Electrical World

If a fault occurs in the underground cable, it is essential that the type of the fault and location of the fault should be determined as quickly and accurately as possible. Accuracy is important in order to avoid excessive trenching work. The type of fault which is most likely to occur is single conductor to ground fault. In multi-core cables, the fault current will likely give rise to excessive heating at the fault causing further damage to the insulation and extending the fault to remaining conductors. Open circuit faults may occur occasionally which be usually at cable joints.  Cable fault type identification:  Prior to the location of the fault on the power system it is important to determine the type of fault so as to make a better choice of the method to be used for fault location Isolate the faulty cable and test each core of the cable for earth fault. One terminal of the insulation tester is earthed and each conductor of the cable is in turn touc...

Silicon Carbide Arresters (SIC): The Non linear lightning arrester basically consists of set of spark gaps in series with the silicon carbide non linear resistor elements. Lightning arresters are connected between the phase conductors and ground. During normal system operating voltage conditions, the spark gaps are non conducting and isolate the high tension (HT) conductors from the ground. However whenever an overvoltge of magnitude dangerous to the insulation of the apparatus protected occurs ( these over voltages or over surges may be caused due to lightning strikes on the conductors or due to Extra High Voltage (EHV) switching) the spark gap breaks down and allows the high voltage surge current to flow through the ground. Working Principle of Silicon Carbide (SIC) Lightning Arresters: The volt-ampere characteristics of the non linear resistor in the lignting arrester can be approximately described by expression V = KI β . Where K and β are dependent on the co...

Electric Energy Generation Utilisation Interview Questions & Answers If you are preparing for a technical interview for a lighting systems related products(LED, Lamps etc) company, then you have landed in a correct page.  This post will serve to refresh the Lighting concepts, illuminations, related laws and important terms.  Here we had collected some of frequently asked questions related to illumination.  In addition to that we had added Anna university previous years questions on EEE 8th sem paper Electric Energy Generation Utilisation [Paper code EE1451].  [1] Define luminous flux It is defined as the total quantity of light energy emitted per second from a luminous body.  It is represented by symbol F and is measured in lumens.  The conception of luminous flux helps us to specify the output and efficiency of a given light source. [2] What is meant by luminance? It is defined as the luminous per unit ...

Ques.1 What is electric traction? Ans: Electric traction means using the electric power for traction system (i.e. for railways trains, trolleys etc). Electric traction means use of the electricity for all the above machines. Now a days, magnetic traction is also used for bullet trains.and basically dc motors are used 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 chokes,otherwise it's not possible to ionize the particles in tube light with normal voltage. Q:What is "pu" in electrical engineering? A:Pu stands for per unit and this will be used in single line diagram of power distribution and it is like a huge electrical circuit with no of components (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 the component is c...

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 ...

Hello and wellcome. Do you know what is corona effect?              First consider a conductor system to which voltage is applied. If the potential applied is raised, gradually, beyond a limit, a pale voilet glow will appear. This will be accompanied by a hissing noise indicating the ionization of surrounding air of the conductor surface with characterstic smell of ozone. This phenomenon is known as corona.             Simply we can say, phenomenon of violet glow, hissing noise and production of ozone gas in an overhead transmission line is known as corona effect.            High electric field at conductor surface provides enough energy to the molecules of surrounding air that causes breakdown of air.        In case of a.c. Transmission ionized particles get attracted and repelled to conductor once du...

Hello Engineers. Q.1 Feeder is designed mainly from the point of view of- A. Its current carrying capacity B. Voltage drop in it C. Operating voltage D. Operating Frequency Ans: A Q.2 Distributors are designed from the point of view of - A. Its current carrying capacity B. Operating voltage C. Voltage drop in it D. Operating frequency Ans: C Q.3 Transmission and distribution of electric power by underground system is superior to overhead system in respect of- A. Apperance and public safety B. Maintenance cost C. Frequency of faults, power failure and accidents D. All of the above Ans: D Q.4 The main drawback(s) of underground system over overhead system is/are- A. Exposure to lighting B. Heavy initial cost C. Exposure to atmospheric hazards such as smoke, ice, wind etc. D. Inductive interference between power and commuication circuit Ans: B Q.5 The main drawback of ovehead system over underground syste is- A. Underground system is more flexible...

Hello. Q.1 Corona is- A. Partial breakdown of air B. Complete breakdown of air C. Sparking between lines D. None of these Ans: B Q.2 Which of the following statements is true regarding corona- A. Corona takes place at a voltage lower than breakdown voltage B. Corona takes place at a voltage higher than breakdown voltage C. Corona is a current phenomenon D. Corona increases the transmission line efficiency Ans: A Q.3 Corona is accompanied by- A.Violet visible discharge in darkness B. Hissing sound C. Vibration D. Power loss E. Radio interference F. Ozone G. All of the above Ans: G   Q.4 Ozone effect can be detected by A. Presence of ozone detected by odour B. Hissing sound C. Faint luminous glow of bluish colour D. All of the above Ans: D Q.5 Corona loss increases with A. Decrease in conductor size and increase in supply frequency B. Increase in conductor size and decrease in supply frequency C. Increase in both conductor size and supply frequency D. Decrease in ...

In case of D.C., current density is uniform over cross section of conductors. On the other hand, in a conductor carrying A C there is a tendency of current to crowd near the surface of conductor that means alternating current flowing through a conductor doesn't distribute uniformly and concentrate near the surface of conductor. In AC System no current flows through the core and entire current is concentrate on surface regions. Due to this effective area of conductor is reduced so ac resistance of conductor increases. This phenomenon is known as Skin Effect as it causes concentration of current at the skin of conductor. To explain skin effect, we assume conductor which is made up of a number of concentric cylinders. Magnetic flux linking a cylindrical  element near the centre of conductors is greater than that linking another element near the surface of conductor. It is due to the fact that former elements is surrounded by internal as well as external flux, while latter element by ...

Q. What is meant by knee point voltage? A. 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). Query:What is reverse power relay? Resolution: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. Q:What is the difference between Isolator and Circuit Breaker? A: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. it is manually operated and does not contain any solenoid unlike circuit breaker. it should not be operated while it is having load. first the load on it must be...

Q. What do you mean by zone of protection? A. The protection is organized to provide a ring of security around each and every element of power system. If there is any fault associated within the ring the relays associated with it must trip all the allied circuit breakers so as to remove any faulty element from rest of the power system. This ring of security is called ‘Zone of protection’. Q. What are internal and external faults? A. Faults that occur within the zone are termed as Internal Faults and that occur outside the zone of protection are termed as external faults (can also be called as through faults). Q. What do you mean by reach and reach point of the relay? A. The farthest point from the relay which is still inside the zone of protection is called reach point and the distance between relay and reach point is called reach. Q. Why does the adjacent zones of protection overlap? A. If the adjacent zones do not overlap there will be some portion of the power sys...

Q. What is a load duration curve? A. It is the plot of load in Kilowatts versus time duration for which it occurs in the descending order of magnitude, irrespective of time of occurrence. Q. What is load factor? A. The ratio of average load to the maximum demand during a given period is known as load factor. Q. What is average load? A. The average of loads occurring on the power station in a given period is known as average load or average demand. Q. What is maximum demand? A. Maximum demand is the greatest demand of load on power station during a given period of time. Q. What is demand factor? A. Demand factor is the ratio of maximum demand on the power station to its connected load. Q. What is meant by connected load? A. Connected load is the sum of continuous ratings of all the equipment connected to the supply system. Q. What is diversity factor? A. Diversity factor is the ratio of sum of individual maximum demands to the simultaneous maximum demand on t...