Electrical World

Hello Engineers. Today we are sharing alternator interview questions with answer. Q. 1. What are the two types of turbo-alternators ? Ans.  Vertical and horizontal. Q. 2. How do you compare the two ? Ans. Vertical type requires less floor space and while step bearing is necessary to carry the weight of the moving element, there is very little friction in the main bearings. The horizontal type requires no step bearing, but occupies more space. Q. 3. What is step bearing ? Ans. It consists of two cylindrical cast iron plates which bear upon each other and have a central recess between them. Suitable oil is pumped into this recess under considerable pressure. Q. 4. What is direct-connected alternator ? Ans. One in which the alternator and engine are directly connected. In other words, there is no intermediate gearing such as belt, chain etc. between the driving engine and alternator. Q. 5. What is the difference between direct-connected and direct-coupled units ? Ans...

ElecticalQuestion 1: What is Electrical machine? Electrical machine is an electro mechanical device which converts input motive power ( prime mover like turbine in case of generator or electrical supply in case of dc motor) to output motive power (Electrical power in case of the generator or mechanical output in case of motor). This uses the principle of electro magentic induction principle. Electrical Question 2: What is the advantage of DC motors over AC motors? Answer: With the advert of the ac power generation and transmission over long distances with less losses using electrical transformers, dc machines were out ruled by the ac machines in industrial and home applications. However dc motors still exist in the industries because of some special properties of the dc machines where ac drives have failed to attain. DC motors have some special properties such as: High Starting Torque Excellent speed control capability For traction applications in electr...

Q:What are the 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: What is the diff. btwn. Electronic regulator and ordinary rheostat regulator for fans? A : The difference between the electronic and ordinary regulator is the fact that in electronic reg. power losses tend to be less because as we minimize the speed the electronic reg. give the power necessary for that particular speed but in case of ordinary rheostat type reg. the power wastage is same for every speed and no power is saved. In electronic regulator triac is employed for speed control. by varying the firing angle speed is controlled but in rheostatic control resistance is decreased by steps to achievespeed control. Q: What is 2 phase motor? A : A two phase motor is often a motor with the the st...

Q:Why we use ac system in India why not dc ? A:Firstly, the output of power stations comes from a rotary turbine, which by it's nature is AC and therefore requires no power electronics to convert to DC. Secondly it is much easier to change the voltage of AC electricity for transmission and distribution. thirdly the cost of plant associated with AC transmission (circuit breakers, transformers etc) is much lower than the equivilant of DC transmission AC transmission provides a number of technical advantages. When a fault on the network occurs, a large fault current  occurs. In an AC system this becomes much easier to interupt, as the sine wave current will naturally tend to zero at some point making the current easier to interrupt. Q:Which type of motor is used in trains, what is the rating of supply used explain Working principal? A:Dc series is in the trains to get high starting torque while starting of the trains and operating voltage is 1500v dc. Q:Battery banks are in connected...

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...

Q. What are the different types of transmission lines based on capacity? A.    1. Short transmission lines (up to 50 Km) (<20 KV)     2. Medium transmission lines (50-150 Km) (>20 KV & <100 KV)     3. Long transmission lines (>150 Km) (>100 KV) Q. What is per unit value? A. Per unit of any quantity is defined as the ratio actual to base value expressed in decimal. Q. What are the advantages of per unit system? A.    1. The pu impedances of machines of same type and widely different ratings lie within a narrow range.     2. Per unit values referred to either side of the transformer remains same. Pu impedance of a 3 phase transformer is independent of type of winding     3. Computational efforts are reduced by a great extent.     4. The chance of confusion between line and phase quantities in a three phase balanced system is greatly reduced. 5. Manufactur...

Q. What is a load curve? A. The curve showing the variation of load on the power station with respect to (w.r.t) time is known as a load curve. Q. What is the difference between base load and peak load? A. Base load:  The unvarying load which occurs almost the whole day on the station is known as base load. Peak load:  The various peak demands of load over and above the base load of the station is known as peak load. Q. What is power factor? A. The cosine of angle between voltage and current in an a.c. circuit is known as power factor. Q. What are the disadvantages of low power factor and how to improve it? A. Disadvantages: Large KVA rating of equipment, Greater conductor size, High copper losses, Poor voltage regulation The low power factor is mainly due to the fact that most of the power loads are inductive and, therefore, take lagging currents.  In order to improve the power factor, some device taking leading power should be connected in parallel with ...

Q.1 What does 10V AC mean? Is it the RMS voltage or Peak voltage or Average voltage? Answer. In general,  AC voltages and currents are mentioned in RMS values only. It is sensible to compare with steady DC voltages and currents. For example 230V AC supply means, 230Vrms AC Supply. Q.2  What does the Voltmeter in AC mode show? Is it RMS value or peak value? Answer. Multimeter in AC mode shows RMS value of the voltage or current. Also when it is DC mode it will show the RMS value only. Q.3 Can fuses with an AC voltage rating be used in a DC applications? Answer: Fuses must be rated for the voltage AC or DC in which they will be used. Generally, fuses have a DC voltage rating that is half of the maximum AC voltage rating. Q.4 Why in a three pin plug the earth pin is thicker and longer than the other pins? Answer: It depends upon R=ρL/A where area (A) is inversely proportional to resistance (R), so if  area (A) increases, R decreases & if R is less the l...

Q. What is an Electric Drive? A. The entire unit consisting of an electric motor, the energy transmitting shaft and the control equipment is called an electric drive. Q. What are the advantages of electric drives? A. 1. These drives are available in wide range torque, speed and power. 2. Flexible control characteristics. 3. They are adaptable to any type of working conditions 4. They can operate in all the four quadrants of speed torque plane, which is not applicable for other prime movers. 5. The operation is pollution free. 6. Lower noise, less maintenance. 7. Their efficiency is high as no load losses are less Q. What are the different classes of duty? A. continuous duty: Operation at a constant load for long duration of time. Continuous duty, variable load: Sequence of identical duty cycles consisting of periods of operation under load and no load. Short time duty: Operation at a constant load for small period of time followed by rest. Intermittent periodic duty: Sequen...