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Q: what will happen when power factor is leading in distribution of power?

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

1.losses in form of heat will be reduced,

2.cable becomes less bulky and easy to carry, and very

cheap to afford, & 3. it also reduces over heating of tranformers. 

Q:whats the one main difference between UPS & inverter ? And electrical engineering & electronics engineering ?

A:uninterrupt power supply is mainly use for short time . means according to ups VA it gives backup. ups is also two types : on line and offline . online ups having high volt and amp for long time backup with with high dc voltage.but ups start with 12v dc with 7 amp. but inverter is startwith 12v,24,dc to 36v dc and 120amp to 180amp battery with long time backup. 

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:Advantages of vvvf drives over non vvvf drives for EOT cranes?

A:1.smooth start and stop.

2.no jerking of load.

3.exact posiitoning

4.better protection for motor.

5.high/low speed selection.

6.reliability of break shoe.

7.programmable break control.

8.easy circutry

9.reduction in controls

10.increases motor life 

Q:What is the significance of vector grouping in Power Transformers?

A:Every power transformer has a vector group listed by its manufacturer. Fundamentally it tells you the information about how the windings are connected (delta or wye) and the phace difference betweent the current and voltage. EG. DYN11 means Delta primary, Wye Secondry and the current is at 11 o clock reffered to the voltage. 

Q: which type of A.C motor is used in the fan (ceiling fan, exhaust fan, padestal fan, bracket fan etc) which are find in the houses ? 

A:Its Single Phase induction motor which mostly squirrel cage rotor and are capacitor start capacitor run. 

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 meant by armature reaction?

A: The effect of armature flu to main flux is called armature reaction. The armature flux may support main flux or opposes main flux. 

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:Which motor has high Starting Torque and Staring current DC motor, Induction motor or Synchronous motor?

A C Series motor has high starting torque. We can not start the Induction motor and Synchronous motors on load, but can not start the DC series motor without load. 

Q:what is ACSR cable and where we use it?

A:ACSR means Aluminium conductor steel reinforced, this conductor is used in transmission & distribution. 

Q:What is vaccum currcuit breaker.define with cause and where be use it Device?

A:A breaker is normally used to break a ciruit. while breaking the circuit, the contact terminals will be separated. At the time of seperation an air gap is formed in between the terminals. Due to existing current flow the air in the gap is ionised and results in the arc. various mediums are used to quench this arc in respective CB’s. but in VCB the medium is vaccum gas. since the air in the CB is having vaccum pressure the arc formation is interrupted. VCB’s can be used upto 11kv. 

Q:How tubelight circuit is connected and how it works?

A:A choke is 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: whats is MARX CIRCUIT?

A: It is used with generators for charging a number of capacitor in parallel and discharging them in series.It is used when voltage required for testing is higher than the available. 

Q:What is encoder, how it function?

A:An encoder is a device used to change a signal (such as a bitstream) or data into a code. The code may serve any of a number of purposes such as compressing information for transmission or storage, encrypting or adding redundancies to the input code, or translating from one code to another. This is usually done by means of a programmed algorithm,especially if any part is digital, while most analog encoding is done with analog circuitry. 

Q:What are the advantages of speed control using thyrister?

A:Advantages :1. Fast Switching Characterestics than Mosfet, BJT, IGBT 2. Low cost 3. Higher Accuract. 

Q:Why Human body feel Electric shock ?? n in an Electric train during running , We didnt feel any Shock ? why?

A:Unfortunately our body is a pretty good conductor of electricity, The golden rule is Current takes the lowest resistant path if you have insulation to our feet as the circuit is not complete (wearing rubber footwear which doing some repairs is advisable as our footwear is a high resistance path not much current flows through our body).The electric train is well insulated from its electrical system. 

Q:what is the principle of motor?

A:Whenever a current carying conductor is placed in an magnetic field it produce turning or twisting movemnt is called as torque. 

Q:what is electric traction?

A:Traction means using the electric power for traction system i.e. for railways,trams, trolleys etc. electric traction means use of the electricity for all these . now a days, magnetic traction is also used for bullet trains. basically dc motors areused for electric traction systems. 

Q:How can you start-up the 40w tube lite with 230v AC/DC without using any choke/Coil?

A:It’s possible by means of Electronic choke.otherwise it’s not possible to ionise the particles in tube. light, with normal voltage. 

Q:what is “pu” in electrical engg?

A u stands for per unit and this will be used in power system single line diagram there it is like a huge electrical circuit with no of componenets (generators, transformers, loads) with different ratings (in MVA and KV). To bring all the ratings into common platform we use pu concept in which, in general largest MVA and KV ratings of thecomponent is considered as base values, then all other component ratings will get back into this basis.Those values are called as pu values. (p.u=actual value/base value). 

Q:Operation carried out in Thermal power station?

A:The water is obtained in the boiler and the coal is burnt so that steam is obtained this steam is allowed to hit the turbine , the turbine which is coupled with the generator generates the electricity 

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 the diff. btwn. electronic regulator and ordinary rheostat regulator for fans?

A:The difference between the electroic and ordinary regulator is that in electronic reg. power losses are lessi.e.for as we decrese 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 controled but inrheostatic ctrl resistance is decreased by steps to achieve speed control. 

Q 1. Why the capacitor works on AC power supply?

A: We know C=1/2pfc, since AC voltage has frequency " f " so capacitor do the work on AC. and it pass the AC voltage through it but it block DC voltage because DC voltage has no frequency. 

Q 2. What is CT & PT? Explain details. 

A: CT means Current Transformer, PT means Potential Transformer, are known as instrument transformer in circuit where measure high current and high voltage involved they are used there. Practically when a measuring device like ammeter or voltmeter is not able to measure such high current and voltage we can measure this high voltage and current by using CT & PT. High value can damage the measuring device so CT and PT are introduced in the circuits. Ex: A CT of 200/1 A show that if a ammeter connected in the secondary of a CT indicate 1 amp that measure there 200 is following in the primary of CT that in HT line. when a 132KV/ 110 V PT if voltmeter in secondary of a PT indicate 110 V 

Q3.What will happen when DC supply apply on the primary of a transformer?

A: Generally Transformer has low resistance and high inductance. in this case of this circuit there is no inductance only resistance will act . so high electrical current will flow through the circuit primary side of the transformer. in this case coil will burn out. so be care fully don't apply DC supply in the Transformer. 

Q4. What is the full meaning of KVAR?

A: We know that, the three type of power in Electrical - 

a) Active Power.

b) Reactive Power.

c) Apparent Power.

so KVAR is stand for Kilo Volt Amps with Reactive elements. 

Q:What is inrush current?

A:Inrush current is the current drawn by a piece of electrically operated equipment when power is first applied. It can occur with AC or DC powered equipment, and can happen even with low supply voltages. 

Q:In a Tap changing transformer where is the tap connected, is it connected in the primary side or secondary side? 

A:Tapings are connected to high voltage winding side, because of low current. If we connect tapings to low voltage side, sparks will produce while tap changing operation due to high current. 

Q:Why transformer ratings are in kva? 

A: Since the power factor of transformer is dependent on load we only define VA rating and does not include power factor .In case of motors, power factor depend on construction and hence rating of motors is in KWatts and include power factor. 

Q: What is difference between fuse and breaker?

A: Fuses are burned at the time of over current flows in the circuit but breakers are just open(not burn) at the time of over current flow. Fuses are used in only one time but breakers are used by multiple number of times. 

Q:What is the difference between delta-delta, delta-star transformer?

A:Delta-delta transformer is used at generating station or a receiving station for Change of Voltage (i,e) generally it is used where the Voltage is high & Current is low.Delta-star is a distribution kind of transformer where from secondary star neutral is taken as a return path and this configuration is used for Step down voltage phenomena. 

Q: Capacitor is load free component but why ampere meter shows current when capacitor bank breaker close?

A: As we know that Electrical is having two type of load, Active and Reactive .Capacitor is a reactive load which is not considering as a load,& its factor is Isin@ .Meter is design based on Current RMS value because of it meter is showing the current RMS value. 

Transformer Interview Questions

Transformer works on which principle?

Answer: Electrical Transformer works on Faraday's law of electromagnetic induction. In electrical transformer the emf induced will be of Stationary Induced EMF. In stationary induced emf, emf will be induced in such a manner that the electrical conductors (windings) are kept stationary and magnetic field is varied ( varying magnetic field in transformer core) results in production of induced emf. 

Why efficiency of transformer is high?

Answer: Electrical transformer is a static device which transfers the power from one circuit to other through electromagnetic induction. In electrical transformer as there are no moving parts, no friction and windage losses occur and other losses in transformer are less as magnetic path of a transformer is a closed loop ( no air gap exist like induction motor between two circuits). Losses in the transformer are very less compared to any other rotating machine, hence efficiency of transformers will be very high. Efficiency will be of the order of 95% to 98%. 

What is the emf equation of transformer?

Answer: emf equation of transformer E = 4.44*f*N*fmax volts

f = applied frequency of voltage wave

N = Number of turns on primary or secondary winding.

fmax = Maximum flux ( fmax = Bmax x A)

Bmax = Maximum flux density

A = Area of cross section of the core.

What is the Ideal transformer?

Answer: Transformer which has characteristics such as no winding resistance, no magnetic leakage, no iron loss or core loss ( hysteresis and eddy current loss), and zero magnetising current is termed as Ideal Transformer. Ideal transformer is assumed for better explanation and understanding of practical transformer. 

What is the Significance of voltage per turn?

Answer: Voltage per turn for primary winding side and secondary winding side of the transformer is same. This helps in explaining that primary and secondary of transformers are related to each other by turns ratio (K). 

( V1/N1) = ( V2/N2) = K (turns ratio).

(V2/V1) = (E2/E1) = (N2/N1) =K

What is excitation current or magnetising current in Transformer?

Answer: The no load primary current provided to the transformer is called magnetising current or excitation current. This current is used to produce the flux in the transformer core and overcome the no load losses (core losses) of the transformer. This excitation current will be of the range from 2 to 5 percent of the rated full load primary current. 

Why power factor of the transformer under no load is very low?

Answer: During no load condition of transformer, the excitation or magnetizing current flow in the primary winding of the transformer. This excitation current is made up of large component of magnetizing component of current (Im) which is in quadrature with the applied voltage and comparatively small in phase component of current (Ie) which is in phase with the applied voltage. Thus due to large magnetizing component, power factor of the transformer will be very low. Power factor will be usually 0.1 to 0.2 lag. 

What is the relation between applied voltage and emf induced with respect to flux wave?

Answer: Under no load condition and considering no losses

• Induced emf in both primary and secondary lags behind the main flux by 90o.

• Applied voltage to primary winding leads the main flux by 90oand is in phase opposition with the induced emf in the primary winding (V1= -e1) 

• Secondary voltage V2=e2 as there is no voltage drop in the secondary. 

What are the different losses of Transformer?

Answer: Transformer has two types of losses 1. Iron losses 2. Copper losses Iron losses or core losses: Iron losses are the no load losses in transformer. This losses remain unchanged at any load of the transformer. Iron losses are categorized as Hysteresis loss and Eddy current loss. Copper loss: This loss is due to the I2R loss in the windings of the transformer. This is a variable loss varies with the load on the transformer. Other losses include stray load losses and dielectric losses. 

If supply frequency f transformer is made double keeping voltage unchanged what happens?

Answer: Hysteresis loss will decrease and eddy current loss remains unchanged. 

1. The function of a transistor used in any of the ICs is to perform SWITCHING action and not AMPLIFICATION.Then why DIODES are not used instead of TRANSISTORS as diodes also exhibit the same switching action? 

Answer : I agree Digital ICs use transistors as switches. But Analog (Linear) ICs Do Use transistors as Amplifiers. Consider the differential pair of transistors that form the front end of an op amp. The advantage of transistors over diodes, is that ... 

2. In a MOSFET, What does the pinch off voltage refers to?

Answer: In any (electronic) device controlling parameter is current it is called current controlled device. eg bilpolar transistor- output current is a function of base current. In any (electronic) device controlling parameter is voltage it is called voltage ... 

3-Meter works on which principal?

A direct-reading instrument which measures the Q of an electric circuit at radio frequencies by determining the ratio of inductance to resistance and which has also been developed to measure many other quantities. Also known as quality-factor meter. 

4.Why we need biasing for Transister, FET and MOSFET.?What is the importance of the biasing in transister circuits. 

Answer: Basically transister contains active region, saturation, cut off region. In saturation and cutt of region transister is used as a switch. To use transister as amplifier the operating point should be in exact middle of the active region. As transistor ... 

5.Why making capacity of the circuit breaker is higher than breaking capacity?

Answer :Why making capacity of the circuit breaker is higher than breaking capacity? 

Latest Answer : Making capacity is the max fault current it can carry during closing of breaker, e.g. You are closing a breaker on fault. The making capacity is always higher because it is expressed in peak value not rms, and also because of the DC offset, voltage and ... 

6. Why do we convert Frequency Domain to Laplace Domain? 

Answer: Frequency domain ----> deals with jw Laplace domain ----> deals with s, but s = (sigma) + ( jw )so with sigma = 0, laplace domain and frequency domain are the same. We convert time domain to either laplace domain or frequency domain to study various ... 

7.What are potential transformers? 

Answer: Potential Transformer is designed for monitoring single-phase and three-phase power line voltages in power metering applications. The primary terminals can be connected either in line-to-line or in line-to-neutral configuration. Fused transformer models ... 

8.What problem arise if we use regulators without/before filters? 

Answer: Filters are used for reducing ripples. A regulator output will be having many ripples. So filters are used in a circuit for conversion of pulsating AC to DC .. 

9.What is meant by filter? What are the different types of filters?

The output of the rectifier pulsating in nature, it consists of a desired DC component of voltage and unwanted ripple components. These ripple components are removed by placing filter circuit at the output of the rectifier. 

Types of filters:

1. capacitor filter

2. series inductor filter

3. LC filters of following two types

(a)capacitance input filter 

(b)inductance unput filter

4.RC filters. 

An electrical circuit which is used to remove unwanted signals from the output of a system is called a filter. Filters can be classified into many types based on how they are built the purpose they serve the range of filtering etc. 

Typically they are classified as 

1) Low Pass filters(allows frequencies upto a cut-off freq)

2) High Pass filters(allows frequencies above a cut-off freq)

3) Band Pass filters(allows input frequencies in a specified range)

4) Band Reject filters(rejects frequencies in a specified range)

10. What is the meaning of Tristate Signal in Electronics? 

Answer: Tristate device is 3 terminal device & it has three states. They are logic 0, logic 1 & high impedance state or tristate. This device can be used as switch. For ON logic 0 or logic 1 (depending on active low or active high appl) OFF as high independence 

Why star delta starter is preferred with induction motor?

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.

State the difference between generator and alternator



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. 

Why AC systems are preferred over DC systems?

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.

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