Most Important Electrical Engineer Interview Question and answer

Most Important Electrical Engineer Interview Question and answer

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Prepare By Eng. Syed Muhammad Afreen Ali (MSc . BSc - Engineering)

1.What are the three most common types of cable for transmitting power?

• An understanding of voltage capacities

• An understanding of cable sizes

• An understanding of the voltage volumes that differentiate high from low

• Multiple versus solitary power sources

• Systems with one versus multiple cables

• The effects of multiple cable systems on voltage

2. Could you explain about reverse power relay?

Example: "Cable types are typically categorized by either size or capacity. With respect to capacity, there are three types: low, high and super tension cables. Cable that carries less than 1,000 volts is low tension; between 1,000 and 23,000 volts is high tension; and anything between 66 kV to 132 kV is super tension."

3.What type of cables are used for transmissions?

Types of Data Transmission Cables

·         Twisted-Pair Cable. A twisted pair cable consists of two copper conductors, each one with its own plastic insulation and twisted together. ...

·         Coaxial Cable. Coaxial cable (coax) carries high frequency signals than twisted-pair cables. ...

·         Fiber-Optic Cable. A fiber optic cable transmits signals in the form of light.

 Why is AC systems preferred to 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. ... Primarily, for distribution/transmission reasons - It has lower losses because it can be stepped up and down easily

4. What is the difference between generator and alternator?

An alternator can be called a type of generator. ... Both alternators and generators convert mechanical energy into electrical energy. The main difference between them is in regard to what spins and what is fixed. In an alternator, electricity is produced when a magnetic field spins inside the stator (windings of wire).

5. What is the basic loading condition Transformer?

Transformer Voltage Regulation. The voltage regulation of a transformer is defined as the change in secondary terminal voltage when the transformer loading is at its maximum, i.e. full-load applied while the primary supply voltage is held constant.

6. What are the possible causes for low power factor?

Causes of low Power Factor. The main cause of low Power factor is Inductive Load. As in pure inductive circuit, Current lags 90° from Voltage, this large difference of phase angle between current and voltage causes zero power factor

6. Why motor are rated as KW while transformer rated in kVA?

Copper losses ( I²R)depends on Current which passing through transformerwinding while Iron Losses or Core Losses or Insulation Losses depends on Voltage. So the Cu Losses depend on the rating current of the load so the load type will determine the powerfactor P.F ,Thats why the rating of Transformer in kVA,Not inkW.

7. Say there is air conditioner of 1Ton, what does that mean?:

1 Ton AC covers 80 to 120 sq.ft area. The 144 sq ft is on border range. If you have many windows or if your room sun facing then buying 1.5 Ton AC is good choice.

8. If I have a 25kVA generator, how many 1.5 Ton Air conditioner can be used?

EER(Energy Efficiency Ratio)=cooling capacity of ac/power consumed by ac. cooling capacity of 1 ton is equal to 3.517 kW of power. AC consists of two units, Indoor unit which is called the evaporator and the Outdoor Unit which called the Compressor.

9. You would be aware that transformer has an insulating oil, which oil is that?

Transformer oil or insulating oil is an oil that is stable at high temperatures and has excellent electrical insulating properties. It is used in oil-filled transformers, some types of high-voltage capacitors, fluorescent lamp ballasts, and some types of high-voltage switches and circuit breakers.

10. You may have noticed there are fuse and circuit breakers. What is the difference between the both?

A fuse is a small, thin conductor designed to melt and separate into two pieces for the purpose of breaking acircuit in the event of excessive current. A circuit breaker is a specially designed switch that automatically opens to interrupt circuit current in the event of an overcurrent condition.

11.Can you explain Norton's Theorem in a single sentence?

Example: "One power source and one resistor is equal of multiple power sources and resistors on a linear circuit."

12.What is an induction motor?

Basic working principle of an Induction Motor. In a DC motor, supply is needed to be given for the stator winding as well as the rotor winding. But in aninduction motor only the stator winding is fed with an AC supply. Alternating flux is produced around the stator winding due to AC supply.

13.What is difference between fuse and relay?

So to sum up, a fuse is a one time protection device that interrupts a circuit. A relayis a device controlled by another part of the circuit and operated to connect or interrupt the circuit many times. ... Relay switches current flow on and off when energized/de energized.

14.What are the advantages of fuse?

Advantages of an Electrical Fuse. It is the cheapest form of protection, and it does need any maintenance. Its operation is completely automatic and requires less time as compared to circuit breakers. The smaller sizes of fuse element impose a current limiting effect under short-circuit conditions.

15.What is the difference between relay and switch?

Switches are manually actuated by the user. Relays are controlled by energizing an electro magnet, which in turn causes the contacts to open/close. Usually, at least in the US, the relay is said to “make” (close) or “break” (open). In eaaence, a rely is aswitch, controlled by another device.

16.What is the difference between relay and contactor?

Contactors and Relays perform the same task of switching a circuit. ... Both are electromagnetic switches and operate under similar principles. The differencecomes if we see from the application perspective. Contactors are used for high voltage switching purposes whereas relays are used for low voltage switching.

17.How does an electrical relay work?

A relay is an electromagnetic switch operated by a relatively small electric current that can turn on or off a much larger electric current. The heart of a relay is an electromagnet (a coil of wire that becomes a temporary magnet when electricity flows through it).

18.What is the difference between circuit breaker and isolator?

Difference between Isolator and Circuit Breaker: Isolator is an off-load device while, circuit breaker is an on-load device. Isolator is a switch operated manually, which separate the circuit from the power main and discharges the trapped chargesin the circuit. ... ISOLATOR is a Mechanical device which acts as a switch.

19. What is the use of overload relay?

Thermal overload relays are economic electromechanical protection devices for the main circuit. They offer reliable protection for motors in the event of overload or phase failure. The thermal overload relay can make up a compact starting solution together with contactors.

20. What is protective relay in power system?

In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected. ... Important transmission lines and generators have cubicles dedicated to protection, with many individual electromechanical devices, or one or two microprocessor relays.

21.What is MHO relay?

A mho Relay is a high-speed relay and is also known as the admittance relay. In this relay operating torque is obtained by the volt-amperes element and the controlling element is developed due to the voltage element. It means a mho relayis a voltage controlled directional relay.

22.What is Translay relay?

TRANSLAY SCHEME FOR FEEDER PROTECTION. This system is similar to voltage balance system except that here balance or opposition is between the voltages induced in the secondary windings wound on the relay magnet and not between the secondary voltages of the line current transformers

23.What is backup protection?

When remote backup is used to provide backup protection for a single ProtectionSystem failure or a failure of a circuit breaker to interrupt current, the relays at the remote station are set sensitive enough that they can detect all faults that should be cleared from the adjacent (local) substation for which backup

24. What is primary protection?

The main protection or primary protection is the first line protection which provides quick-acting and selective clearing of a fault within the boundary of the circuit section or element it protects. The main protection is provided in each section of an electrical installation.

25. What is zone of protection?

“Zones of protection” is one strategy that can be used to provide the level of security demanded today. Protective relay engineers keep utility grids and equipment safe from faults and system unbalances by dividing the grid into zones, each with a unique protection scheme. Overlapping zones provide backupprotection.

Project experience

• Describe your favorite project you’ve worked on.
• What was your role?
• Describe a technical problem you encountered and how you solved it.
• What quality controls did you employ?
• What did you do best while working on this project?
• What could you improve on?
• What did you learn from this project?
• What design tools are you familiar with?
• What is your favorite part of the project lifecycle?
• Do you have any technical writing experience?
• What has been your greatest achievement in engineering so far? 

What is the formula of kW?

Need to Find:	Formula
Kilowatts	(Volts x Amps x PF x 1.732)/1000
Amperes DC	Watts / Volts
Amperes AC	(746 x Horsepower)/(Volts x eff x PF x 1.732)
KVA	(Volts x Amps x 1.732)/1000

How do you convert kW to rpm?

1. Torque (lb.in) = 63,025 x Power (HP) / Speed (RPM)
2. Power (HP) = Torque (lb.in) x Speed (RPM) / 63,025.
3. Torque (N.m) = 9.5488 x Power (kW) / Speed (RPM)
4. Power (kW) = Torque (N.m) x Speed (RPM) / 9.5488.

How do you convert kW to kwh?

Divide the number of watts by 1000 to convert the number from watts to kilowatts. 60W divided by 1000 results in 0.06kW. Multiply the number of kilowatts by the number of hours the device will be used. If the device will be used for three hours, multiply 0.06kW by three to produce 0.18kWh.

1. Torque (lb.in) = 63,025 x Power (HP) / Speed (RPM)
2. Power (HP) = Torque (lb.in) x Speed (RPM) / 63,025.
3. Torque (N.m) = 9.5488 x Power (kW) / Speed (RPM)
4. Power (kW) = Torque (N.m) x Speed (RPM) / 9.5488.

What is difference between seamless Pipe and ERW pipe?

What is difference between seamless Pipe and ERW pipe?

A Seamless steel pipe is extruded and drawn from a billet whereas a welded (ERW) pipeis produced from a strip that is roll formed and welded (ERW )to produce a tube. Since aSeamless steel pipe offers a higher range of safety measures it is more expensive than a( ERW) welded tube.

What is meant by ERW pipe?

ERW pipes means Electric Resistance Welded Pipe. API 5L ERW pipes are used in various engineering purposes, fencing, scaffolding, line pipes etc. ERW pipes are available in various qualities, wall thicknesses, and diameters of the finished pipes. China Hua Yuan Steel Pipe is one of the best ERW Pipe manufacturer.

What does seamless pipe mean?

Seamless Pipe and Tube. Seamless pipe, as the name suggests, is a pipe without a seam or a weld-joint. Seamless Steel Pipe is made from a solid round steel 'billet' which is heated and pushed or pulled over a form until the steel is shaped into a hollow pipe.

A centrifugal chiller utilizes the vapor compression cycle to chill water and reject this heat collected from the chilled water plus the heat from the compressor to a water loop cooled by a cooling tower.

A centrifugal chiller utilizes the vapor compression cycle to chill water and reject this heat collected from the chilled water plus the heat from the compressor to a water loop cooled by a cooling tower.

Evaporator 

The evaporator in a centrifugal water cooled chiller is usually a shell and tube heat exchanger that removes heat from the entering chilled water lowering its temperature in the process. The heat is used to boil the refrigerant changing it from a liquid to a gas. Chillers use a flooded type evaporator, which is very energy efficient. Flooded evaporators place the chilled water in the tubes and refrigerant in the shell completely submerging the tubes in refrigerant. Large chillers can have over five miles of tubing in their heat exchangers. 

Compressor

 The compressor assembly is made up of a prime mover and a centrifugal compressor. Chillers use liquid refrigerant cooled hermetic electric motors. The centrifugal compressor is a dynamic device similar to a centrifugal water pump. It raises the pressure and temperature of the refrigerant by converting kinetic energy into pressure. In this document we will refer only to centrifugal compressors. 

Condenser

 Like the evaporator, the condenser is usually a shell and tube heat exchanger. In this case, it removes heat from the refrigerant gas causing it to condense to a liquid. The heat raises the temperature of the cooling water often referred to as condenser water. The condenser water then carries the heat to the cooling tower where the heat is rejected to atmosphere.

Different type of Chiller Capacity, Specification and function with Details

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Reciprocating chiller: 

Reciprocating compressors are categorized as positive displacement machines. These are available in two basic types: hermetic sealed units and units of open construction. In hermetic sealed units, the motor and the compressor are direct-coupled and housed in a single casing that is sealed to the atmosphere. In open construction units, the motor and the compressor are in separate housings. In general, open construction units have a longer service life, lower maintenance requirements and higher operating efficiencies. The hermetic sealed units are most common particularly in small capacities. Single stage reciprocating machines have an ability to operate at compression ratios of 10 to 12. The capacity control in reciprocating machine is achieved through ‘On-Off’ or ‘LoadingUnloading’ of compressor cylinders. Reciprocating machines are manufactured in capacities from 0.5 to 150 TR. The main factors favoring reciprocating machine is low cost. The other advantage is that multiple reciprocating machines can be installed to closely match the building loads. Multiple units allow flexibility to operate machines per the need. If properly managed this could attribute to significant energy savings during low loads. A major drawback is a high level of maintenance requirement’s, noise and vibration. Since the capacity is limited to 150 TR, multiple units cost more than other options. Multiple chiller configurations require large space and consume more energy per ton of refrigeration. 

Centrifugal Chillers

 Centrifugal chillers are categorized as variable volume displacement units. Like reciprocating machines these are also available in both hermetic and open construction. Commercially the hermetic sealed units are more widely used, despite its lower operating efficiency. Centrifugal chillers for refrigeration applications are generally designed for a fixed compression ratio of 18. The capacity control is achieved through the use of inlet vanes on the impellers that restrict refrigerant flow. The centrifugal chillers are manufactured in capacities from 90 to 2000 tons. The main factor favoring centrifugal machine is their high operational efficiency at full load, compact size and availability in large sizes. The biggest drawback of centrifugal machine is a very poor part load performance and inability to operate at low cooling loads. At extreme low loads, these chillers are prone to a condition known as surging. The main limitation is that these are not suitable for air-cooled condenser options and require water and cooling tower. 

Screw Chillers 

Rotary or screw chillers, like reciprocating machines are positive displacement compressors. Rotary is a wider term that may include vane, eccentric, gear or screw types. The commercial refrigeration installation rely more on screw machines. Screw compressors are available in several designs, both single screw and twin screw, with oilfree and oil-injected designs in both types. Twin-screw oil-injected compressors are slightly more energy efficient at moderate compression ratios. Twin-screw compressors have an ability to operate at compression ratio of 30. Units are available in both hermetic sealed and open construction. The capacity control in screw compressor is achieved thorough a moveable slide stop valve, which will vary the compressor internal volume ratio to achieve optimum energy consumption during part load operation. Screw chillers are available in capacities ranging from 20 to 1000 tons and even higher from few manufacturers. The factors favoring screw chillers is their compact size, lightweight, quite & vibration free operation and high energy efficiency both in full and part load operation. The major drawback is their high cost. For smaller loads, reciprocating machines are less expensive to purchase and for large loads centrifugal machines cost less.

Scroll Chillers 

Scroll compressors have been used in commercial practice for systems that have capacity less than 30 TR. On such small sizes, these do not affect the life cycle economics drastically and therefore not discussed further. 

OVERVIEW OF ROLE, RESPONSIBILITY& SCOPE OF MECHANICAL ELECTRICAL PLUMBING (MEP)

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OVERVIEW OF ROLE, RESPONSIBILITY& SCOPE OF MECHANICAL ELECTRICAL PLUMBING (MEP) 


INTRODUCTION

 Mechanical Electrical Plumbing focus on mechanical drawing, mechanical drafting & design services with knowledge of Electrical and plumbing equipment. The Mechanical part of MEP is known as HVAC. It is responsible for the installation and maintenance of A.C heating and ventilation meaning changing fillers and installing furnace. It also involves Electrical parts for outlets and application but also lighting switches, fire alarm, security system,as well as lighting protection when necessary. The plumbing part also handles fine suppression system and storm pipe system as well as gas delivery system in Medical and laboratory setting. The Civil technologies deal of energy and water, along with sophistical and secure methods of delivery. Modern building requires substantial ventilation environmental control as well as safety precaution.

ROLE AND RESPONSIBILITY OF MEP ENGINEER 

MEP Engineer is a single –level professional classification responsible for planning and design in the area of Mechanical, Electrical and plumbing (MEP) system including developing policies standard, inspection procedure and evaluation tools for MEP matters involving judicial branch facilities, along with prepare, review drawing, specification and cost estimates for the mechanical, Electrical, and /or Plumbing. 

MEP Engineer has to develop best practice and maintenance management measure including the review and update of standard on a routine basic. 

MEP Engineer has to develops policies/review and standards for capital projects, facility database, and master plan information. 

MEP Engineer conduct engineering and feasibility and economics studies and prepare reports on finding develops standard for design and technical specification, investigates new MEP design concept and technical development of systems which are applicable to engineering problem. 

MEP engineer has to review plans and specification according to plan. 

MEP Engineer has to manages oversee the work of subordinate staff contact architects or Engineer. MEP Engineer has to prepare plans, details, specified and cost estimated of plumbing, heating, ventilating, air conditioning and general piping system. 

MEP Engineer has to provide technical advice to staff designer,supervisor,inspector and contracting service provider, regarding installation and maintenance of MEP System. 

MEP System has to analyze mechanical, Electrical and /or plumbing engineering problems and formulate solutions. 

MEP Engineer has to identify problems in design, plan, manage and deliver multiple projects. 

MEP Engineer has to plan, organize review and evaluate the work of consultant,contractor and others.

 MEP Engineer has to knowledge of MS office, AutoCAD and Project management software. 

MEP Engineer has to prepare and deliver effective oral presentation whenever required

What the mechanical engineers do?

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What the mechanical engineers do?

Mechanical engineers design power-producing machines, such as electric generators, internal combustion engines, and steam and gas turbines, as well as power-using machines, such as refrigeration and air-conditioning systems.Mechanical engineers design other machines, Plumbing, Fire Fighting inside buildings, such as elevators and escalators.

Being a mechanical engineer means applying the basic engineering principles and mechanical processes needed to create the machines and devices we use every day. Students discover concepts connected to thermodynamics, heat transfer, quality control and product design. There are also courses on materials used in the manufacturing processes. Practical learning happens through individual or team projects, which encourage students to apply their theoretical knowledge.