Interview Questions Paper - 2 - Electrical Engineering

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Electrical Engineering Questions, Competitive Exam Preparation , Electrical Theory And Questions ,

Interview Questions Paper - 2

(1) what is Potential transformer?????

Ans: potential transformer are used for the information of voltage from higher values to a lower values.

(2)Potential transformers are used for ?????

Ans: measurement and protection.

(3)potential transformer winding consist of few turns of thick wire and is called which winding??

Ans: The secondary winding

(4)which is the primary winding of the potential transformers???

Ans: which have relatively large number of turns of thin wire and is called primary winding.

(5)For lower voltages up to 3.3kv which type potential transformer are used???

Ans: dry type PTs are used

(6)for high voltages (more than 3.3kv) which potential transformer is used????

Ans: oil immersed PTs are used

(7)describe bar type CT??

Ans: In bar primary type CT, he primary is a straight conductor passing through the center of a hollow core and the secondary has a ring hollow core type iron core on which the wound uniformly over the entire periphery.

(8)short not on wound type CT??

Ans: The wound type CTs have magnetic core. Figure shows wound type CT. The two windings are wound on a magnetic iron core. The primary winding consists of a few turns of thick wire, they can not be distributed uniformly over the iron core. Therefore wound type CTs have high leakage flux and hence possesses high reactance.

(9)when we can done tap changing in transformer???

Ans: The tap-changing may be done when the transformers are disconnected from the circuit or when operating on load.

(10)how many type will be there for tap changing in transformer???

Ans: There are two types of Tap-changers:

(i) OFF-circuit Tap Changer

(ii) ON-load Tap Changer (OLTC)

(11)which type of tap changing is made by ON- load tap changer (OLTC). ??

Ans: The daily or short time voltage adjustments .

(12)give the reason The tapping are provided on the high voltage(h. v.) winding?????

Ans: reason is give as below:

(i) The number of turns in High Voltage winding (h.v.) is large and therefore a fine voltage regulation can be obtained.

(ii) The current on the h.v. side is small.

(iii) The Lv. winding is placed on the inside nearer to the core while hv winding is placed on the outside.

(13)practical considerations tap changer is proferred to provide on which winding.??

Ans: high voltage

(14)when The transformers are said to be connected in parallel????

Ans: when the primaries of two or more transformers are connected to a common source or supply and the secondary's are connected to supply a common load.

(15)Necessity of parallel operation of transformers???

Ans:(i) to supply the load in excess of the rating of an e existing transformer, an additional transformer can be connected in parallel

(ii) when one transformer in taken out of service for maintenance or repair, the other transformer maintains the continuity of supply to the consumers

(iii) if any one transformer fails to operate, there is no interruption of the power supply

(iv) to increase the reliability of the power system

(16)give essential condition of connection of transformer in parallel???

Ans:(i) Same polarity

(ii) same voltage ratio

(iii) same phase sequence

(iv) Zero relative phase displacement

(17), give the desirable conditions to be satisfied for better load sharing and operating power factor in parallel connection of transformer????

Ans:

(i) Equal per unit impedances and

(ii) Equal ratios of resistance to reactance(R/X)

(18)Which is the most economical connection for small, high voltage transformers. ???

Ans: star/star

(19) Which connection have Possibility to provide neutral connection. ??

Ans: star/star

(20) Which connection is more suitable for large, low voltage transformers.??

Ans: Delta/Delta

(21)which connection is satisfactory performance even if there is large unbalanced in load. ??

Ans: Delta/Delta

(22)what is disadvantage of Delta/Delta connection of transformer??

Ans: The absence of star or neutral point

(23)The third harmonic voltages are absent from the line voltage in which connection???

Ans: star/star and delta/delta

(24)Which connection is most commonly used for power supply transformers ???

Ans: star/delta or delta/star

(25)what is advantage of star/delta or delta/star connection??

Ans: The neutral point allows

(26)Which connection reduces the third harmonic voltages ??

Ans: Zig-Zag connection

(27) For a given total voltage per phase, the Zig Zag side requires how many turns as compared to normal phase connection. ??

Ans:15% more

(28)what is right hand thumb rule???

Ans :if the straight conductor is held in the right hand such that the thumb indicates the direction of current then the other fingers curled around the conductor point the direction of magnetic field.

(29)what is the corkscrew rule???

Ans:When this screw is to be inserted in a wooden plank, it is to be rotated in the clockwise direction. If the direction of advancement of the screw indicates the direction of current, then the circular rotational motion of the screw indicates the direction of the magnetic field.

(30)in the right hand thumb rule the finger is give direction of????

Ans:direction of field

(31)sumpner test is use for????

Ans: This test on transformer is performed for finding efficiency, regulation and heating (temperature rise) under loaded conditions.

(32)what is advantage of sumpner test??

Ans: In sumpner's test, actual loading conditions are simulated and hence it is more accurate method of determining the efficiency and regulation than O.C. and S.C. tests.

(33)which and how manny transformers are use in sempner test??

Ans:Two transformers of identical rating are needed to perform this test .

(34)when The performance of a transformer at any load and power factor can be determined without actually loading the transformer by which test???

Ans:(i) Open Circuit (O C.) test and

(ii) Short Circuit (S. C.) test

(35)O.C. and S. C. testes which type of test and why???

Ans:These tests are convenient and economical because the power required to test a transformer is very small.

(36)by open circuit test which type property we can find??

Ans:The aim of conducting this test is to determine the following.

(a) Iron losses

(b) No-load current and

(37)In open circuit test which winding will be open??

Ans:H.V.

(38)using short circuit test which property we can find??

Ans: (a) Full-load copper losses

(b) Equivalent impedance (Z1, or Z2) referred to metering side.

(39)In short circuit test which winding will be shorted???

Ans:L.V.

(40)When in the short circuit test the applied voltage is very low that timr the iron losses will be ???

Ans:very small

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