AT group

2. How can you start-up the 40w tube lite with 230v AC/DC without using any choke/Coil? It’s possible by means of Electronic chokes,otherwise it’s not possible to ionize the particles in tube light with normal voltage. 3. What is “pu” in electrical engineering? 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 considered as base values, then all other component ratings will get back into this basis.Those values are called as pu values. (p.u=actual value/base value). 5. Why link is provided in neutral of an ac circuit and fuse in phase of ac circuit? Link is provided at a Neutral common point in the circuit from which various connection are taken for the individual control circuit ...

51. what is boucholz relay and the significance of it in to the transformer? Boucholz relay is a device which is used for the protection of transformer from its internal faults, it is a gas based relay. whenever any internal fault occurs in a transformer, the boucholz relay at once gives a horn for some time, if the transformer is isolated from the circuit then it stop its sound itself other wise it trips the circuit by its own tripping mechanism. 52. What is SF6 Circuit Breaker? SF6 is Sulpher hexa Flouride gas.. if this gas is used as arc quenching medium in a Circuitbreaker means SF6 CB. 53. What is frantic effect? Output voltage is greater than the input voltage or receiving end voltage is greater than the sending end voltage. 54. What is meant by insulation voltage in cables? explain it? 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. 55. Why we do 2 types of earthing on transformer (i...

101. In three pin plug 6 Amp. 220v AC rating. why earth pin diameter is higher than other two pin? what its purpose ? 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.( R=Pl/a area of the conductor increases resistance value decreases) 102. Difference between megger test equipment and contact resistance meter test instruments? Megger test equipment used to measure cable electric resistance, conductor continuity, phase identification where as contact resistance meter test instruments used to measure low resistance like relays ,contactors. 103. When we connect the large capacitor bank in series ? we connect large capacitor bank in series to improve the voltage power supply at the load end in balanced transmission line when there is considerable voltage drop along the balanced transmission line due to high impedance of the line.So in order to bring...

140. What is ACSR cable and where we use it? ACSR means Aluminium conductor steel reinforced, this conductor is used in transmission & distribution. 141. Why star delta starter is preferred with induction motor? Star delta starter is preferred with induction motor due to following reasons: • Starting current is reduced 3-4 times of the direct current due to which voltage drops and hence it causes less losses. • Star delta starter circuit comes in circuit first during starting of motor, which reduces voltage 3 times, that is why current also reduces up to 3 times and hence less motor burning is caused. • In addition, starting torque is increased and it prevents the damage of motor winding. 142. State the difference between generator and alternator Generator and alternator are two devices, which converts mechanical energy into electrical energy. Both have the same principle of electromagnetic induction, the only difference is that their construction. Generator persists stationary ma...

1. Which of the following does not change in a transformer ? (a) Current (b) Voltage (c) Frequency (d) All of the above Ans: c 2. In a transformer the energy is conveyed from primary to secondary (a) through cooling coil (b) through air (c) by the flux (d) none of the above Ans: c 3. A transformer core is laminated to (a) reduce hysteresis loss (b) reduce eddy current losses (c) reduce copper losses (d) reduce all above losses Ans: b 4. The degree of mechanical vibrations produced by the laminations of a transformer depends on (a) tightness of clamping (b) gauge of laminations (c) size of laminations (d) all of the above Ans: d 5. The no-load current drawn by transformer is usually what per cent of the full-load current ? (a) 0.2 to 0.5 per cent (b) 2 to 5 per cent (c) 12 to 15 per cent (d) 20 to 30 per cent Ans: b 6. The path of a magnetic flux in a transformer should have (a) high resistance (b) high reluctance (c) low resistance (d) low reluctance ...