The currents in the coils connected to a brush are either all towards the brush (positive brush) or all directed away from the brush (negative brush). Therefore, current in a coil will reverse as the coil passes a brush. The reversal of current in a coil as the coil passes the brush axis is called commutation.
2. Tell us who Is A Power Plant Operator?
A power plant operator is a person who operates a power plant. He has got to be good at the technical skills of using the power plant and must be equally talented in distributing the work to the other workers who are working with the power plant.
3. Explain when Is The Auto-relight Function Activated?
Whenever an engine is at or below idle with the fuel control switch in RUN. FCOM 1 70.20.8
4. Explain What Is Acsr Cable And Where We Use It?
ACSR means Aluminium conductor steel reinforced, this conductor is used in transmission & distribution.
It is a procedure that is used for the protection of the workers and the equipments during the maintenance or repair of the power plant.
6. Tell us why Do We Use Compensation Windings?
Compensation windings are used to neutralize the cross magnetizing effect of armature reaction.
7. Explain me what is 2 phase motor?
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.
8. Tell us how Many Ignitors Are Used For In Flight Starting?
Dual ignitors are always used for in flight starts. FCOM 1 70.20.8
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.
Gate signal is to be applied to the thyristor to trigger the thyristor ON in safe mode. When the thyristor starts conducting the forward current above the minimum value, called Latching current, the gate signal which is applied to trigger the device in no longer require to keep the scr in ON position.
11. Explain me 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 3-4 times Of current of Direct online starting.
Hence the starting current is reduced , the voltage drops during the starting of motor in systems are reduced.
12. Do you know what is the principle of motor?
Whenever a current carrying conductor is placed in an magnetic field it produce turning or twisting movement is called as torque.
13. Explain me the methods for starting an induction motor?
The different methods of starting an induction motor
☛ DOL:direct online starter
☛ Star delta starter
☛ Auto transformer starter
☛ Resistance starter
☛ Series reactor starter
14. Do you know what Is Voltage Regulation?
The change in terminal voltage of a generator between full and no load (at constant speed) is called the voltage regulation. It is usually expressed as a percentage of the voltage at full-load.
%Voltage Regulation= (VNL-VFL)/VFL*100
☛ VNL= Terminal voltage of generator at No load.
☛ VFL= Terminal voltage of generator at full load.
15. Explain me the difference between a four point starter and three point starter?
The shunt connection in four point starter is provided separately form the line where as in three point starter it is connected with line which is the drawback in three point starter.
What is the difference between synchronous generator & asynchronous generator?
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.
16. Tell us types of dc generator?
DC Generators are classified into two types
1)separatly excited DC generator
2)self excited DC generator, which is further classified into;
☛ 1)series
☛ 2)shunt and
☛ 3)compound(which is further classified into cumulative and differential).
17. Do you know what Is Holding Current?
When scr is conducting current in forward conduction state, scr will return to forward blocking state when the anode current or forward current falls below a low level called Holding current
Note: Latching current and Holding current are not same. Latching current is associated with the turn on process of the scr whereas holding current is associated with the turn off process. In general holding current will be slightly lesser than the latching current.
18. Tell me what are the Application of DC Motors in Thermal Power Plant?
In thermal power plants dc motors are employed for certain control and critical emergency operations which are supplied by dedicated batteries. DC motors operate as backup drives for normal ac drive systems when ac power supply to the plant is lost.
In thermal power plant, the dc motors finds applications for performing control functions such as
☛ Turbine governor motor
☛ Governor limit setting
☛ Motor operated rheostats
☛ Emergency lubrication for the turbines (main, boiler feed pumps)
☛ Generator (H2 oil seal).
☛ DC motor operated valves
19. Tell me two basic speed control scheme of DC shunt motor?
1. By using flux control method:in this method a rheostat is connected across the field winding to control the field current.so by changing the current the flux produced by the field winding can be changed, and since speed is inversely proportional to flux speed can be controlled
2.armature control method:in this method a rheostat is connected across armature winding by varying the resistance the value of resistive drop(IaRa) can be varied, and since speed is directly proportional to Eb-IaRa the speed can be controlled.
20. Tell us how would you describe (needed electric motor or your) work style?
My work style matching exactlty what cashier job requires by: being reliable, responsible, and dependable, and fulfilling obligations, being careful about detail and thorough in completing work tasks, being pleasant with others on the job and displaying a good-natured, cooperative attitude, persistence in the face of obstacles, a willingness to take on responsibilities and challenges.
21. Tell me do You Know Armature Reaction?
Armature reaction is the effect of magnetic field setup by armature current on the distribution of flux under main poles of a generator. The armature magnetic field has two effects
☛ It demagnetizes or weakens the main flux
☛ It cross-magnetizes or distorts it.
☛ The first effect leads to reduced generated voltage and second to the sparking at the brushes.
22. Tell us what Is The Function Of Anti-pumping In Circuit Breaker?
When breaker is close at one time by close push button,the anti pumping contactor prevent re close the breaker by close push button after if it already close.
Dc series is in the trains to get high starting torque while starting of the trains and operating voltage is 1500v dc.
DC 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.
Its Single Phase induction motor which mostly squirrel cage rotor and are capacitor start capacitor run.
26. Explain me how much experience do you have working with automobiles?
If you haven't worked on automobiles in a professional setting, don't sweat it! You can include your experience working on your own cars or others. When you respond to this question, you want to go in depth about the type of work you have done, sharing your knowledge and areas of expertise. Rather than saying, "I have about 8 years of experience,"
27. Tell me will A D.c Shunt Motor Operate On An A.c Supply?
The Shunt winding has a large number of turns so that it has appreciable inductance. When A.C is applied to a shunt motor, the large inductive reactance of shunt winding will reduce the field current too much. Consequently, Shunt motor will not usually run on A.C Supply.
28. Tell me why is the starting current high in a DC motor?
In DC motors, Voltage equation is V=Eb-IaRa (V = Terminal voltage, Eb = Back emf in Motor, Ia = Armature current,Ra = Aramture resistance). At starting, Eb is zero. Therefore, V=IaRa, Ia = V/Ra ,where Ra is very less like 0.01ohm.i.e, Ia will become enormously increased.
29. Do you know what are the main job duties and responsibilities of electric motor employee?
Electric motor responsibilities are to disassemble defective equipment so that repairs can be made, using hand tools; record repairs required, parts used, and labor time; inspect and test equipment to locate damage or worn parts and diagnose malfunctions, or read work orders or schematic drawings to determine required repairs;
repair and rebuild defective mechanical parts in electric motors, generators, and related equipment, using hand tools and power tools; lubricate moving parts; measure velocity, horsepower, revolutions per minute (rpm), amperage, circuitry, and voltage of units or parts to diagnose problems, using ammeters, voltmeters, wattmeters, and other testing devices; scrape and clean units or parts, using cleaning solvents and equipment such as buffing wheels; solder, wrap, and coat wires to ensure proper insulation; read service guides to find information needed to perform repairs; adjust working parts, such as fan belts, contacts, and springs, using hand tools and gauges; inspect electrical connections, wiring, relays, charging resistance boxes, and storage batteries, following wiring diagrams; weld, braze, or solder electrical connections; reassemble repaired electric motors to specified requirements and ratings, using hand tools and electrical meters; rewire electrical systems, and repair or replace electrical accessories;
assemble electrical parts such as alternators, generators, starting devices, and switches, following schematic drawings and using hand, machine, and power tools; lift units or parts such as motors or generators, using cranes or chain hoists, or signal crane operators to lift heavy parts or subassemblies; remove and replace defective parts such as coil leads, carbon brushes, and wires, using soldering equipment; maintain stocks of parts; sharpen tools such as saws, picks, shovels, screwdrivers, and scoops, either manually or by using bench grinders and emery wheels; clean cells, cell assemblies, glassware, leads, electrical connections, and battery poles, using scrapers, steam, water, emery cloths, power grinders, or acid; reface, ream, and polish commutators and machine parts to specified tolerances, using machine tools; hammer out dents and twists in tools and equipment;
test equipment for overheating, using speed gauges and thermometers; test battery charges, and replace or recharge batteries as necessary; verify and adjust alignments and dimensions of parts, using gauges and tracing lathes; test conditions, fluid levels, and specific gravities of electrolyte cells, using voltmeters, hydrometers, and thermometers; steam-clean polishing and buffing wheels to remove abrasives and bonding materials, and spray, brush, or recoat surfaces as necessary; repair and operate battery-charging equipment; set machinery for proper performance, using computers; cut and form insulation, and insert insulation into armature, rotor, or stator slots; inspect batteries for structural defects such as dented cans, damaged carbon rods and terminals, and defective seals; drain and filter transformer oil and refill transformers with oil until coils are submerged; rewind coils on cores in slots, or make replacement coils, using coil-winding machines;
clean, rinse, and dry transformer cases, using boiling water, scrapers, solvents, hoses, and cloths; add water or acid to battery cell solutions to obtain specified concentrations; pour compounds into transformer-case terminal openings to seal out moisture; position and level battery cells, anodes, or cathodes, using hoists or leveling jacks, or signal other workers to perform positioning and leveling; seal joints with putty, mortar, and asbestos, using putty extruders and knives; bolt porcelain insulators to wood parts to assemble hot stools.
30. Why do you want to work for our organization as Electric Motor Repairer?
The interviewer wants to know that you're not just interested in any place that will hire you. They want to know that you want to work for them, specifically. Before the interview, learn as much as you can about their garage. You can search customer reviews to learn about their reputation. An auto repair shop with good reviews reflects their values as well. Think about the places you have worked. What did you like most about them? If you can't find much online or through asking around beforehand, try to list at least three things you have read that you like about their garage. Prepare questions for any remaining areas that are unclear, but focus on values and qualities, such as work environment, employee training, and customer care.
31. Explain me what Are The Different Types Of Losses In Dc Machines?
The losses in a d.c. machine (generator or motor) may be divided into three types:
☛ Copper losses: These losses occur due to currents in the various windings of the machine.
☛ Iron or core losses: These losses occur in the armature of a d.c. machine and are due to the rotation of armature in the magnetic field of the poles. They are of two types
☛ Hysteresis loss: Hysteresis loss occurs in the armature of the d.c. machine since any given part of the armature is subjected to magnetic field reversals as it passes under successive poles.
☛ Eddy current loss: The voltages induced in the armature conductors produce circulating currents in the armature core known as eddy currents and power loss due to their flow is called eddy current loss. The eddy current loss appears as heat which raises the temperature of the machine and lowers its efficiency.
☛ Mechanical losses: These losses are due to friction and windage. These losses depend upon the speed of the machine. But for a given speed, they are practically constant.
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 generator The motor generator set can used in the following different ways:
☛ 1.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
The Knowledge of machines and tools, including their designs, uses, repair, and maintenance, arithmetic, algebra, geometry, calculus, statistics, and their applications, the practical application of engineering science and technology. This includes applying principles, techniques, procedures, and equipment to the design and production of various goods and services, principles and processes for providing customer and personal services. This includes customer needs assessment, meeting quality standards for services, and evaluation of customer satisfaction, the structure and content of the English language including the meaning and spelling of words, rules of composition, and grammar.
34. Tell us how would your co-workers describe your attention to detail?
My co-workers would describe my attention to detail as very strong. I can very easily point out discrepancies on a report and will notice the small things like an engine sounding slightly off. I think big-picture as well but have always had a knack for details.
35. What is principle Of Operation Of A Generator?
An electric generator is a machine that converts mechanical energy into electrical energy. An electric generator is based on the principle that whenever flux is cut by a conductor, an e.m.f. is induced which will cause a current to flow if the conductor circuit is closed. The direction of induced e.m.f. (and hence current) is given by Fleming's right hand rule.
