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# ELECTRICAL TECHNICIAN INTERVIEW QUESTIONS AND ANSWERS PDF

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Mcb specification are done on maximum current flow in circuit. What is excitation? Excitation is applying an external voltage to DC shunt coil in DC motors. In three pin plug 6 Amp. Because Current flow in the conductor is inversely proportional to the conductor diameter.

So if any short circuits occur in the system first high currents bypassed in the Earthling terminal. What are Motor Generator Sets and explain the different ways the motor generator set can be used Answer: Motor Generator Sets are a combination of an electrical generator and an engine mounted together to form a single piece of equipment. Motor generator set is also referred to as a genset, or more commonly, a generatorThe motor generator set can used in the following different ways: Alternating current AC to direct current DC 2.

DC to AC 3. DC at one voltage to DC at another voltage 4. AC at one frequency to AC at another harmonically-related frequency What is power quality meter? Power Quality meters are common in many industrial environment. Small units are now available for home use as well. They give operators the ability to monitor the both perturbations on the power supply, as well as power used within a building, or by a single machine or appliance.

In some situations, equipment function and operation is monitored and controlled from a remote location where communication is via modem, or high-speed communication lines. So we can understand the importance of power measurement through power quality meters. What is the different between digital phase converter and ordinary phase converter? Digital phase converter are a recent development in phase converter technology that utilizes proprietary software in a powerful microprocessor to control solid state power switching components.

This microprocessor, called a digital signal processor DSP , monitors the phase conversion process, continually adjusting the input and output modules of the converter to maintain perfectly balanced three-phase power under all load conditions. Explain the operation of variable frequency transformer? A variable frequency transformer is used to transmit electricity between two asynchronous alternating current domains.

A variable frequency 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.

The variable frequency transformer behaves as a continuously adjustable phaseshifting transformer. It allows control of the power flow between two networks. What is the main use of rotary phase converter? 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.

The reason that 4ma is chosen instead of 0 mA is for fail safe operation. For example- a pressure instrument gives output 4mA to indicate 0 psi, up to 20 mA to indicate psi, or full scale. Due to any problem in instrument i. So if range is mA then we can differentiate whether it is due to broken wire or due to 0 psi.

Two bulbs of w and 40w respectively connected in series across a v supply which bulb will glow bright and why? What is meant by knee point voltage? Knee point voltage is calculated for electrical Current transformers and is very important factor to choose a CT. It is the voltage at which a CT gets saturated. CT-current transformer. What is reverse power relay? Reverse Power flow relay are used in generating stations's protection.

A generating stations is supposed to fed power to the grid and in case generating units are off,there is no generation in the plant then plant may take power from grid. To stop the flow of power from grid to generator we use reverse power relay. What will happen if DC supply is given on the primary of a transformer? Mainly transformer has high inductance and low resistance.

In case of DC supply there is no inductance ,only resistance will act in the electrical circuit.

So high electrical current will flow through primary side of the transformer. So for this reason coil and insulation will burn out. What is the difference between isolators and electrical circuit breakers?

What is bus-bar? Isolators are mainly for switching purpose under normal conditions but they cannot operate in fault conditions. Actually they used for isolating the CBs for maintenance. Whereas CB gets activated under fault conditions according to the fault detected. Bus bar is nothing but a junction where the power is getting distributed for independent loads. What are the advantage of free wheeling diode in a Full Wave rectifier? It reduces the harmonics and it also reduces sparking and arching across the mechanical switch so that it reduces the voltage spike seen in a inductive load 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 cable catalog considering derating electrical current.

After that measure the length of cable required from supply point of load to load poin. What are HRC fuses and where it is used?

HRC stand for "high rupturing capacity" fuse and it is used in distribution system for electrical transformers. Which power plant has high load factor? All base load power plants have a high load factor.

If we use high efficiency power plants to supply the base load,we can reduce the cost of generation. Mention the methods for starting an induction motor? The different methods of starting an induction motor DOL: What is the difference between earth resistance and earth electrode resistance?

Only one of the terminals is evident in the earth resistance. In order to find the second terminal we should recourse to its definition: Earth Resistance is the resistance existing between the electrically accessible part of a buried electrode and another point of the earth, which is far away.

The resistance of the electrode has the following components: A the resistance of the metal and that of the connection to it. B the contact resistance of the surrounding earth to the electrode. What is use of lockout relay in ht voltage? A lock-out relay is generally placed in line before or after the e-stop switch so the power can be shut off at one central location.

This relay is powered by the same electrical source as the control power and is operated by a key lock switch. The relay itself may have up to 24 contact points within the unit itself. This allows the control power for multiple machines to be locked out by the turn of a single key switch.

What is the power factor of an alternator at no load? At no load Synchronous Impedance of the alternator is responsible for creating angle difference. So it should be zero lagging like inductor.

How electrical power is generated by an A. C Generator?

## 400 TOP ELECTRICAL ENGINEERING Interview Questions and Answers Pdf- EEE

For the generation of elect power we need a prime mover which supplies mechanical power input to the alternator, can be steam turbines,or hydro turbines. When poles of the rotor moves under the armature conductors which are placed on the stator ,field flux cut the armature conductor ,therefore voltage is generated and is of sinusoidal in nature Why an ac solenoid valve attract the plunger even though we interchanges the terminal? Will the poles changes?

Yes because the poles changes for every half-cycle of ac voltage so the polarity of AC voltage is continuously changing for every half cycle. That's why the ac solenoid attract the plunger even though it's terminals are interchanged. What is derating? The current currying of cables will change depending upon the site temperature location of site , type of run it will run through duct, trench, buried etc.

Considering this condition actual current currying capacity of cable reduce than current currying capacity which given to cable Catalogue this is called derating. Why temperature rise is conducted in bus bars and isolators? Bus bars and isolators are rated for continuous power flow, that means they carry heavy currents which rises their temperature.

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? 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, for a better protection of the system. If one lamp connects between two phases it will glow or not?

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.

What is meant by regenerative braking? When the supply is cutt off for a running motor, it still continue running due to inertia. In order to stop it quickly we place a load resitor across the armature winding and the motor should have maintained continuous field supply.

This type of breaking is called as "Regenerative Breaking". Why is the starting current high in a DC motor? At starting, Eb is zero. What are the advantages of star-delta starter with induction motor? The main advantage of using the star delta starter is reduction of current during the starting of the motor. Starting current is reduced to times Of current of Direct online starting.

## Engineering Questions

Hence the starting current is reduced , the voltage drops during the starting of motor in systems are reduced. For lighting loads, neutral conductor is must and hence the secondary must be star winding. To minimize the current unbalance in the primary we use delta winding in the primary. Why in a three pin plug the earth pin is thicker and longer than the other pins?

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. Why series motor cannot be started on no-load? Series motor cannot be started without load because of high starting torque.

Series motor are used in Trains, Crane etc. ELCB is used to detect earth leakage fault. Once the phase and neutral are connected in an ELCB, the current will flow through phase and that much current will have to return neutral so resultant current is zero.

Once there is a ground fault in the load side, current from phase will directly pass through earth and it will not return through neutral through ELCB.

That means once side current is going and not returning and hence because of this difference in current ELCB wil trip and it will safe guard the other circuits from faulty loads.

If the neutral is not grounded, fault current will definitely high and that full fault current will come back through ELCB, and there will be no difference in current.

Why we do 2 types of earthing on transformer ie: The two types of earthing are Familiar as Equipment earthing and system earthing. In Equipment earthing: In this neutral of the supply source Transformer or Generator should be grounded. With this,in case of unbalanced loading neutral will not be shifted. We can protect the equipment also. With size of the equipment transformer or alternator and selection of relying system earthing will be further classified into directly earthed,Impedance earthing, resistive NGRs earthing.

MCB is miniature circuit breaker which is thermal operated and use for short circuit protection in small current rating circuit. MCCB moulded case circuit breaker and is thermal operated for over load current and magnetic operation for instant trip in short circuit condition. Normally it is used where normal current is more than A.

What is the difference between Isolator and Circuit Breaker? Isolator is a off load device which is used for isolating the downstream circuits from upstream circuits for the reason of any maintenance on downstream circuits. But circuit breaker is onload automatic device used for breaking the circuit in case of abnormal conditions like short circuit, overload etc. Boucholz relay is a device which is used for the protection of transformer from its internal faults, it is a gas based relay. What is SF6 Circuit Breaker?

SF6 is Sulpher hexa Flouride gas.. Output voltage is greater than the input voltage or receiving end voltage is greater than the sending end voltage. It is the property of a cable by virtue of it can withstand the applied voltage without rupturing it is known as insulation level of the cable. Tell me in detail about c. The term C. T means current transformer,and the term P. T means potential transformer.

In circuit where measurements of high voltage and high current is involved they are used there. Particularly when a measuring device like voltmeter or ammeter is not able to measure such high value of quantity because of large value of torque due to such high value it can damage the measuring device.

## Electrician Interview Questions & Answers

They work on the same principle of transformer, which is based on. They work on the ratio to they are designed. 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?

## Electrician Interview Questions

The motor has max load current compare to that of transformer because the motor consumes real power.. Power factor should be high in order to get smooth operation of the system. Low power factor means losses will be more. What happens if i connect a capacitor to a generator load? You can join the red wire to another red wire or to a black wire Blue and Yellow wire: These wires are also used to carry power but are not wiring the outlets for common plug-in electrical devices.

They are used for the live wire pulled through the conduct. You will see yellow wire in the fan, structure lights, and switched outlets. White and Gray: This color wire is used as a neutral wire.

It carries the current unbalanced load to the ground. You can join white and gray only to other white and gray wires Green: It is connected to the grounding terminal in an outlet box and run from the outlet box to the ground bus bar within an electric panel 7 Explain RLC circuit? An RLC circuit carries an electrical circuit consisting of a resistor R and inductor L and a capacitor C , connected in parallel or series.

This circuit is called a second order circuit as any voltage or current in the circuit can be described by a second order differential equation. Wire is sized by American Wire Gauge system. Your installation of conductors will depend on a few factors like gauge of the wire, wire capacity, etc. For wires, smaller the wire gauge larger the ampacity or capacity of the wire to handle current. For example, low voltage lighting and lamp cords will have 18 gauge, electric furnaces or large electric heaters are of 6 gauge.

There are two types of semi-conductors intrinsic and extrinsic. Again in extrinsic semi-conductors you will have N-type semiconductors and P-type semiconductors. Transistors are comprised of several combination of n-type and p-type semi-conductors. Transistor has the ability to amplify the current, due to the reason that output power can be higher than the input power. If the resistance total in a series circuit doubles the current will reduce to half. If the series current gets double then, the resistance is halved.

When a string of resistors in a series will divide the source voltage into proportion to their values. Reverse polarity is referred in a condition where one or more of your receptacles are connected incorrectly. To fix the reverse polarity, check the wire connection at the outlet and inspect your receptacle.Strengthen rotary kiln daily maintenance data analysis of the pack; be helpful for equipment management work.

At the time of motor taking normal current rated current the speed of the motor is called rated speed. Would be grateful if u may fwd the pdf on my email id vhabhi gmail.

The first number specifies the gauge. Start applying now.

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