What is the difference between earth and neutral?

Neutral is a return current path for equipments and earthing is protection for humans. Earth is a support for neutral. If neutral is not present, the machine we are using will get in full phase and we will get a shock. So earthing is done to avoid such shocks. 

What is the difference between an Insulator and a Dielectric?

Dielectrics are used to store the electric charges, while insulators are used to block the flow of electric charges. All dielectrics are insulators (they don't allow the flow of electric charges through them) but all insulators aren't dielectric because they can't store charges unlike dielectrics.

Is Cu loss affected by power factor? Why?

Yes, Cu loss varies inversely with power factor

Cu loss depends on current in the primary and secondary windings. It is well-known that current required is higher when power factor is lower.

Q.Why AC systems are preferred over DC systems?

A.Due to following reasons, AC systems are preferred over DC systems:

a. It is easy to maintain and change the voltage of AC electricity for transmission and distribution.

b. Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission

c. From power stations, AC is produced so it is better to use AC then DC instead of converting it.

d. When a large fault occurs in a network, it is easier to interrupt in an AC system, as the sine wave current will naturally tend to zero at some point making the current easier to interrupt.

Q.Why star delta starter is preferred with induction motor?

A.Star delta starter is preferred with induction motor due to following reasons:

• Starting current is reduced 3-4 times of the direct current due to which voltage drops and hence it causes less losses.

• Star delta starter circuit comes in circuit first during starting of motor, which reduces voltage 3 times, that is why current also reduces up to 3 times and hence less motor burning is caused.

• In addition, starting torque is increased and it prevents the damage of motor winding.

Q.What is Corkscrew Rule?
A.As current flows along a wire, the magnetic field rotates in the direction of a corkscrew

Q:What is the main use of rotary phase     converter ? 

A:Rotary phase converter will be converting single phase power into true balanced 3 phase power,so it is often called as single phase to three phase converter .Often the advantages of 3 phase motors, and other 3 phase equipment, make it worthwhile to convert single phase to 3 phase so that small and large consumers need not want to pay for the extra cost of a 3 phase service but may still wish to use 3 phase equipment.

Q:What is the difference between synchronous generator & asynchronous generator?

A:In simple, synchronous generator supply's both active and reactive power but asynchronous generator(induction generator) supply's only active power and observe reactive power for magnetizing.This type of generators are used in windmills.

Q:Why syn. generators are used for the production of electricity?

A:synchronous machines have capability to work on different power factor (or say different imaginary power varying the field emf. Hence syn. generators are used for the production of electricity.

Q:How do you select a cable size (Cu & Al) for a particular load?

A:At first calculate the electrical current of the load, after that derate the electrical current considering derating factor(depending on site condition and laying of cable) after choose the cable size from cablecatalog considering derating electrical current.After that measure the length of cable required from supply point of load to load poin. Calculate the voltage drop which will max 3% (resistance and reactance of cable found from cable catalog of selecting cable) if voltage drop>3% then choose next higher size of cable.

Q.State the difference between generator and alternator.

A.Generator and alternator are two devices, which converts mechanical energy into electrical energy. Both have the same principle of electromagnetic induction, the only difference is that their construction. Generator persists stationary magnetic field and rotating conductor which rolls on the armature with slip rings and brushes riding against each other, hence it converts the induced emf into dc current for external load whereas an alternator has a stationary armature and rotating magnetic field for high voltages but for low voltage output rotating armature and stationary magnetic field is used.

Q.What is Scott- connected transformer?

A.A Scott-T transformer (also called a Scott connection) is a type of circuit used to derive two-phase electric power (2-φ, 90-degree phase rotation) from a three-phase (3-φ, 120-degree phase rotation) source, or vice-versa. The Scott connection evenly distributes a balanced load between the phases of the source.

Q.What is Phase Swinging?

A.When a synchronous motor is used for driving a varying load, then a condition known as phase swinging or hunting may occur. Hunting may also be caused if supply frequency is pulsating (as in the case of generators driven by reciprocating internal combustion engines).

Q.Is corona more in AC or DC?

A.Corona Loss p = .00241[(f+25)/$]*[root of (r/d)]*square of[Vp-Vo]

f= supply frequency 

$= air density correction factor

Vp = operating voltage

Vo= critical disprutive voltage

r= radius of conductor

d= distance of separation for fine weather

Now for DC f=0, there is a certain power loss by corona but less than AC corona loss.

What are the advantages and disadvantages of Compact Fluorescent Lamps?

The advantages are

· CFLs are up to four times more efficient than incandescent bulbs

· While initially they may cost more, CFLs are less expensive in the long run as they last much longer than incandescent bulbs

· CFLs are highly versatile and can be used in any setting that you would normally use incandescent bulbs

The disadvantages are

· CFLs when used outdoors need to be covered and protected from the elements. They are also sensitive to temperature

· While CFLs are supposed to last about 10,000 hours, turning them on and off too frequently can reduce that lifetime substantially

· CFLs are not suitable for focused or spot lights or where narrow beams of light are required. They are meant only for ambient light.

What is a meant by a Phase-Splitter?

It is a device consisting of a number of capacitors so connected in the motor circuit that it produces, from a single input wave, three output waves which differ in phase from each other.

Q.What is a synchronous capacitor?
A.An over excited synchronous motor is called synchronous capacitor, because, like a capacitor, it takes a leading current

Q:How tube light circuit is connected and how it works?

A:A choke is a connected in one end of the tube light and a starter is in series with the circuit. When supply is provided the starter will intrupt the supply intermittant cycle of AC. Due to the sudden change of supply the chock will generate around 1000volts . This volt will capable of to break the electrons inside the tube to make elctrone flow. once the current passess through the tube the starter circuit will be out of part. now there is no change of supply causes choke voltage normalised and act as minimise the current.

Q:why link is provided in neutral of an ac circuit and fuse in phase of ac circuit?

A:Link is provided at a Neutral common point in the circuit from which various connection are taken for the individual control circuit and so it is given in a link form to withstand high Amps. But in the case of Fuse in the Phase of AC circuit it is designed such that the fuse rating is calculated for the particular circuit (i.e load) only.So if any malfunction happen the fuse connected in the particular control circuit alone will blow off.

Q.What is a variable frequency transformer?

A.A variable frequency transformer is used to transmit electricity between two asynchronous alternating current domains. A variablefrequency transformer is a doubly-fed electric machine resembling a vertical shaft hydroelectric generator with a three-phase wound rotor, connected by slip rings to one external ac power circuit. A direct-current torque motor is mounted on the same shaft. Changing the direction of torque applied to the shaft changes the direction of power flow; with no applied torque, the shaft rotates due to the difference in frequency between the networks connected to the rotor and stator.The variablefrequency transformer behaves as a continuously adjustable phase-shifting transformer. It allows control of the power flow between two networks .

Q:Why Delta Star Transformers are used for Lighting Loads?

A:For lighting loads, neutral conductor is must and hence the secondary must be star winding. and this lighting load is always unbalanced in all three phases. To minimize the current unbalance in the primary we use delta winding in the primary. So delta / star transformer is used for lighting loads.

Q: What is actually a zero watt bulb?

Answer: A zero-watt bulb is a lightbulb that uses little power. Contrary to the name, these bulbs are not in fact zero watts. The reason they are colloquially called "zero watt" bulbs is because when they were first made, they only had a power consumption rate of 15W but testing equipment at the time was unable to detect such low wattage causing people to think they didn't use any power. Todays "zero watt" bulbs re as little as 10W.

Q.What is the difference between a capacitor and a condensor?
A.There is no difference with the exception or semantics and argument. Tesla use to call a capacitor a condenser we now call a condenser a capacitor. Schematics symbol for both are the same!
Main diff. b/w Condensers and capacitors are i. Condensers are rotating while capacitors are static ii.Smooth flow in KVAR can be obtained through condensers while it cannot be obtained through switching capacitor banks.

Q.What is reactive power? Is it necessary for power system operation?

A.Reactive power is the virtual oscillating power in the power system that enables active power to do the work in the system.So it is necessary for the power system.

Reactive power is one which is useful for internal activation of system. if reactive power is zero the system o/p is zero.

Question:When voltage increases then current also increases then what is the need of over voltage relay and over current relay? Can we measure over voltage and over current by measuring current only? 

Answer:No.We can't sense the over voltage by just measuring the current only because the current increases not only for over voltages but also for under voltage(As most of the loads are non-linear in nature). So,the over voltage protection & over current protection are completely different. Over voltage relay meant for sensing over voltages & protect the system from insulation break down and firing. Over current relay meant for sensing any internal short circuit, over load condition ,earth fault thereby reducing the system failure & risk of fire. So, for a better protection of the system.It should have both over voltage & over current relay. 

Q.why do we need three phase power for heavy load?????

A.With a single phase, the voltage drops to 0 every half-cycle. Therefore, the amount of power you can get out of the line is not constant over time, it has a very large 120-hz ripple. With a large motor, this can cause vibration, and also means that larger wires are needed for the same power load. The same is true for so-called "2- phase" power, 2 voltages 180 degrees apart. They both cross zero at the same time, which is why this is normally also referred to as single- phase. It isn't any better than single phase. With 3-phase power, however, there is never a time when all the voltages go to 0. In fact, if you are extracting power from all 3 phases, (like in a motor) the power stays constant throughout the whole cycle. This gives a vibration-free drive (and also allows for simpler motor design because 3- phase power has an inherent "direction" which 2-phase or 1-phase power does not).

Q:Two bulbs of 100W and 40W respectively connected in series across a 230V supply which bulb will glow bright and why?

A:Since two bulbs are in series they will get equal amount of  electrical current but as the supply voltage is constant across the bulb(P=V^2/R).So the resistance of 40W bulb is greater and voltage across 40W is more (V=IR) so 40W bulb will glow brighter. 

Q:What are HRC fuses and where it is used?

A: HRC stand for "high rupturing capacity" fuse and it is used in distribution system for electrical transformers.

Q.If one lamp connects between two phases it will glow or not?

A.If the voltage between the two phase is equal to the lamp voltage then the lamp will glow. When the voltage difference is big it will damage the lamp and when the difference is smaller the lamp will glow depending on the type of lamp

Q.What is universal motor?

A.The universal motor is so named because it is a type of electric motor that can operate on both AC and DC power. It is a commutated series-wound motor where the stator's field coils are connected in series with the rotor windings through a commutator. It is often referred to as an AC series motor. The universal motor is very similar to a DC series motor in construction, but is modified slightly to allow the motor to operate properly on AC power. This type of electric motor can operate well on AC because the current in both the field coils and the armature (and the resultant magnetic fields) will alternate (reverse polarity) synchronously with the supply. Hence the resulting mechanical force will occur in a consistent direction of rotation, independent of the direction of applied voltage, but determined by the commutator and polarity of the field coils.Universal motors have high starting torque, can run at high speed, and are lightweight and compact. They are commonly used in portable power tools and equipment, as well as many house hold appliances.

Q.What is traction motor?

Traction motor refers to an electric motor providing the primary rotational torque to a machine, usually for conversion into linear motion (traction).

Q:what happen if we give 220 volts dc supply to d bulb r tube light?

A:Bulbs [devices] for AC are designed to operate such that it offers high impedance to AC supply. Normally they have low resistance. When DC supply is applied, due to low resistance, the current through lamp would be so high that it may damage the bulb element.

Q. What is Vernier motor?

A.Vernier motor is a PM motor and has a high torque at low speed. It operates on the principles of "magnetic gearing effect".The vernier motor is mainly used where require low speed and high torque.

Q:Why in a three pin plug the earth pin is thicker and longer than the other pins?

A:It depends upon R=rho l/a where area(a) is inversely proportional to resistance (R), so if (a) increases, R decreases & if R is less the leakage current will take low resistance path so the earth pin should be thicker. It is longer because the The First to make the connection and Last to disconnnect should be earth Pin. This assures Safety for the person who uses the electrical instrument.

Q: why, when birds sit on transmission lines or current wires doesn't get shock?

A:Its true that if birds touch the single one line (phase or neutral) they don't get electrical shock... if birds touch 2 lines than the circuit is closed and they get electrical shock.. so if a human touch single one line(phase) then he doesn't get shock if he is in the air (not touching - standing on the ground if he is standing on the ground then touching the line (phase) he will get a shock because the ground on what we standing is like line (ground bed - like neutral)। and in the most of electric lines the neutral is grounded... so that means that human who touch the line closes the circuit between phase and neutral.

Q:what is stepper motor.what is its uses?

A:Stepper motor is the electrical machine which act upon input pulse applied to it. it is one type of synchronous motor which runs in steps in either direction instead of running in complete cycle.so, in automation parts it is used.

Why Negative Feedback is Prefered in the Control System?

The role of Feedback in control system is to take the sampled output back to the input and compare output signal with input signal for error ( deviation from the desired result). 

Negative Feedback results in the better stability of the system and rejects any disturbance signals and is less sensitive to the parameter variations. Hence in control systems negative feedback is considered.

Qwhat is 2 phase motor?
A:A two phase motor is a motor with the the starting winding and the running winding have a phase split. e.g;ac servo motor.where the auxiliary winding and the control winding have a phase split of 90 degree.

Q:There are a Transformer and an induction machine. Those two have the same supply. For which device the load current will be maximum? And why? 

A:The motor has max load current compare to that of transformer bcoz the motor consumes real power.. and the transformer is only producing the working flux and its not consuming.. hence the load current in the transformer is because of core loss so it is minimum.

Q: what is the diff. btwn. electronic regulator and ordinary rheostat regulator for fans?

           A:The difference between the electronic and ordinary regulator is that in electronic reg. power losses are less i.e.for as we decrease the speed the electronic reg. give the power needed for that perticular speed but in case of ordinary rh type reg. the power wastage is same for every speed and no power is saved.In electronic regulator triac is employed for speed cntrl. by varying the firing angle speed is controlled but in rheostatic ctrl resistance is decreased by steps to achieve speed control.