIPh Cosθ (in Three Phase AC Circuits)	Apparent power (S) = V I Apparent Power = √ (True power2 + Reactive Power2) KVA = √KW2 + KVAR2	Reactive power (Q) = V I Sinθ Q =√ (Apparent Power2– True power2) VAR =√ (VA2 – P2) KVAR = √ (KVA2 – KW2)

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